Differential pinion height

[camelotr]

I am planning a Big Healey banjo rebuild.

I have some problems with it.

- the factory workshop manual tells me to use a special tool for positioning. Unfortunalty I dont have this item - and if I am righ, it is not available any more.

- it would also be nice to know the exact factory distance from the differential axle to the pinion top - but I have not found any source for this kind of data.

- as an alternative method, many sources recommend to measure and fix the existing pinion height, and to bring the pinion back there after replacing the bearing. Clear as springwater. I have made some plans for a simple tool which would make it easy to achieve. BUT I moved on thinking about the subject, and I find this not problemfree. As the bearings now in my diff are quite well worn (after 50+ years) they must bring thurder away the pinion from the factory spec. Is it worth bothering with the pinion height, or better to install the new bearings, set preload, backlash etc, and check the contact pattern with a contact compound (and reposition the pinion if needed)? Or bearing wear does not alter pinion height by much?

[stevieturbo]

I would hazard a guess and say that if you re-used the same pinion but with new bearings. Re-fitting any shims that are currently installed on the pinion in the same place. They it will probably be fine.

With no information, you could check for the gear mesh patter on the pinion and crownwheel. But that could be a very very slow and tedious operation, with many build/rebuild cycles.

Pinion depth is a nightmare !!

[camelotr]

Thanks Steve.
I am also tending to do what You recommended. Best would be to measure 4-5 diffs and work out an approx. data, but without this, I think it would be best to reuse the original shims and check the mesh pattern.

[anonymous-user]

The problem is that the tooth mesh wear pattern on your diff will have worn "into" the mean position of the bearings as they currently are (depending on the "mean" loadings during the running period)
Even if this position is not entirely correct (by the manual) if you re-shim the worn parts to the new position the diff will whine like a good 'un!

Least worst solution is to probably just measure where it all sits currently, and restore it to that position. (and even this could be noisy on inital running because the new bearings will be stiffer, and the pinon will move less under load than it did)

[camelotr]

Thanks for the info and double thanks for reasoning it!!
I will take measurements of the pinion height before replacing the bearing, and recheck after it.Just to see how much difference it will show.

Edited by camelotr on Sunday 23 January 16:05

[camelotr]

Hi,

I have recived the parts and completed the tools.
After a bit of trial, my pinion eight rest 0.04mms higher than original. The next shim will take it 0.01mm lower.

I am a bit afraid of going below the worn height as the running in wear wll bring it thurder from the original position, while if I set the pinion a bit higher, the rining in time will bring it closer to original position.

Whats Your opinion? ÛIs it k to leave the pinion 0.04mms higher than the original position?

[stevieturbo]

camelotr said:

Hi,

I have recived the parts and completed the tools.
After a bit of trial, my pinion eight rest 0.04mms higher than original. The next shim will take it 0.01mm lower.

I am a bit afraid of going below the worn height as the running in wear wll bring it thurder from the original position, while if I set the pinion a bit higher, the rining in time will bring it closer to original position.

Whats Your opinion? ÛIs it k to leave the pinion 0.04mms higher than the original position?

Either or, both are incredibly small measurements. I think both will be safe enough

[GavinPearson]

I'd leave it.

I did a similar rebuild on a diff a few years back that was a nightmare to get spares for that was similarly 'out' and it has been no trouble whatsoever.

[camelotr]

Ok, here is the contact pattern. I think the pinion is a bit close (high), or?...

[camelotr]

Backlash is 0.2mms (factory data 0.18mms).

[GavinPearson]

Based on contact pattern you need to pull the pinion away from the crownwheel. Order more shims and a couple of extra collapsible spacers.

[camelotr]

0.07mms lower the pattern is getting better I think. Though I will try to lower it more.

[camelotr]

Another 0.04mms lower.

Is this pattern acceptable? I think it is stil a bit high, but the running-in time will loer it a bit. Or?

[anonymous-user]

Under what torque are you generating that pattern??


with say 200Nm (flywheel) in 1st (say 2.8:1), so 560Nm on pinion, if mesh radius is say 25mm (guess), that is 22400N (2.285 tonnes!!) pushing things apart! (ignoring the gear pressure angles!)


I'd set it a bit high to start with, the real test is how much it whines!!!



(ETA: the bit about pressure angles i forgot about.....;-)

Edited by anonymous-user on Thursday 10th February 16:38

[stevieturbo]

Max_Torque said:

Under what torque are you generating that pattern??


with say 200Nm (flywheel) in 1st (say 2.8:1), so 560Nm on pinion, if mesh radius is say 25mm (guess), that is 22400N (2.285 tonnes!!) pushing things apart!


I'd set it a bit high to start with, the real test is how much it whines!!!

Whilst I'm not big on maths etc....

I was impressed when calculating the torque applied to my half shafts, and I guess from that the diff itself.

Say a good hard launch could easily generate over 6000lbft at the rear shafts !!

Does make you wonder how things do stay together !

[anonymous-user]

absolutely! remember to get a 1g accel, the force at the wheel/road interface must be equal to the mass of the car, and the driveshaft diameter is VERY small compared to the tyre OD !!!

If you do the sums for a modern turbo diesel, with a low 1st gear, you can see why the diff / shafts are pretty big ;-)