Lotus Elan

Hot rear discs

PostPost by: RichardS » Sat May 18, 2019 7:50 am

Noticed that both rear discs are too hot to touch after only a mile or so, and a few light dabs on the brakes. Front discs cool. (Elan Sprint)

Just had MOT and brakes fine, they checked that the rear pistons were not sticking, and handbrake pads are clear of the discs. Wheels turning freely, no binding.

Is this normal after a short drive?

Thanks

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PostPost by: mark030358 » Sat May 18, 2019 1:00 pm

It’s probably the hand brake pads. Had it before where I adjusted and left clearance, but needed backing off a tad.
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PostPost by: RichardS » Sat May 18, 2019 6:06 pm

Thanks Mark, will try that
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PostPost by: Grizzly » Sat May 18, 2019 9:45 pm

I'd throw a set of handbrake return springs at it too, if they are on the old side or have been bent back a couple of times they loose their spring and it causes the pads to drag when the handbrake is fully off.

Also check the disk is in the center of the handbrake pads....... i fitted a pair of rear disks supplied by a specialist (can't remember which on it was a while ago) and they weren't machined accurately, what happened was because the disk wasn't in the center of the handbrake pads one pad would always be touching as they don't have much out of center tolerance.
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PostPost by: Elanman99 » Sun May 19, 2019 9:31 am

Just to Clarify what Chris (Grizzly) said above.

The springs he is referring to are the 'Centralising Strips' and do not look like any conventional spring. In fact they are made of ordinary (not spring) steel and are designed to deform and bend in use. They do have some springiness which is enough to hold the pad off the disk surface but as the pad wears the strip gets bent so eventually need reforming when the pads are changed.

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PostPost by: billwill » Sun May 19, 2019 11:14 am

I echo that, the strips need to be re-bent outwards (10 to 20 degrees) evey time you fit new handbrake pads. Item 17 on this diagram

Image


If there is not one already there you might want to also fit a lightweight coil compression spring on the adjuster rod (item 9) to push the pads apart

.
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PostPost by: RichardS » Sun May 19, 2019 4:52 pm

Thanks everyone- advice is spot on!

I had fitted new handbrake pads when the car was off the road having the gearbox seen to.

Looking back at previous posts on adjusting the handbrake, and thanks to the replies, I had not realised the centralising strips need bending with new pads. Having just been under the car both inboard pads are up against the discs, even with the callipers slackened off. They looked ok when the car was up on the stands, but I now realise the geometry changes when on the road.

I do have the springs over the caliper rods, but they are not enough to counter the strips!

So not quite back on the road yet, but know what I have to do

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PostPost by: Elanman99 » Sun May 19, 2019 8:10 pm

I bought my Elan as a kit in 1968 and had to fit new handbrake pads the first time it was MOT'd about 3 years later. I then found I needed new pads for nearly every subsequent MOT because I had not read the manual! The car covered a high mileage with lots use on motorways and salted roads.

I'm not even sure if the workshop manual of the day mentioned the need to reform the strips but I was not aware of their true purpose so just kept putting them back in thinking they were some sort of pad retainers. In the mid 80s I fitted a new chassis and overhauled the calipers and then it dawned on me what they there for.

At one time I had fitted springs over the adjuster bolts thinking they would help retract the pads, now though I realise that they just cannot do that. The spring might push the two levers that press the pads against the disk away from each other, but as the pads are not attached to the levers the pads stay where they are.

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PostPost by: Grizzly » Sun May 19, 2019 9:04 pm

Yep sorry if i wasn't clear....... If the centralizing strips look grotty/old just replace them it's really not worth the aggravation, they make a huge difference to a properly operating handbrake.

The last set i got was from Classic Automotive http://www.classicbrake.co.uk/

I find it ironic that after struggling for years with the handbrake on our +2 for the mot i finally master it at more or less the time they get rid of the MOT :lol: at least i got the satisfaction of passing the MOT once first time.
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PostPost by: RichardS » Mon May 20, 2019 9:05 am

It’s the first time in 37 years of ownership I have realised they are not just retaining strips! The strips are in good condition so will hopefully respond to a little gentle bending!

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PostPost by: RichardS » Tue May 21, 2019 5:10 pm

Job done.

As you can see from the photos initially the inboard pad was tight up to the disc, and after some bending of the strips now have adequate clearance. Just been for quick run and discs warm to the touch, but not hot. May back off the adjuster nut a little.

Thanks for all the advice - have checked both my workshop manual and Brian Buckland’s book and no mention of this issue.

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PostPost by: MarkDa » Wed May 22, 2019 7:14 am

If pushed on disc centralisation you can shim caliper on hub - only one way of course but it worked for me.
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PostPost by: 69S4 » Wed May 22, 2019 8:36 am

There's a bit of a mismatch between the allowable brake disc runout - .004" and the handbrake pad clearance - .003". If you have a disc runout near or above the maximum the handbrake pads will rub (and heat) and eventually wear, as the disc revolves. That's why the spring strips are so important, to pull the pads back as far as possible.

Getting the rear disc runout down to under 4 thou can be a real problem. Moving the disc itself round on the mounting bolts can help (or make it worse!) but it takes forever to mount it all, measure the runout, take it all apart again, move everything round one hole, reassemble, measure etc. It doesn't take much to get a slight distortion in one of the drive shaft ears or a piece of grit in there and the disc is all over the place.
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PostPost by: Andy8421 » Wed May 22, 2019 10:14 am

RichardS wrote:Job done.

As you can see from the photos initially the inboard pad was tight up to the disc, and after some bending of the strips now have adequate clearance. Just been for quick run and discs warm to the touch, but not hot. May back off the adjuster nut a little.

Thanks for all the advice - have checked both my workshop manual and Brian Buckland’s book and no mention of this issue.

Richard

AA00D70A-B3A5-4340-9249-876495CC3337.jpeg


Are the pads the wrong way around? The cutoff corner should line up with edge of the disc?
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PostPost by: MarkDa » Wed May 22, 2019 10:23 am

Well spotted!
Arguably that reduces the friction area to do the heating though - not that's the issue.
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