Center Axle Disconnect Replacement Options


Chris

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One of the mighty downfalls of the YJ's axles (aside from the d35c) is the Center Axle Disconnect. Every YJ has them stock, and if you haven't been acquainted with yours yet, it may only be a matter of time!

So what is the Center Axle Disconnect? Its the little box on the passenger side housing of your front d30 axle, it houses a shift collar that is vacuum operated. The purpose of the CAD is to use vacuum to slide a shift collar and lock the 2 piece axle shafts together, thus allowing you to be in 4wd. What may end up happening is the vacuum motor will fail, or vacuum lines end up cracking/splitting/etcing, causing your jeep to no longer engage 4wd. This can end up being a headache trying to replace the vacuum motor, or trace down broken vacuum lines.

This thread is meant to give you several different options to work around the potential unreliability of this vacuum system. It's also worth noting by doing modification number 1 or 3, that your axle shafts, and front driveshaft will be in constant rotation while driving. According to the engineers at Jeep this will roughly translate into a 0.1, to 0.3 loss in miles per gallon. The TJ, and JK wranglers do not have a CAD, as it was ditched after the 1995 model year YJ.

1) Replace passenger side 2 piece axle shaft, with solid 1 piece axle shaft.
(This particular workaround will give you the strongest results!)

Whats involved:
a) Sourcing a solid passenger side axle shaft. These can be found in 92-99 XJs (Cherokee) and 97+ TJs. The 96-99 XJs, and any TJ axle shaft will have the larger 297x u-joints. (Make sure you don't get one with CV joints!) If you do find 96+ shafts, you might as well grab the drivers side and upgrade too!
b) Purchasing a drivers side axle shaft seal
c) Either fabricating a block off plate, or re-using the old shift fork housing

How to do it!:
1. Apply emergency brakes, and chock the rear tires, jack front end up and support with jack stands.

2. Remove tire, and the cotter pin on the axle nut. Remove brake caliper, there are two 13mm bolts on the back. Pull rotor off wheel studs. Torque setting is 11ft/lbs

3. Remove axle nut, it requires a 36mm six point socket this may require a breaker bar, and an air impact wrench if you have one. Be sure to use an impact socket! Torque setting is 175ft/lbs

4. Remove three 13mm twelve point bolts on the back of the unit bearing. Torque setting is 75ft/lbs

5. If the unit bearing is stuck, a BFH with a gentle hit in the right places, paired with a pry bar can make easy work. It may benefit you to use anti-seize on the contact areas to make this step easier in the future.

6. Place a small container oil catch container under the CAD housing, unplug vacuum lines from the housing, use either bolts or vacuum line caps to plug them with. Remove the four 11mm bolts holding the housing on and remove housing. Let any oil drain from the housing.

7. Slide the outer axle shaft out and remove the collar on the shaft. Pull the inner shaft out. Remove the seal on the right side of the CAD housing.

8. Seat the new seal, you can be creative here, or rent a seal puller from an auto parts store.

9a. If you decide to make a back off plate to replace the vacuum housing, use the existing housing as a template for size and bolt positioning. When reinstalling use a gasket sealer, such as RTV to seal the back off plate to the housing.

9b. You can also reinstall the existing vacuum housing back in its original location, you do not need to hook anything back up to it if you don't want to, as it will be useless.

10. Trace back vacuum lines, and wiring harness and remove as necessary. In the case of the wiring harness, just move up into the engine bay.

11. Repeat steps 2-5 for drivers side if you are replacing this shaft as well.

12. Grease splined shaft ends of replacement axle shafts, and where the axle seals ride along the shafts.

13. While sliding in new axle shafts, support them next to the axle tubing as to not catch on the axle seals.

14. Reinstall the remainder of the components in reverse order, make sure to torque to spec.

15. Refill differential with recommended gear lube. Typically 90 weight for open differential. If an aftermarket Limited Slip Differential has been installed, you may also be required to mix in a friction modifier.

2) Replace system with Posi-Lok cable system

Not to be confused with a posi-traction or limited slip, or any other type of locker, the posi-lok cable installation will allow you to mechanically engage and disengage the shift fork. The benefit of this will allow you to run in 2Lo in addition to 2Hi, 4Hi, and 4Lo.

3) Inexpensive vacuum shift motor fix
(This is by far the cheapest solution if you're working on a budget!)

1. Remove the four 11mm bolts that secure the shift motor to the axle housing and remove the shift housing assembly, have a drip pan ready.

2. Remove the 2 "E" type retaining clips that hold the shift fork on vacuum motor and the 1 "E" type retaining clip that holds the vacuum motor to the shift housing.

3. Pull the vacuum motor out of the shift housing which will slide the shift fork off the shaft.

4. Take the shift motor to the hardware store.

5. Buy a long spring that is just large enough to slide over the shaft of the vacuum motor shaft and take it home.

6. Slide the spring onto the shaft of the vacuum motor, put the shift fork back inside the shift housing and slide the vacuum motor back inside the housing so as to fully compress the spring. The spring will be too long so make a rough guess as to how much to trim off so that the vacuum motor will go all the way back into the shift housing.

7. Once the spring is the correct length slide the vacuum motor back in and install just the 1 large "E" type retaining clip that holds the vacuum motor into the shift housing. The other 2 are no longer needed.

8. Slide the shift collar inside the axle housing over to engage the front axle.

9. Apply RTV to the housing and install back on the axle housing making sure to align the shift fork up with the center of the shift collar inside the axle housing.

10. Refill differential with recommended gear lube. Typically 90 weight for open differential. If an aftermarket Limited Slip Differential has been installed, you may also be required to mix in a friction modifier.
 

Utok967

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I've done the Posi-Lok fix, and it works, sort of. You need to be moving when you engage it or it ain't going in. I also had trouble with it disengaging under heavy load. Kinda scary. I wasn't impressed. I'll be trying the axle shaft replacement this weekend. I have a D30 from a Grand with new axle shafts in it I'm going to scavange from. Might fit, might not. I'm also thinking I'll need to replace the front driveshaft with one from an XJ. I know I'll have to shorten it.
 
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rrrjr

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I did the tj solid shaft swap on my yj a long time ago and i need the part # on seal you go for it because ive tried numerous ones and theyve all failed on my and left my slinging gear oil everywhere 🤢
 

Wolfe

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I saw a vid where the guy completely removed the fork because it somehow broke and used 2 hose clamps to keep the collar over the shaft. Supposedly they have been driving like that for 2 years if i recall.
I'm going to give it a whirl this weekend. I was also thinking I could use a piece of pex pipe to keep my fork slid over as well
 
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ian.thomas

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My fork is cracked which prevents proper engagement. I removed the fork and went the clamp route. Only been a few days but so far so good. I imagine this will wear the front axle joints more quickly but that's easier to deal with than chasing down "why can't I go into 4wd today".
PXL_20201109_222831525.jpg
 

machoheadgames

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My fork is cracked which prevents proper engagement. I removed the fork and went the clamp route. Only been a few days but so far so good. I imagine this will wear the front axle joints more quickly but that's easier to deal with than chasing down "why can't I go into 4wd today".View attachment 116600
If by joints you mean driveshaft u-joints, maybe. If you mean axle shaft u-joints, won't make a lick of difference because they turn all the time anyways. Doesn't really matter at the end of the day, TJs were setup to spin full time from the factory and they didn't have issues from it. It's fine. Enjoy your more reliable setup.
 

machoheadgames

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I did the tj solid shaft swap on my yj a long time ago and i need the part # on seal you go for it because ive tried numerous ones and theyve all failed on my and left my slinging gear oil everywhere 🤢
Napa 11800 is the one I used and it seems to have been perfect for me. No issues at all.
 

jeepjoe43

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Anyone know what seals will be required for a D30, 30 spline set-up?
Planning on ordering the parts for my D30 soon and I'll be talking to the experts, but service parts are good to have.
 

machoheadgames

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Anyone know what seals will be required for a D30, 30 spline set-up?
Planning on ordering the parts for my D30 soon and I'll be talking to the experts, but service parts are good to have.
You need a TJ Rubi 44 seal for the front left seal (I’d recommend Spicer 54381) and then the axle companies (Revolution for example) carry part numbers that fit the right side. I do not know the numbers, but I know Revolution sells kits for YJs that come with 3 seals. The one at the CAD isn’t even really necessary once you put the one at the right side of the diff, but they include it anyways. Call them and ask what they provide. They may even be able to sell you some for cheap.
 
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jeepjoe43

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You need a TJ Rubi 44 seal for the front left seal (I’d recommend Spicer 54381) and then the axle companies (Revolution for example) carry part numbers that fit the right side. I do not know the numbers, but I know Revolution sells kits for YJs that come with 3 seals. The one at the CAD isn’t even really necessary once you put the one at the right side of the diff, but they include it anyways. Call them and ask what they provide. They may even be able to sell you some for cheap.
Thx, I plan on eliminating the CAD altogether. I'm guessing the seals will probably come with the R&P bearing kit for those axles.
I'll be getting my parts from ECGS, and the axles will probably be Yukons. But good to know!, Thx Brother!
 

machoheadgames

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Thx, I plan on eliminating the CAD altogether. I'm guessing the seals will probably come with the R&P bearing kit for those axles.
I'll be getting my parts from ECGS, and the axles will probably be Yukons. But good to know!, Thx Brother!
No choice, you have to ditch the CAD in order to go 30 spline. Proper seals will not come in an R&P master kit, they don’t differentiate, or at least I haven’t ever seen that. Usually if they give you any seals, they would be for stock 27-spline axles and they would be for a basic non-CAD axle that just has two simple seals in the diff, like a TJ or CJ.

In Revolution’s YJ axle kit, they give you 3 seals, a factory Rubi left seal, a different seal for right side of diff, and a third seal for the CAD. The one for the CAD is basically unnecessary, I think they just give it to you in case anything ever made it past the right diff seal. The axle shaft isn’t machined for a seal there though so I don’t really get the point.

The only axle kit as far as I know that ECGS sells is the $525 axle kit. It is just the simple imported kit that all the brands sell reboxed. It is sold as Revolution’s “discovery” series, and all the other companies main set of 30 spline shafts.

Also, I dunno what gears you’re buying but Revolution have been the finest quality I’ve ever seen, and that is confirmed by guys who know how to setup gears too. Yukon is not as good lately, they created their own line from China and they have not been promising. Motive is pretty good. Motive and Revolution are both out of stock currently. I’m personally waiting on my set to ship and they said 4 weeks.
 
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SirDoopYJ

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What was the purpose for having a two piece axle shaft to being with? Do CJ's use vacuum or are they just locking hubs?
 

machoheadgames

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What was the purpose for having a two piece axle shaft to being with? Do CJ's use vacuum or are they just locking hubs?
CJs are just locking hubs. It’s basically a TJ front axle, except with locking hubs and the diff is passenger side.

I’m not 100% sure why they went the CAD route, I believe it was for higher EPA ratings. Then they later saw how miserably it fails (many 87s were definitely failing by the time the 97 TJ came out in 96) so I’m guessing they deleted it for that reason, and especially after they realized it doesn’t really save any fuel anyways.

The XJ followed a similar history except it ditched the CAD even earlier. They had a HP30 CAD from the 80s to early 90s, then had a HP non-CAD 30 from 92ish to 96, then 97-01 they used the same LP non-CAD 30 that the TJs used.
 

jeepjoe43

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No choice, you have to ditch the CAD in order to go 30 spline. Proper seals will not come in an R&P master kit, they don’t differentiate, or at least I haven’t ever seen that. Usually if they give you any seals, they would be for stock 27-spline axles and they would be for a basic non-CAD axle that just has two simple seals in the diff, like a TJ or CJ.

In Revolution’s YJ axle kit, they give you 3 seals, a factory Rubi left seal, a different seal for right side of diff, and a third seal for the CAD. The one for the CAD is basically unnecessary, I think they just give it to you in case anything ever made it past the right diff seal. The axle shaft isn’t machined for a seal there though so I don’t really get the point.

The only axle kit as far as I know that ECGS sells is the $525 axle kit. It is just the simple imported kit that all the brands sell reboxed. It is sold as Revolution’s “discovery” series, and all the other companies main set of 30 spline shafts.

Also, I dunno what gears you’re buying but Revolution have been the finest quality I’ve ever seen, and that is confirmed by guys who know how to setup gears too. Yukon is not as good lately, they created their own line from China and they have not been promising. Motive is pretty good. Motive and Revolution are both out of stock currently. I’m personally waiting on my set to ship and they said 4 weeks.
I realize I don't have a choice on the CAD.
Just assumed the fronts would be Yukons, that's what came with the rear anyway they were in a Yukon box.
As for the R&P, I hadn't given the brand too much thought, figured I would just buy what they've got.
Don't recall seeing too many choices on their site.
I also realize the likelihood of breaking one goes up with stronger shafts.
But I've never broke a R&P, just axles, and lots of them (7 in just One Summer on the Flatty).
 

machoheadgames

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I realize I don't have a choice on the CAD.
Just assumed the fronts would be Yukons, that's what came with the rear anyway they were in a Yukon box.
As for the R&P, I hadn't given the brand too much thought, figured I would just buy what they've got.
Don't recall seeing too many choices on their site.
I also realize the likelihood of breaking one goes up with stronger shafts.
But I've never broke a R&P, just axles, and lots of them (7 in just One Summer on the Flatty).
I get it. My main point was regardless of what axle kit you buy, reach out to revolution for the seals because they will tell you the ones to get. None of the brands come with them except the Rev USA series. So just reach out to them for what seals you need. They won't come in a gear kit either.

The R&P you get doesn't really matter, Revolution has been told to me by gear setters that they are the best they have ever seen, so that's what I buy and recommend. Heavy wheelers still recommend the 30-spline shafts and so far, I have not seen reported extra R&P breakages, so I would not worry about that really at all.

Looks like ECGS has no 30 Reverse in stock, so you'll be waiting regardless. The 30 is the holdup on my 30/44 Revolution kit I ordered too.
 
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jeepjoe43

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I get it. My main point was regardless of what axle kit you buy, reach out to revolution for the seals because they will tell you the ones to get. None of the brands come with them except the Rev USA series. So just reach out to them for what seals you need. They won't come in a gear kit either.

The R&P you get doesn't really matter, Revolution has been told to me by gear setters that they are the best they have ever seen, so that's what I buy and recommend. Heavy wheelers still recommend the 30-spline shafts and so far, I have not seen reported extra R&P breakages, so I would not worry about that really at all.

Looks like ECGS has no 30 Reverse in stock, so you'll be waiting regardless. The 30 is the holdup on my 30/44 Revolution kit I ordered too.
Thx again for seal info, I will look into Revolution.
Figured I might end up waiting from ECGS, but I'm not in a hurry.
I did ask them about sourcing and building a D30HP for a drop & swap, but they wouldn't do it.
I suspect they're more about building stuff for Rock Bouncers, and stock swaps are just a sideline.
Though I have to say their customer service is outstanding. For that kind of $ it ought to be....
I'm not worried about R&P strengths, that damage is the realm of HP and bouncing.
I neither have, or do either.
 

machoheadgames

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Thx again for seal info, I will look into Revolution.
Figured I might end up waiting from ECGS, but I'm not in a hurry.
I did ask them about sourcing and building a D30HP for a drop & swap, but they wouldn't do it.
I suspect they're more about building stuff for Rock Bouncers, and stock swaps are just a sideline.
Though I have to say their customer service is outstanding. For that kind of $ it ought to be....
I'm not worried about R&P strengths, that damage is the realm of HP and bouncing.
I neither have, or do either.
Yeah unfortunately they will not really do anything not on their website. I wanted to buy an empty 44 housing from them with YJ perches welded on because I don't need half the stuff they require you to buy when you build one. Nope. Same as you said as well that they won't build a 30 for a YJ yet they will sell regeared/locker built HP30s from Cherokees for TJs.

I get it, it's about money, but they would make more catering more options than they are getting from me not buying at all. One thing I do like them for though is price matched, no tax, and free shipping over $500. They are a great choice to buy from if you need a locker or something, or anything else up above $500 if you want to beat another place by price matching them.
 
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jeepjoe43

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Yeah unfortunately they will not really do anything not on their website. I wanted to buy an empty 44 housing from them with YJ perches welded on because I don't need half the stuff they require you to buy when you build one. Nope. Same as you said as well that they won't build a 30 for a YJ yet they will sell regeared/locker built HP30s from Cherokees for TJs.

I get it, it's about money, but they would make more catering more options than they are getting from me not buying at all. One thing I do like them for though is price matched, no tax, and free shipping over $500. They are a great choice to buy from if you need a locker or something, or anything else up above $500 if you want to beat another place by price matching them.
True That!