Lotus Elan

Elan S3 Rear Train Rebuild: Final Drive

PostPost by: PacoGago » Sat Dec 19, 2015 9:22 am

Hello All,
As i first stage of the full restoration of my Elan S3 i am starting with the Rear Train.
Asking for pricing of spares, i got 2 questions:
a) A Suplier did me the recomendation to change the Diff Outputshafts and the Hub Wheel Shafts independing of the stage of them, as a very important thing for safety reasons. Because the Bill as i could become would be a bit high, should I attend absolutely this recomendation from the Spares Supplier and to change all the Shafts for strength reasons?
b) Differential Rebuild: all the Bearing seem to be OK, and the surfaces of the Tooth o the Gear look right. Then the only thing as i am proceeding is with the change of all the oil seals. Since i have not dismantled the Front Bearing, and didn?t touch the Collasible Spacer: do I need to have some special consideration torquing the nut of the Pinion Hub. Do I need to check the Preload? Just in case, how to proceed with this?

I thank you in advance for your comments and help.

MARRY CHRISTMAS AND A VERY HAPPY NEW YEAR TO ALL YOU.
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PostPost by: rgh0 » Sat Dec 19, 2015 9:59 am

Have a look carefully at the splines of the diff output shafts. If you have a slight twist on the spline where it enters the diff gear then its on its way to failure and replacement is advised. There is no hazard if it fails just inconvenience as you loose drive totally when one fails. Many diffs have had replacement shafts fitted as most have failed by now.

Replacement of wheel hub shafts with high strength replacements is advised if you are planning to race the car or use modern sticky tyres very enthusiastically on the road. If doing that you also need to replace the wheels also as the original wheels will probably crack before your shaft fails. For a road car and "normal" use I would just crack test the original shafts. However failure of these shafts results in loss of the wheel which can be more than an inconvenience so replace them based on your planned use and crack testing results if at all concerned.

Retorque of the pinion flange nut after seal replacement with nothing else changed can be done but is a little tricky to get right. Measurement of the bearing preload is hard to measure as the pinion gear is engaged with the crown wheel. You can remove the crown wheel, torque the pinon and measure the preload and then reassemble the crown wheel to the correct back lash and tooth engagement. Alternatively you can try to watch the torque needed to just move the pinion the backlash of a few thou before it tries to start moving the crown wheel as you torque up the nut to preload the pinon bearings.

Personally I would do a full diff rebuild if I did not know the condition or previous use of the car / diff. The bearing that normally fails is the rear pinion bearing as it carriers most of the load and you cant assess this condition without fully dismantling the diff and by then you may as well rebuild it with new bearings.

regards
Rohan
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PostPost by: seniorchristo » Sat Dec 19, 2015 3:46 pm

Rohan
If the carrier bearing caps and the differential carrier are removed, can the pinion bearing then be inspected? If the carrier is then reinstalled, should the positioning of the crown wheel to pinion remain the same? I know if the rear pinion bearing is changed pinion depth will have to be reset.
Thanks
Chris :)
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PostPost by: rgh0 » Sat Dec 19, 2015 10:06 pm

Hi Chris
If you remove the diff carrier and have removed the pinion gear drive flange then you can withdraw the pinion gear to inspect the condition of the rear pinion bearing. If all the bearings are OK then you should be able to carefully reassemble the diff to the correct pinion pre-load and tooth engagement. A little sealant on the rear face and spline of the pinion to ensure it seals and you don't get an oil leaking out the spline is a good idea.

If the tooth engagement was correct before dis-assembly then you should be able to replace the pinion bearings and reuse the same pinion shim if you rebuild using bearings from the same manufacturer

cheers
Rohan
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