Brake pedal sticking down

[ianc9]

I've just bought a restored '68 Series 1.5 2+2 and pretty well immediately driven it from London down to the Bordeaux area via Netherlands. So a quick 1,00kms on the clock.
The only issue I had was with the brakes. When the car was cold the pedal would travel down about 50% of the way and a quick pump would bring it up to "modern normal" level.
When the car got pretty hot then the pedal would not return up when I tired to pump it (actually the pedal does come up but the master cylinder piston doesn't) and also the brakes would bind slightly for a moment after I lift off the pedal.

Its as if the return spring inside the Servo was too weak.

It has an upgraded setup (I'm not sure what exactly). I will take a few photos when it cools down here later this evening.

Any pointers on where to investigate?

Ian

[christopher storey]

The pedal master cylinder piston sticking is a little bit unusual : the far more common fault is that the piston in the servo master cylinder sticks on momentarily, which is a common cause of your very short term brake binding. If you can get hold of red rubber grease you could dissolve some in brake fluid and flush the system which might just give the lubrication of the rubber seals you need. Even if you can't get any rubber grease in France, it is worthwhile flushing the system with clean brake fluid anyway

[ianc9]

The pedal master cylinder piston sticking is a little bit unusual : the far more common fault is that the piston in the servo master cylinder sticks on momentarily, which is a common cause of your very short term brake binding. If you can get hold of red rubber grease you could dissolve some in brake fluid and flush the system which might just give the lubrication of the rubber seals you need. Even if you can't get any rubber grease in France, it is worthwhile flushing the system with clean brake fluid anyway

It is just the master cylinder sticking. I'll do system flush and try to get my hands on red rubber grease. Fingers crossed :)

[ianc9]

I got the stronger reaction valve spring today and I'm trying to fit it but it looks too big to me.
The one on the left was what I was sent. Has anyone else fitted this and does it look right?

[gtjoey]

Ian, before you do that.......PLEASE
With the cover off, put your finger over the piston in the middle of the cylinder, have someone VERY GENTLY PUSH THE BRAKE PEDAL TILL YOU FEEL IT MOVE ON YOUR FINGER.
Then depress the pedal and you push the piston back in.......
You will feel the rubber o ring bind.
Get MERCURY BOAT CLEAR MOISTURE PROOF GREASE OR DIALECT GREASE, As the other person taps the pedal again, put that grease on the edge of the piston as it lubes the seal!!!!!
You will freeup the stick. The repro o rings are tooooo tight.
Then put cover back on with OLD SPRING.....I bet yourbrakes will work again.
LUBE THE PISTON AND O RIND.
GOOD LUCK
GTJOEY1314

[ianc9]

I've actually done exactly that :)
The brakes didn't bind when I took it out for spirited spin yesterday evening. But more tests needed.

I haven't put the spring in because I just wasn't comfortable with the big difference in length..
I do still want to know if it is correct in case I haven't resolved the problem.

[gtjoey]

You did, its a known issue for about 25 years...There was a cheap batch of India made masters where the internals were actually crushed from new.....
Try to rebore an original master . SNG makes the best of the new ones......
Good luck. I grease that seal once every couple of years and it never binds.
GTJOEY1314

[ianc9]

The car has a SNG unit fitted. It's about 3 years old.

Can anyone tell me if that stronger replacement spring looks correct?

I'm still getting some brake sticking and would like to try the spring in the nose of the reaction valve - but I also don't want to force it in and possible do more damage.

[mgcjag]

Hi Ian...please try to put your name and car model in the signature area....in my opinion the large spring looks far too long....the short original one should be up to doing its job......quite a while ago i had the sticking brake issue it turned out to be the small metal flap thats inside the cylinder at the bottom that operates the piston....on close inspection it looked like it was made by stamping it out.....it had one side with rounded edges the other sharp square edges that seamed to stick in the bore...i just took off the sharp edges....worked fine then....Steve

[gtjoey]

Reality check.......All the repros border terrible to okay.
The last 10 we did , 3 were good.
The real answer , add more grease , find an original core or nos then have it rebored.
Good luck.
Terrible repro, but at least the SNG is getting better.
GTJOEY1314

[ianc9]

Grr! Still sticking
Steve - can you point me to where that bit of metal is?

[mgcjag]

Hi......bottom left on the drawing......its the very first part that goes into the cylinder bore...its what pushes on the tiny piston......Steve

[gtjoey]

IMHO, GET ANOTHER MASTER CYLINDER......Get 9 more and rotate till one works.
Sad to say.
gtjoey1314

[abowie]

This is a new problem to me.

I don't think what you are describing relates to reaction valve malfunction. That causes the brakes to stay on.

If the piston is not coming back out of the master cylinder it suggests to me that there is something wrong inside of the master cylinder.

Now you could strip it and rebuild it but these are difficult to get apart unless you are experienced with them.

Personally I suggest you just buy a new master and replace yours.

EDIT. You don't say if your car is LHD. If so the master can be affected by heat from the exhaust manifolds. There is a big heat shield on LHD cars to prevent this. I have no experience with LHD cars so apart from mentioning this as a potential source of trouble I can't be of any help there.

[gtjoey]

I went through 3 to get a good one.
You know where the hose goes to the master? Unscrew it and see if its crushed underneath. Then its one of the INDIA specials......
Order 3 from SNG , THEY have the latest version, one will work. Pray.......
I went Willwood on the clutch master and have a trick Willwood NON power if this latest one starts to stick.
Good luck
gtjoey1314
Blunt......THEY ARE ALL CRAP.

[ianc9]

EDIT. You don't say if your car is LHD. If so the master can be affected by heat from the exhaust manifolds. There is a big heat shield on LHD cars to prevent this. I have no experience with LHD cars so apart from mentioning this as a potential source of trouble I can't be of any help there.

It is LHD and it does have the heat shield fitted and its in very good condition. However, everything gets pretty hot under the bonnet :).

I'm going to take it off, strip it down clean and grease it up and then flush the system with fresh fluid with some red grease dissolved in it. I'll also look at the component with the sharp edge Steve talked about and see if it needs attention.

I'm currently in France and so there is absolutely nothing open today (Sunday) so it will be a next week job :)

[mgcjag]

Just to add...the flap i mentioned with the sharp edge is in relation to the small piston not returning so brakes sticking on ......and not with the pedal not returning.....Steve

[ianc9]

The pedal IS returning, but I can feel that the master cylinder piston is not.

One way or other, I think the master cylinder needs stripping.

[ianc9]

Stripped the master cylinder out and it was immediately clear there is severe binding in the mechanism.
Started dissembling it and found a number of issues:
1) there was no retaining circlip (17) installed
2) The plastic disc (13) was approximately where the circlip should be and was so tight fitting it was doing the job of the circlip.
3) Parts 15 and 14 were next in that order and facing the wrong way around and also very tight fitting
4) all plastic bits have some scoring but I dont think its terminal as they don't provide any seal.
The rest was fine . Piston and bore are in excellent condition.



So options are to purchase a new assembly or rebuild this one - but I need a circlip.

[Series1 Stu]

Wow! Some people shouldn't be let near a toolbox!

Numbskulls and braking systems - a recipe for disaster.



Regards