Lotus Elan

Hopping Rear

PostPost by: Elanman99 » Thu Jul 21, 2022 12:33 pm

Andy8421 wrote:
Elanman99 wrote:
Lastly, washers are not used on the caliper bolts. Its a horrible thought, but I wonder if someone put them on to disguise a damaged lug.

Ian

Ian,

I would like to understand more about this. The rear caliper bolts pass through the aluminium lug at the bottom of the strut, and screw into a thread tapped into the cast caliper body. As I mentioned above, I believe it is usual practice to place a washer under a bolt head when a soft material is being clamped to avoid the bolt digging in to the soft material. The engine (for example) has a washer under every nut or bolt where it is up against an aluminium casting.

Do you have technical knowledge in this field, or are you basing your comments on the parts list diagram?

Thanks,

Andy.


No I dont have any specific knowledge but based my reply on how Lotus dealt with this particular fixing.

As you say it is good practice to use a washer to spread the load when there is risk of damaging a soft material. The particular bolts in question are mainly subject to shear so I dont expect they were meant to be particularly tight (I dont have the torque figure to hand) and the wirelocking just prevents them from loosening off and backing out. In the late 60's early 70's I saw, and was involved with many brand new Elans and every one had thees bolts wirelocked.

If one wanted to use a washer on a caliper bolt it should at least be a substantial (thicker) one, rather than the 'penny' washers seen in the pictures. By 'damaged lug' I meant it might be cracked and/or welded and the large washer used to hide it.

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PostPost by: Andy8421 » Fri Jul 22, 2022 7:57 am

Thanks Ian.

I agree that the lockwire is a good idea. In the spirit of full disclosure, I have used flat washers under my rear caliper bolts along with lockwire.

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PostPost by: billwill » Sat Jul 23, 2022 12:54 am

As mentioned by Ian, you also have to get the doughnut bolts the right way around or you wont be able to get them out. the heads of the bolts point outwards, not inwards towards the diff.

In the parts diagram it isn't clear which end is which, but i definitely think the left hand side of the diagram is the Diff end of the drive shaft.

Image


This topic viewtopic.php?f=37&t=16456&hilit=+doughnuts which I wrote way back in 2008 describes the process of changing/fitting the doughnuts.
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PostPost by: Donels » Sat Jul 23, 2022 12:47 pm

This is what I have to secure the callipers. Spring washers and lock wire. It may be belt and braces but it is safety critical. They are required as you’re bolting aluminium to steel and help to keep the bolt tight during expansion/contraction from heat cycling, which there is a lot of with brakes. I added the thin flat washers to prevent the spring washers digging into the soft aluminium. As far as I know the spring washers are original but not shown or mentioned in the manual.

7FD1152D-00E2-4805-9F6B-143A579FDDA1.jpeg and


Lock wire is not required at the front as you’re clamping steel to steel with steel bolts so the expansion is matched, however, springs washers are still used.
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PostPost by: snowyelan » Sun Jul 24, 2022 1:24 pm

Found this years ago while researching the value of lockwashers. Page 9.
https://ntrs.nasa.gov/api/citations/199 ... 009424.pdf
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PostPost by: Andy8421 » Mon Jul 25, 2022 5:39 am

snowyelan wrote:Found this years ago while researching the value of lockwashers. Page 9.
https://ntrs.nasa.gov/api/citations/199 ... 009424.pdf

Thanks for this. Page 9 has: (my emphasis at the end)

Lockwashers

The typical helical spring washer shown in figure 14 is made
of slightly trapezoidal wire formed into a helix of one coil so
that the free height is approximately twice the thickness of the
washer cross section. They are usually made of hardened
carbon steel, but they are also available in aluminum, silicon,
brome, phosphor-bronze, stainless steel, and K-Monel.
The lockwasher serves as a spring while the bolt is being
tightened. However, the washer is normally flat by the time
the bolt is fully torqued. At this time it is equivalent to a solid
flat washer, and its locking ability is nonexistent. In summary,
a Iockwasher of this type is useless for locking.
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PostPost by: Craven » Mon Jul 25, 2022 11:03 am

snowyelan wrote: At this time it is equivalent to a solid
flat washer, and its locking ability is nonexistent. In summary,
a Iockwasher of this type is useless for locking.


The type of split locking washer I have used has raised edges at the split, angle of ration such that compresses easily but digs in reverse direction locking the bolt head and the surface together.
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PostPost by: snowyelan » Mon Jul 25, 2022 12:05 pm

|While I agree that the raised edge will (eventually) stop rotation, it cannot do so until the tension on the bolt is reduced enough for the tooth to dig into the bolt head and mating surface. Unfortunately the bolt is loose at this stage. It's like laying a blade edge flat to a surface. It wont cut until you increase the angle regardless of how hard you press.
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PostPost by: Craven » Mon Jul 25, 2022 12:21 pm

One has to wonder then why this type of washer is manufactured and used in their millions as lock washers.
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PostPost by: Donels » Mon Jul 25, 2022 1:12 pm

Craven wrote:One has to wonder then why this type of washer is manufactured and used in their millions as lock washers.


Yes indeed. He might be from NASA but it doesn’t mean he’s right. He ignores the sprung load that the washer imparts to the bolt always keeping it loaded. Nevertheless Lotus still thought it important to added wire locking.
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PostPost by: rgh0 » Mon Jul 25, 2022 1:43 pm

A spring washer is not much use but better than nothing. If it's important use Loctite or lock wire it or torque it or stretch measure it depending on the joint design, critical joints don't use lock washers
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PostPost by: elangtv2000 » Mon Jul 25, 2022 2:10 pm

rgh0 wrote:If it's important use Loctite or lock wire it or torque it or stretch measure it depending on the joint design, critical joints don't use lock washers


Agreed. For example, rod bolts, main bolts, head bolts, flywheel bolts.

Lack of locking tension and/or digging into the base material aside, lock washers aren't used when there is the potential for them to break, as does occasionally occur. I've recently disassembled two rear differentials and a gearbox - each had at least one broken lock washer. In a static environment it's not a huge risk, but in a reciprocating/rotating environment, it could spell disaster.
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PostPost by: alanr » Mon Jul 25, 2022 2:26 pm

Different thing I know but my other hobby is light aircraft and In the light aircraft world you almost never see a spring washer used. Almost always bolts are plain washer and lockwired, split pins on nuts, or on minor items you may see a full metal tapered locknut.

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PostPost by: Elanman99 » Mon Jul 25, 2022 3:03 pm

Whilst the discussion on washers is interesting its drifted off topic regarding the OP's problem.

There is a standard and correct set of hardware for holding the rear suspension and drivetrain together and whilst no doubt it could be upgraded to aircraft or racing spec it is not needed for a road car. Based on the OP's pictures and information I would suggest that all the fixings involved should be replaced.

Billwill's method of assembly viewtopic.php?f=37&t=16456&hilit=+doughnuts
make sense but the images seem to have disappeared now.

Most importantly these bolts are not standard items from a hardware shop and I suggest they should be purchased from a Lotus specialist.

Hopefully the OP will let us know whether he has made any progress.

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PostPost by: bitsobrits » Mon Jul 25, 2022 8:10 pm

For rear calipers, an AN spec drilled head bolt with the correct diameter and grip length will do. Off the shelf stuff in the U.S. at least, and a fraction of the price of the Lotus specialists. As the bolt is threading into to caliper itself I would use a thread locking compound and a thin hardened flat washer (AN spec) rather than a spring washer, then follow up with locking wire.
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