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Excessive play in differential
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Good morning,
I have justy got a Austin 7 AG and there is excesive (I believe) play on the Diff (90 Deg.)! Please see picture of dif. Can any one advise if I can tighten it up or do I need to take it to someome? 
30-08-2021, 02:18 PM
Hi Tim
Congrats on A7 ownership. As part of that momentous step you should consider buying the Austin Seven Manual by Doug Woodrow (sold by cherished suppliers and direct from Mercury press I think) it will help you understand your car and assist in any work you do on it. I’ve just finished building an axle like yours and yes you can adjust backlash fairly easily. However it is also easy to do some adjustments that could cause more harm than good, to the meshing of the gears. So I think you should perhaps consult a Seven owner who may be able to help. My second bit of advice is to join your local club which I guess is the PWA7 club Cheshire section?? I’m sure you will find someone to look over the car and advise. Best Regards Howard 
30-08-2021, 02:26 PM
Is it noisy? If yes, then a rebuild is imminent. If no, it could be play in a number of places, including the half shaft/hub joint or the diff gears. You should probably have someone with some experience have a look at it in this case.
30-08-2021, 03:27 PM
(This post was last modified: 30-08-2021, 06:42 PM by Dennis Nicholas.)
Tim. Are you saying the play is felt when you turn the pinion and propshaft back and forth or when you have one wheel jacked up and you turn the wheel back and forward without the propshaft moving?
If 90 deg of play at the pinion flange then I would not drive it any further without proper adjustment! A backlash of .004 inches between teeth (as per Austin's advice) is equivalent to 1/16 inch movement at a radius of 7 inches from centre of pinion. There was a works assembly jig which helped to easily set up crown and pinion meshing. I dont know how many are around in private hands I only know of one in Cornwall..see the Cornwall club site). Crown and pinion meshing is done by a combination of shimming the crownwheel from side to side in the casing or as in your case levering round the adjusters that live under the 2 plates, one of which you can see held on by 2 screws and shimming the pinion casing in and out. You should find engraved on the centre casing the date of the axle...that will give you the information as to which of the variants you actually have fitted. Dennis 
30-08-2021, 05:23 PM
The picture in the original post looks like the axle introduced in 1930. If so case adjustments are done easily.
The pinion can be moved in and out by rotating the torque tube. The crown wheel can be moved side to side using the notched wheels behind the plates on the back of the axle either side of the diff. No shims needed. However just which adjustment should be done is a more difficult question. Help from an experienced helper would be the best course. It is quite possible that adjustment would sort it out.
Jim
30-08-2021, 05:48 PM
(30-08-2021, 05:23 PM)AustinWood Wrote: The picture in the original post looks like the axle introduced in 1930. If so case adjustments are done easily. Hi Jim I think this is the later long nose banjo requiring shim adjustment. Screw in torque tube banjos have a plate secured by four set screws on the back of the case (in order to extract the pinion). But agree with your suggestion that a helper who is familiar with back axles should be called in. 90 degree twist seems a lot! Cheers Howard
30-08-2021, 08:53 PM
(This post was last modified: 30-08-2021, 08:54 PM by Bob Culver.)
90 deg of rotation rear of any universal suggests far more than meshing. Meshing is the last thing to tinker with even if expert. The input flange can be loose on its taper and the keyway damaged. If applying force could even be a loose hub and damaged keyway. The crown wheel can be wedged thru plug hole to narrow the range of possibilities
30-08-2021, 10:25 PM
Yes, you're right Howard. Shims for the torque tube.
This implies that either the crown wheel adjustment has slipped somehow, which is unlikely, or there is a problem with the bearings behind the pinion.
Jim
30-08-2021, 10:42 PM
My two penn'orth - get someone who knows A7 axles well to assist with checking play; more precisely, identifying where it is coming from. Might be the diff gears, CWP, propshaft or even gearbox adding something. Rear axle adjustment is not to be trifled with - if you intend going in there do your background reading first. 4 thou backlash is all very well for new gears but in my (admittedly limited) experience worn ones may require considerably more.
31-08-2021, 10:21 AM
To all,
Many thanks for your comments. I think this is great and feel pleased to have an old car with this much support. As I am not familiar with the setting up of a Dif, I will seek out someone how does. I will get the Manual but does anyone know someone (commercial you other) who can help? I am very keen to know more so happy to work with someone. I can take out the rear assembly and load it into a car. We live just south of Chester CW6 9UR |
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