Lotus Elan

DIFF CASE

PostPost by: types26/36 » Sun Aug 31, 2014 5:31 pm

Any one happen to know why there is a difference in the shape of some English diff casings? they appear to be the same internally but have a different shape for the nose and the top, was one a Ford casing and the other a Lotus? was it just a modification for strength? an upgrade? a different supplier? or some other obscure reason?
The one on the left came from an Elan and the right from an Escort or Anglia.
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PostPost by: promotor » Mon Sep 01, 2014 12:45 pm

The 105e casing which is smaller inside and out, and the later type - think it's number is something like 73AG ###### - has more room for the cw&p.
They are both Ford cases with Ford part numbers on them.
The later ones were introduced around the release of the mk1 escort RS2000 to allow fitment of a dimensionally larger 3.54 cw&p (different to the Lotus 3.55) and also to cope with the extra torque of the pinto and weight of the later cars.

That's my reasoning on it - it's not gospel but I get to see a fair few diffs so that's my view acquired over time!
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PostPost by: types26/36 » Wed Sep 03, 2014 9:53 am

Thanks thats interesting, I have a 3.54 and a 3.55, although the crown wheels appear about the same size the pinion on the 3.54 does seems a little larger.
I am rebuilding the 3.55 and obviously dont have all the correct tools but do have tools to set pinion pre-load and backlash, in your experience does using the same pinion shim (in the same diff case) give the correct pinion depth with new bearings? my reasoning being bearings are made to such fine tolerances that they should be the same?
Setting the carrier bearing pre-load seems a bit iffy if set by the casing spread method, any idea how much more (drag) pinion pre-load would there be if the pinion is set then the crown wheel pre-load added?
I have never had much success using engineers blue to check tooth contact, could never get a decent imprint, is there anything better to use?
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PostPost by: Elan45 » Wed Sep 03, 2014 2:46 pm

I have been told by Dave Bean Engr and others over here, this side of the pond and I believe also Burtons that the pinion height shim is matched to the diff housing. They are not available loose by themselves. And you are correct that the bearings are ground to such precision that they match just fine. This also means that the pinions must be ground that precise too.

I always had trouble with what I considered engineers blue to set gear patterns. That was the liquid painted onto metal fabrications so that scribe lines show up better.But engineers blue is a paste that is specifically for setting wear patterns. There is also a material called "red lead", also used to set patterns. The only time I've ever seen it used was over 30 years ago. Contrary to its name, it was supplied as a golden yellow powder that was mixed with oil to make a paste. But, lead is such an anti-environmental word today that I have no idea if it is still available

I also have some liquid graphite, that was used to paint steam engine boilers back in the day. My father procured some years ago to paint leaf springs and I inherited it. It might be something that could be used to check patterns, but it remains tacky for a long time, perhaps too long to be of use in this application.

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PostPost by: types26/36 » Thu Sep 04, 2014 4:46 pm

Roger,
Thanks for your thoughts, Burton's do sell the crown wheel and pinion and they also sell the shim:
http://www.burtonpower.com/crown-wheel- ... cwe35.html
http://www.burtonpower.com/catalogsearc ... inion+shim
although I dont think it would be to difficult to get a shim as there are lots of shims available for various things, the trouble would be determine the thickness.
If by checking the tooth contact the shim has to be changed the pinion inner bearing would have to be removed to fit it which would probably end up destroying the bearing.......bit of a vicious circle so hopefully by fitting the original shim the pinion depth will be correct.
The yellow powder you mention is probably a form of yellow ochre as I have heard of this being used.
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PostPost by: promotor » Thu Sep 04, 2014 9:27 pm

Normally using the same pinion and shim works but different brands of bearings give a different reading due to being machined to differing final tolerances (a couple of thou makes a big difference which is evidenced by the range of pinion shims available) and require adjustment with a different shim.

If I remember correctly Koyo bearings and Timken bearings tend to have a difference between them of 3 or 4 in the shim range, with Koyo tending to match the original factory spec ie no need to change the pinion shim. Of course if the diff has been rebuilt prior to getting in there yourself it may not work out like this but generally diffs haven't been rebuilt - they get noisy and then get removed.

You are right about damaging the pinion head bearing (and more likely the pinion teeth!) if you don't have the correct bearing removal tool. Remember to put the pinion shim with the chamfer on the shim facing the head of the pinion - you don't want a fracture caused by a sharp edge being seated against the pinion head bearing/shim surface.

Diffs are not easy to do even with the correct tools as the contact patch can be non-existent in a lot of cases due to diffs running out of mesh for any substantial amount of time.

Regarding the bearing carrier cap spread affecting the pinion pre-load in short it doesn't - the method is to set and re-check the pre-load with the diff carrier removed. I don't think you could get the pinion pre-load tool to move if it had to overcome the friction of the diff carrier bearings and the gears in mesh.
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