Calliper Piston Material question

[rgh0]

The other thing that can cause excessive initial pedal travel is taper wear on the disks or pads or misalignment between the disks and calipers due to distorted mounts. The lack of alignment means excessive travel until the disk is fully contacting the disk when pressure is applied. Check all components are square and truely aligned in the brake assembly

regards
Rohan

[Robbie693]

Kieth,

I had the same problems when I fitted new front calipers.

With help from Stuart (thanks Stuart ) I was able to detremine that the pistons were rolling back slightly, giving the symptoms you describe.

Press the pedal down hard and release. Wait a few minutes. Feel the pads for slackness against the disk. If they are loose you have rollback.

To cure it, wedge the pedal down with a block of wood or something overnight. Check rollback again and repeat as necessary.

I left my pedal wedged for a couple of days and things improved dramatically, driving the car sorted it completely.

Hope this helps

[tower of strength]

Thanks Dave. Yes I have checked all that. Wheel bearings good, runout within. Yes I was interested to read the comments about stainless pistons causing this but couldn't understand it myself. As it does this whilst stationary I must assume it is air in there, but I cant find it or get it out. It is ok, livable with, but a nice high pedal would be better. I'll just have to live with it.

I had a "longish" soft feeling pedal on my old 130/5, after rebuilding the calipers, new master cylinder, new discs&pads, I bypassed the servo/remote cylinder and "Voila!!" nice firm brake pedal. My servo dodnt have any leaks but i suspect it was the wrong one for the car (wrong ratio?) as I found the brakes very sensitive and easy to lock.
I'm going to try my current resto project without a servo.

Mark

[GrUmPyBoDgEr]

I wanted some ditroted mounts for my car but was told that the Australians had bought them all up.
Have a nice weekend Rohan

John

[patrics]

Hello all, lots of debate here!
Anyway,
Aussie john you did well to spot that I am sure it caused a bloody big headache.

Sorry Dave-M but everything you said just isn?t true.
Chrome is used for performance not cost.
Chrome pistons corrode from the outer face exposed to the air and damage from pushing the piston back when changing pads etc nothing to do with the fluid.
If your pistons move by 0.015 ? 0.020? then you have big problems but to be fair I?m sure they don?t move anything like this amount.
The piston isn?t supported centrally but at one end and they most definitely do wear.
Aluminium pistons have a hard coating and different problems.

Keith Scarfe, Yes it is true! If you need help send us a mail with more info and I will do my best to point you in the right direction.

Dave-M. The amount of piston rollback is down to the amount of seal nip on the piston and the design of the seal groove, also of influence is the piston material the type of ?rubber? and the type of brake fluid.
The disc runout will create some clearance but excessive amounts are cause by the flimsy suspension.

Having said all that if I had stainless pistons and didn?t have any pedal feel problems then I would be happy, but if you do have problems then it?s nice to know the potential issues.

As Aussie john said you can have problems with incorrectly machined ?standard?? pistons.

Regards
Steve

[stuartgb100]

Robbie,
Thanks for the applause, but to be fair, it was Patrics (Steve) who put me right, and is due the credit.

I had just upgraded to +2 front brakes, with new disks (runout within limits). I had refurbed the calipers with teflon-coated black pistons (at least I think it was teflon).

However, I forgot to soak the rubber seals in brake fluid overnight, before fitting, so ended up with horrendous rollback. This gives the impression of a spongy pedal, but all that is happening is that the first pump moves the piston(s) into a more correct position, and the 2nd pump is firm.

As Robbie says, a feeler guage will show if rollback is occurring. Anything much more than 1 thou is not acceptable !

With use, the new seals should wear in. Trouble was that they wear in differently. So if you poodle along and don't use the brakes for a while, then hit the brakes, you can get a "snatching" sensation as the brakes bite unevenly and the car pulls to one side !!

One caliper proved a real problem. I solved the rollback by fitting a 2nd anti-squeal shim to take up the clearance.

Following a very enjoyable newbie track day last week, the brakes are now well bedded-in, so that shim will be removed.

Now I just need to find out where the disappearing brake fluid has ended up (see other post, same group).

Regards,
Stuart.

[Dave-M]

Patrics, Have to disagree with you.
Stainless pistons do not corrode!!!! inside or outside
Chrome pistons do corrode from the outside of the seal and from the inside as well if not used regularly.

Have to agree that I missed a zero out in the quoted numbers (0.0015 to 0.0020).

How can the pistons wear if they only move the above amount on each application. OK they may show some slight rub marks but that will be it.

How can flimsy suspension cause knock back?? Everything is connected to the upright and even if the suspension is made from rubber it will not alter the relationship between disc and caliper.

Are you telling me that for a given seal and piston diameter that the chrome/stainless piston would perform in a noticably different way?

This is discussion not argument
Regards
Dave

[rgh0]

Hi John

To much good Australian red wine affects my typing accuracy I think. That and rushing because I am trying to pack and sort out a lot of other stuff before flying out to Germany on Monday.

cheers
Rohan

[patrics]

Hi Stuart
You never said you had non standard pistons. You should not be adding shims to composite for piston movement there is some thing very wrong here.

Hi Dave

The piston wears because it doesn?t sit centrally in the seal when braking. There is a tangential force operating here so it tends to pivot inside the housing.

The stub axle can bend relative to the up right.

And yes

Cheers
Steve

[AussieJohn]

Hi Stuart, is soaking seals in brake fluid overnight the norm? I,ve never done it but does it really help with rollback problems? cheers, John.

[bcmc33]

As young impressionable apprentices in the late 50?s, we were told to soak seals overnight by my friend?s father while working on my friend?s Morris 8. (Anyone remember them?)

?Good Practice? we were told.

Mind you, I would have thought things had moved on since then.


Brian Clarke
(1972 Sprint)

[garyeanderson]

I guess there is one thing that we all agree on it that there is no consensus among us on caliper piston material, seals, rotor, type of calipers, boosters, or any thing that is used in the Elan and Plus 2 braking system. That said I have been using stainless caliper pistons since around 1993, my pedal has always been firm and hard and up high. I?ve had no issues using them either. I have never had a booster in a Elan, I've never driven a Plus 2 so I can't comment on them other that the pedal box mounting is not very substantial. I always use a 5/8 inch or .7 inch master and the fronts have been LF14's with stainless pistons and rears stock with stainless pistons. I have spent hours removing those horrible excuse for chrome plated pistons from all of the Elans I have dragged home and never want to use them ever unless that is all I can find. So I guess I agree with Dave-M

Gary

[bengalcharlie]

Just to stir things up my plus two is fitted with stainless steel pistons and silicon brake fluid which means that I have no braking problems for the next 100 years!
Car brakes perfectly and rolls freely and I am able to push the car forward with only 2 fingers.
Over the last 25 years have used silicone brake fluid in all kind of cars.
disc and drum brake applications, 4WD etc.with great success

Love the stuff and love stainless steel!
cheers
Robin

[kenny]

With the "stalled project" car I bought new lines and re-furbed calipers etc. had been fitted.
Judging by reciepts etc. and what PO had said car had stood for 5 years with fluid in the system.
The brakes functioned perfectly after all this time. I have obviously now changed fluid and needed to replace a seal in a front caliper he'd "nicked"
but chrome pistons were like new and everything was as though it had been built yesterday.
It must have a lot to do with how a car is stored I would have thought.

Kenny

[AussieJohn]

After much brakework including new standard pistons in the front calipers I finally managed to get reasonable brakes but on two applications of the pedal it was better than one. I was convinced there was no air in the system as I had put gallons of fluid through it I thought that Robbies suggestion of jamming the brake pedal down overnight sounded like an old wives tale but being intrigued I tied it overnight, voila, a great pedal, and three days later I still have a great pedal, Keith, give it a try, John.