Ben 84 RX-7

I bought a 4.44 ring and pinion direct from Racing Beat and it arrived yesterday. I called my shop guy to install it...and he asked me if I got the shim with it. I ordered all they had as far as new seals, crush tube etc. But there was no shim, and none offered for sale. I called Racing Beat...and they told me that the ring and pinion are a direct replacement...and I don't need to set or adjust lash or pinion depth?!?! Can this be true? I have never heard of making any changes in the third member without having to reset the tolerances. Anyone have experience with this?

Rx7carl

The way I was explained this is as follows. The housings were not made to the same tolerances as the pinions were. So Mazda says to keep the shim with the housing always. The pinion shafts were made to such a good tolerance that for all intents and purposes, they are identical. So just reuse the shim that came out of the pumpkin and you should be fine. I rebuilt mine on the racecar a couple of years ago and went to a 4.88 gear and did the setup by the book and its been like butter. As far as lash, you need a dial indicator, also some gear marking compound works wonders. I set my pinion bearing preload using the uber low scale torque wrench I bought. I dont see how you can do this without one.

Ben 84 RX-7

Thanks Carl!

Kyrasis6

You are suppose to check and adjust where the ring and pinion gears ride and adjust backlash any time you work on a rear end assembly. If you could trust them to be perfect from any manufacturer they wouldn't make shims for them.

Does anybody know where you can get shims that fit Mazda rear ends??? I'm trying to swap a set into my truck.

grendel

Mazdatrix sells them I think. I bought some from Rotary Performance, but they don't really sell them.

Rx7Carl, what if your lash is just a little under spec? I just installed a new 4.30 R&P and a 1.5 way LSD and my pattern is, I believe, correct. (I used Precision Gear's guide photos) But, my lash isn't quite as high as the TM says it should be. The rear end isn't in the car yet, nor does it have gear oil in it yet, so this is probably a good time to find out....

Rx7carl

So your saying your gears are a little tight and cant be brought any closer to spec? Whats the lash? I'd have to go back and look in the FSM as its been a couple of years since I set mine up. Backlash is adjusted by using the side adjusters to move the ring left or right. The shim only sets the pinion height relative to the ring so the contact area is correct. When you load the R&P by driving it, the pinion tries to "climb" up the ring gear. This is compensated for by the engineers when they determine static pinion height. I think were having a bit of confusion of terms here.

grendel

I used the factory TM guidelines (94 FD), with the only exception being that I didn't measure the distance across the rear end and subtract the LSD's width. (very general explanation because I don't remember it accurately, but I'm sure you're familiar with it) The unit wouldn't move without binding with the original shims, so I bought the next size shims required to move it the direction that would take the bind off of it. It does move, and it moves smoothly, but the lash is pretty tight according to the dial indicator.
I'm out of state for the rest of the month, but when I get home I'll post or PM you the backlash settings. I do believe that it could be adjusted further, but how much will that change the patten? I do want to take the time to do it right, and I appreciate any advice you can give me. I'd rather ask questions and show my inexperience than take it to a shop and never know how to do it properly.

Thanks

Doug

Rx7carl

I'd have to look at an FD TM so I can see how they set that one up. I was speaking of FB's in my posts here and dont want to give out bad info, as they may be set up differently. Any chance of there being an online one that I can study?

grendel

http://www.iluvmyrx7.com/ has a 94 TM online. Reference pages are M39 and M40.
Chapter M - Front and Rear Axles - Differential.

The backlash settings are .0035-0043 inches. Mine is more like .0030 inches. (I can check it again in a month.)

Rx7carl

I see now. What a sucky design. Well not really, just a bit of a pain to adjust. On the FB's those side bearing carriers are threaded and adjustable. Did you mic the shims? Old and new to make sure you do have matched pairs? My suggestion would be to follow the manual and do all the measurements with the same caliper to cancel out any error. See what your results are. I dont know what the next size shim will do to your backlash, might put it too far out.

grendel

Well, I didn't mic it with an accurate micrometer. Plus, I need to get one that'll measure the entire rear end. Or, at least that's what I gathered in the TM.

I think part of the problem might be that I didn't measure the dimensions of the new LSD, so just assuming that I could move it over proportionally like I did is probably why it's off. I just tried the old shims, saw they didn't fit, and ordered the next size of each to move it the way it looked like it should be moved. I used a mic to measure the original shims, but it was nowhere near the size needed to measure all the dimensions required.

I guess I'll do it over again when I get back home.