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MG MGB Technical - Banjo diff backlash

I am rebuilding a banjo axle that I acquired damaged from a friend.

The w/s manual says the backlash should be marked on the back of the crown wheel. There are a couple of markings on the back of the crown wheel. The one that looks most likely says "005". I assume that means 0.005 inch of backlash.

The instructions about where to measure the backlash are a bit brief. I have measured it by putting the dial guage against face of a tooth very close to its outer end. When I hold the pinion drive flange still and rock the crown wheel I get a backlash of 0.003 inch.

In a note on Barny Gaylord's website about MGAs he says to set it to 0.008 +/- 0.003

So am I measuring it correctly?
Is a difference of 0.002 something I need to adjust?

I have also blued the crown wheel to check the mesh. I understand ideal to be a wear pattern the centre of which is halfway along the tooth and halfway up the tooth. My wear pattern is offset from halfway along the tooth going towards the outer end. That might be consistent with wear to the trust washer behind the pinion head. If I fitted a thicker thrust the backlash would close up further.

Will I regret not addressing this point?
David Witham

David
There is an old diff building saying which must be used

Toe and heel move the wheel
Face and flank move the crank

From what you have described, your mark is in the centre of the tooth but out towards the end.(heel) - If this is how it is it means you need to reduce the backlash by moving the crownwheel across closer to the pinion to move the contact patch in.
However you have measured .003" so you can't really do that
You appear to be measuring it correctly but have you tried measuring at a few different spots around the crownwheel to check for variances there
Also try holding the flange in a vice to get it rock solid and clamp the housing to hold that solid so that you are absolutley sure you are getting an acurate backlash measurement - measurements are done dry.
Cheers Willy
William Revit

What does "damaged" mean, and what parts were changed?
The "thrust washer" is not a thrust washer, but a spacer, and there should be no wear on it, unless the pinion nut was run loose for a long time.
If the housing and that spacer have not been changed, the pinion position should be OK.

The crown wheel lateral position is set by the book, and after that:
You would increase backlash by changing the shims on the carrier bearings to move the crown wheel away from the pinion, while maintaining the .002 preload on the bearings. .002 shims moved from one side to the other should change backlash by about the same amount.

In general, backlash on a used gear set might be slightly more than marked, but it would never be less.

The contact pattern is more critical than the backlash. If anything involved in the pinion positioning has changed, it can be a cut and try to get the pattern right. The BMC books do not show contact patterns, but any book that does can be used to decipher this (as long as it is for a hypoid gear set). Comparison of the pattern on both sides of the teeth lets you decide how to move things. If both sides cannot be made to agree, it is best to favour the "drive" side. Well used gears may have "fuzzy" patterns, do your best!

FRM
FR Millmore

Thanks for your input both.

Another question though. To move shimms from one side of the carrier to the other I need to remove the new bearings I fitted.

How would you do that? When I took off the originals with my puller it hooked round the outer race which popped off, the balls were released by the cage going all over the bench and the floor leaving the inner race stuck fast. As the puller would not hook around the inner race I had to cut it off and use new bearings. I had planed to change the bearings as they felt a little rough so that was not a big issue. However if I remover the bearings the new bearings to swich the shimms I would like to do it without wrecking them. Any ideas?

David
David Witham

David

What sort of puller are you using on your bearings?
Dave O'Neill 2

As Dave O'N implies, the bearing puller must pull on the inner race only. These are angular contact bearings, and must be fitted and removed correctly.
Of course, there is a factory tool with suitable adapters, shown in the WSM.
There are tools known as "bearing splitters" that will do the job. It is two plates with a relieved center/beveled edge that gets in narrow spaces, held together by two bolts, and providing something to grab with a puller or press.

FRM
FR Millmore

Having googled "bearing splitter" I can see there is a better tool for this than the universal claw type puller I am using. I will get one and see how I get on. Thanks.
David Witham

To set the C/W position correctly, I use a pair of bearings that I've had honed to give a minute interferance fit. This allows me to fit and remove the 'dummy bearings' until I'm happy with the shimming and subsiquent C/W to P markings.

Mark.
M T Boldry

After a bit more measuring I discovered the backlash was not constant all the way round. The crown wheel had more runout than the 2 thou max in the workshop manual. So I removed the crown wheel, releaved the edges of its mounting holes and rotated it 180 degrees. One back together runout was less then 2 thou and the backlash was in apec as well so I left the bearings alone.

Once I have stripped and painted the axle case we will see how it does on the car.
David Witham

This thread was discussed between 29/09/2011 and 17/10/2011

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