Diff/Rear End Question
 

I've got a rythmic noise coming from the rear end of my 85 GS that I'm thinking is coming from the differential. I don't think its the U-Joint. Either I've got some bad gears in the differential, or I'm wondering if the axel is slightly loose laterally and is pulling to the outside allowing the gears to not mesh completely. The noise is not constant. Increases and decreases in proportion to speed with the clutch in or out.

What kind of shop is best to go to for differential work? A tranny shop? If I do get into a problem in the gear rings, should I expect an expensive job or should I try to find another used differential? Lastly, if I do go the used route, is there any better performance is in the GSL or SE differentials that could easily be swapped out for my GS?

Thanks,

The GSL rear end will give you 4 wheel disc brakes, with out having to change the front breaks. But more importantly it will give you Limited Slip Diferential.

I don't know what the swap is like but I don't think it is overly difficult.

The -SE has larger breaks, and a different bolt pattern then the rest of the models, but would give you the LSD as well

anthrax

not just any 3rd member will work, 84-85 axles are larger,,O.D. so stick to the same year as your car for a direct 'drop-in' type deal. The GSL rearend will give you rear disk brakes and the LSD, but remember one can have the LSD with drum brakes. it's just a matter of changing the 3rd member(pumkin) the flange will be the same for 84-85's. You might check the fluid level in your
rearend now to make sure..Also if you go LSD, you will need to fill the rearend with limited slip oil.

you could also get a torsen from a miata

For my 85 GS, I chose just to get the LSD center section (3rd nember or pumpkin) from a known good 84-85 GSL rear, and replace the open rear. While ultimately the GSL disc rear is probably better, I felt the pumpkin swap was easier, particularly since I was doing in my garage.

Going to a complete GSL rear also requires swapping the e-brake cables. The Master Cylinder should also be swapped as the brake bias required is different between the disk and drum cars.

Having said that, depending on mileage and history on the car, you may also end up having to replace the rear axle bearings and seals (as I did). If the axles pop out real easy, you should probably replace the bearings and seals.

In the end, effort-wise, it probably would have ended up about the same overall!

Rich

1st and 3rd eh? :)
My rearend made a sort or rythmic thumping sound before it ate itself. You could really feel the slop when going from the power to coasting side of the gears. If the bearings are shot, you can jack up the rear and push/pull on the wheel. If it moves anymore then a fraction the bearings are shot.
First things first. Is it a thumping noise or scraping noise. If it's a scraping noise: Make sure the heat shield isn't comming loose and/or the tranny mount broken. I had that happen (it was rubbing the front u-joint only under certain conditions) and I thought for sure a u-joint or bearing was going. Make sure the dust shield isn't bent and rubbing. Also, make certain the u-joints are ok.
It all else checks out I'd recommend swapping an entire 84-85 GSL rear. The disk brakes make a marked feel and braking improvement over the drums. All that is needed is the rearend, rear portion of the e-brake cables, and the master cly/prop valve. It's no harder then swapping the 3rd member.
As mentioned above, the -SE rear had a different bolt pattern and gear ratio.

Rear end noise is caused by the pinon bearing in the diff.

U-joints that are worn cause vibrations.

I rebuilt my rearend and it's beautifull, smooth and quiet.

Not expensive to do yourself but some rearend knowledge is needed. Also expect atleast 2-3days to get it done.... unless you already have the part or parts.

*out of forum comment*

Jimmy...dude that is a sweet ride ya got there. Just wanna know what kit you have on it? particularly the front spoiler....who did it, how much, what is it? looks great with that grill.

Thanks man!!

It's a Factory IMSA front spoiler. It was a factory option and it's a 3 piece wrap around.

Check mazdatrix.com I think they might still carry them