Differential Adjustment

[Graham Barker]

I see the removable plates on the back of the differential of my 1937 Ruby for access to the adjustment.  Are these for making adjustment while the axle is still in the car i.e. keeping the car in running condition or is it only for adjusting after a refurbishment of the differential?
I currently experience some diff noise. The total backlash through the diff established by twisting the prop shaft is 7 degrees.  Would the adjustment alone, improve these things?
Regards
Graham

[Bob Culver]

Nothing is forbidden and much is possible. Total backlash includes the differential spur gears so means little. And unless the cwp was originally set up very correctly and is very unworn even the backlash of the cwp alone (latter can be wedged thru the drain hole) is a doubtful indicator.  When first asembeld the side adjustment is supposed to just support the cw laterally with no movement but this state is not easy to establish.Should not be able to lever  the cw laterally thru the plug hole. Adj is normally by slackening one and then tightening the other. Unless there is actual movement any existing preload is uncertain and it is not prudent to much increase blindly but if has done  high mileage and assembled OK originally with no subsequent careless change of divider gasket thickness,  can bring up the lhs a little. Adjusters are 20 tpi with 14 teeth and the cover plate enables half moves so can work out the effect. Certainly one half tooth reasonable. It is vital bearings not over compressed.
All mesh can be adjusted externally but gears develop wear steps and unless removed significant adj can move mesh onto these with puzzling effects. Mesh pattern can be marked thru the drain hole but all very tedious in place, and can fritter hours seeking an ideal pattern not acheivable with used gears. Older books as likely held by VCC cover the patterns and noises.
The oil is an indicator of conditon. If like silver paint the pinion is probably well worn. Generate a huge amount of metal and noise before likely to fail.

[Howard Wright]

Hi Graham

I believe that the adjusters are really only there to get the CW&P set up correctly when rebuilding the axle.  As Bob says nothing is set in stone and I have, in the past, adjusted an axle slightly in situ albeit with little change in axle noise  .

However unless the noise is unbearable (when a full rebuild is needed) I’d leave well alone.  

Drain the oil and refill sparingly.

Cheers

Howard

[Parazine]

The side adjusters control the horizontal movement of the crown wheel relative to the pinion. It is normal, with a new or unmarked CWP, to set the backlash to 1/16", using this adjustment, after the depth of engagement, or meshing pattern has been set.

The depth of engagement is set by shims on post 1931 axles, located between the torque tube and the case. This controls how far the pinion sticks into the casing and will largely set which parts of the teeth are making contact and carrying the load. This adjustment is carried out with engineers blue, the objective is to get the pattern of blue into the centre of the tooth, on both sides at the same time. 

The backlash adjustment also has an effect here so the 1/16" should be maintained.

It's a complicated and frustrating adjustment with the two variables interdependent. Complete silence is rarely achieved. However, the main thing is to avoid over-tight contact or over-deep meshing, which runs the risk of fracturing the teeth.

[Nick Turley]

Best not to fiddle with unless it is very noisy.

[Stuart Giles]

Not normally necessary once the axle is built to mess with the star wheels behind the two plates. As said they govern the depth of engagement/backlash of the crownwheel; if you do adjust them so that the pinion is now running on an unworn/less worn high spot on the crownwheel, the axle is likely to be even more noisy for some time.

Has the axle recently started making (more/new) noise? If the noise is different on drive and overun, it's likely that the pinion bearings, usually the thrusts which control the pinion mesh are needing attention.

[Jack in the Box]

Stuart,

I have just PM'd you.

Alan

[Graham Barker]

Thanks for the helpful replies.
Bob, there was some "silver paint"( i.e. metal flakes) in the oil when I drained it recently.
Stuart, I don't recollect whether the diff noise changes from drive to overrun.  Will check that on next outing.
The descriptions from Woodrow and others of refurbishing a diff make it sound to be a very tedious undertaking.  I am not keen on that. Maybe I should "run it til it busts"?
Cheers
Graham.

[Stuart Giles]

The descriptions from Woodrow and others of refurbishing a diff make it sound to be a very tedious undertaking.  I am not keen on that. Maybe I should "run it til it busts"?

The silver flakes are most likely from the crownwheel or pinion; so there is likely to be some damage already. 'Running it till it busts' means that the CW & P will definitely need replacing - around £400 for a new one, finding a decent secondhand one and setting it up to run quietly in your axle case might be a bit of a mission. Or you could buy a complete Girling rear axle and hope that it's better than yours; personally I would rebuild the existing axle, not a cheap option with all those bearings to buy, but at least you know that it's a job properly done.

[Graham Barker]

Stuart, thanks. Have sent you a pm.
Regards
Graham.