Bristol 400 rear axle gears

[Hydroglen]

Norman,
Thank you for taking the time to write such a detailed and clear explanation
and yes.... certainly illuminating.
I appreciate that with regards to the main bearing caps it is the line
boring that counts. However on other cars that I have worked on, including
Alfa and Hudson, the housing and caps were a very close fit comparable to a
connecting rod. Hence my surprise at the ledge.

You are of course correct on the pinion housing and I did use some heat as
well as gentle tapping to work, but a slide hammer is a good idea. I tend to
use mine for axle shafts and forgot about it on this job. This is what
prompted me to say, that playng around with fitting and removing shims was
going to be a long job. Further on this.......
To reassemble it, I was set to use our kitchen oven and the freezer. My wife
returned in time to discourage me....something about the oily smell
lingering on and doing something to the Christams turkey!
So I improvised, and being in Canada, I set the Pinion housing out on a tray
in the snow and -10c. The main housing was placed in front of a roaring
fire and an hour later the parts slid in very nicely.
Yes you are correct on bearing numbers altering over the years. Glad you
mentioned it, as some people don't beleive this can happen. Found it out
the hard way years ago.

I am also perplexed at how this axle worked for so long. To recap: Worked
fine for some 5 years + whatever miles the previous owner put on. He died
before I could met him and althoughI have an extensive file on the car, the
rear axle is not mentioned. In October it started whining badly at the rear
as I drove down the driveway one day. It had been fine the day
before.Basically this happened suddenly not gradually.
I backed it in to the garage, jacked it up on all 4 wheels on special
stands and had my wife "drive " the car while I listened. I then got under
( engine off and gearbox in neutral) and found I could move the output shaft
at the pinion considerably. I suspected a broken bearing. I left it and
returned to it several weeks later and dismantled the unit.
The nut with it's locking tab securing the companion flange to the pinion
was still in place, but the flange could be pushed in and out enough that
the pinion touched the Crown nuts and this caused and or contributed to the
noise. When I dismantled the unit, it did not match what I expected to see
from my manual. Then via this site I was told I probably had a 401 shimmed
adjustment unit. I pulled a picture off of Ashley's site ( courtesy Geoff)
and also went through some of my own files. So now I could see what I had
and what I did not have. I was missing the spacer washer that sits between
the companion flange and the taper bearing. Without it you can't preload the
bearing very well. I made one up as per the thickness quoted in the manual.
I can see now that I have more threads showing from the pinion than I had
before dismantling it. In other words the pinion has now been drawn up
properly on/against the bearings. I must assume that the bearings were
never loaded properly.

I agree that it is strange it worked well for so long but I don't have any
other explanation. There were no broken pieces or bits falling out. The oil
seal and companion flange would keep any loose pieces inside.

No I was not planning multiple extractions to set backlash as this will not
set backlash. I mentioned extractions as given that this unit is called a
"shimmed adjustment type" some poor sod must have spent time heating and
cooling to get the unit opened and closed and different shimms tried. As
mentioned above.

I agree with the MD measurement but not having the actual specs, I used a
dial indicator for a initial backlash, and then mounted a pulley to the
companion flange and belt drive to a variable speed electric motor. I
lubricate the unit and run it up and listen for axle whine and adjust
accordingly.
Probably not the most scientific but it has served me well on other axles
and I preferr it ot the "marking blue". If you should try this, make sure
you are wearing a bow tie and not a regular tie!

And yes the wheel bearings will be renewed.
Thanks again for the invaluable help and confirmation on some strange
thoughts on bearings. And anybody else who can come up with a "why" the
pinion floated.......please let's hear from you.

Regards

Dorien Berteletti
Toronto
CANADA