Bristol 400 rear axle gears

[N.W.GEESON]

Dorien

Ashley James has suggested that I look at this axle thread and make any suggestions that I think may help. Firstly you must understand that I do not necessarily recognise the Bristol Cars by model name or relate car model to axle type, but perhaps you will bear with me on those points. My comments relate to the axle types that were fitted across this car range in general and I hope they might be helpful, and who knows, perhaps illuminating.

Of general interest. When I can get hold of Ashley’s axle, which is the screwed pinion type with that horrible so called ‘semi-thrust’ bearing, it is intended to try to adapt it to taper bearings. They are much more suitable for this particular axle pinion thrust application. The only reason these ‘semi-thrust’ bearing were used is that Timken Taper bearing manufacturing was then in the USA and the British bull dog neither had the Dollars, nor the interest to buy abroad. ENV were in good company even R-R suffered from that muddled thinking and used semi-thrust bearings.

From what I can gather from this web thread, as the facts are in short supply, you have an axle that has tapered pinion bearings and has a crown wheel retained by castellated nuts and bolts. That I believe would mean that the pinion bearings are one off 32307 at 35mm x 80 mm and one off 32206 at 30mm x 62 mm. For the record this axle can be converted to the heavier pinion with the Imperial taper bearings and a Crown wheel that is retained by setscrews, although the manuals tell you it cannot be done. As I have done this conversion and taken photographs, it will eventually be listed on Ashley’s Web site once I have had chance to look over his axle and complete the write up.

The main bearing carrier caps on the differential housing will almost for sure have a ledge as you have shown in your images, and the reason is obviously not understood. I could show you other images of ENV axles, or Salisbury for that matter that clearly show these bearing cap steps. Although the finished housing is line bored with the caps in place and from that point onwards the assembly is kept, sold and fitted as a matched unit, the component parts may be made at different factories. It is the line boring that matters not the external cap fitting, even the materials between the housing and caps can be different. The caps on these axles look as though Leys of Derby may have produced them, and they would only have been rough fettled on their outer edges.

You appear to have had trouble extracting the pinion housing. Ideally it helps to attach a slide hammer to the flange in order that the extraction is square. In any case heat MUST be applied to the differential housing to expand it before attempting to extract the pinion housing. The axle design means that this housing must be tight. As this heating need to be done quickly, because the materials are identical, it is best to use two gas fired blow lamps (If you only have one borrow another from a friend!). Wear leather gardening gloves (Hot housing) and use a copper / hide mallet, whola, it will extract like lightening. Use the same method for refitting the housing. Heat up just enough so it is uncomfortable to touch with bare hands.

There is a general misunderstanding amongst car enthusiasts (and often bearing agents) that the measurements of bearings with the same numbers never alter. On Rolls Royce post war Timken taper pinion bearings for instance; each bearing design has varied in depth by some 0.012 inches over 50 years. This means that a straight bearing change will not only alter the pinion bearing pre-load but also alters the pinion penetration MD position, with two bearings up to 0.024inch. Using the same shims or spacers after a bearing change should be done with caution, and only after the measurements have been checked. Of course utilising the old spacers / shims as a starting point is acceptable, I am not saying the ENV bearings sizing has altered, but I bet they have since the axle was made.

Still on the bearing subject, you will notice these axles have both Imperial and Metric bearings, once again it is not generally known but Imperials are usually made to Positive tolerances and Metric to Negative tolerances. Now you know why that typical Metric 40 mm bearing rarely measures 40 mm! and it can matter if you are swapping over bearings.

I cannot see how your axle can possibly have been in operation for long with the potential pinion bearing end float that you indicate. Are you sure that the small inter bearing spacer did not stick to the outer bearing only to be dropped on the floor later? The bearing forces are quite massive and the end loads are high, which is why axles become noisy as soon as the bearings wear. Failing that I would have thought something had broken, maybe a flange that retains an outer bearing track. Something is strangely amiss.

You will be aware that axles are notorious for being noisy and it is not always obvious to the car enthusiast that the crown wheel and pinion are worn. Often neither gear face will be galled and they will appear polished. What will not be obvious is that they have been running out of line for some time and worn accordingly, this wear will only be apparent to an experienced eye. This axle design is spiral bevel, with the emphasis on “spiral” as the helix angle is very large. These particular axles are nearly as difficult as a hypoid to set up, and the helix angle is as steep as some hypoid pinions. As a general rule the steeper the helix, the more accurate you need to be and the more likely it is to make some noise if you are out with the settings.

You mention making up some spacer washers for the bearings, but I am afraid that if the CW & P are good at the moment, they will have a doubtful life afterwards. Due to wear on the bearings and possibly the gear set it is unlikely that you are going to position the bearings or pre-load them so that they are in the same MD position. In addition you are probably thinking of attempting multiple extractions of the front bearing housing to reshim in order to achieve the backlash…WRONG. This is like adjusting the handbrake cable on a car in order to adjust the rear brakes.

Once the bearing preload has been set, using the lowest poundage tolerance listed in the instance of the ENV axles, then the pinion must be assembled in the correct MD position - 0.001 to 0.0015 inch.

The ONLY objective in setting a CW & P is to have it assembled in the axle in the position in which it was both designed and ACTUALLY CUT. In essence it means that it is necessary to either calculate the pinion manufacturing distance (MD) or better still have the drawings on hand so that the distance can be read off. If anyone has detailed drawings of the Crown Wheel and pinions, I could advise you on how to achieve that setting. This distance needs to be accurate to within 0.001 inch at worst and preferably less than 0.0005 inch and it can be replicated using measuring methods.

This MD measurement sets the only position for the axle pinion and it copies the manufacturing position and sets the pinion an exact distance from the Crown wheel centre. Following this the main bearing carrier adjusters are set to move the crown wheel sideways in or out of mesh to achieve the correct backlash. If you have read the workshop manual you will have read about the dogs dinner method of setting the pinion and crown wheel with marking blue. A method used by those that do not thoroughly understand rear axle gear sets. The average out of position for a pinion set using this method is 0.015 inch, unless a really experienced axle person has done it. Remember no one has tried to build rear axles on a production line using marker blue, they use measurements and rarely get them wrong.

One other small point that has already been mentioned in respect of the axle centre unit. The main bearing carrier trunnions can break across behind the bearing abutment and in my experience this is nearly always caused by one of two faults. The first is a lack of a sufficient radius on the carrier or bearing inner track or more likely the failure of a rear wheel bearing. On no account whatsoever rebuild a rear axle without renewing both rear wheel bearings!!

I trust the points may be helpful, or my mentor, Mr James will be telephoning me bright and early tomorrow morning!


Regards

Norman Geeson
Peterborough
England

[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

[N.W.GEESON]

DORIEN

I am hoping that along with this post you will be able to see the steps that are present adjacent to the ENV axle main caps. I just hope the attachment works.

It does not surprise me that you found the axles fully fettled on the Alfa etc, but the ENV was an industrial type unit offered out to specialist car builders, or as an option for their normal fitting. The need to keep costs at a minimum meant that fully finishing a unit that could not be seen would be out of the question.

Regards

Norman

[Hydroglen]

Norman,
Thanks for the links. Yes,.... they clearly show the steps we talked about.
I had posted pictures of mine a week or so ago, and some of us thought that
the steps were due to mismatched castings and although bored/machined to
size, nevertheless a bit of a bodge. You have helped us to better understand
the way ENV produced their units.
Thanks again
Dorien