I have a 3.636 R&P on order, and a used 4.1 torsen on the way to my house right now.

Is a R&P replacement something I can do myself with basic hand tools plus a dial indicator?

I did the used rear end purchase to eliminate down time on the car since it is my daily driver, and I will sell my current 4.3 torsen and the 4.1 R&P after the swap.

Also, how hard is bushing replacement in rear end mount points? Used one I am getting had 155K miles.

Keith

 

M

 

I accidently hit send on phone half way through initial post... had to edit to complete.

Keith

 

What exactly are you doing? If you are just changing R&Ps and trying to keep the diff. Leave the R&P in the same housing that they came in, do no loosen the pinion bolt, and just put your LSD in the place of the open unit on the diff with the ratio you do want. Then you only need a dial indicator and 7-8" ID Mics to set the diff up, and you can do this part of the setup in like 20-30 minutes.

The diff bushings are in the aluminum part of the housing, just keep your old one. The bushing replacement can be anything from a piece of cake, to half an hour of cussing and sweating while using the oxy acetylene torch and the pneumatic hammer per bushing.

 

Can't link it from my iPad, but if you do a yahoo or google search you should find a post from miata.net laying out the procedure. It's fairly simple and just takes some patience. The hardest part is torquing down the pinion nut to get the proper load on the crush sleeve. I had a 3ft cheater pipe on a half inch breaker bar and seriously thought I was going to snap the breaker bar and go to the hospital. If you have access to 3/4" drive stuff you're going to want to use it.

 

I am purchasing a new 3.636 R&P to place in the used rear end I just purchased that currently has a 4.1 R&P.

Are you saying not to bother replacing the 155K mile old bushings in the rear housing?

Keith

 

I do have a 3/4 breaker bar. I purchased it long ago and used it once... can't even remember what I used it on I will search m.net for the "how to".

Thanks,

Keith

 

You made it sound like you had bushings you liked in your current diff and you were buying a whole seperate used diff and were wondering about the bushings.

Putting the new R&P in is more complicated than just setting the backlash and preload and I've never done it before. You could avoid the crush sleeve sillyness with one of these Weir Performance - Solid Pinion Spacer Kits

 

Hmm, 4.778 with rebuild kit for $385...
No need to strip a Kia diff and that ratio is just perfect for me if I move to a 6sp (=>7krpm in 6th on my longest straight, with some room for power/driver improvement).

 

As others have said, hardest part is removing and re-torquing the pinion. Backlash and bearing preload are described in the m.net writeup, and require a dial indicator with mag base, and a 7-8" mic. I used a set of harbor freight 12" calipers for min, worked fine. Obviously use those at your own risk.

3.636+6 speed FTW.

 

I looked over the procedure for setting the pinion gear depth and was totally confused as to what it was actually doing. The procedure involves three or four special Mazda tools that aren't explained or pictured very well. Since screwing this up wrecks an expensive gear set in short order and I couldn't find any good explanations of how to do it online, I elected to take it to a shop. Hauled the diff, gears, OEM Mazda replacement seals/washers/etc, and my credit card over to a local 4x4 shop, and they did it for about $200 (labor rates are high here in the bay area).

And yeah, 3.636 + 6-speed is very nice.

--Ian

 

No mazda tools requires. Just a little creativity ( defined as a punch and a hammer ) to turn the adjusting rings. Also used large calipers rather than a mic.

 

God you guys and your calipers, I'm just going to go lalalalalalala an not think about the amount of luck it takes you to get within spec with those. In theory if you aim right for the middle of the spec you should be within spec like better than 90% of the time.

Oh who am I kidding, the last time I set preload and backlash I did it by feel while the owner of the diff was collecting the measuring tools from around the shop and then checked it quick once he got back and it was within spec.

 

^not sure if serious?

If serious, **** off.

If not serious, hahaha.

You can also drill some holes in a piece of bar stock and put a bolt through the holes for the preload adjusters. Works like a DIY spanner.

 

I was already thinking of the "take it to a professional" method, and this has convinced me to take that path

Looking at pictures in the "how to" threads, it looks like the differential carrier is a separate piece from the differential housing... can this be removed from the housing by pulling the axles out and unbolting the carrier and pulling it out from the front of the housing?

If so, it makes the question about why change the differential housing bushings make more sense. If I don't have to remove the housing from the car I will not bother to change those bushings... mine only have 50K miles on them. I seem to remember a bunch of crap being in the way in front of the differential when I did my transmission, but I also think with the drive shaft out it may be able to rotate down enough to clear the stuff that was in the way... any insight into this?

Keith

 

You want to leave the housing in the car and just take the carrier out? Why? It's only 4 bolts to get the housing off, and trying to separate them while the housing is still attached to the car sounds like a real pain.

--Ian

 

I don't have a problem taking the whole thing out, I was just wondering if it was easier the other way.... sounds like it isn't!

I will just drop the housing and then swap in the new setup if it looks like my rear housing is in better condition.

Keith