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-   -   YJ Trans swap, BA-10/5 to AX-15 ** Write Up (

Richmond88yj 09-05-2006 08:09 PM

YJ Trans swap, BA-10/5 to AX-15 ** Write Up
This is a write up to put a 94 Ax-15 out of a 4.0 YJ, replacing a stock BA-10/5 in an 88 YJ 4.2. Some known changes are the AX-15 needs a different pilot bearing and also it has an external slave as opposed to the internal one on the BA-10/5.

Legal disclaimer, yadda yadda yadda.. This is how "I" did it, and it's for reference only, if you follow this write up and screw up your ride, it's not my fault.

I started by spending about 1/2 a day cleaning up the garage, rounding up all my tools and making sure I had all the basics. I left plenty of room around the YJ to be able to work. Normally it's a complete pit and I generally have tools all over the floor, but for the write up I thought I'd try a bit harder to stay organized.

I also went and got a bunch of these quart bags with some 3x5 cards and a sharpee to mark all the nuts and bolts etc as I pulled them off. Normally I use a shoebox and figure it out as I re-assemble, but this seems like a much better approach. The big clip/sealer thing makes it easy to zip/unzip with mechanix gloves on.

First up is to block the YJ from rolling, with the driveshafts out, don't trust the e-brake. Set the brake and also put bricks under each wheel. Then disconnect the battery and double check your wheel chocks. This is the time to also find those safety glasses, 20 years of crap will be raining down on you all through this job, regardless of how clean your rig is.

Start with the rear shaft. Unbolt the 4 bolts, 8MM, and remove the clips. Jiggle the shaft a bit and then when the rear is free, pull it out of the tail cone. A little ATF will drain out so have a pan and a rag ready. (book says to replace these and not re-use the bolts or clips)

I was quite surprised to see my needle bearings on the rear U-joint were dust. The lifetime guaranteed u-joint was only about a year old.

Next up is the skid. Place a jackstand under the tailcone to hold the tranny/t-case. the whole drivetrain only attaches at 3 points. The skid plate and the two motor mounts. If you don't support it, it will pivot on the motor mounts and the tranny will go to the floor, prolly taking out the radiator and possibly the front clip. Support it securely.

DO NOT USE JUST YOUR FLOOR JACK FOR THIS SUPPORT, it will not hold the pressure for 5-xxx hours as you complete the job. It will slowly drop and you will cry as your fan/waterpump/alternator slowly push forward and munch your radiator and front clip.

To unbolt the trans from the skid, loosen and remove the 2 mounting bolts 5/8", and the outrigger bolt. (this is a little weird, 2 bushings, 3 nuts,5/8" on a threaded rod). Fart with it for a few minutes with a couple of wrenches and you'll see how it goes together.

Remove the 2 bolts (1/2") from the cat damper. This is the bracket thing that holds your exhaust to the front part of the skid just in front of your catalitic converter. The damper is actually connected to the outrigger. Next remove the 2 bolts (5/8") holding your exhaust downpipe to the exhaust manifold. This is needed so you can move the exhaust out of the way a few inches so the bellhousing will clear when you slide the trans back. (you may need plenty of PB Blaster for these)

Place a jack under the skid and remove the outer two bolts from each side (3/4"). Then loosen and remove the center bolts, the skid can now be lowered and moved out of the way. Make sure you do this slowly watching your support on the t-case tailcone assy.

Richmond88yj 09-05-2006 08:10 PM

Disconnect the wires and vents from the trans and t-case. There should be your speedometer cable, 1 elec connection on the trans (backup light switch), 1 4-way vac assy on the T-case and one vent hose for both the trans and the t-case.

Then disconnect the slave cylinder tubing coming down from the master cylinder. Be careful with this, some use a flare wrench, don't strip the nut. It helps to have 2 wrenches and kinda brace one of them on the nut holding the tube on the master cylinder side, the slave cylinder side is the one that spins out.(The master cylinder side DOES NOT SPIN, don't force it, only hold it.

Master clyinder side (this one is sealed to the tube and doesn't spin)

Slave Clyinder side (this one turns)

Now take out the front driveshaft. Remove the 4 bolts (8MM) and the straps on the front side first. Then do the rear. The shaft will spin, so take a long screwdriver or prybar and wedge it into the U-Joint to keep it from spinning as you unbolt the straps. Jiggle it a bit and the shaft will come free from the yokes. The front is a telescoping shaft, so just pull the front part toward the rear, shortening it and it'll come right out.

Next up is removing the starter. These are two different sized bolts, one front (5/8"), one rear (9/16"), this one also holds the pulse air brackets. If you've long since lost your pulse air, dump it, if not draw a pic of how it looked, and place it in your ziplock with the bolts and the bracket, it's a little tricky to re-attach right. Take the starter out and leave the wires connected, just secure it to the spring and out of the way. Long ty-wraps work good for this.

Now remove all but the side two bell housing bolts. just loosen these slightly. Drain your trans (easier now with skidplate gone) and your Transfer case. Once all drained. Place transmission jack under the trans, center it right to compensate for the weight of the transfer case and snug it up good. Attach straps or chains to keep it from twisting/rolling off and sinch them up tight. Now remove side two bolts and place in the bellhousing bolt baggie with a label (you are doing this right?). Wiggle the trans/tcase assy back guiding the loosened exhaust under it. Once the input shaft clears the clutch you can gently lower it down. If you have less than about 6-7" of lift and 33's or 35's you'll prolly have to take it off the trans jack while it's under the rig and slide it out. If you have the lift, just roll it out on the jack.

After pulling it, I noticed the shreds from the pilot bearing. The input shaft is kinda chewed up also. I've replaced 2 rear main seals trying to find this leak.

Richmond88yj 09-05-2006 08:10 PM

Separating the transfer case from the POS Ba-10/5 is the next step. If you are re-using your transfer case, you will need a new 23 spline input shaft, the one on the Ba-10/5 is a 21 spline shaft. If your using a new or new to you transfer case that has a 23 spline shaft, skip this step. Be careful though, most of the transfer cases on the YJ Ba-10/5's were NP-231-AMC which has a yj style mount for the levers. If you get a transfer case out of an XJ, more than likely it's a NP-231-J which does not have the holes for the lever brackets in the right place. Additionally the -AMC case, for yj's is "clocked" 10 degrees clockwise from those on XJ's. This means it will sorta work, but your tcase will be rotated 10 degrees down. (same hold true for XJ guys trying to put a -AMC transfer case into an XJ, it will hit the floorboard. Double check the tag on the rear of the t-case.

One the POS is on the ground, start by loosening the adjustment linkage bolt (1/2") but leave it in. Then take off the two bracket bolts (9/16") and put in the baggie. Lastly take off the one by the shifter pivot and the nut on the shifter bellcrank. (other end of the adjustment linkage) Remove the shifter assembly and bag the bolts.

Now remove the other three 9/16" bolts and wiggle the transfer case from the POS Ba10/5. It's a bit heavy, watch your toes.

The Ba-10/5 is a skinny little POS next to the AX-15. The AX-15 is made much better and will hold up to all but the beefiest 350's. Either bellhousing will work, all the holes are the same, both on the trans side and the engine side. Howver.... If you're changing to an external slave cylinder for your AX-15, go with an AX-15 bellhousing if you can, The Ba-10/5 bellhousing has a different hole for the slave cylinder and you'll have to booty-fab up the mounts if you use the Ba10/5 for an external slave. There is no shame in staying with an internal slave on the AX-15, it's just more of a PIA when you need to change it out. (do all this crap again).

The Ba-10/5 does measure exactly the same from bellhousing to transfer case.



Richmond88yj 09-05-2006 08:11 PM

Now with the trans out, it's time to make a few phone calls and a trip to the boneyard. You're going to need a few things.

a 23 spline input shaft for the t-case. $189.
A pilot bushing $20
Master cylinder $79
Slave cylinder $40
Tube to connect the two $4

A quick call to Advanced adapters and the 23 spline input shaft was on the way. The BA-10/5 has a 21 spline output shaft and the AX-15 has a 23 spline(stronger). So rather than change out the trans output shaft, change out the input shaft on the t-case. While you're on the phone with Advanced, go a head and get the pilot bearing also. it's only 20 bucks, and although it's not a perfect fit into the crankshaft, it's close. A little sanding/filing and you'll be good to go.

Start by taking the t-case apart. Remove the tailcone and the oil slinger cover. 7 1/2" bolts.

Have your starsocket handy as two of them are that goofy starnut bolt. #12 starnut. Also Note the pic, two bolts have washers on them, only two, mark them, it is critical these go back on the two same holes.

Once the t-case is cracked, work loose the oil slinger tube from the slinger (this big disk thing like a plate covering the tailcone. Once the oil slinger tube is out, remove the slinger. Now remove the last snap ring and seperate the case. Inspect the case now on the inside for any gunk, metal shavings etc. I got lucky with mine, it literally looked brand new. Not bad for a 20 year old rig.

Remove the front yoke with a bigass socket. I think it's 1-1/4". It's a rusty dog too, use plenty of PB Blaster, I needed an impact wrench on mine. Once it's off, pull the whole assembly out as one big peice and set aside. The last part left in there is the input shaft. Flip over the casing, remove the one snapring and it comes right out. Slide the new one in and replace the snap ring by slinding over the shaft and pressing it in place with a screwdriver.

Now would be a good time to install that SYE kit if you've been wanting to). Clean up all gasket areas and remove all traces of sealant. I also took this time to really clean the case up. A wire brush on a drill made it look almost new.

Re-assemble the t-case in reverse order you took it apart. Make sure to keep track of those little plastic bushings, they are a pain, but if you lose one you'll regret it. Use plenty of "form-a-gasket" RTV on all mating surfaces and torque down to the specs in the book.

Richmond88yj 09-05-2006 08:12 PM

Mount the re-assembled t-case on to the donor trans. Torque down all the nuts except for the two that hold the bracket/linkage assembly for the t-case shifter.

Test fit the shifter linkage. It will need a little adjustment. There is a bolt hole in the wrong place, it sticks out about an inch.

It's cool, because it's not needed and can be shaved flat with the housing. Break out the grinder and carefully grind it off.

Now that this hurdle is overcome, go find that bucket of bolts. The center bolt from the mount on the BA-10/5 is smaller than the hole on the AX-15. You'll need to find a bolt that will fit the hole. 3/8x1/5 worked on this trans.

Now tighten down these last 3 bolts. Hook up the linkage on the bell crank and torque down to spec.

Now for the pilot bearing. In no uncertain terms this is a total PIA. If your rig is like mine, it's been in there for 15+ years. It's tough to get out. I thought I'd be smart and spend 25 bucks on this nifty shifty pilot bearing puller from Harbor Freight so I didn't have to fight with it.

I carefully followed the directions, secured it and cranked away. In an effortless turn of the crank a simple "pop" and the puller fell free. With the glorious sounds of all the angels in heaven singing, my satisfaction in a job well done was overwelming, I was like little Ralphie on that Christmas show when he finally go to shoot the bullseye in the target. But just then, as the bb hit poor Raphie in the movie, the wqves of anger and depression crashed over me. CRAP!, the POS puller broke. So I tied the pack the hole full of grease meathod and hydrolically press it out. Well, after a big mess, I gave up and grabbed the hacksaw blade. Cut it in half and tapped it out with a pin puch in about 20 minutes. Don't wast your money on the pilot bearing puller.

With the old one out, time for the new one, that according to the directions is made from some sort of oil impregnated alloy that you must soak overnight in 20w40 oil, which I did.

But when it came time to press it in, the inside diameter was right on, but the outdside was to big. P wrapped a big drill bit in electrical tape, pressed on the bearing and spun it up. I slowly used 80 grit then 100 then 200 on it until it was shaved down to the right diameter. The with a few taps teated it into the crankshaft. I covered the hole and then hit my flywheel up with some 150 grit sandpaper to clean it up a bit. Normally you should have this resurfaced, however since I'm going EFI shortly and have to get a different one anyway, I just did it by hand.

Richmond88yj 09-05-2006 08:12 PM

Once all back together, double check every bolt. It's easier to do it now while it's out than to fart with it under the rig. Fill the trans with about 3 liters of your favorite 75-90 gear oil. I like Penzoil Syncromesh, but the store was out of it so I had to settle for Mobil-1. Also now is a good time to fill the t-case with ATF if you haven't already.

Now, attach the cluch and pressure plate using your clutch alighment tool and following all the normal clutch replacement steps.(won't re-write all those steps, it's pretty easy to find in the manuals or on the web). Just a note, use the clutch and pressure plate for your engine, not the trans. I have an 88 4.2 motor and a 94 AX-15 trans. I need the clutch for an 88 4.2 as that is the flywheel I have.

Using the trans jack, slowly, safely and carefully guide the trans back up to the flywheel. Go slow. The tolerances on the pilot bushing and the input shaft of the trans are very small. If you force it you will dammage your pilot bearing and have to do all this crap again soon. Slowly align and adjust the trans and slide it home. Install the two outer bolts first just beyond finger tight. Then install the rest, tighten to spec.

Place a jackstand (Not a Floor Jack) under the tailcone like you did on removal and remove the trans jack. Remove the jack holding the motor up.

Install the starter and connect all the wires and plugs. (speedo, vent, etc) your backup swtich from the ba-10/5 will not work in the AX-15. Just cut the wires on each and splice them together. Which one doesn't matter, it's a simple contact closure switch. Tape them up.

Install the front driveshaft, then the rear. Then re-attach the skidplate and torque down. If you're lucky as I was, the mound from the AX-15 will drip right down into those 2 little holes in the skidplate.(I always wondered why they were there). Seems the skids even on 88's were cut for both trans types. Bolt up the trans and the outrigger to the skidplate and make sure to leave the outgigger a little loose. It's not supposed to be cranked down hard.

Re-attach exhaust dowpipe and cat bracket.

Remove jackstand and drink a beer, almost done. Install trans tunnel plate, shifters and shifter boots. Re-install carpeting and any other misc little crap you skipped until now.

Last challenge, the clutch slave and master cyclinders.

I have an 88 (with 88 pedals) the trans is a 94 which needs a longer throw on the slave cylinder. Solution is to buy a new slave and master for a 94. Just a few problems. The holes in the firewall don't quite fit and the tube that goes between the master and slave have different fitting types. My old 88 had the screw on ones and the 94 master/slave had the newer roll pin versions.

**Pics to be edited in**

So... A quick trip to the boneyard $4 bucks later, I found out every post 93 with external slave have the exact same tube and fittings. YJ, XJ, ZJ, MJ, TJ etc all the same. So I scarfed one out of a 96 XJ tossed the guy 4 bucks and sure enough it fit perfectly. Now to overcome the 94 master in the 88, a little modding needs to occur. The ring thing that hood to the clutch pedal on the master needed to be opened up a bit, it's plastic to sit only takes a sec. And also only one of two holed line up for the master on the firewall. I used the top one and re-drilled the bottom one in the master and it fits perfectly. Add a bit of DOT-3 fluid and bleed and your ready for a test run.

A few notes....

This swap was a bit more expensive than I thought going in, but was definately worth it, and also is much cheaper than going to AAMCO or your local garage for a replacement BA-10/5

Trans $300
23 Spline Input shaft $200
Master $79
Slave $49
Pilot Bearing $20
Misc paint, fluids, gasket rtv, trip or two to the store $40
Total $650

*Add $130 for clutch pressure plate and throwout bearing (I didn't need em)

So far about 50 miles on the new trans and other than the clutch needing to be bled a bit better, it is a welcome upgrade. No more whining of gears, no more popping out of reverse and no more "surprise, it's stuck in 1st again" moments which always come at the worst time.

And lastly time for the swap. It took collectively 26 hours over the course of 2 weeks by myself with just the occasional harrasment by my wife. It may have gone quicker but I wanted to journal it. Hope this answers a few questions if you're looking to do the same swap.

BigDeaner 11-18-2008 01:50 AM

i did the same swap but couldn't managae to find the breather cap for the ax15? Any suggestions?

Kool2BSquare 12-06-2008 10:14 PM


Originally Posted by BigDeaner (Post 6025490)
i did the same swap but couldn't managae to find the breather cap for the ax15? Any suggestions?

The breather cap? Are you speaking of the vent on the shifter plate?
The BA10 has the vent in the case, the AX15 vents out the shifter plate.
If you are using an aftermarket shifter like a B&M or Hurst then you'll need to drill either the shifter plate or the case.
Otherwise there isn't a hose that goes to it like on the BA10, (at least there wasn't on the AX15 I got out of a 96 XJ.)

There's info on that in this article:

Awesome write up the pics! :2thumbsup:

YJ_Dominator 01-15-2009 09:26 AM

Excellent writeup, great pics

87blackjeep 01-20-2009 08:41 AM

I was wondering why you have to get a new flywheel if going to efi? I have 87 4.2w/4.0head,howell efi,and they said nothing about a flywheel swap?????

rustywrangler 01-20-2009 08:57 AM

This is a trans swap thread, not an efi swap thread. He got a new flywheel because he wanted to.

87blackjeep 01-22-2009 11:34 AM

If you would read the article instead of running your mouth ! I had a legitamite ?and he didn't get a new flywheel he was going to when he went to EFI

87blackjeep 01-24-2009 11:14 AM

I have a 23spline from a buddy that I'm going to put with a nv3550 ,how much of a pain is the linkage on the 231j

srf4life 03-27-2009 09:02 AM

Thanks for the write-up. I need the seals for my B/A-10 replaced so instead of spending the money to get just seals replaced I am going to replace the B/A-10 with the AX-15.

This thread/write-up cleared up alot of questions. THANKS AGAIN!!!

jimmyjames330 04-10-2009 08:01 PM

i just bought a 88 wrangler it has a jasper 4.2 , a rebuilt ax15,and a rebuilt transfer case.20k miles ago but when i bought it every time i would start it , it would grind so i put a new starter in it. when i had the starter out i checked the fly wheel and it had a spot on it where two of the teeth where chipped off. and it was better for like two days then it just stopped grabbing so now i want to change the flywheel. but i dont know what flywheel to get should i get the one for the 4.2 or the one for the 4.0 that the ax15 came on.

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