RA29 Build part 7: AE86 rear axle swap
Posted on July 09 2010
Yes, yes, I know it’s been a little while since we have visited our RA29 project. It just so turns out that I have been working on cars quite a bit more than talking about working on them
With our new power plant in place we have decided that better brakes and and a LSD were next up on the list of mods. Once again we turn to the fabulous AE86 Corolla again for parts as the RA29 chassis actually has quite a bit in common with it making it a great donor. As some of you may know the GT-S Corollas came with factory LSD’s and rear disc brakes, a definite upgrade from our RA29′s open diff and drums. There is only one bad thing about the AE rear axle, is that if I recall correctly it’s about 40mm total, or 20mm per side wider then the RA axle. Being that I am opposed to running flares on our RA, I don’t want to mess with the front to rear track width, and I am trying to fit as wide of a wheel as possible all around, losing that amount of wheel width I can run is unacceptable.
The next option? Take all the goods from the the AE axle and swap them in the RA. The first thing you need to know is that you need a Zenki, or earlier model (83-85) donor axle due to the difference in axle diameters between the two. Here we have the two side by side.
The first thing that needs to be done is removing the RA axles and taking them to a machinist to turn down the hub flange (the side with the wheel studs on it) enough to fit under the new AE disc rotor. The best thing to do is match the AE axle, or bring down the rear rotor and make sure the axle fits inside it when it’s done. You also need to remove about 6mm off the splined end of each RA axle to make up for the difference of width in the AE diff. Next up is filling and re drilling the holes on the AE caliper brackets to match the RA axle. This shows a the different bolt pattern between the two.
After measurements are made to assure that the calipers end up on the RA axle in the exact same orientation as the AE, the holes need to be filled, smoothed and re drilled. This shows the approximate orientation and as you can see, all the holes need to be re drilled.
Holes welded up…
And re drilled. Note the cutout on the bottom which allows the diff fluid to drain out the bottom and not on the rotor should there be a leak.
From here you will notice that the RR spring perch needs to be modified just a bit to clear the parking brake actuator.
Since we are using all AE suspension and brake components front and rear we also decided to use the AE swaybars as well. This means we will need to remove the swaybar mounting brackets from the AE axle and re weld them on the RA one. I made a pretty simple jig to assure they would be mounted exactly the same way.
If you are careful with your die grinder you can cut them off without losing any material…
Here they are tacked into place on the RA axle. Don’t forget this means we will have to make mounts on the chassis as well but that is for later.
With all the major fabrication out of the way, it’s now time to install all new bearings, seals, and gaskets on the new rear axle and also rebuild the old differential.
Pressing out old bearings can be easy, or a huge pain. In this case, they were all pretty seized on which required cutting some of the old bearings off. You must be very careful when doing this though not to touch the surface that the bearing is mounted to. I usually don’t cut all the way through, instead I keep grinding until the surface is thin enough to crack. This will relieve enough pressure to release the bearing and assure you don’t nick the mounting surface. In other words, use the grinder like a surgeon uses a scalpel This is the Pinion gear bearing, and you can see the very slight crack after grinding…
Same on the wheel bearings, you can also see here where the hub flange has been machined.
Sometimes the hardest part about pressing bearings in and out is finding a way to mount whatever you are working on in the press. This will require some ingenuity and possibly even making some of your own specialized tools….
And cringing until you hear that big BANG!! and the bearing finally comes loose.
Good old fashioned puller here…
Installing the new bearings is a breeze as you can usually use the old bearings and races to press the new ones in…..
I actually had a hard time finding gaskets so I just made my own… don’t forget that important cutout.
Setting up the rear differential is a whole other complicated subject that I wont get too much into here but that yellow stuff on the ring gear shows the contact patch between the ring and pinion gears.
If it looks like this, you’re on the right track…
Now we can’t just slap a rusty old axle in there, so stay tuned for part 8 where I show you how to properly treat and re coat the axle with some POR 15. We will also be installing the AE86 front brakes, coilovers, and new bushings all around.
Back to work!!!