Lotus Elan

Braking Bad

PostPost by: JJDraper » Mon Mar 16, 2015 7:40 pm

I had a problem last year with serious vibration under braking at a specific speed, around 45mph in my +2. Warped disks I thought, so had a look under the car, rear disks looked a little poor, fronts OK, but Oh Dear, CV boot perished on the drive shaft conversion. I considered doing the work & even got the bits, but poor weather and a lack of time forced the decision to take it to Spyder ? asked for new rear disks, pads, Handbrake pads & CV boots.

After a quick test, Andy agreed with diagnosis? Two days later, called up & Oh dear ? all work done, but vibration was the same. OK, I said see if you can track down the problem. Next phase is that Andy tried isolating each axle?s brakes to see which axle it happened on ? definitely rear. He inspected and replaced all bushes ? some wear but nothing he considered excessive. Still got the same problem.

Considered drive shunt ? replaced CV & prop joints. He tried skimming the drive shafts to see if there was anything out of line ? all fine. Are you keeping up? I went to visit & took the car for a test, with Andy ? still vibrating between 40-50. Tried swopping wheels around ? no. I tried left foot on the brake & right on the accelerator to maintain 45 with hard braking & the vibration remained. Creepy.

So what next? Diff was mentioned & as I had a spare (without back cover) we agreed that this would be fitted. Partial success, reduced vibration, but the (reconditioned ? huh) diff made a noise like a filling toilet at all speeds. Now we had to accept defeat as both Andy & Sean were more than a little concerned (as was I) at the mounting cost. Andy had never seen anything like it. Nearly six months & 3k miles down the road, the vibration is much less, but just perceptible. Noise of the diff has reduced, but I still am fed up with diff ?reconditioners? ? so far three done, one total failure ? seized up the rear end at speed (scary), one whiny and one sounding like a toilet filling.

This has been an expensive learning experience, and I wondered if anyone else has suffered from unexplained vibration under braking. Was it just an accumulation of lots of little bits of drive line flex coming together at a particular frequency? I don?t know, but I (and Andy) would like to hear if anyone else has suffered in a similar way.

At least all those bushes & joints are now replaced...

Jeremy
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PostPost by: billwill » Mon Mar 16, 2015 8:48 pm

Unbalanced prop-shaft?
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PostPost by: JJDraper » Mon Mar 16, 2015 9:34 pm

billwill wrote:Unbalanced prop-shaft?


Unlikely, as this only occurred under braking and should get worse at speed (on the way up as well as the way down).

Oh and by the way did I mention the new wheel & diff output bearings?? The list of work ran to two pages! At the time I suggested a box of matches may help, which was greeted without much humour.. With the passing of time the pain in the wallet is becoming more of a memory.. and at least the car now feels reasonable to drive.

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PostPost by: rgh0 » Mon Mar 16, 2015 10:05 pm

The issue appears to not be in the drive train as you say the vibration is unaltered whether you load the drive train or just brake in neutral.

You replaced the rear disks and pads and I presume checked you have no seized pistons so you don't believe it is related to the brakes themselves.

You have replaced all the bearings and swapped wheels and I presume checked the whole rotating assembly for run-out with no result

That really only leaves the suspension but you have checked / replaced all the bushes. Have you checked the rear shocks, springs and shock top mount? its about the only thing you did not list in the post. Do you have the standard Lotus strut rear suspension or the Spyder twin wishbone rear end?

A strange issue, and nothing like that I have seen on my Plus 2 but there must be a solution somewhere.

Have you tried pulling the trim out of the back and having someone crawl around listening for where the vibration is coming from when you brake? I had a friend with a new Audi that had a vibration from the rear. He took it many times back to the dealer and they could not find the source. After about 6 months and many trips back to the dealer he finally found it was a bracket on his roof rack for carrying his bikes that was vibrating !!

cheers
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PostPost by: AHM » Mon Mar 16, 2015 11:03 pm

What frequency is the vibration?

Which gear? does it do it out of gear?

Hard braking/ Light braking?

Have you checked for runout on the hub/shaft/disc
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PostPost by: alan.barker » Tue Mar 17, 2015 7:22 pm

imho put a DTI to check rear disks run out.
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PostPost by: john.p.clegg » Tue Mar 17, 2015 8:02 pm

If any of the discs are running out you will feel the pulsing in the brake pedal....

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PostPost by: elansprint71 » Tue Mar 17, 2015 8:45 pm

When you say "definitely rear"... might be worth a quick look at the front again.
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PostPost by: patrics » Tue Mar 17, 2015 10:24 pm

Hi,
As has already been said you really need to take some measurement not go on what somebody thinks is wrong. Start again and measure front and rear disc runout with a dti - the amount of money you have wasted at spyder you obviously could have brought the equipment 10 times over.
Check all of the bushes - it's not easy to do this, for instance on mine I had a vibration and every thing looked ok but when I removed lower diff mounting from chassis I could moved it back and fore - that was with new bushes obviously wrong thickness, that was causing vibration generally not just under braking.

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Steve
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PostPost by: billwill » Wed Mar 18, 2015 1:13 pm

JJDraper wrote:
billwill wrote:Unbalanced prop-shaft?


Unlikely, as this only occurred under braking and should get worse at speed (on the way up as well as the way down).


Jeremy



Don't totally discount the propshaft, remember that during braking the U/Js are being stressed in the opposite direction to normal/ Check the U/Js.
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PostPost by: alan.barker » Wed Mar 18, 2015 4:16 pm

Bill said
"Don't totally discount the propshaft, remember that during braking the U/Js are being stressed in the opposite direction to normal/ Check the U/Js.".

hi Bill, i think only if you don't depress the clutch
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