Any Jag 4HU diff experts out there?
Discussion
I have an 4HU poen diff fitted with a 4.01:1 ratio crown and pinion. I am trying to fit a Powerlok unit taken out of a 3.54:1 diff but it seems that the 4.01:1 crown wheel is thinner than the 3.54:1 crown. Ths means that it is not quite on the correct axis and does not mesh with the pinion. Plan is to install a 1/8" (ish) spacer between the crown and the LSD flange and a 3/16" (ish) spacer on the pinion shaft to push it further in. (does this make sense?) Hopefully in doing this the crown and pinion will mesh toghether. Has anybody done this? am I flogging a dead horse? any other suggestions?
Thanks for reading.
Thanks for reading.
NTEL said:
I have an 4HU poen diff fitted with a 4.01:1 ratio crown and pinion. I am trying to fit a Powerlok unit taken out of a 3.54:1 diff but it seems that the 4.01:1 crown wheel is thinner than the 3.54:1 crown. Ths means that it is not quite on the correct axis and does not mesh with the pinion. Plan is to install a 1/8" (ish) spacer between the crown and the LSD flange and a 3/16" (ish) spacer on the pinion shaft to push it further in. (does this make sense?) Hopefully in doing this the crown and pinion will mesh toghether. Has anybody done this? am I flogging a dead horse? any other suggestions?
Thanks for reading.
No!!!!Thanks for reading.
If you are putting the Powrlok unit in your existing diff then the pinion should stay exactly where it is, and all the adjustment should be on the crown.
Assuming you are using new bearings all round I would set the pinion in place and adjust it to suit your existing open diff so you know it is in the right place. Then you need to put the powrlok unit in and work out what spacer is going to be required. Make it out of EN8 and have the faces ground. Trial fit and make the final adjustment with shims.
What used to be GKN Salisbury rebuild diffs so you can always go to them if you need advice on parts etc.
You don't necessarily need any spacers.
The crownwheel on your 4.0 unit is thin becasue the input pinion is large diameter. The pinion on your 3.54 gears is naturally smaller diameter than the 4.0 one, and so to make up the difference the crownwheel is thicker. The crownwheel mounting flange (with one notable exception) always ends up in the same position relative to the diff case.
The pinion head height is critical to correct gear meshing and must be set-up correctly. The thickness of the shim behind the pinion bearing is calculated by the distance between the bearing seat and the main bearing bore centres and adjusted by the 'optimum position' marked on each pinion individually.
Adjustment of the shims behind the main carrier bearing mainly adjusts the backlash.
Not the easiest job to do if you don't have the experience/tools to do it. eg ideally you need a fixture to spread the case as the crownwheel assy is preloaded into the case.
Russ
The crownwheel on your 4.0 unit is thin becasue the input pinion is large diameter. The pinion on your 3.54 gears is naturally smaller diameter than the 4.0 one, and so to make up the difference the crownwheel is thicker. The crownwheel mounting flange (with one notable exception) always ends up in the same position relative to the diff case.
The pinion head height is critical to correct gear meshing and must be set-up correctly. The thickness of the shim behind the pinion bearing is calculated by the distance between the bearing seat and the main bearing bore centres and adjusted by the 'optimum position' marked on each pinion individually.
Adjustment of the shims behind the main carrier bearing mainly adjusts the backlash.
Not the easiest job to do if you don't have the experience/tools to do it. eg ideally you need a fixture to spread the case as the crownwheel assy is preloaded into the case.
Russ
Thanks for the replies chaps. I've managed to get my hands on a Powerlok unit from an early XJS with exactly the same dimensions as my existing carrier. Saves all that buggering about with spacers and the like. Cost a few quid but at least I know it will be right and the crown will be in the right place.
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