Prop shaft and differential

[Mr Spigot]

I am about to put a reconditioned differential in my back axle, but the workshop manual states that the prop shaft flange needs to be marked so that it is replaced in the same relative position to the differential flange. However, if I am fitting a new differential, this will not be possible. Am I missing something?

[ManyMinors]

No. Just fit it the best way you can. Hopefully all will be well

[Mr Spigot]

Thanks. Presumably if there is any vibration I just need to try it in a different position.

[olonas]

The propshaft rear flange only fits one of two ways. I have never bothered marking them and not had any issues. Only the propshaft is balanced.
I only mark the relative positions of the propshaft parts when disassembling for fitting new u.js. I wonder if that is even essential, e.g. replacing non greasable with greasable u.js. or vice versa, will the grease nipples or lack thereof cause an imbalance? Particularly with the extended nipples.

[Bill_qaz]

Universal joints accelerate and decelerate during rotation. That's why the front and rear have to be re-aligned if the slip joint is separated but prop shaft to differential flange is irrelevant, Any position that fits the bolt pattern is ok.

[oliver90owner]

It is only necessary to make sure things are replaced the same way when UJ’s are changed. The prop shaft should be balanced. The differential is a separate unit, although it is recommended to replace it in the same position if removed and replaced. It does change shape fairly rapidly when the shaft is not straight (during suspension movements).

[Mr Spigot]

Thanks for all the advice. The new differential was put in yesterday and going from 4.22:1 to 3.9:1 has made a huge difference and the car drives much more happily now. I was surprised to find that all 4 of the bolts holding the prop shaft to the diff were slightly loose, even with lock nuts, but I had already ordered 4 new bolts which are now nice and tight. Also a good time to give the UJs a shot of grease and check there was no play in them. Now all set for the National Rally!