Lotus Elan

brakes

PostPost by: worzel » Fri Nov 12, 2010 7:08 pm

Hi

An odd one-maybe!

I've a sprint I've fitted with plus 2 front anchors and have deleted the servo. Car easily passed the MoT rolling road test but- (always seems to be a but) if I don't use the car for a couple of weeks almost invariably on its first outing the car pulls fairly strongly to oner side or the other.

When this first occurred I just swapped the pads from side to side and the problem disappeared. Now I don't do that I just use them really hard and it cures the problem (temporarily at least).

I'm puzzled how this can be happening- pads are all equally worn and all 4 are of the same type, caliper pistons are definitely free to move, hoses aren't ballooning, wheel bearings are fine both sides, the discs are a matched pair, there is definitely no air in the system, the tyres are at the same pressure (and the same make), the tracking is fine.

I reasoned out that maybe one side of the car was more exposed to the weather so the disc on that side was filming over with more rust than the other side whilst the car wasn't in use but today, using the car after 5 weeks off the road, it pulled towards the more "sheltered" side.

I've never experienced this before with this car (or any other for that matter)- is it remotely possible that by deleting the servo the lowered brake force is just showing up what was previously there but the servo assistance somehow "masked" the problem by creating a lot more clamping effort to begin with or is that a nonsense theory?

Any ideas?

Regards

John
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PostPost by: Galwaylotus » Fri Nov 12, 2010 7:28 pm

I wouldn't think the servo would have anything to do with it. I was going to suggest the possibility of an internal hose fault until I read that it happened on a second side the last time. Could one of the caliper piston seals be sticking and not releasing? :?
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PostPost by: AHM » Fri Nov 12, 2010 10:51 pm

I would suggest a sticking seal as the previous poster.

Nonsense theory - Probably as the servo reduces pedal effort not braking effort.

For some lateral thinking ..... you don't mention the rears in your analysis

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PostPost by: elansprint71 » Fri Nov 12, 2010 11:13 pm

I also have a Sprint with +2 bits up front and a servo in the skip. How can you be certain that there is no air in your system? When I changed my chassis a few years ago ALL the braking bits were changed- pipes, calipers, master-cylinder, rear cylinders, Aeroquips, the lot and yet I'm willing to bet that if I bled the system today I would still pump a few bubbles out (this despite two complete fluid changes since the rebuild).

My solution is to drive around the problem; make sure the brakes are working properly before I get to the end of my road. :twisted:
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PostPost by: worzel » Sun Nov 14, 2010 11:35 am

Hi-again

Thanks for the input.

Just to clarify- when I said I'd deleted the servo I meant that I don't have one in the system rather than I'd bypassed it.

I'm pretty sure I can rule out a sticking piston- the front calipers are new with new pistons/seals and each piston moves freely-I've checked manually and also confirmed it on the MoT rollers. Likewise the back calipers aren't new but have just been overhauled with new seals- the pistons are stainless and have been on the car for around 25 years. the rolling road again confirmed they weren't sticking.

I've had cars with jammed pistons in the past- in my experience they inevitably cause the disc to warp leading to noticeable judder. Likewise I've had air in brake systems but have never found the symptoms to vary- the pedal is softer than normal and any pulling caused by imbalance doesn't move from one side to the other (as this is doing).

Is it remotely possible that the pads are at fault- I don't see how since they are Ferodo and not copies?

Regards

John
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PostPost by: curly type 26 » Sun Nov 14, 2010 12:21 pm

just a thought whats the disc runout did you use dial gauge? :idea: curly
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PostPost by: worzel » Mon Nov 15, 2010 9:09 am

Hi

Thanks for the further input.

Re the disc runout- I'm assuming that since the MoT rollers didn't reveal any pulsing etc and the brake effect was within 1% of each other on the fronts (and rears) that runout can be eliminated.

As for air in the system- well I cannot be 100% certain there isn't any but as I said I figure that if air was present on the left side for example that the car would persistently pull to the right. The fact that it pulls to both sides on different occasions suggests that the problem lies elsewhere.

When it first occurred (ages ago) I tried swapping one pad from each side to the other- this immediately fixed the problem thereby suggesting the pads themselves were somehow the problem- but if so I cannot figure out why since as I said they are genuine Ferodo.

Regards

John
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PostPost by: curly type 26 » Mon Nov 15, 2010 11:01 am

Hi John, I would still check disc runout with a dial gauge could be enough to just knock pads back, as it sounds like you cure it after moving pad position check pads not jamming in caliper or change pads i have had some in the past that gave a horrible spongy pedal, after many bleeding sessions changed to nother make & cured. Is it the heat range? :wink: good luck Curly
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PostPost by: worzel » Mon Nov 15, 2010 11:35 am

Hi

Message to Pete in Wilmslow

Picking your brains- which pads are you using and how do you find the system without the servo. Are you still using the std 0.7inch master cylinder or have you dropped the size to 0.625 inch. In view of the other info posted on this I'm looking more and more at the pads possibly being the problem- in the past I've tried EBC green but wasn't impressed by them.

I thought the pedal pressure was too high with greenstuff pads so switched to the smaller master cylinder but one penalty is the longer travel. My memory might be playing tricks on me but the S4 I had back in the 1970's didn't have a servo as std but I don't recall ever consciously thinking about the stopping power- it seemed to stop very well even on the smaller std calipers. Perhaps in those days the pad material was particularly soft.

I'd much appreciate your views on your alterted system.

Regards

John
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PostPost by: collins_dan » Mon Nov 15, 2010 1:45 pm

I have an S4 with no servo. I was planning to change to Ferodo DS2500's. Do a search of the archives, there has been a good amount of discussion about them. I'm not unhappy with my brakes, but would like a bit more bite. Pedal is very firm, but I like that. Good Luck, Dan
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PostPost by: Galwaylotus » Mon Nov 15, 2010 7:25 pm

worzel wrote:Hi

- in the past I've tried EBC green but wasn't impressed by them.

I thought the pedal pressure was too high with greenstuff pads so switched to the smaller master cylinder but one penalty is the longer travel.

I deleted the servo on my S3, went to a tandem m/c (still 0.7 inch), added steel braided brake lines (Aeroquip) and Greenstuff pads. I certaiinly don't feel excessive force is needed at the pedal but I do notice at very slow speeds it takes a bit more force. In normal open road driving I don't even notice the difference when braking so I'm very happy with the set-up. :D
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PostPost by: Tonyw » Tue Nov 16, 2010 11:55 am

Worzel,

I think your brake pulling is unlikely to be air in the system. If I understand you correctly if the car is laid up for a while and then driven the brake pull either right or left, not always the same I gather. So I think you might have a problem with the caliper seals, I suspect that the seals do not pull back consistently and when you are parked up for a couple of weeks you may find that one set of pads is or is not in contact with the discs, if only one set is in actual contact then you will have a nice clean disc under the pad where the others will or may have some oxidization on the disc alternatively the reverse is true as well. This should be fairly easy to check by taking the wheels of before you take it for a drive.

you also say that when you changed the front pads from left to right the problem went away. Perhaps you may want to replace the front pads, chasing brake pulling can be very frustrating i know from experiance but there will always be a pattern of some sort so it really requires you to try to eliminate each issue one at a time.

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PostPost by: worzel » Wed Nov 17, 2010 10:12 am

Hi

Re Tonyw input.

Sounds feasible to me about the seals. The problem does alternate between sides which is why I concluded (like you) that air in the system wasn't the issue. Looks like I'll have to change them. Godd opportunity to switch to stainless pistons at the same time.

Regards

John
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PostPost by: worzel » Mon Dec 13, 2010 11:51 am

Hi again

A bit of a follow up.

Since the last post I've done a few checks-

Re-bled the brakes just to be certain- there definitely was not any air in the system.

Checked the tracking/suspension bushes/dampers- all of the usual suspects

Checked tyre pressures and swapped around the wheels

Nothing revealed by the foregoing.

I'm convinced the pads are the problem (incidentally the discs are a matched pair so these can be ruled out). The pads are Ferodo non- servo spec as listed for an early Triumph GT6 bought from a reputable Triumph specialist.

As I've said, if I don't use the car for a few days on first use it pulls to the right quite noticeably, however being a bit brutal with the anchors the problem begins to reduce and after a few hard stops the car pulls up dead straight.

A test on the MoT rollers reveals no sticking pistons and checking this myself by hand immediately after a period of disuse (and before using the car) the pistons on each side are easy to retract.

As I said I think the cause is the pads even though I can't see any reason why- perhaps there is a mismatch on the linings or somehow thre are "layers" of odd friction material that exert different grip (okay- clutching at straws).

Next step is try different pads.

regards

John
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PostPost by: ivor badger » Mon Dec 13, 2010 1:12 pm

Try glaze busting the discs with some wet and dry, 150/180 grit before use.
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