suspect excessive diff backlash/ due to slight knock

[Hawksfield]

Hi all

Some advice regarding my differential play at the pinion prop shaft pulley, with the wheels locked solid with hand brake and no drive shaft play I have radial play of 5/16?, is this excessive ? . I know that the crown wheel pinion backlash was set at 0.005? so the remaining is planetary gear backlash. The manual does not quote a dimension, other manufacturers just quote minimum backlash.

I am considering replacing one diff output shaft as it is an early type (although no spline distortion ) and would remove diff to carry out this work and check and reset diff side gear thrusts.

So anyone know what the back lash should be ?

Thanks in anticipation

[rgh0]

I don't believe 5/16 inch at the pinion flange due to spider gears back lash is excessive. If you have a knock from the diff I would look for other sources before pulling the diff apart

cheers
Rohan

[Hawksfield]

Rohan

Thanks for your reply, I have checked all other parts associated with the rear drive without finding any other play.
The CV's have been replaced with new GKN parts and are good with no play, all bolts are tight again no play.
I also checked this diff play by locking one drive shaft with the disc brake and the pinion drive flange locked solid and recorded 12mm on the remaining disc.
sometimes I can get this knock with the hand brake hard on engine running going from reverse to forward on the clutch, but it does happen all always.

On the road the knock I get only happens if I stop on a slight incline and then restart, its very light but to me definitely from take up from the diff although it does not happen at all times.
All other parts of the rear suspension are good ie new diff mounts and torsion bar rubbers new prop shaft UJ's
This has been a long story including a diff rebuild that by a so called expert that had to much pinion back lash and whined at around 50mph.

Am I correct in thinking that you feel this play could not be caused by the planetary gears alone, could it be caused by the distortion of the one early diff output drive shafts spline's that I am about to replace ?

Hope you can give me any further pointers to correct this play

my output drive shafts that were fitted when I purchased the car in1986

[promotor]

I've just been to the workshop and done a check for you - hopefully this will be what you are after.

This is a diff I've just rebuilt with new CWP (for Mazzini on here) set with 0.005-0.007" tooth backlash. Diff centre unit is in good unworn condition with minimal backlash between planet and sun gears. It's better than most so should be fairly quiet on "take-up".

I put the complete final drive unit on the press (just to hold it in place and also stop the driveshafts from turning) and have measured 0.011" backlash at the pinion flange. Driveshafts are a nice fit in the sun gears.

It's difficult to be exactly accurate with the dial gauge as with the driveshafts "trapped" the diff wants to swing (side to side as you look at it) when I turn the pinion flange once the backlash has been taken up. The 0.011" was fairly repeatable though.

[Hawksfield]

Promotor

Thanks for your response and test checking.

I measured a peripheral distance but it is still around 3 times what you measured, something is clearly wrong as stated by Rohan.
I have at least got figure to work to and thank you for that.
I will go through my external diff checks again for play but I am confident that the excess is within the diff
After further checks I will measure again to recheck my play but it is far in excess of your result

I have a new output shaft to fit so a diff inspection may be a good idea.

Some years ago,maybe twenty I had planet wheel break and exited the rear of the alloy diff case could it be that I have a problem with the diff gears.

[Quart Meg Miles]

Promotor

I measured a peripheral distance but it is still around 3 times what you measured ......

You reported 5/16" radial, which is 0.312" and nearly thirty times 0.011". Have I misunderstood something?

Are you sure your clonk isn't coming from those CVs?

[david.g.chapman]

I noticed a you tube video on a differential with a similar layout to ours:

https://www.youtube.com/watch?v=n96vqaNs--M

It shows where the pinion backlash can occur inside the diff.

My +2 diff also has noticeable backlash ( I can't remember how much, but it must be a few mm). It's otherwise quiet and works ok, and has done for 50000 miles since it was refurbished.

Dave Chapman.

[Hawksfield]

Dave

I also noticed that video It shows how the play can build up to quite a lot of movement I am looking to strip the diff to check it out.

Quart meg miles

Your quite correct re my calculation

There is no play in the new GKN CV's recently installed as part of the problem

[promotor]

Promotor

Thanks for your response and test checking.

I measured a peripheral distance but it is still around 3 times what you measured, something is clearly wrong as stated by Rohan.
I have at least got figure to work to and thank you for that.
I will go through my external diff checks again for play but I am confident that the excess is within the diff
After further checks I will measure again to recheck my play but it is far in excess of your result

I have a new output shaft to fit so a diff inspection may be a good idea.

Some years ago,maybe twenty I had planet wheel break and exited the rear of the alloy diff case could it be that I have a problem with the diff gears.

Play in the diff gears is a likely possibility - there can be a number of factors at play: the housing for the sun gear stub(s) could be worn allowing them to wander before take-up; thrust face of the sun gear (unlikely), thrust washer and thrust face in the diff housing; thrust washers of the planet gears; wear of the centre pin for the planet gears; worn gear teeth; worn splines on sun gears.

First check is to "rock" the sun gears while in the housing to see how much play they have. Another indication of how good the diff centre is is how tight the gears are to rotate. Better ones you can feel the diff teeth contacting each other. They don't want to be too tight though (which is unlikely to be your problem by the sounds of it).

[Hawksfield]

Hi Promotor/Rohan

I?ve had the diff out to replace an early output shaft and checked out the play and found it as follows

1. the fit of the early type output shaft was poor in the sun gear (diff)
2. The same sun gear (diff ) was also sloppier than the other side when compared using the new billet output shaft
3. The planet gears (diff pinion) had a little back lash but looked quite good

I replaced the planetary thrust washers to take up the back lash, fitted a new output shaft with a replacement sun (diff) gear that was a better fit.

When it was boxed up I did a comparison check as Promotor did measuring the pinion flange play with spiders locked, the figure I got was 0.015? and was satisfied with a differential backlash of 0.005? to 0.007?

When the differential was back in the car the pinion pulley measured 0.125? with the brakes on and no movement on the spiders.
This made me wonder why it was larger measurement when installed in the car, as this was the same test, I can only conclude that when I locked the spiders on the bench using a bolt each side to lock it against the diff case, it pushes the shafts at an angle taking up play maybe you can figure it out

Rohan
You were quite right that the play must be more than the planetary gears alone

I have run the car for a few miles and all seems fine I can feel the better pick up and I am pleased with the results

Thanks again for all your help and support

condition of the diff gears

good use of old drive shaft

[promotor]

Glad you've made progress. I wish I could help you with a comparative check with a diff in a car but unfortunately I can't. I'm sure the answer is there somewhere.
Are you sure the diff wasn't "climbing" slightly when you did the in-car measurement? That would give extra movement to add to the overall figure.

[Hawksfield]

Promoter
Maybe Mazzini could measure his when he gets it installed, it would give us a standard for future checks
I am off to get it MOT'd today will check on the lift to see if it is the same or lifting
Thanks again
John

[promotor]

Promoter
Maybe Mazzini could measure his when he gets it installed, it would give us a standard for future checks
I am off to get it MOT'd today will check on the lift to see if it is the same or lifting
Thanks again
John

You're welcome.
Fingers crossed for the MOT.