Lotus Elan

Shakin' all over

PostPost by: stuartgb100 » Thu Sep 22, 2005 6:01 pm

Sadly that's what's happening .... to the car, I mean!

Up around 75-80 mph it really starts to shake, enough so that I back off,
and that's not usually in my nature.

Only had the car a few months, but noticed it almost from the start. I had the impression that the previous owner would not have ventured much above 60 mph.

Here's what I've done so far:

a) freed off an offside rear caliper.
b) had all wheels balanced (tyre wear is minimal, and they look true).
c) checked wheel bearings - all ok.
d) steering seems pretty good, ditto suspension.
e) not had prop checked, but figure whip would show before this speed.

I guess I could push on past 80 and see what happens....... but I could end up in a field, or worse.

Not having had the opportunity to drive/sit in another Elan, I'm not able to make comparisons. Should I be right to expect more from a 35 year old car?

One further point: the tyre fitter said the tyres (GoodYear Grand Prix S 70 155/70 SR 13) haven't been made for at least 15 years .... !!!
So apart from the fact that I need to replace these pdq, could they be a factor?

Thoughts/comments most welcome.

Regards.
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PostPost by: DrEntropy » Thu Sep 22, 2005 6:38 pm

At a minimum the tires are 15 years old?!?!
The list you checked would be "the usual suspects" and just MHO; I'd not even drive TO the tire shop on those old bladders! YIKES!

Methinks if you "reshoe" the ol' dear, that vibration will go away. Rubber that old, will take a "set" and likely the compound is now waaay past trusting at any speed.
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PostPost by: types26/36 » Thu Sep 22, 2005 6:42 pm

If the wheels were able to be balanced even though the tyres are old (not good) I doubt they are the problem, think I would be inclined to suspect the propshaft. Have a look at the engine/gearbox mountings but they way you describe it sounds like something is out of balance.
(You haven't got an engine driven fan with a blade broken?)
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PostPost by: DrEntropy » Thu Sep 22, 2005 7:06 pm

Right, Brian... I didn't think that thru. But I ~STILL~ wouldn't roll around on those old tires, balanced out or not. I paid the price with a bent L. Cortina
wheel a long time ago. The "post haste" was a knee-jerk reaction at seeing reference to 80 MPH on old rubber.

Driveline or old donuts (another scary scenerio) most likely.
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PostPost by: stuartgb100 » Thu Sep 22, 2005 9:16 pm

Thanks both for the suggestions.

Yeah I know tyres are a serious issue, and I'm going to post anew, which will reopen the Minilite issue.

However, back to this post.

I cannot see the propshaft to be the issue.

Say the vibration occurs at 75/80 in 4th
I can do 60mph in 3rd with no vibration... I would suggest this is the equivalent prop revolution to 75/80 in 4th?

Cannot be too specific about rpm, because tacho not working (see earlier post), but now sent away to SpeedyCables.

As regards doughnuts ...... yes there is wear, but not serious. A move to solid driveshafts is planned this winter.

With regards to the fitter's comments ... I need to check them.

As regards engine mounts ..... they're fine, and fan is electric.

Hmmm..... where to go from here ?
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PostPost by: ppnelan » Thu Sep 22, 2005 9:35 pm

I think you're getting confused :? If the car is going at, say, 70mph then the propshaft rpm is the same whatever gear you're in ! It's connected 'directly' to the wheels through the diff, remember....

I have a similar problem on my 5-speed +2, but it happens at about 65-70mph. I know I need to replace the rear dampers, and will replace the top mountings (Lotocones) and probably all the diff bushes too to see if this helps at all. But I think it is more likely to be propshaft or maybe gearbox output bearing related. Gearbox/propshaft removal & inspection will have to wait....

You could check that the bottom of the diff is clear of the chassis. They're very close, and mine used to be resting on it which caused varying degrees of vibration most of the time before it was 'adjusted'...

Also, mine has Lotus alloy wheels and the garage told me they were particularly difficult to balance due to poor casting...

Let us know if you fix the problem !

Regards,
Matthew
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PostPost by: type26owner » Thu Sep 22, 2005 9:44 pm

http://www.tirerack.com/images/tires/vibechart.pdf
A tire is subject to going out of round when spun up to speed. One belt that slipped a wee bit is all it takes. At zero rpms they go back to running true. This type of problem can be a real hair puller.
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PostPost by: types26/36 » Thu Sep 22, 2005 9:54 pm

[quote not had prop checked, but figure whip would show before this speed.quote]

Not sure what you mean there, are you saying if it were the prop out of balance then the vibration would come sooner?
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PostPost by: 1964 S1 » Fri Sep 23, 2005 1:54 am

Do you feel safe driving that fast on fifteen year old tires? Do you know if the car ever sat for say two or three years without being moved. I'm betting you've got at least one defective old tire. You could try switching front to rear, is the vibration more or less pronounced in the steering wheel versus shakin all over? I'd just buy four new tires, if that doesn't fix the problem (I'm betting it does) then proceed safely to the solution. Does the vibration have any clunking, nearly metallic traits?
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PostPost by: worzel » Fri Sep 23, 2005 8:11 am

Hi all

I've had my sprint for 27 years and during all of that time have experienced something similar.

Correct wheel balancing (by a bike specialist who knows his stuff) and various tyre changes reduced but didn't entirely eliminate the problem-until- I switched from the standard steel wheel rims to minilites.

Result- an instant transformation- no shakes/vibrations etc and my car is 5 speed so higher crusing speeds are easy.

I'm not a technical specialist but I reckon it's got something to do with the greater accuracy of the alloys and the "damping" effect of the thicker metal. The whole effect is to produce a more refined driveline- somehow.

Regards

John
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PostPost by: rgh0 » Fri Sep 23, 2005 10:09 am

My guess would be something out of round in the wheels or tyres or eccentric mounting of a wheel on its hub. The wheel / tyre combination can be balanced on a machine but if out of round or not mounting properly will give vibration as the speed increases. The "out of roundness" may not be measurable in the tyre radial dimension as it may be in just the tyre radial stiffness. The Elan with its light weight is particularly vulnerable to vibration due to tyre radial stiffness variation around the circumference.

At 15 years old the tyres are stuffed anyway so replace them and if the problem goes away good, if not then investigate further the wheel roudness and mounting.

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PostPost by: stuartgb100 » Fri Sep 23, 2005 10:17 am

Several points to answer:

Yes, I drove at 75/80 a couple of times, but not since I found out about the tyre-age problem.

As regards the propshaft issue: I only get this shaking in 4th at 75/80 (no idea what it's like at higher speed). Would I not have experienced something similar when accelerating hard through the gears, if it were propshaft-related?

Many thanks Keith, for the tirerack link.

So my conclusions so far:

tyres must go
steel rims have to go
fit solid driveshafts ASAP

Thanks for the help. Will post anew re Minilites and tyres.

Regards.
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PostPost by: david.g.chapman » Fri Sep 23, 2005 11:15 am

I had the same problem on my +2: vibration in the car and steering wheel at speeds above 70 mph. I checked the side to side run out of my steel wheels and changed them to get a run out of less than 1-2mm.

This gave a slight improvement.

The thing that fixed it for me was changing the budget front tires for a set of avon tires - supposedly half way up the quality scale. The vibration all but disappeared!

It seems that it is difficult to balance out cheap tires with their inherent variations in thickness etc.

Dave Chapman.
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PostPost by: steveww » Fri Sep 23, 2005 12:06 pm

I had a vibration issue with my S4 and traced it down to the steering rack. There way some play on the steering arm coming out of the rack.
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PostPost by: elansprint71 » Fri Sep 23, 2005 5:38 pm

Even if the tyres are not causing the bad vibes, you will find that they are absolutely useless in the wet. I scared myself silly when I first got my Sprint. Also have a friend who had them on his S4- exactly the same, rubbish.

Get rid of them; you know it makes sense. To paraphrase Sir Robert Mark, former boss of the Metropolitain Police who advertised these abominations just after he retired!

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