Lotus Elan

Differential pinion depth

PostPost by: promotor » Tue Jan 22, 2019 10:42 am

This is a reproduction CWP showing contact patch almost as good as it gets with engineers' blue and a bit of oil:

dsc03828.jpg and
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PostPost by: 2cams70 » Tue Jan 22, 2019 11:11 am

Whilst still on the subject of diffs may I ask what kind of fixture are people using to hold the carrier whilst assembling it? Some of the torques required during assembly are pretty high - eg. when tightening the pinion nut and side adjuster rings. It needs to be securely held somehow. Pictures especially of any home made implements would be much appreciated. Whilst disassembly on the floor is Ok, assembly is a bit more critical!
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PostPost by: Hawksfield » Tue Jan 22, 2019 4:21 pm

promotor
Al
That's a good contact result
I found getting the consistency of the paste was critical, you have got it correct in this example
Your experience is obvious
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PostPost by: promotor » Tue Jan 22, 2019 4:35 pm

Hawksfield wrote:promotor
Al
That's a good contact result
I found getting the consistency of the paste was critical, you have got it correct in this example
Your experience is obvious


Thanks John. I think you're right on the consistency.

Regarding my experience I think the quote " the more I practice the luckier I get" applies! :lol:

I've thought about using yellow ochre but have just stuck with the blue as I use it for checking valve seat sealing too.

Does the yellow ochre give you a more obvious distinction between contact and non-contact over engineers' blue? Of the articles I've seen using ochre I find it harder to pick out the patch! Is it soluble in oil so doesn't need removing before using the diff?
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PostPost by: Hawksfield » Tue Jan 22, 2019 4:53 pm

2cams70

Here is my method of doing the spread and backlash, the pinion was done during a previous poorly rebuild and not setting the backlash correctly.
I think the builder replaced the bearings and set it up to the previous setting marks, the pinion preload was ok
I just reset the backlash to the Lotus manual spec of 0.005 - 0.007
The pinion flange is held locked with mole grips

Diff is now fine and runs quietly

dsc03709.jpg and
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PostPost by: Hawksfield » Wed Jan 23, 2019 7:02 pm

promotor

Al
I was having trouble with my engineers blue( possibly as it was around 50 years old :oops:) so I purchased the yellow ochre from English Diff. At the first attempt it was too thick and it squashed and wiped the gears clean, I realised that it needed to be a thin even coating which was achieved by mixing with oil to give a good result.
Your right to say that the yellow ochre does not give the results and must be mixed with oil, as from the tin it is quite thick.
The yellow ochre is soluble with oil and no danger to the diff

The contact chart supplied by English Diffs looked as though there should be definite contact marks but as you know it is just a light wipe of the contact area, a good example shown in your image.

I am still on the learning curve but getting nearer to the top :)

The chart

Gear marking paste0001.pdf
(929.98 KiB) Downloaded 75 times
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PostPost by: promotor » Sun Jan 27, 2019 1:43 pm

Thanks for the details on the ochre.
The contact patch drawings are "ideal world" and really only help when the CWP are either new or as good as new.
When the contact patch is vague I have to go with as good as I can get it rather than "book spec" as book spec doesn't exist very often!
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PostPost by: seniorchristo » Thu Feb 21, 2019 12:29 am

Sorry for the late follow up as my work limits my Elan time. Today I installed the pinion and bearings and set the pinion preload. It took judicious use of an impact gun to crush the sleeve properly. I did so without the oil seal so as to more accurately get the proper 9-11 inch pounds. Question: Is a 1 lb.weight 10" from flange center equivalent to 10 inch lbs.? I got very close and then removed the flange to install the oil seal. I reinstalled the flange, torqued to 35 ft. lbs. and noticed much less than the original 9-11inch pounds to spin the pinion. I guess the crush sleeve expands when the pressure is off? I than had to retighten the nut to get the correct preload. I'm guessing about 75-80 lbs. of torque. I don't remember this problem when I rebuilt my 3.55.
I than rechecked the pinion height and came up with about .001 -.002 difference from original measurements, that being a lower pinion height. The original bearings were British, the replacements Japanese NTN from Paul Matty. I'm going to leave it alone with hopes I can get a good enough pattern through adjustments. :)
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PostPost by: 2cams70 » Fri Feb 22, 2019 10:20 am

Whilst that's the correct way to calculate pinion torque (force x distance) your specification seems wrong (too low fortunately so you won't require a new collapsible spacer). Ford specs. for new bearings as follows:

20 to 26 lb.in (including oil seal drag)
13 to 19 ib.in (excluding oil seal drag)

halve these figures for used bearings.

Note that later Ford manuals do not quote a figure for torque including oil seal drag. They advise that the oil seal drag be determined by measuring it with zero preload on the bearings. Presumably this is to account for different seal suppliers and types used during manufacture. Early seals were leather and later were synthetic rubber.

Note also that it is easier to measure pinion torque and oil seal drag using a direct reading spring balance unless you have a variety of weights or are comfortable sliding the weight over an adjustable distance to determine torque.

Once you have reached the correct preload it is strongly recommended not to back the nut off again as you have done here unless you use a new spacer.

The pinion torque figures in the manual are for the pinion by itself - i.e not meshed with the crown wheel.
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PostPost by: seniorchristo » Fri Feb 22, 2019 1:21 pm

Thank you so much 2cams! :)
I bought a pack of (10) nuts so no problem starting over. Intuitively 26 in. lbs. sounds like a lot of resistance as even 9-11feels like substantial pressure on the bearings. It does make sense new bearings require more preload.
Am I correct in assuming the crush washer expands a little when the pressure is backed off? What do you think about pinion height being different by .002? It varied from the original measurement, not necessarily the correct one.
Thanks
Chris
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PostPost by: 2cams70 » Sat Feb 23, 2019 11:31 am

The crush washer may expand a bit when the nut is backed off but really you are only supposed to crush it once. Given the crude way of measuring it .001-.002" is probably within the tolerance of measurement inaccuracy so I would not assume the actual pinion height has changed by that much.
I'd just do a trial assembly using the current pinion shim and see what the contact pattern looks like before changing the shim thickness. Note that you are best to not install a crush washer if it's only a trial assembly and you are only checking the contact pattern or determining the oil seal drag. Saves the crush washer for final assembly and also makes setting the pinion preload for trial much easier not having to compress it.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
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2015 Honda City 5spd.
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PostPost by: davidj » Sun Aug 04, 2019 12:53 pm

Afternoon,

I recently replaced the input seal and crush washer on my diff using a (very expensive!) torque gauge to measure the rotation torque of the pinion, and set it at 22 lbf in (with the seal). This is the figure from the Haynes Escort manual and various forums - the Escort uses the same diff. However, the is no mention of using half the figure for used bearings and indeed the manual assumes the original bearings are being used.

Do you think I have over tightened the assembly?

Yours worried,

David



2cams70 wrote:Whilst that's the correct way to calculate pinion torque (force x distance) your specification seems wrong (too low fortunately so you won't require a new collapsible spacer). Ford specs. for new bearings as follows:

20 to 26 lb.in (including oil seal drag)
13 to 19 ib.in (excluding oil seal drag)

halve these figures for used bearings.

Note that later Ford manuals do not quote a figure for torque including oil seal drag. They advise that the oil seal drag be determined by measuring it with zero preload on the bearings. Presumably this is to account for different seal suppliers and types used during manufacture. Early seals were leather and later were synthetic rubber.

Note also that it is easier to measure pinion torque and oil seal drag using a direct reading spring balance unless you have a variety of weights or are comfortable sliding the weight over an adjustable distance to determine torque.

Once you have reached the correct preload it is strongly recommended not to back the nut off again as you have done here unless you use a new spacer.

The pinion torque figures in the manual are for the pinion by itself - i.e not meshed with the crown wheel.
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PostPost by: 2cams70 » Sun Aug 04, 2019 1:05 pm

davidj wrote:Afternoon,I recently replaced the input seal and crush washer on my diff using a (very expensive!) torque gauge to measure the rotation torque of the pinion, and set it at 22 lbf in (with the seal). This is the figure from the Haynes Escort manual and various forums - the Escort uses the same diff. However, the is no mention of using half the figure for used bearings and indeed the manual assumes the original bearings are being used. Do you think I have over tightened the assembly?Yours worried, David


Did you measure the preload with the pinion still in mesh with the crownwheel? The workshop manual figure is for the pinion by itself and does not include the drag induced by the preload on the crownwheel carrier bearings.

Yes the figure is supposed to be halved for used bearings.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
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PostPost by: davidj » Sun Aug 04, 2019 6:28 pm

Hello,

Thanks for your reply. I torqued the pinion with the seal fitted but without the crown wheel I have never heard about using half the torque figure for used bearings, and annoyed there is no mention in the haynes manual. Looks like I have to buy another spacer and seal. :(

Cheers,
David
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PostPost by: davidj » Mon Aug 05, 2019 2:04 pm

Hello,

Just so it is on the record for other owners wishing to set the diff pinion preload, I can confirm 2cams is correct; after some more digging I have discovered for used bearings the preload has to be halved. Consequently it will be 11 lbf in, with the seal.

This is not mentioned in the haynes manual. :oops:

Cheers.

David
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