Lotus Elan

Hopping Rear

PostPost by: Temmck » Sun Jul 17, 2022 4:57 pm

One the first couple of drives with the S4 I felt a pronounced bouncing in the left rear to which I chalked up to a bad strut. This caused the card bounce when driving in slow speeds. Since my local roads are fairly bumpy it fit my damper assessment. But, today I was moving the car, very slowly over a flat, smooth surface and felt the left rear lifting and falling as the car slowly rolled forward - definitely not a damper problem. I pulled the rear wheel thinking it may be out of round but rotating the hub by hand raised the lowered the body. Could this be a rotoflex problem?
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PostPost by: StressCraxx » Sun Jul 17, 2022 8:03 pm

Yes, it possible it might be a rotoflex problem, or even a tire belt/sidewall separation. Time to jack it up and have a close look at everything. If the tires are old, belt or sidewall separations are possible.
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PostPost by: Temmck » Sun Jul 17, 2022 11:19 pm

Tires are brand new. And I saw the problem without the wheel on the car. With the car on jack stands, I removed the wheel and rotated the hub by hand. The body would rise and fall with the rotation of the drive shaft, one rotation of the driveshaft, one rise and fall of the body. It's a large rise and fall - the "I can see it from across the street" kind of movement.
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PostPost by: mbell » Mon Jul 18, 2022 12:19 am

Any play in the rear wheel bearings or shaft? Could the rear hub not be on correctly/square?
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PostPost by: Temmck » Mon Jul 18, 2022 2:02 am

I do not feel any movement up and down or side to side. Certainly nothing that would cause this large a body motion. The only thing I can think of is that the drive shaft is not in the center of the rotoflex.
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PostPost by: rgh0 » Mon Jul 18, 2022 2:08 am

Yes a broken rotoflex or failed rotoflex bolt can cause this sort of issue - been there done that many many years ago
I cant think of anything else that would do it.
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PostPost by: Elanman99 » Mon Jul 18, 2022 9:23 am

Temmck wrote:Tires are brand new. And I saw the problem without the wheel on the car. With the car on jack stands, I removed the wheel and rotated the hub by hand. The body would rise and fall with the rotation of the drive shaft, one rotation of the driveshaft, one rise and fall of the body. It's a large rise and fall - the "I can see it from across the street" kind of movement.



If the car is on jack stands how can the body rise and fall?

Are the stands supporting the body or have you somehow placed them under the struts/hub carrier, even so there must be something seriously off centres to generate enough force to move the body.

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PostPost by: berni29 » Mon Jul 18, 2022 12:47 pm

Hi

As others have said there is no way that the body could be moving relative to the chassis. From what you have said it must be something driveshaft or possibly suspension top mount related.

Will be interesting finding out what is going on. Best of luck!
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PostPost by: Temmck » Tue Jul 19, 2022 1:56 am

It surprised me as well. The jack stand was under the suspension "A" frame not under the body. I'll try to upload a video (can you do that on this form?) tomorrow.
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PostPost by: Andy8421 » Tue Jul 19, 2022 7:38 am

Temmck wrote:It surprised me as well. The jack stand was under the suspension "A" frame not under the body. I'll try to upload a video (can you do that on this form?) tomorrow.

Assuming it is a rotoflex (and it certainly sounds like it) you ought to be able to spot the problem just by looking at them. They don't fail in graceful way.

If you support the car in a way that lets the wheels droop, that will put the rotoflex under stress and should expose any split rubber or broken bolts as you turn the wheel.

Just as a FWIW, on my Elan with ancient rotoflex it is surprising how much effort is required to turn the wheels at full droop in comparison to my Elan with UJs.
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PostPost by: elangtv2000 » Tue Jul 19, 2022 1:57 pm

This would be a good time to post some good photos.
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PostPost by: Elanman99 » Tue Jul 19, 2022 3:14 pm

Temmck wrote:It surprised me as well. The jack stand was under the suspension "A" frame not under the body. I'll try to upload a video (can you do that on this form?) tomorrow.


So somehow you have got the car raised off the ground with the rear stands being under the A frames but still allowing the wheels to rotate. Jacking under the A frames is not recommended practice other than on the outer longitudinal tube between the outer bushes (which is quite close to the tyre so not that easy to access)

Is the rear suspension compressed such that the drive shafts are more or less straight?

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PostPost by: Temmck » Tue Jul 19, 2022 6:04 pm

I'll shoot some pictures when i get home tonight but...

When raising the corner I place 2x4 under the "A" frame as close to the brake disc as possible. I figure this has to be better than letting the suspension fully drop.

I inspected the rotoflex and they look in good condition, no cracks or other wear signs. But I do have new ones that I plan to install.
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PostPost by: Temmck » Wed Jul 20, 2022 5:18 am

Seems I can't upload a video so i will attach a few picture of the situation. One show the body in the lower position and another at the upper position. It rises a little over a half an inch. it looks more pronounced in person and in the video. i also added a couple of pictures of the inboard rotoflex. i Couldn't get a good picture of the outboard but the condition is the same is the inboard.
Attachments
IMG_2469.jpg and
IMG_2468.jpg and
IMG_2465.jpg and
IMG_2464.jpg and
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PostPost by: 512BB » Wed Jul 20, 2022 6:35 am

Well there is certainly something amiss with the donut bolts and nuts. One nut is barely done up and has a washer underneath it. There should not be any washers in the donut setup at all and the next bolt appears to have a round head or some sort of sleeve, so that all wants looking at.

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