Brake pedal travel - again!

[Gresley]

Is it normal to have long brake pedal travel on the Stag? I am still not happy with the brakes on mine, I have what seems to be an awful lot of brake pedal travel, probably about 2" with the engine running. I have so far done the following: had the drums off and adjusted the shoes manually, replaced the rear wheel cylinders, fitted stainless braided hoses, fitted a recon servo, renewed the brake discs and changed the fluid. I also fitted a new master cylinder recently which resulted in the firmest brake pedal since I have owned the car. The pedal box bushes seem OK but there is a little wear in the pedal where the clevis pin goes through. The pedal seems to have an intial spongey bit of travel, as is something in the servo is compressing, before becoming very solid. The brakes actually work OK. I have followed a few suggestions previously but can find nothing wrong, so I am wondering if anyone has had this problem or if anyone has any ideas of what to do next? It is spoiling the drive of an amazing car. Could the PDWA cause this?

I'm a bit desperate now as I really cannot think what to do next...The 'spongey' bit of travel is also there with the vacuum exhausted, and I have bled the brakes several times. Also, to add to this the is a sort of jerky movement from about 10 mph down, as if a disc is warped, but both discs seem fine.

Any ideas much appreciated!

Brian

[Guest]

imported post

Hiya Brian, long travel can be caused by the rear shoes wearing down, have a close look at the condition of the self adjusters, if the teeth are in any way worn, they will de-adjust.
I hate that system with a will - always have, if I could modify the Triumph 2000 Mk1 backplate to fit the Stag, with its manual adjustment, I would !
I know Kryten disagrees, perhaps you should take his advice as I'm unbalanced about the subject ! Martin

[dasadrew]

imported post

Gresley wrote:

........Also, to add to this the is a sort of jerky movement from about 10 mph down, as if a disc is warped, but both discs seem fine.

Any ideas much appreciated!

Brian

If the discs are indeed warped in some way or had a bit of flaky rust underneath them when fitting, then they will be nudging the caliper pistons back into their housings as you drive along. Then, when you apply the brakes, the pistons first have to travel a millimetre before the pads are pressed on to the disc.

May really be worth checking the disc run out with a gauge or at least making sure that rust build up on the disc rim isn't encroaching on the area where the pads run.

I would think that, to rule out the rear brakes, you could apply the handbrake lightly which should move the shoes nearer to the drum to simulate correct rear working of the adjuster. (Not checked this exact mechanism on the Stag itself, mind you)

[ethel]

imported post

Gresley wrote:

I also fitted a new master cylinder recently .......Any ideas much appreciated!

Brian

Brian,

I also rebuilt almost the entire system including a new master cylinder - from a reputable supplier - and the travel seems too long before anything happens, though the car does stop quickly enough once that point is reached. As I put more miles on it my confidence in the system is increasing. The one thing that did occur to me was that the new m/c is Lucas branded not Lockheed, do you think there could be some subtle internal difference?

John.

[Giles]

imported post

ethel wrote:

the new m/c is Lucas branded not Lockheed, do you think there could be some subtle internal difference?

I fitted one of those recently, my travel is fine so I doubt that is the problem.

As Dasadrew suggests might be worth checking for a warped disc - this might be giving you a bit of knock off which will give you a longerpedal. Front wheel bearings ok? if there is some play might do the same ? Just a long shot

[Gresley]

imported post

Hi guys,

thanks for the help with this pain of a problem. The adjusters actually look Ok and click positively and the front wheelbearings are fine, but I am a little suspicious of the n/s disc. The brakes actually work fine, I think some of this problem is me being too fussy! My new master cylinder is Lucas, but I had long pedal travel before I changed that so I doubt they are internally different. I'll either buy or borrow a dial gauge and check that disc...

Thanks again

Brian

[GDPR]

imported post

Warped discs would give many other braking symptoms but not long travel. Loose front hub bearings would almost have to be falling apart and clonking before the pedal travel would be badly affected and would pump up on the second push. If its the rear brake adjusters having the handbrake on will reduce the pedal travel.
I would be looking at something like the brake pedal/servo pushrod/clevis pin being worn where the servo joins the pedal - a small amount of wear here translates to a lot of pedal movement!

Russ

[sax player]

imported post

Hi Brian,

this may sound daft but is the plunger , from the pedal into the master cylinder the correct length. Was thinking a short one would have to take up the travel before engaging the master cylinder piston.

shaun.

[dasadrew]

imported post

Russ,

it's not the warped disc itself which gives long travel, it's the effect it can have on knocking off the pads from the disc. This produces extremely long travel for a very small movement. It has to do with the relationship between the surface area of the caliper pistons and the surface area of hte master cylinder piston. That provides an enormous multiplier. If you just push back the pistons a small amount to get the pads out, for example, when you first brake after then you normally need to pump the pedal 2 or three times to get the pads back into braking contact with the discs.

The pedal geometry is also, of course, a possibility but it is not correct to say that pad knock-off (as caused by warped discs, disc fitted askew or rust build up in the wiped area) will not cause long pedal travel.

You are correct that warped discs would cause other symptoms too, but this is what the original poster Gresley (Brian) stated - namely that he has a judder like a warped disc.

Drew

[GDPR]

imported post

Drew

Having spent 21 years of my working life repairing cars professionally, 16 years in a Triumph main dealer, I think I'm aware what a warped disc would do. What I'm saying is if a warped disc was on this car, bad enough to push the pads back to give 2 inches pedal travel, then Brian would have complained about an appalling brake judder, and the car being virtually undriveable.

[dasadrew]

imported post

kryten wrote:

Drew

Having spent 21 years of my working life repairing cars professionally, 16 years in a Triumph main dealer, I think I'm aware what a warped disc would do. What I'm saying is if a warped disc was on this car, bad enough to push the pads back to give 2 inches pedal travel, then Brian would have complained about an appalling brake judder, and the car being virtually undriveable.

That's why I rule this out as pure conjecture.

You're the Big Daddy, Russ!

I just got the idea out of a "Cars for Dummies" book I bought in WH Smiths.

Drew

[Giles]

imported post

Brian - Russ has a very good point - knock off whenever I have had it in the past always pumps up with a second application ( always had to remember to give the pedal 2 pumps!) so forget my suggestions!!!!Sure you will find it somewhere

[Gresley]

imported post

Hi again guys,

Thanks for the replies. I've had a very quick check of the clevis pin and indeed there is wear / movement here so I'll get a new one and change it next week. thanks Russ! The pedal travel is no different with the handbrake on so the adjusters must be OK. I really don't know if I have the wrong plunger but it is a recon servo and it looked the same as the old one, thanks for the idea Shaun, I'll mention it next time I am at Paddocks. There is still a sort of jerky movement from 5mph down but there is certainly no violent juddering making the car undriveable. Thanks for the encouragement Giles!

Brian

[Gresley]

imported post

After much searching I think the problem is solved

As a last resort I took the brake pads out to have a look. I was sure they would be Ok because they have only been in for about 9 months. What I found is in the picture below:shock:

I have put a new set in and I now have a very firm pedal with no sponginess and I have confidence in my brakes again. They work, yippee!

[Arbman Al]

imported post

Gresley wrote:

After much searching I think the problem is solved

As a last resort I took the brake pads out to have a look. I was sure they would be Ok because they have only been in for about 9 months. What I found is in the picture below:shock:

I have put a new set in and I now have a very firm pedal with no sponginess and I have confidence in my brakes again. They work, yippee!

Hi Brian,

What make of pads were they? :shock:

I think I want to avoid them.

Cheers...Al