Lotus Elan

Brake Pedal Travel

PostPost by: Stuart+2 » Sun Sep 09, 2012 12:29 am

My 1968 +2 has the Girling MkIIA servo fitted.

I reconditioned it 2 years ago and it works fine.

The only annoying thing is that there's around one quarter to half an inch of pedal movement before the pedal is firm. There is no sponginess at all.

It's not 'play' in the linkage - it feels more as if the piston in the servo needs to move a short way before things happen.

The pedal is as solid as a rock and the brakes work fine - as I said, it's annoying as I would much prefer the pedal to bite as soon as the normal play is taken up, ie pretty well immediately, rather than have to move down that small distance.

Maybe this is just a feature of the MkIIA - I'd like to hear how other pedals feel and if there is anything that can be done.

Cheers
Stuart - Sydney
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PostPost by: 45bvtc » Sun Sep 09, 2012 9:13 am

That's typical of a servo assisted (Girling or Lockheed) brake system; the Elan and +2 (both Girling) were always thus.

If you want a zero travel brake pedal then you need to throw away the servo and fit a smaller (5/8" diameter) master cylinder.
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PostPost by: J.E.S » Sun Sep 09, 2012 8:02 pm

Hi Stuart - You might try checking the run out on the discs, particularly the rear. If you have a lot of movement here the discs may be pushing the pistons back in to the callipers, which you then have to push back out before you get any pedal feel (are you are experiencing more peddle travel when driving than when pushing the pedal when stationary?). Appropriate placing of shims between disc and outer drive shaft mounting can help to true things up. If your disc run out is not the problem and you decide to try running without a servo remember that the pedal box mounting area was not designed to take the extra stress caused by having to push the pedal harder, may be wise to reenforce this area if you follow this route (imo driving without a servo makes the car an accident waiting to happen). Good luck John.
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PostPost by: Stuart+2 » Sun Sep 09, 2012 10:27 pm

Thanks John and '45BVTC'.

Yes I thought so as everything is otherwise fine.

To your question John - yes it's the same whether I'm driving or stationary.

I'll stay with my servo (mind you they fetch a pretty penny on Ebay!).

Cheers,
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PostPost by: 45bvtc » Mon Sep 10, 2012 10:59 am

Hi Stuart, your conclusion is right for the +2 "stay with it".

The long pedal travel was always the characteristic encountered with brake servos of the period: Elan, Vitesse, GT6, etc.

However, if you'd like to test pedal travel with and/or without servo, just disconnect the vacuum to the servo and drive (slowly): but be prepared to brake hard, and long?

As for brake disc run-out, you could easily check that by carefully spinning the hub/disc against the brake pads, but you'd feel that on the pedal anyway, +2 or otherwise.
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PostPost by: CBUEB1771 » Mon Sep 10, 2012 1:11 pm

J.E.S wrote:Hi Stuart - You might try checking the run out on the discs, particularly the rear.


Also check the float in the front wheel bearings to make sure this is within specification.
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PostPost by: Foxie » Mon Sep 10, 2012 5:27 pm

I had that problem since I got the car many years ago.

I bled ad nauseam
Minimised hub play
Checked disc run-out
Fitted anti knockback springs
Fitted extra bleed nipple at servo outlet

All these improved matters slightly, but I recently fitted an adjustable pushrod, and cut a small access opening in the top of the brake box.

Result is a now perfect pedal :mrgreen:
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PostPost by: Stuart+2 » Wed Sep 12, 2012 1:41 am

My sincere thanks for your replies.

I checked my wheel bearings and there's some play there so I'll take it out on the weekend.

The adjustable pushrod sounds promising as well as there's too much play there too.

Thanks again.

Cheers,
Stuart - Sydney
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PostPost by: Limey » Wed Sep 12, 2012 7:32 am

I have had a similar problem.
Long brake travel on first application of the brake, but ,even worse, if I come off the brake and then re-apply, then the pedal is really hard, with hardly any travel.

When this happens the brakes are locked on.
The trick for releasing them is just release the brake pedal, but then just give it a light, quick "prod".

This happens occasionally, with no particular reason. E.g. Being hard or soft on the brakes doesn't seem to make any difference the chance of it happening.
The brakes always work, and they are efficient.

I must try to see what difference having the servo operative or other wise makes.

Anyone else had this problem?

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PostPost by: J.E.S » Wed Sep 12, 2012 9:11 am

Hi Steve - I experience the same braking issue when I first had the +2. Alarming length of pedal travel or non at all leading to brakes locking up at the slightest touch - both made driving the car an experience!

I tried a number of things:

Rebuilt the Girling MkII servo - twice - to no effect - servo worked when on test on the bench but inconsistent in the car.
Replaced non return valve in servo vacuum pipe - no effect
Replaced the Girling servo with a Lockheed unit - success

Also fixed the excessive run out on the rear discs - required replacement of one outer drive shaft and bearings and shimming of both near and off side discs.

The only explanation I have (and this may be wrong but I can see no other explanation) is that the excessive disc runout was causing the servo to stick as fluid was pushed back through it (as the pistons were pushed back into the callipers) - the lockheed unit seems to be less sensitive to this and was an instant fix. Correcting the disc run out also improved pedal feel - I now have consistent and predictable braking though pedal travel is longer than a non servo car or a direct servo set up.

I'd be interested to hear any alternative diagnosis of the braking symptoms both Steve and I have experienced from the experts on the forum.

Thanks John.
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PostPost by: Stuart+2 » Thu Sep 13, 2012 1:43 am

Steve,

Yes that's exactly the characteristic that I'm experiencing.

The MkIIA internal workings incorporate some degree of mechanical movement of pistons, etc before the hydraulic pressure gets to the brakes. This is not the case for more modern servos.

Pumping of the pedal quickly once will bring it to where we want it to be, but this is because the internal mechanism is caught before it returns to equilibrium.
Naturally, this has nothing to with air in the system.

I'll take the good advice to set the wheel bearing float accurately and do what I can to sort the excessive free play in the pedal. This should make a big difference.

Cheers,
Stuart - Sydney
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PostPost by: Limey » Thu Sep 13, 2012 6:37 am

I don't have any significant brake disc runout on my +2, and have reduced the free play in the master cylinder and pedal assembly to as little as I can.
My theory about the locking up is that when the pedal is released, and the master cylinder piston returns to its resting place, it should also pull back the small piston that covers the resevoir hole. If so then there can be no pressure in the brake lines.
However, in a lock up situation, there's so much pressure in the line between the master cylinder and the servo that it presses the master cylinder piston back against the pedal, resulting in a very hard pedal, and also presses the resevoir piston the opposite direction so the fluid can't escape.
Which puts the finger of blame on the servo.
The servo on my car is fairly new, and I have stripped it to ensure correct operation.

The investigation continues........

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PostPost by: Stuart+2 » Thu Sep 13, 2012 8:18 am

It's a bit of a different issue that you're raising there Limey.

It sounds to me as if you may have reduced the free play in the pedal too much, thereby making it more likely that the reservoir hole is not exposed sufficiently upon release. This is then keeping pressure in the line between the master cylinder and the servo.

Anyway, good luck :)
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