1978 later model differential rebuild

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red
Posts: 11
Joined: Tue Sep 20, 2011 10:35 am
Your car is a: 1978 spider

1978 later model differential rebuild

Postby red » Sun Mar 19, 2017 1:34 pm

I have a 1978 spider with a later version rear opening differential. It was noisy so I am rebuilding it. I also am changing the gear ratio at the same time from 10/43 to 10/39. My question is about the side load shims in the diff to each axel side. Will changing the gear ratio significantly change the shim sizes ???? I took out shims measuring 6.8mm and 7.1mm The range of shims listed at Midwest Bayless are from 6.52mm to 7.5mm. With the diff gears in place and the proper backlash adjusted and the gear pattern looking nice I have a much thinner 2.65mm on the left and a much larger 10.92 on the right. Is this acceptable or expected with the gear changes and bearing replacements ??? The total of the two side shims is as expected but the internal gear unit seems to have shifted to the left about 4mm

Thanks for any input
RED

djape1977
Posts: 985
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: 1978 later model differential rebuild

Postby djape1977 » Sun Mar 19, 2017 1:52 pm

every bearing and or gears swap requires re adjusting diff. in most cases changing shims as well

TwinFast
Patron 2020
Patron 2020
Posts: 102
Joined: Thu Oct 13, 2016 2:06 am
Your car is a: 1978 Fiat 124 Spider

Re: 1978 later model differential rebuild

Postby TwinFast » Sun Mar 19, 2017 6:37 pm

red wrote:I have a 1978 spider with a later version rear opening differential. It was noisy so I am rebuilding it. I also am changing the gear ratio at the same time from 10/43 to 10/39. My question is about the side load shims in the diff to each axel side. Will changing the gear ratio significantly change the shim sizes ???? I took out shims measuring 6.8mm and 7.1mm The range of shims listed at Midwest Bayless are from 6.52mm to 7.5mm. With the diff gears in place and the proper backlash adjusted and the gear pattern looking nice I have a much thinner 2.65mm on the left and a much larger 10.92 on the right. Is this acceptable or expected with the gear changes and bearing replacements ??? The total of the two side shims is as expected but the internal gear unit seems to have shifted to the left about 4mm

Thanks for any input
RED


I also have the same problem when i try to change the gear ration on my 1978 Spider from my broken 10/43 crow/pignon to 10/41. I finally buy another crown and pignon with the same ratio, of 10/43 and it work fine. For the shims, i don't think that it's a good solution to have an important difference between the right and left side. The torque is too important, and you could broke your differential
Fiat 124 Spider 1.8L 1978
Jaguar XKR 4.2L 2009
Harley Davidson Fat Bob 96Ci 2011


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