Lotus Elan

Differential clearance.

PostPost by: arendjankleijn » Sun May 21, 2006 1:02 pm

Does somebody know what is supposed to be the clearance between the differential and the lower chassisplate. If there is any. On my Sprint the differential is resting on the chassis, can that be the reason of the constant noise coming from the back of the car at any speed.
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PostPost by: nebogipfel » Sun May 21, 2006 1:31 pm

It is definitely the cause of the noise on the back of your car.

There should be a running clearance but it doesn't need to be a very big gap. This is assuming the mountings and torque rod bushes are in good condition.

I can't remember the specified gap and don't have the manual to hand but I'm sure someone will tell you :D

I think the idea is to have as small a clearance as practical to get as near a straight run for the driveshafts as possible?
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PostPost by: Emma-Knight » Mon May 22, 2006 2:07 pm

...the diff installation is described in the back of the manual in chapter "R" (behind "bodywork"). The space is adjusted between diff top
and upper cross member - 1/8 in - by using one or two big washers
between top diff lugs and crossmember. But You better read this in the manual... :?

(my diff is also resting on the chassis - the mounting bolts were not
tightened correctly)

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PostPost by: arendjankleijn » Sat Jun 17, 2006 8:21 am

I renewed the two top mounting rubbers, the differential is only just free from the chassis when I don't juse the big spacers!
Will this have any consequences to the differential casing? Beeing a Sprint the extra bracket on top is present. The noise disapeared finally.
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PostPost by: types26/36 » Sat Jun 17, 2006 8:50 am

It should not cause any problems with the casing but the washers are there to prevent the mounting "spreading" and the surface area of the bracket is quite small, would there be enough space to get one thin washer in and still have clearance on the diff ?
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PostPost by: jkolb » Sat Jun 17, 2006 7:33 pm

I had the same problem. Purchased TTR's improved mounts and new poly bushings for the strut rods, and the diff just floats - the way it was meant to. The TTR mounts are mostly steel, and have the correct thickness washers. Comes complete with bolts and nuts as well. Recommended.

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PostPost by: stuartgb100 » Sun Jun 18, 2006 1:04 pm

IIRC somewhere (in the manual, I think) it says that a minimum of ONE washer must be used.

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PostPost by: rgh0 » Sun Jun 18, 2006 1:06 pm

IIRC it also says somewhere that the Sprint diff brace counts as the minimum of one washer. So if you have the diff brace you can get away with no washers

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PostPost by: stuartgb100 » Sun Jun 18, 2006 1:35 pm

That could be a help, but obviously I never read that bit <g>.

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PostPost by: davidj » Fri Oct 11, 2019 5:44 pm

Afternoon,

Sorry to resurrect an old thread, but just checking the diff clearance in the chassis before I fit the body.

Now the manual says......

..and adjust to give a clearance between the top of the unit and the chassis crossmember of 5/32 in. (3,97 mm) maximum and 3/32 in. (2,38 mm) minimum - ideally 1/8 in. (3,17 mm).

I have a spyder chassis, and the instructions say the clearance between the lower chassis member and the diff should be 4mm. To achieve this, I would have to have three thick washers and the diff brace and would also have to use longer bolts The gap between the top of the diff and the chassis would be a lot more than 1/8" To further complicate the situation, the Mick Miller drive shafts require the diff as low as possible in the chassis.

So, should I ignore the lotus manual and fit the longer bolts and washers?

Thanks in advance for any advice!

David
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PostPost by: oldelanman » Sat Oct 12, 2019 10:34 am

davidj wrote:So, should I ignore the lotus manual and fit the longer bolts and washers?


Yes. The Spyder crossmember is higher than in the Lotus chassis to give more clearance for removal/fitting of the diff so additional spacers are needed to lower the diff to it's correct original position.

spyder-chassis-fitting.jpg and
Spyder Chassis Fitting Instructions
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PostPost by: davidj » Sat Oct 12, 2019 3:07 pm

Thanks. That confirms what I have discovered. By my, rather crude measurements, a 4" bolt, 1/4" longer that standard will just enable 2 thick washers and the cross brace to be fitted, and still result in a gap of approximately 8 mm, 4 more than recommended.

This suggests I should go for even longer bolts and use 3 washers? This must be a common issue with any car fitted with the Spyder chassis but strangely there is little mention how to resolve. When I spoke to Spyder, they questioned if the rubber mounts were correct. (they are). Maybe there are hundreds of Spyder cars running around with the diffs too high. How many washers/bolts have other owners of Spyder cars used?

To further confuse matters, Brian Bucklands book suggests mounting the diff as high as possible to allow for saging of the mountings.

Yours very confused.

David
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PostPost by: Donels » Sat Oct 12, 2019 4:00 pm

I recently refitted my diff and had read all the stuff on dimensions and Brian?s advice. I set the diff so there is equal-ish clearance at the top and bottom. The clearance at the nose of the diff changes when you tighten the torque rods in that it raises the nose.

All stuff about getting it right for driveshafts seems rubbish to me. If the shafts are that sensitive then how are they going to cope with suspension movement. I suggest you get a balanced clearance top and bottom. As the diff is rubber mounted the clearance will change side to side with torque and up/down with bumps. You don?t want it to hit the chassis under any condition.

Mine is a Lotus chassis not Spyder, so adjust advice accordingly.
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PostPost by: William2 » Sat Oct 12, 2019 4:29 pm

On my car I have just the Sprint diff cross brace and no washers. Gives me about 1/8" clearance at the bottom and hasn't given me any problems.
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PostPost by: davidj » Sun Oct 13, 2019 10:07 am

1/8" sounds what is recommended in the manual. If you have a Spyder tubular chassis then maybe they (Spyder) have changed their diff clearances back to the original lotus Spec. This may also explain why the guy I spoke to at Spyder did not know what I was talking about and thought the problem was to do with the mounts.. However as oldelanman pointed out, the clearance was much greater. On my chassis, (guess circa 1990) with just the brace fitted, I would have a gap around 5/8".
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