Differential Install Problem
 

So I bought a Carbonetics 1.5 diff and a Garage Kagotani 4.77 gear set, all new bearings, seals, etc.

Got the pinion preload set and moved on to installing the diff.

Here's where it gets interesting.

From the manual the width of the diff with races installed should be 158.4 - 159.6 mm.

My stock diff is at 158.3, a bit low due to wear.

The Carbonetics diff is at 160.8, which is 1.2 mm wider than the top of the range, and 2.5 mm wider than the stock diff.

The problem I have is that the shims used to adjust the diff are only supplied from Mazda in a range that begins with 5.5 mm.

As the shims used with the stock case are at 6.09 mm and 6.17 mm, there isn't enough leeway in the shims that I can order to get down to the calculated size which is around 5mm for each side.

The exact size can't be known until the diff is installed, and the gears are marked to determine if the pattern is correct. I may need shims on one side < 5mm.

The problem is not the width of the diff case, as it is on the high side of the width specs at 171.13 mm, when the specs call for 170.9 - 171.1 mm.

This is not (yet) a problem of being able to adjust the diff side to side to set the pattern, but rather a problem of being able to get it in the case at all.

So, it appears I may need shims that are < 5.5mm, maybe even < 5mm.

Mazda of course does not have any shims that size.

I did check the shims for the MX-5 and RX-8, and they use the same range as the FD.

I have contacted the vendor to see if there is someone at Carbonetics I can talk to, but in the mean time I thought it a good idea call upon the collective wisdom of the RX7club.

Suggestions welcome.

Maybe have the shims machined down.

Thanks for the reply, but , I did think of that. :)

The problem is that once the diff is in, the gear pattern has to be checked.

If the pattern is off, the shims must be replaced.

Maybe more than once.

Guess you going have to buy extras then...

Might want to find a local shop that does diffs and have them check it out. I swapped a 4:10 gear into an auto diff a while back, had a guy that does a LOT of truck diffs do the job. Super easy for him, he had all sorts of shims and everything, worked perfectly and was very reasonable price-wise.

Dale

DaleClark is right, a local diff shop or even a tranny shop should have an assortment of shim sizes in different thickness and different diameters.

I hope to hear some reviews of the Carbonetics diff once you get the installation squared away. Good luck.

Thanks for the replies, I will probably need to find a shop that can deal with this.

I was really hoping to do this myself, just because I wanted to.

That's how it goes some days.

Maybe you can call around to different shops and see if they have shims for what you need. Find out what the return policy is, whatever you don't use take back.

Funny you should mention that.

I did some calling around and was referred to Six States Distributors.

Going over there tomorrow to see if we can match up some similar diameter shims that are narrower.

One nice part of the diff design is the width of the shim material does not have to be exact, there's some leeway there, and possibly in the diameter as well.

Ok, I found the problem, and I'm afraid it was me.

Taking a closer look at the bearings I could see that there was still a small gap between the bearings and the differential case.

When the bearings are pressed on, they need to be driven down past the top of the flange. Using standard bearing drifts will only drive them flush, causing the races to add too much to the width.

The solution was to cut the cage off an old bearing, and use the interior race as a drive to seat the bearings properly. Calculations now show that the range of Mazda shims will be sufficient.

The photo shows the inner race.

Thanks for the suggestions, but it was only operator error. :blush: