Diff backlash and preload

[Mac]

Ok, got me fish scales, getting a dial guage.

Anyone know what sort of pinion preload and backlash I should be setting on an old diff.

I'm thinking about half the pinion preload figure for new bearings which is 12-16 ft/lb so about 6-8 ft/lb for the old bearings. Gonna measure the distance from bolt hole on flange to centre of pinion then multiply that by lbs on fish scale.

No idea about backlash figure though. Haven't found anything on the net for Triumph diffs. Those Nissan diff instructions say 0.006-0.008 of an inch ring gear backlash.

Any ideas?

[CharlieB]

I think you need to buy or borrow a factory workshop manual. I could scan the relevant pages from my 1500 one but it might not be the same (collapsible spacers etc)
The preload is quoted as 13 to 20 lb.in (not lb.ft!)
The backlash is not given directly but as far as I understand it you move the crown wheel fully into mesh with the pinion then back it off 0.005" using the shims.

[Nick Jones]

Note that the factory manual is written for assembly of new parts.

Bearings that have already seen use should not be reset to new preloads - they will fail - you probably be fitting new anyway.  Likewise, if you get hung up on trying to get the backlash correct to factory figures on a used CWP set you will probably end up with something that howls (got that T shirt....).

Suggest speaking to someone who actually reconditions these things sucessfully (Mike Papworth, Dave Pearson to name but two)

Nick

[Mac]

CharlieB wrote:

I think you need to buy or borrow a factory workshop manual. I could scan the relevant pages from my 1500 one but it might not be the same (collapsible spacers etc)
The preload is quoted as 13 to 20 lb.in (not lb.ft!)
The backlash is not given directly but as far as I understand it you move the crown wheel fully into mesh with the pinion then back it off 0.005" using the shims.

Yeah it's lb/in thanks Charlie

Think I've got the pinion preload figure mosre or less sorted

Pinion preload
New bearings: 12-16 lb/in
Old bearings: about half that so 6-8 lb/in

Radial distance fom centre of pinion to bolt hole in flange is 3.5cm = 1.4 inches

So lb has to be divided by 1.4

6 lb / 1.4 = 4lb
8lb / 1.4 = 6lb

Set to 5lb on fish scales which should be about 6-8 lb/in preload

About the backlash that 0.005 will be for new CWP set as Nick says so probably going for the 0.008 which is the loosest figure for that Nissan diff unless someone comes up with another figure for a Trumpet diff.

I guess turn and check for no tight spots and check preload is same all the way round. I'll go for looser rather than tighter as I think it was pretty loose before. I'll be measuring the pinion preload and backlash as they are first before tightening them up.

[Mac]

Nick_Jones wrote:

Note that the factory manual is written for assembly of new parts.

Bearings that have already seen use should not be reset to new preloads - they will fail - you probably be fitting new anyway.  Likewise, if you get hung up on trying to get the backlash correct to factory figures on a used CWP set you will probably end up with something that howls (got that T shirt....).

Suggest speaking to someone who actually reconditions these things sucessfully (Mike Papworth, Dave Pearson to name but two)

Nick

Thanks Nick,
Yeah good point about not overdoing the preload with old bearings, I'm going to try using the old ones with a min of preload see how it goes, basically half the preload for new as it says for that Nissan diff. The old bearings are Tinkum, feel and look ok to me. For now I'll change the seals but not the bearings.

Dunno if Dave will pass on a figure like that as he's reconditioning them, and no idea how to contact Mike Papworth. Be great if Dave or Garreth or someone could indicate backlash and preload figures I should be aiming for, but I do appreciate it's their job so maybe not willing to part with such info.
Might just say "it's junk" don't bother.
;-)