The four-wheel drive system on a 2000 Chevrolet Tracker is a complicated nightmare that takes a conventional system and adds cost, weight, and complexity to save maybe 0.1 MPG and some wear on a few cheap parts. It’s been driving me so mad that I’ve taken matters into my own hands, enlisting the services of a blood pressure bulb pump so I can get rid of annoying electronics that don’t seem to work. Check out how I got my Tracker’s four-wheel drive system fixed for just $17.
At first, I thought my $700 Chevy Tracker was the deal of the century. After all, once I’d replaced the main fuse that was preventing the 4×4 from running (and that enabled me to snag the machine at such a low price in the first place), the Tracker fired right up. Between the healthy motor, the lack fo rust, and the beautifully-shifting five-speed manual transmission, I was elated with my purchase. But that joy has subsided in recent days, as the formerly mouse-infested Suzuki-turned-Geo-turned-Chevy has become an electrical nightmare.
At first, the charging system didn’t work, so I replaced the alternator with a junkyard unit. Sadly, the alternator continued struggling to make even 12 volts. Then I bought a new alternator, which also didn’t work. Then, for some reason, it began working! And now it, once again, doesn’t. In fact, it left me stranded in a drive-through the other day when my friend stalled the car and couldn’t start it up again due to a low battery state-of-charge (we just push-started it in the drive-through; it was not ideal).
Given these charging gremlins, when I yanked my transfer case lever into 4×4 and saw no four-wheel drive light pop up on the dash, I can’t say I was really surprised. What did surprise me, as I started digging into the fault, was just how complicated the 4×4 actuation mechanism is on this Tracker.
Disconnecting Hubs Aren’t Uncommon, But Many Are Garbage And The Tracker’s Is Possibly The Worst
To drive home this point, allow me to show you the four-wheel drive mechanism on my 1992 Jeep Cherokee XJ. I simply pull a lever like the one shown on the bottom left of the image below, and — boom — I’m in four-wheel drive:
The Tracker also has a transfer case lever (see below), which actuates the front driveshaft in much the same way that the Cherokee’s transfer case lever does. The difference is that the Cherokee’s front driveshaft is always mechanically connected to the front wheels through the differential, axle shafts, and wheel hubs. So once you’ve moved the lever, the vehicle is locked into 4×4. The Tracker, on the other hand, has a disconnect in the front diff.
A 4×4 front-end disconnect isn’t really uncommon. On older trucks, you’d have what’s called “locking hubs” at the center of each front wheel (see below). These required you to put the transfer case lever into four-wheel drive, then walk out to each front wheel, and literally spin a hub dial from “free” to “lock” to connect the hubs to the front axle shafts to activate four-wheel drive.
I don’t have a closeup of my Jeep’s hubs, but they’re not too different from these Warn units:
On early Jeep Cherokee XJs (prior to my 1992) and Jeep YJ Wranglers, there was a vacuum style motor (see below) that used a diaphragm and engine vacuum to slide a fork, which would move a collar onto and off of two pieces of an axle shaft, either locking them (and thus the “hubs”) to put the vehicle into 4×4 or unlocking them for maximum fuel economy and reduced component wear. Even the current Jeep Wrangler JL uses a similar system to the early XJ’s, though it’s an electric motor and not a vacuum.
Actually, while we’re on the topic, I noticed while at the press launch that the Ford Bronco Raptor even has a vacuum-disconnect front axle disconnect at each front hub:
Anyway, the point is that, even though my 1992 XJ doesn’t have a disconnect function, it’s not uncommon to have some kind of system to prevent the front drivetrain from spinning unnecessarily when the vehicle is in rear-wheel drive. The problem is that many of these “front axle disconnect” systems tend to fail early and often (the XJ/YJ vacuum disconnect one does), so people just replace the systems with something that they can switch by hand.
But even that Jeep system isn’t as bad as the Tracker’s. Just look at this nonsense:
A Look At The Tracker’s 4×4 System
As previously mentioned, the Chevy Tracker’s four-wheel drive system starts with a transfer case lever, just as my Jeep XJ’s does. Yanking that sends power to the front driveshaft, which drives the front differential. But unlike on my XJ, that doesn’t mean the axle shafts are being driven, since there’s a disconnecting front hub system meant to improve fuel economy and reduce wear of rotating drivetrain components. To lock that front “hub” system and engage four-wheel drive requires an army of components to all function properly.
Pushing that transfer case lever in the cabin into four-wheel drive actuates a switch, labeled “1” in the image above. This then tells the 4×4 controller (or ECU on later models), labeled “5” above, to send current to an air pump located behind the front bumper. The air pump is labeled “7” in the diagram above. This pump creates about 6psi of pressure in a rubber hose that runs into the differential, triggering the actuator, labeled “8,” and putting the vehicle into four-wheel drive.
Here’s a look at the pump:
And here is a video and some pictures from eBay of that actuator in the front differential that the pump sends pressurized air to:
This electropneumatic system introduces lots of components that can fail. The switches in the transfer case can fail, the ECU or the wiring from the ECU can fail, and the pump can fail. In any case, the pump would no longer create pressure to trigger the actuator in the front differential. Worse than any of those failure modes is the differential actuator failing, as this would require one to tear apart the whole diff, which is a humongous job.
In my case, it seems that my pump works fine, as it turns on when I hook it up to 12-volts. Oddly, when I hook up a multimeter to the wires going to the pump, I see about 12 volts. So what gives? Well, “12 volts is not 12 volts,” as my brother Tom, a computer engineer, told me. When I hook the pump to the connector, I’m adding a load, and it’s clear that the source (ECU) sending current to the pump is unable to handle that. I bet if I hooked up a multimeter in line with the pump, I’d see a major voltage drop.
In any case, my pump isn’t working, and neither did a replacement junkyard unit. Luckily, I found out later, the actuator in my front diff is functional. This meant I could leverage a brilliant trick.
The Bulb Trick
After considerable research, I learned that some folks had used hand pumps in place of that electric pump behind the front bumper, meaning any issue with the transfer case switches, wiring, 4×4 computer, or electric pump could be bypassed. I had to try this myself, so I headed to harbor freight and bought a bulb-style pump:
This pump is exactly the same unit as the one you might have noticed being used to check blood pressure:
I simply plugged the electric pump’s air inlet hose with a bolt, and pulled the electric pump’s outlet hose off the hardline mounted to the frame. Then I slipped the hand pump’s hose onto that hardline, and zip-tied the bulb in the grille opening (I didn’t want to tie it below the bumper, since this could get damaged while off-roading). Here’s a look at my setup:
After some testing, it seems that three pumps of the bulb is enough to actuate the clutch in the differential, connecting the axle shafts, thus activating four-wheel drive. It’s a $17 fix to an electrical problem that I just don’t want to deal with right now, and though I could route the hand pump hose all the way into the cabin, I don’t mind walking to the front of the vehicle to go into four-wheel drive. It’s no more inconvenient than my Jeep J10’s manual-locking-hubs four-wheel drive system, and it just works.
My coworker Jason has demanded that I mention that these blood pressure bulb-style pumps have been used in vehicles before, specifically to adjust lumbar in the Merkur Scorpio. Here, have a look:
The bulb-style hand pump really is a brilliant contraption.
A $700 car has lots of issues? I wish I could post a photo of my shocked face.
Please don’t call this a repair. It’s a bandaid which helped the overall diagnostics. Otherwise, pretty sweet.
I must have missed it: How do you disengage the locked hubs after you’re done with 4wd?
You spin the dial on the bulb to release pressure, just like when the check you blood pressure.
Today I learned WARN is a brand name and not some vague threat to bodily/automotive injury.
Fixing your car with air. This clears some cobwebs for me.
First car was a ’63 Beetle. (In the late 60’s, it seemed like everybody’s first car was a ’63 Beetle). I did a brake job, and could not get the brakes bled enough to eliminate a very soft pedal. Tried and tried, using the pop bottle full of brake fluid with a tube to the bleeder valves method. No dice. I was at least smart enough to know that the problem with air in the brake lines was that it compresses, whereas brake fluid does not, I decided to pre-compress the air. I disconnected the windshield washer reservoir from the spare tire and the washer nozzle, and dumped out the washer fluid. I ran the outlet tube to the master cylinder reservior cap (I don’t remember what kind of fitting I put on the cap), filled the reservoir with brake fluid, and reconnected it to the spare tire. This put a constant pressure on the brake fluid, compressing the air enough to get a firmer pedal. I drove it that way for quite a while. Any time the pedal got soft, I just bumped the spare tire pressure back up a bit.
Air was free, and I was broke. It was, for a while, a winning combination.
That’s nuckin’ futs!
I love it.
So is the pump designed to constantly supply positive pressure when 4wd is engaged? I’d think that’s another strong argument for routing the bulb somewhere within reach of the driver, that way you could re-pressurize the system on the fly if needed
I think it’s got a check valve so you can pump it up and it stays pressurized until you turn the bleeder and let the air out. Like when you get your blood pressure checked.
It shouldn’t leak down unless something is wrong. On mine (01 Tracker) the o-rings coming from the air pump were letting a bit of air leak past, therefore the pump had to keep reactivating in order to keep pressure on the diaphragm. 2 cents of o-ring (and a tiny bit of emory cloth) later and the pump doesn’t run past its initial pressurization.
Reebok is missing a perfect branding opportunity here.
https://www.reebok.com/us/pump-shoes
David man, I love hacks like this! While not the same thing I swapped out the gauge cluster from a 2016 Veloster into my 2013, much updated look, worked 100% perfectly! (wish you could post pics in comments).
You’re just a few drop of moisture away from that thing making hilarious fart noises every time you put it in four wheel drive.
If you ask me it would totally be worth it to route that bulb up into the cabin and make some kind of reasonable mount for it that doesn’t involve obvious exposed tubing in the cabin area. It wouldn’t require much extra effort, and would elevate this from a clever hack to a genuine improvement over the factory setup. Maybe mount it down in the driver’s footwell somewhere, like a foot-operated parking brake?
I say mount the bulb on the roof rack. Let your ingenious freak flag fly!
I quite like the bulb solution, but I agree with other commenters that, specially as this is meant to be a socially acceptable car, it’d be a good idea to route the tube into the cabin, if you want to further improve the car I’d also delete the electric pump and replace it with an appropriate resistor so you never have to look at it again. You’ll be happy you routed it inside when Winter comes, or if a leak pops up and you need to pump it up repeatedly over the course of an off-roading session. It doesn’t need to be visible, just tuck it under the dash and you’re golden.
If you get lumbar on a Corbeau seat, they use the bulb as well.
Early Trackers had manual locking hubs. Could you retrofit those?
Kinda-sorta. The hubs are technically always engaged. The locking occurs in the differential. I think you have to weld the diff when you add locking hubs. I could be mistaken, but this has always been my understanding of the system. You of course could just replace the front diff with sidekick bits, which had traditional locking hubs.
Even better, once you’re done cannibalizing the blood pressure system for the bulb, you can sell the cuff to a C5 Corvette owner to fix a blown out inflatable bolster. 🙂
David,
One thing I didn’t see mentioned when discussing “12V is 12V” is that it’s possible the power supply you used to hook up 12V is capable of supplying more current than whatever the pump connects to on the car.
Nicely done! I am all in favor of ditching complex electronic systems in favor of simple mechanical ones wherever possible.
I remember driving another car with those inflatable lumbar supports, but I can’t remember which one. Might have been my old Chrysler Laser, or maybe my dad’s Taurus SHO.
Chrysler Laser/Dodge Daytona.
Fun fact: the seats with the inflatable lumbar were designed and built by none other than Recaro. They are 100% genuine Recaros.
So my buddy Jon broke a genuine Recaro seat on the passenger’s side? Maaaan…
Then Lear Siegler must have stolen the idea for their seats in Mustangs, Buicks, etc.
They did not, in fact.
Recaro didn’t want to build everybody’s seats and nobody wanted to pay. So they licensed the patents on it.
I had a 1984 Toyota Celica GT-S that had the bulb-inflatable lumbar supports as well. Since they were the same seats as the Supra of that time, it must have had them as well.
Correct. Chrysler Lasers and Dodge Daytona’s (Pre 87) used a bulb pump to adjust the lumbar.
Great hack! Reminds of of when I used a house light switch to make sure the radiator fan was running on my old ’76 Dasher.
One of these bulbs could also save your bacon if your home furnace’s draft inducer fails. You could use the bulb to fool the interlock into firing up the furnace. Not so safe, but at least you won’t freeze to death.
David buys a 22 year old car that has clear signs of rodent infestation. Seller is willing to get rid of it for only $700. David seems surprised that those rodents have made a mess of vehicle wiring.
I swear David must just buy these wrecks as source material for the site. Same as on the other site when he would buy a broken vehicle on the other side of the country and then drive it back doing repairs in AutoZone parking lots instead of paying less to just ship the car.
I don’t buy cars for blogging material, I buy cars because I want to.
A Tracker isn’t exactly the most popular vehicle to write about, nor is the other car I bought recently. (More on that soon!).
David, I swear to god, if it’s that purple car?
It’s going to disappear from your driveway.
And if you stomp on the gas when it mysteriously returns looking better than before, you absolutely certainly will die.
(To be clear: did you know you can fit 200HP in extremely small places? No? Buy that purple thing, and you will…)
It’s not the purple car, but it’s similarly sized.
… okay, I’m gonna need you to stay in Australia for at LEAST two months.
Jason, Mercedes, go get the trailer ready and start practicing your “we definitely did not give your tiny car to RootWyrm” faces.
European friends, I need you to find me a Mitsubishi 6A12 non-MIVEC.
Everyone else, you’re on alibi duty.
“ A Tracker isn’t exactly the most popular vehicle to write about, nor is the other car I bought recently. (More on that soon!).”
You already bought another vehicle? In my finest Ricky Ricardo-
Daaaaviiid! You got some splainin’ to do!
Oh my god, the tracker isn’t even his most recent purchase!
This is why I love this site
DT, we talked about this. You need to clear all purchases with your life coach.
As David’s life coach, I told him he wasn’t allowed to buy any more Jeeps until he fixed the Golden Eagle. Which I then amended to ‘anything with 4WD’ after the Tracker.
Look, it’s DAVID! How the fuck was I supposed to know he would buy something almost normal?!
To be fair to David, he’s a lot like me. He gets interested in a kind of vehicle, sees one for sale for cheap, then ends up buying it because it’s just too hard to pass up. Being able to write about it is just a byproduct!
Of course, he does eventually get around to selling his stuff, unlike me……………
I can relate in a way – I used to buy broken vintage appliances back in Brazil, spend time restoring them, and then selling them online. Thing is, I never once mustered the courage to put the ads online, so I never sold a single one! They were all swiftly disposed by my family once I emigrated (not their fault, they simply didn’t have infinite storage capacity – although I wish they had consulted me first for some of the items).
Sidenote – You could get a cheap 12v buck converter to stabilize your voltage if you think voltage loss is the culprit. A little less than the bulb dealy from the harbor.
Sigh. Well, that tears it.
Every electrical problem is directly leading to the behind the dash harnesses. Especially with a motor load fault. I presume by this point you’ve already checked and repaired the ground strap if it needed it, since it’s easily accessed. That would be the only other probable cause.
Which means it’s one of two things: corrosion in a connector or damaged wiring. Well, that would be 100% consistent with my diagnosis of rodent damage. If it was an ECU fault, you’d have more problems. This is all pointing to physical wiring damage consistent with rodent chewing and rodent droppings (which are extremely corrosive.)
I agree with you, and I’m concerned.
What worries me more than anything is you have reported IPC fault and a motor load fault. Those are on two physically separated harnesses. And the ECU is, to my recollection, directly below prime rodent real estate with lots of insulating material and paper. I’m worried that it’s got major corrosion damage in the connector assembly. The ECU itself on these is generally pretty well sealed, but the pins are not replaceable, so if they’re damaged it’s a BIG problem. Hopefully it’s just minor and can be cleaned up.
Despite the deceptive simplicity, it has a shitton of pins. Swapping the ECU and splicing in new connectors isn’t a realistic repair – I would only ever write it up as new harness and new ECU. It’s literally a shorter repair than trying to splice 80+ wires. 🙁 Hopefully it’s just individually damaged wires and some cleanable corrosion.
Sometimes you just have to embrace the suck and block off a weekend to do a yard sale repair. Remove the seats, remove the center console, the dash, all of it. Bring out your test light and multimeter and start making some good solders or butt splices. Bonus points if you can scare up a wiring diagram from ALLDATA or something.
I agree. Gird loins.
Even if you’ve already checked the grounding, I’d double-triple-quadruple check it. Because inability to drive current means you have unusually high resistance somewhere. Usually that’s a loose or corroded connector, or a bad ground. Try unplugging, cleaning, and reconnecting the wiring harnesses, and make super certain of all your grounding points.
Neat! That’s pretty solid. I watched the linked video on the differentials. Does your tracker really have 5.13 gears? dang. I guess just be glad it’s not GM’s thermal actuator.
Yep. Had one of those on a 1996 Tahoe. Was great to cool off and go out of 4wd when off, then it’s not locked in when you start … for a while. Thankfully, it’s simple to replace with an electric motor.
This is a brilliant fix for a dumb-ass problem.
David, your “date vehicle” does not need 4WD.
The last thing you want to do is say… “hang on, before we can proceed through this snowstorm, I need to get out and and pump up my 4wd”.
Please do what you can to make this “acceptable” date car acceptable. This fix is not. Clever, yes. Acceptable, no.
The J10 is the date vehicle. Bench seat up front for drive-in movies!
so this one is just the daily going to town rig?
You are trying to date women, right? The J10 is date 4 material, after you have already convinced her you are a catch. THEN you bring the J10 out for the drive-in movie make-out special.
J10 on date 1 is dating suicide. Unless you want to search for 20 years for a spouse, I guess.
Think about it this way…. if you were to see her gigantic My Little Pony collection on the first date, you might be deterred a bit. Same thing.
It’s a filter.
Jeep girls are a thing still right? We just need to find him one.
What’s wrong with the J10?!
To us? Nothing.
To a non-car chick it probably looks like you are poor and can’t afford a reasonably priced golf/civic/Corolla and instead have to drive an old truck. Might score some bonus points for Marlboro man cool but once you pull in to your driveway she is going to be calling an Uber.
Do you really want to be with some who doesn’t like or at least know what you’re passionate about?
My wife knew what a weirdo a am about cars and a lot of other stuff pretty much from the moment we met. She doesn’t share all of the same interests but she appreciates that it something that I care a lot about. If she was the type that was scared off by my POS FJ80 that was our first date car then I wouldn’t have wanted to spend more time with her anyway.
She’s been here through the LC, a Volvo 240 (that I agreed to buy non running, sight unseen, and 3 hours away) , and now my shittiest purchases yet, an 86 F150 that died three times on the way home.
Find you someone that likes you because of your questionable taste in vehicles, not in spite of it.
Nothing is wrong with the J10!!!
BUT, she won’t fart until the 4th date in this vehicle. You want to love her first before you smell that!
Seriously, MOOOOOOST women would simply prefer you show up in this on the first date versus the J10. That rare find is already married, sorry (at your age).
Also, if you show up with this, then can you BRAG about the J10 (and the…..12? other vehicles you own). Love you man!!!!
“The last thing you want to do is say… “hang on, before we can proceed through this snowstorm, I need to get out and and pump up my 4wd”.
This sort of thing is my bag baby!
Better than saying you need to “pump up” some other types of equipment before your date.
https://youtu.be/3Y71iDvCYXA
This doesn’t sound right to me. An overly complex Suzuki?
That must have been a GM contribution.
Nope, this is pure Suzuki.
Because Suzuki is a small, cash poor company, developing automatic locking hubs was simply not on the menu. Nor was buying a custom automatic locking hub from a larger manufacturer like Warn, where they would also be competing with companies like the Big 3 who want exclusivity deals.
So in the JA12 (circa 1995) Jimny, they introduced air-locking hubs. Why air locking hubs? Because Suzuki had all the parts for that already. Air locking hubs were already very well understood and very well developed – the Jeep SJ in fact, uses air locking hubs. Air locking hubs come in two varieties – positive pressure, and negative pressure. This commonly correlates to the engagement mechanism as well; a positive pressure hub is normally disengaged, and a negative pressure hub is normally engaged. (But this is NOT always true.) It’s a simple physics thing – vacuum sucks a piston away, pressure pushes a piston in.
So it’s WAY less complicated than you think. It’s literally just a 12V pump that supplies a small amount of air pressure to a piston which engages the lock. So long as the system remains pressurized, which can be achieved through valves, solenoids, etc. after pressurization, the piston remains engaged. Suzuki elected to skip all those potential failure points that create a much more complex system, and instead simply uses a simple electric air pump and a single hose.
This reduces the system to the absolute minimum number of components: air supply, one hose, and the piston. No more and no less. And as you can see, in an emergency or failure situation? The failure is predictable, can be immediately diagnosed, can be remedied with nothing more than hand tools (even blowing into it can work potentially,) and the failure mode is inherently safe by disengaging the axle. (Meaning the vehicle can be axle towed DESPITE the failure, if necessary. SJ’s are the OPPOSITE: if you have a failure of the BW1339’s ’emergency mode,’ not only are you taking it on a flatbed, you are scrubbing tires.)
And as David has already found – the pump itself is fine. The hose is fine. It’s under load that the pump is not receiving enough power to operate – which is a really, really tiny amount of power. That points to electrical damage.
Yeah, and it points to the kind of electrical damage that causes fires. We’re talking about chewed wiring with just a couple of strands still intact, connectors that barely connect anymore, that kind of thing. High resistance, in other words. Which generates heat. That’s how electrical fires happen.
The power for the air pump is super low draw, so I don’t have real worries about that. Especially since it DID get voltage, no dead short, and just did not deliver. It’s a completely unfused connection. Look at the wires – they’re around 20-22ga, 5-7′ run, so you’re talking 1A or less. And the affected part has been removed.
It’s not great and it’s something that must be addressed, sure. And absolutely it could cause damage if there’s a short to ground. But we have NO indication of a short to ground, NO indication of a dead short, NO indication of a broken ground path. Voltage is full until motor load, which in full context, points us to a loose or corroded connection. Removing the motor load basically eliminates the fire risk – at least from this connection.
That’s true, but in a car that is known to have hosted a rodent infestation, it’s probably not the only damaged piece of wiring. And a ground short isn’t the only possible issue—what I was thinking of was an overcurrent situation, where the wiring is no longer capable of safely carrying the needed current due to broken strands and/or poor connections.
There’s a reason my company’s service department uses a thermal camera during our check-ups of our O&M customers. We look at all the connections in the customer’s equipment and make sure none of them are running hot. If they are, it’s almost certainly because of an undertorqued lug that isn’t giving a good connection. Those are much higher-current situations, but the same principle applies—if you have a damaged wire or a marginal connector, it will heat up and may burn. Fires can start from a tiny, tiny source and spread from there. Poorly-made connections and damaged wires are among the most common causes of electrical connections.
The inability of the wiring to drive the pump despite giving 12V at no load indicates that there’s more resistance on the circuit, and therefore more voltage drop under load, than there should be. Excessive resistance in a wire creates heat, which increases resistance (resistance increases as temperature increases), which creates more heat, and then boom your wire has melted and possibly set fire to whatever was nearby.
The pump circuit is disabled now, so it’s not a hazard. However, there may well be other horrors hiding behind the dashboard or in the engine bay.
It’s certainly on my list of concerns, but on these cars, it’s very low. Again, this goes back to the batshit electrical. Look up the fuse box diagrams – barely anything in this car is fused. Because barely anything in this car can draw amperage. The only things I’d be significantly concerned about actual current load on are the lights and radio, which are all fused.
Everything else is genuinely low voltage, low current – the high draw bypasses the ECU entirely. And that’s where I’m certain the damage is – in the low current harnesses. I mean this is literally a system that has so many corners and costs cut, the ECU’s permanent power is through the rear dome light with a shared fuse. And the IPC has no fuse at all.
I certainly would not leave the battery connected while unattended just as a precaution, but with the correct size fuses, I wouldn’t have any real fire worry while doing diagnostics. At least not in any high risk areas. Now, melted bulb connections, yeaaaaaaaah…
Not just Suzuki. My 2002 F250 has vacuum powered front hubs. They are well known for developing leaks in the seals around the hub and axle, and you have to take the front axle apart to repair. That and the hubs themselves would freeze and you couldn’t even move them manually. At least I was able to replace the hubs and can lock them manually. At some point, I might even fix the seals.
Thank you for this. But you did completely take the wind out of my snark. 😉
So much wrong on the BW1339 Quadra-trac. First off, the BW equipped SJ doesn’t have air locking hubs. It doesn’t have hubs at all in fact, it has drive plates. The BW1339 transfer case is a full time 4wd transfer case, so the front axle needs drive all the time. The Emergency Drive (I’m going to shorten this to e-drive) switch sends vacuum to one of 2 ports located on the transfer case, which either locks the front and rear driveshaft together mechanically (e-drive, which duplicates 4wd mode on a part time system,) or disengages the drive coupler and allows the transfer case to send power to the driveshafts through a differential equipped with a limited slip mechanism. There is no default position for the actuator, if you send vacuum to one port it engages e-drive, and if you send it to the other port it disengages e-drive. Problems with e-drive are typically vacuum problems with hoses having leaks or breaking. It’s actually pretty easy to bypass the switch and you can generally attach a hose directly from an engine vacuum port to the vacuum actuator in the event you need to keep it in one position or the other (more than likely you would want to send it to the non-e-drive position to drive back home on the roads.) Source – I have a 1339 equipped 76 CJ-7, and I have had to juggle the vacuum lines to get it out of e-drive mode.
Now let’s get to David Tracy. If you know the air pump works, why wouldn’t you just bypass the stock computer and run a fused 12V line from the battery (or fusebox or other 12V source) to a switch, and then from the switch to the pump You could even get fancy and use a relay. The cost would be even cheaper than 9.99 (I bet you have a switch and wire laying around, in fact,) and you can put the switch in a blank spot on the dash. Then you just have to pull the lever and hit the switch, boom, you’re in 4wd and you don’t have to leave the truck and blow up some air bulb. Then if you ever want to fix the stock wiring you just splice the wires you cut back together and it’s back to stock.
Agree with Andyindividual, took some of the wind out of my sail…when I swapped TJ rubicon axles into my non-rubicon, I had a friend at the dealership and he installed the rubicon axle pump assembly, but then told me the ECU wasn’t compatible and wouldn’t work. I was fine with that…in the end the mechanism
Is just two small air pumps and all they need is power…simple switch and relay set up and I was good!
So simple switch would be good, in fact would be easy to tap into the current switch already connected to the transfer case shifter and ECU, then use that signal to have it actuate the pump. A few cheap components and everything would operate as intended…but does not get to the root of the issue, which is why is the ECU signal no longer able to drive the pump…that would take some probing!
Isn’t this kind of situation exactly why electrical relays were invented? The power from the ECU should be enough to trigger a relay which is hooked up to a big fat wire hooked up to the battery. Zzzzzt! Pop! and you’re in 4WD.
Or am I missing something here? I do have some English ancestry so it’s possible I have some Lucas genes, but even so….
I wish some of your comments were expanded and posted as full articles 🙂
Oh look, here it is! Was looking for it a while ago!
What a terrible location to put that electric pump. Cross a stream too deep, you could lose front drive and water could even get in the diff. Not the best design.
On another note, glad to see I’m not the only one who likes to drive barefoot.
It seems to be pretty happy in that spot. Technically the pump should be sealed. I’ve blasted through some pretty deep water in my tracker, and the little pump is still going after 230,000 miles. (minus one o-ring re seal)