49 replies to this topic

[Steve TPF]

Long story short: my diff bearings were making horrible noises so I decided to swap the the whole axle over while I got my diff sorted. Aquired new axle complete with rear discs - so far so good. The new brakes needed a cleanup etc so I thought no worries, I'll use my drums to get me back on the road - and that's where things got interesting.

 When we bolted up the left-hand axle it got tight and didn't want to turn - as though it was jamming on the diff somehow. Tried swapping left/right axles - same deal.  After the usual headscratching and swearing I removed the diff cover and discovered that the left axle was JAMMING ON THE PINION SHAFT! WTF? Measuring tape showed the disc/drum axles as being the same length from outside of bearing to axle tip, so no clue there. Close examination of the new diff revealed that the crownwheel was about 3 mil thicker than my old one - which meant that the diff assembly (and therefore the pinion shaft) sat 3 mil further to the left - causing the axle to jam.

 Cutting 4 mil off the axle solved the problem and it now turns freely with no jamming, but I'm curious. Has anyone encountered this before? And why would the crownwheels be different thicknesses? The old diff is a 3.08, the new one is a 3.9 if that makes any difference.

[yel327]

Disc and drum axles are different lengths, so may be part of you problem.

[EunUCh]

And crownwheels are a different thickness depending on ratio.

[Steve TPF]

And crownwheels are a different thickness depending on ratio.

 

 Apparently so. Any idea why? apart from making life difficult for people like me that is.

[UCSLE]

 you just cut rare hard to get axle , like the others have said they are different lengths .

[Steve TPF]

Disc and drum axles are different lengths, so may be part of you problem.

 

Overall, they are the same length - I have both types. There is a difference - but it's on the  outer section of the axle, past the bearing as seen in this diagram:

 

 

 

 

So the axle length inside the housing should be the same. The disc axles have a spacer fitted on the outside of the seal to allow for the greater thickness of the caliper mount compared to the drum brake plate, but the length inside the housing should be the same.

Edited by Steve TPF, 18 October 2014 - 06:52 PM.

[Steve TPF]

 you just cut rare hard to get axle , like the others have said they are different lengths .

 

 

No, I cut the common and easy-to-get DRUM axle. And it still protrudes a few mil past the side gear, so there is no loss of contact area. In any case, the lenght difference is in the distance between the outer edge of the bearing and the location of the wheel flange, as shown in the above diagram.

Edited by Steve TPF, 18 October 2014 - 06:57 PM.

[UCSLE]

sounds like your diff center is a bitsa

[EunUCh]

Thickness of pinion difference i think has something to do with the number of turns the pinion needs to do,3.9 has a rather large pinion gear 

compared to other ratios because it is spinning more roundy roundies,probably bigger because if it was small it would wear out quick.

my theory anyway.

Only thing i have ever read around here is that the disc brake axles were a tad longer to allow for the disc assy. 4mm sound about right.

Don't understand why it was only on one side though ?

[Steve TPF]

Thickness of pinion difference i think has something to do with the number of turns the pinion needs to do,3.9 has a rather large pinion gear 

compared to other ratios because it is spinning more roundy roundies,probably bigger because if it was small it would wear out quick.

my theory anyway.

Only thing i have ever read around here is that the disc brake axles were a tad longer to allow for the disc assy. 4mm sound about right.

Don't understand why it was only on one side though ?

 

 

 Don't know about the pinion gear, but the crownwheel is definitely thicker by 3-3 mil. This has the effect of moving the whole diff assembly (and therefore the pinion shaft in the diff assembly, not the input pinion) 3-4 mil to the left - which is why it was only jamming on one side. The pinion shaft is not in the centre of the axle housing, it's to the left. The thicker crownwheel moved the whole diff another 3-4 mil to the left and thus caused the problem with the axle.

 

Overall, the disc/drum axles are the same length from axle tip to stud tip. The difference is that the flange on the disc axle sits 12 mil closer in and the studs are 12 mil longer, to allow for the thickness of the disc. The disc axles use a 7 mil spacer on the outside of the seal to allow for the caliper mount being thicker than the drum brake backing plate.

Edited by Steve TPF, 18 October 2014 - 07:10 PM.

[Steve TPF]

sounds like your diff center is a bitsa

 

That is a possibility. If that's the case then I need to get mine sorted pronto and back on the car so I can take a closer look at the new one.

[yel327]

Don't know about the pinion gear, but the crownwheel is definitely thicker by 3-3 mil. This has the effect of moving the whole diff assembly (and therefore the pinion shaft in the diff assembly, not the input pinion) 3-4 mil to the left - which is why it was only jamming on one side. The pinion shaft is not in the centre of the axle housing, it's to the left. The thicker crownwheel moved the whole diff another 3-4 mil to the left and thus caused the problem with the axle.

Overall, the disc/drum axles are the same length from axle tip to stud tip. The difference is that the flange on the disc axle sits 12 mil closer in and the studs are 12 mil longer, to allow for the thickness of the disc. The disc axles use a 7 mil spacer on the outside of the seal to allow for the caliper mount being thicker than the drum brake backing plate.

That is correct, axles are shorter by the thickness of the disc and use longer studs for the same reason. Spline end is also shorter, has to be as the bearing is machined further into the flange which pushes the axle further into the housing. From memory the centre hub also sticks out further like the longer studs. In the end I agree the total assembly is the same length but the actual axle from flange face to spline tip is shorter. On HZ's and A9X the flange diameter is also smaller than drum axle so the disc can fit over it.

Edited by yel327, 18 October 2014 - 07:28 PM.

[Steve TPF]

That is correct, axles are shorter by the thickness of the disc and use longer studs for the same reason. Spline end is also shorter, has to be as the bearing is machined further into the flange which pushes the axle further into the housing. From memory the centre hub also sticks out further like the longer studs. In the end I agree the total assembly is the same length but the actual axle from flange face to spline tip is shorter. On HZ's and A9X the flange diameter is also smaller than drum axle so the disc can fit over it.

 

According to the diagram I posted above, the spline end is the same - both axles are the same up to the end of the seal area. They are differnet lengths beyond that point: the flange on the disc axles is actually closer in so the with the disc in place the wheel sits in the same position. The wheel track is thus identical for both axles.

 

Any rate, I know why the axle was jamming, just curious as to whether anyone has encountered this problem before and why the crownwheels would be different thicknesses??

[TerrA LX]

Crownwheels are different thickness so they can use the same housing (pinion location) for a range of ratios.
Why were the axles jamming?

[Steve TPF]

The left hand axle was jamming on the diff pinion shaft, because the 3.9 diff sat further to the left because of the greater crownwheel thickness.

[TerrA LX]

Something doesn't sound right.

[76lxhatch]

The large Salisbury diffs have two different centre carriers which have different offsets for the crownwheel mounting face. One offset is used for the tall gears (e.g 3.08) and another for the shorter gears (e.g. 4.44). As mentioned above the shorter (higher ratio) crownwheels are thicker to make up for the smaller pinion, but this offset in the carrier means that they don't have to be excessively so.

I know that Heath said he found a similar offset difference in the Banjo diffs (where it doesn't matter much due to the room for adjustment), this may be the case with the small Salisbury also? If you have a crownwheel on the wrong carrier then this would move it over to one side quite a bit, you'd notice the difference in the side shims. If this is the case, as long as the gears have clearance and mesh correctly it won't be a problem, just a pain that the axle clearances weren't enough to begin with.

[S pack]

^^^ Was thinking about the different centres/crown wheel combos for the banjo diffs today and wondered if this may be the same situation for the Salisbury.

 

Reckon you're on the money 76lxhatch.

[Steve TPF]

The large Salisbury diffs have two different centre carriers which have different offsets for the crownwheel mounting face. One offset is used for the tall gears (e.g 3.08) and another for the shorter gears (e.g. 4.44). As mentioned above the shorter (higher ratio) crownwheels are thicker to make up for the smaller pinion, but this offset in the carrier means that they don't have to be excessively so.

I know that Heath said he found a similar offset difference in the Banjo diffs (where it doesn't matter much due to the room for adjustment), this may be the case with the small Salisbury also? If you have a crownwheel on the wrong carrier then this would move it over to one side quite a bit, you'd notice the difference in the side shims. If this is the case, as long as the gears have clearance and mesh correctly it won't be a problem, just a pain that the axle clearances weren't enough to begin with.

 

 

Sounds plausible. At any rate, a test-drive with the new diff produced a loud whining noise when decelerating. That (and the abundance of stripped bolts/nuts on the whole axle assembly) has convinced me that someone has taken the thing apart and thrown it back together with neither care nor skill.  At the very least it got me a second set of rear discs.

 

Will fit another diff from a torry shell I recently bought - hopefully this will get me under way. Would be nice to get the 3.9 diff serviceable though - I'm running a stock blue motor on straight gas - I can use all the help I can get!

 

 

Quick question: the other spare diff is a banjo - are they different lengths or will it bolt up without hassle?

[UCgazman]

Quick question: the other spare diff is a banjo - are they different lengths or will it bolt up without hassle?

 

Nope, upper arm mounts are different.

[Steve TPF]

Nope, upper arm mounts are different.

 

 

Dammit! So I'm high and dry then. Can it be done using the upper arms from the donor car (the one with the banjo), or are the mounts on the body different as well?

[S pack]

The mounts on the body are also different.

[UCgazman]

Different body mounts too. You can get these - http://www.ebay.com....=item2342de0c33 but I've never used them so I dont know if they're any good.

[76lxhatch]

Four cylinder cars (including early Commodore) have the 3.9 gearsets, they've usually had an easier life and easy enough to find

[TerrA LX]

Four cylinder cars (including early Commodore) have the 3.9 gearsets, they've usually had an easier life and easy enough to find

And make for FANTASTIC overtaking power on the highway with a V8.