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MG MGB Technical - Pinion height

Fitting up a new crown wheel and pinion into a Salisbury axle- just a normal ratio change job but I've hit a tiny snag which I know someone will be able to sort for me--------------------I hope, otherwise it turns into a slightly bigger setting up job, easy to do but time consuming

The old pinion was a +3 so running with a .003" thinner shim--all good there, it's been running fine and has good tooth pattern and backlash
The new pinion doesn't have an etched number or zero so I suspect it's a 0 so need to add .003" to the spacer
But the new pinion has a number 96.13mm on it
I believe this is the depth the pinion has to be set at
My question is- is 96.13 the distance from the side bearing tunnel down to the spacer face

Why can't they just leave a good system alone
I can see that having a measurement might be easier if you havn't got the old pinion for referance but the old +1 +2 +3 etc has worked fine for years

First time I've come across this, so just need to hopefully get some info to make life easier

Thanks
willy
William Revit

Willy, I had the same question with a new pinion and crown wheel I’m fitting to a midget diff, (diff cage shims on the Midget BB), they were both marked with an M/D dimension. I took this to indicate mounting distance, see copy of drawing from an old Midget manual. As the markings were different from what I was expecting and also struggling to get the necessary outside shims, I gave it to a local transmission specialist, he told me they have a 71 year old that does these but when he retires next year they won’t be doing them anymore. Bob






R.A Davis

And the crown wheel


R.A Davis

Thanks Rob
i got it sorted this morning and back in the car this arvo
I suspect the c/w and pinion was from the same place as yours, it came from Clive Wheatley, but all it had was the 96.13 and set no.12 on the pinion and set no12 on the crownwheel , nothing else
Had a measure up session and worked out that the 96.13 is the measurement from the face of the pinion spacer to the centreline of the crownwheel carrier
The method i used to sort it was to fit a bolt through the spacer and bearings to resemble the pinion so i could get some preload on the pinion bearings then ran a straight edge side to side accross the surfaces where the sidebearing caps mate up to the housingthen measured from the straightedge to the spacer--It measured at96.25mm giving a 0.12mm difference to the required spec. Added a .004" shim which bought it within 0.02mm--near enough for me (sorry about the metric-imperial measurements)
I had no backlash or side bearing specs so sat the crownwheel carrier in with the original shims but only had .001" backlash and the marking was well towards the toe and fairly deep in the tooth
Made some new side spacers up out of some 3" od steam pipe--Three sets later all was good with 0.005" backlash being the magic spot with a perfectly central mark biased towards the toe
Bit of a process but should be good
Cheers, and thanks again for your input Bob, I'm not sure how it would be possible to measure from the centreline of the pinion to the crownwheel backface for that spec on your crownwheel
More a case of old fella's feel for backlash for me but there is probably a simple method in a w/shop book somewhere, possibly the centre point between the 2 side bearing spacers to the face of the carrier, it'd have to be something measureable
Cheers
willy
William Revit

This thread was discussed on 31/07/2020

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