Lotus Elan

Pinion oil seal

PostPost by: JonB » Thu Jan 11, 2018 1:04 pm

Looking at the exploded diff diagram http://www.lotuselan.net/wiki/RB_-_Differential_%2B2

It appears that all I need to do to replace the pinion oil seal is to undo the flange nut, pull the flange and deflector off the shaft and prise the old seal out. Then, reassemble with a new seal and torque up the nut (to 30-35 lbs/ft according to the technical data for the "pinion bearing nut"). Looks straightforward.

But... I have been reading threads about diff work and one of them mentions the "crush tube" - I don't know what that is or whether I should worry about it (perhaps it is the "collabsible spacer" the manual mentions). There is some hokey technique to do with torquing a nut which I didn't follow. I'm not looking to strip the unit, I just need to replace the front seal.

Is it OK to do as I thought, or do I need a new crush tube and this odd torquing sequence?
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PostPost by: rgh0 » Thu Jan 11, 2018 1:16 pm

The crush tube is a collapsable spacer between the two pinion bearings. As the drive flange is tightened to preload the bearings the tube collapses to hold them in location correctly once preloaded. The preload is measured via the turn torque of the pinion bearing shaft as the nut is tightened.

This can only be properly done when the diff is being reassembled and the crown wheel has not yet been installed

You can do a quicky seal swap it you ensure the pinion shaft drive flange nut is tightened to the same location as before it was dismantled by counting the turns and match marking the nut and flange and shaft before disassembly.

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PostPost by: JonB » Thu Jan 11, 2018 2:09 pm

Righty ho.

Hmm, thread locking compound on the nut too. I guess it has a nylon locking ring and I would be reusing it. Only, I will be using Wellseal per Miles's instructions. Does that have any locking properties? I doubt it.
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PostPost by: Craven » Thu Jan 11, 2018 2:33 pm

There is a school of thought that thinks oil will find its way along the splines on the pinion shaft and leaks out pass the nut, an explanation of why oil is sometimes found in between the flanges.
Using a sealant on the nut flange interface is to prevent this.
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PostPost by: promotor » Thu Jan 11, 2018 2:53 pm

JonB wrote:Righty ho.

Hmm, thread locking compound on the nut too. I guess it has a nylon locking ring and I would be reusing it. Only, I will be using Wellseal per Miles's instructions. Does that have any locking properties? I doubt it.


Early flange nuts are "staked/peened" into a recess cut into the thread on early CWP's. Later type CWP's use a distorted nut to keep it locked to the thread. You can successfully use a late nut with an early CWP but not vice-versa but I would stick to original where possible.

I always use Hylomar blue on the threads and under the pinion nut - make sure the threads are clean before you do final assembly. One of my pet hates is seeing thick silicone under pinion nuts - I've seen some so thick that the nut wasn't actually seating on metal and hence no tension in the thread! No idea how you even begin to do that...
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PostPost by: MarkDa » Thu Jan 11, 2018 5:18 pm

Jon
Sounds like the diff's out then!
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PostPost by: JonB » Thu Jan 11, 2018 5:28 pm

No, it's all talk and no trousers. Don't have so much time to get out in the garage. This weekend though, it's coming out. Any advice? I've read lots of threads about how right it is, how I should remove the brace, etc but not much about the top mounts. They're bolted with the nut on top and the manual says to go under the tank behind the rear set to get to the nut, is that correct? Can I put a braced spanner in there somehow and then go under the car? There's only me doing this, no helpers.
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PostPost by: MarkDa » Thu Jan 11, 2018 5:55 pm

I have a 2 seater and it's easy enough.
You can get at both ends of the through bolts but obviously need to brace one end if you don't have a helper.
Although it may come out with the brace on
I think it makes sense to take it off to save swearing time.
The small bolt at top of diff is a bit fiddly but easy enough.
Comes out on left and needs wishbone at least swung out of way.
Somebody posted about searching YouTube for a video - made it look simple!
Some pundits suggest filling or grinding surplus casting at pinion end etc before reinsertion. I guess if comes out without a struggle then it'll go back In!!
The chassis 'plate' may be buckled up from jacking and prevent removal in which case you'll just have to push it back down.
I've never had bother but it does have a fearsome reputation!
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Last edited by MarkDa on Wed Apr 11, 2018 11:26 pm, edited 1 time in total.
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PostPost by: JonB » Thu Jan 11, 2018 8:15 pm

I think the video made it look easy because the guy had fettled the casing. He also has an inspection pit, whereas I have axle stands and a creeper. I sure hope it doesn't fall on my head!
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PostPost by: MarkDa » Thu Jan 11, 2018 11:01 pm

It's not that hard or heavy really.
Take the wheel off and remove the wishbone - there will be plenty of room.
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PostPost by: Foxie » Fri Jan 12, 2018 12:51 am

rgh0 wrote:The crush tube is a collapsable spacer between the two pinion bearings. As the drive flange is tightened to preload the bearings the tube collapses to hold them in location correctly once preloaded. The preload is measured via the turn torque of the pinion bearing shaft as the nut is tightened.
Rohan


The collapsible spacer is a cheap replacement.

However, you can always "uncollapse" the old spacer by mounting it on a close fitting steel tube and slightly hammering out the bulge section. :)
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PostPost by: 2cams70 » Fri Jan 12, 2018 1:06 am

If the pinion nut is the later style that depends on thread friction for locking effect I would just do as Rohan said. Remove the nut and flange, replace the seal, reinstall the flange and nut tightening the nut back to it's ORIGINAL location in relation to the pinion thread. Job done. No need to remove diff. The original nut can and should be reused.

If the pinion nut is the early style that depends on staking for locking effect you may be better off removing the diff and resetting the pinion preload using a new nut (preferably the later style). The alternative is to use the original nut, reinstall to original position but use Loctite instead of relying on the original staking because the staking will suffer from metal fatigue if stamped twice in the same location. Personally I'm not a fan of using Loctite because it is such a pain to undo and remove particularly as it would be best to use the high strength red type in this application.
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PostPost by: JonB » Fri Jan 12, 2018 8:22 pm

2cams70 wrote:If the pinion nut is the later style that depends on thread friction for locking effect I would just do as Rohan said. Remove the nut and flange, replace the seal, reinstall the flange and nut tightening the nut back to it's ORIGINAL location in relation to the pinion thread. Job done. No need to remove diff. The original nut can and should be reused.

If the pinion nut is the early style that depends on staking for locking effect you may be better off removing the diff and resetting the pinion preload using a new nut (preferably the later style). The alternative is to use the original nut, reinstall to original position but use Loctite instead of relying on the original staking because the staking will suffer from metal fatigue if stamped twice in the same location. Personally I'm not a fan of using Loctite because it is such a pain to undo and remove particularly as it would be best to use the high strength red type in this application.


I'm intrigued by your point above (in bold). Can you really change the pinion seal without removing the diff?
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PostPost by: 2cams70 » Sat Jan 13, 2018 2:57 am

Once you have removed the pinion flange you have access to the seal. I normally remove it by using a sharpened large flat bladed screwdriver and spearing it near where it is pressed into the carrier. Knock the screwdriver with a hammer to spear it. Once you have speared it you can then lever it out by working your way around the circumference. Also once it starts to rise out of the carrier you can spear it in the side and start levering. You need to go very carefully to avoid gouging the carrier surface where the seal seats. Although the seal is an interference fit in the carrier nose it's usually not too bad getting it out. When you spear it do so very carefully so as not to hit the taper roller bearing that lies just behind. Make sure there are no shards of steel left around the pinion bearing from the spearing process.
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PostPost by: JonB » Sat Jan 13, 2018 6:44 am

Ok, but can you confirm it is doable without taking the diff out?
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