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Six speed & NSX-R 4.2 diff problem

Joined
6 September 2004
Messages
1,348
Location
Arundel, QLD, Australia
I've got my six speed trans apart to do the NSX-R 4.2 Final drive & diff upgrade.

I've fitted the new spring & Spacer to the 5 speed diff & breakaway torque is in spec & I fitted new bearings to the diff.

Before I fully disassembled the trans I left the original 6 speed diff in to check the existing preload on the 6 speed diff bearings just to make sure my new dial torque wrench was working ok & had 15 Inch pounds which was a bit on the low side of spec. original bearing shim is 2.12mm

Since fitting the 5 speed diff I can't seem to get any preload. I'm up to 2.5mm shim thickness(I machined) with no preload yet.

I'm now past the thickest shim Honda makes (the autos have thicker shims listed) but i'm past that now.

Can any experts shed any light on this? The manual says not to double up on shims.

I've put the six speed diff back in to recheck and it has preload.
 
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I'm interested in knowing more about this myself. I'm curious as to what the outcome is.
 
Update;
I've made another temporary shim of 2.66mm (Not as accurate as a proper ground shim) & I now have about 5-7 inch pounds of preload.

So I estimate I need around a 2.73mm shim. not a huge amount over the thickest shim Honda makes but still strange.
 
Since, I didn't really get any comments I carried on and ended up fitting a 2.87mm shim to get 20 inch pounds of preload. about 0.5mm larger than the thickest shim Honda makes.

The transmission is back together and all seems good, shifts smoothly as it did before with no unusual noises.
 
I'm glad you figured out how to make it work, but it is very odd that you had to use a shim that large. I'm glad it worked out, though!
 
I'm glad you figured out how to make it work, but it is very odd that you had to use a shim that large. I'm glad it worked out, though!

My only guess is maybe a previous owner of the diff (Bought used from Japan) had maybe damaged the face removing a bearing and had it machined a little to clean up the surface.
 
My only guess is maybe a previous owner of the diff (Bought used from Japan) had maybe damaged the face removing a bearing and had it machined a little to clean up the surface.
I suppose that could make sense. Is it still performing well?
 
Now that this was bumped to the top again I figure I could add to this, I have a first-gen torque control diff that I fitted the 4.23 ring gear, NSX-R breakaway spring plate, and two new taper bearings onto.

I used the original shim N and the new bearing preload was nearly nothing at 2-4 lb-in. I went to the A/T shim table and got a shim W (2.36mm), and the preload went to 12-15 lb-in which still wasn't enough.

Now I ordered shim Y (2.42mm) which is the thickest Honda makes (also from the A/T table) and should hopefully get me in the right preload range, so I'm having a similar issue as you Wayne.

Maybe the manufacturing tolerances of the new parts (bearings, races, ring gear, etc.) have changed since the shim tables were made in 1990? Seems like two anecdotes saying the standard shims are way too thin.

is it true that i have to use a 5speed diff for my 6 speed if i want to do a 4.23 final drive ? mine is in a 1991 and i dont have eps

If you have a stock 6-speed transmission, then yes you will need to get the 1st gen differential to use the 4.23.

The 90-94 transmissions have a torque control differential, the 95+ have a torque reactive differential of a slightly different design. The 4.23 kit will not work with the updated 95+ torque reactive diff, so if you want to use the 4.23 at all, you'll have to get a used 1st gen differential regardless of 5/6-speed or EPS.

I believe the updated diff is not necessarily specific to the 6-speeds, I think it was used for MY 1995-1996 as well which are 5-speeds, so you'd be looking for one from a transmission from 90-94.
 
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