problem with old style brake system
Discussion
A friends Morgan Plus 8 or 1970s vintage had a brake problem following the replacement of shoes and pads and a rear slave cylinder. The rear brakes are drums of the non self adjusting sort and have been adjusted correctly.
The problem is that the first application of the brake pedal goes almost down to the floor though the braking is still good enough to lose front wheel grp on a damp road. An immediate second application gives a harder pedal feel and much less travel of the pedal.
In neither case is the pedal spongy when you push hard on it so I doubt that there is air in the system . What do these symptoms suggest to you? Servo problem / leak? Master cylinder seals?
The problem is that the first application of the brake pedal goes almost down to the floor though the braking is still good enough to lose front wheel grp on a damp road. An immediate second application gives a harder pedal feel and much less travel of the pedal.
In neither case is the pedal spongy when you push hard on it so I doubt that there is air in the system . What do these symptoms suggest to you? Servo problem / leak? Master cylinder seals?
Sounds a bit like knock off.
Does the brakes work OK until you have turned a corner ? Some shifting of the brake calliper can allow the disc push the Pistons back leading to this phenomenon.
Used to get it in my Impreza STi with the 4 pot brembo's when really pushing it in a bend.
I am assuming it's got discs on the front as you mention pads.
Does the brakes work OK until you have turned a corner ? Some shifting of the brake calliper can allow the disc push the Pistons back leading to this phenomenon.
Used to get it in my Impreza STi with the 4 pot brembo's when really pushing it in a bend.
I am assuming it's got discs on the front as you mention pads.
Edited by Gary C on Wednesday 13th September 13:36
I agree with Gary C that disc brake knock-off is most probable. Usual cause is a little slackness in a wheel bearing and I do mean little.
Can't remember what the Morgan's front wheel bearings are, but most makers of their time used taper rollers which have to be done up tight and then backed off a gnat's (technical term for "to the next split-pin hole") to give no more than 4-6 thou. end-float.
ETA Caliper slackness just could be the cause but that's unlikely in my view. It is also possible to get a similar effect if a disc brake piston has seized, but both that and slack caliper would have been spotted when changing brake pads.
Can't remember what the Morgan's front wheel bearings are, but most makers of their time used taper rollers which have to be done up tight and then backed off a gnat's (technical term for "to the next split-pin hole") to give no more than 4-6 thou. end-float.
ETA Caliper slackness just could be the cause but that's unlikely in my view. It is also possible to get a similar effect if a disc brake piston has seized, but both that and slack caliper would have been spotted when changing brake pads.
Edited by Allan L on Wednesday 13th September 15:16
bordseye said:
I dont think that it is knock off since it does the same thing if the car is parked up in the garage.
Oh well.So it's effective but long travel, but readjusts with one prod ?
Ok, master cylinder is normally noticeable as under pressure, it eventually sinks. Hum, so if it works fine, then is left and then takes a large travel but holds pressure with no spongeyness, and there is no self adjuster on the drum their cant initially be enough fluid in the system, but no air, which means either a piston is back in the caliper, or in the slave as when you move the master piston it pressurises, then moves back and pulls in more fluid and then works fine for a bit.
strange.
I take it the brake pedal is sat at the normal position initially ?
I've had a similar problem with one of my cars, ever since a servo rebuild. There is a problem with some servos, something to do with a part that has two o rings but should only have one. I'll be altering that soon to see if it makes a difference ( i already tried wheel bearings and master cylinder and slave cylinders and re bleeding a million times). But as you didn't touch your servo, I don't see how that can be related.
As you only messed with one cylinder it suggests a fault with the new cylinder, or bleeding. So the above suggestions about the master cylinder and the wheels bearings are pretty good shouts for openers.
As you only messed with one cylinder it suggests a fault with the new cylinder, or bleeding. So the above suggestions about the master cylinder and the wheels bearings are pretty good shouts for openers.
lowdrag said:
Sound to me that the car needs the fluid changing? If hygroscopic fluid, the sponginess will be noticeable and pumping the pedal will cause a firmer feel - until the next time. Change the fluid, but if you go to synthetic fluid all the seals will need changing too.
But it's not spongey he says.Firm but long then firm but short.
Servo faults tend to make it firm, short but ineffective.
Stigproducts said:
But as you didn't touch your servo, I don't see how that can be related.
As you only messed with one cylinder it suggests a fault with the new cylinder, or bleeding. So the above suggestions about the master cylinder and the wheels bearings are pretty good shouts for openers.
Problem here is that the owner, a lovely man, has as much mechanical aptitude and interest as my wife. None. He could have been driving around with it like this for the last decade!As you only messed with one cylinder it suggests a fault with the new cylinder, or bleeding. So the above suggestions about the master cylinder and the wheels bearings are pretty good shouts for openers.
Sounds very much like the system needs to be bled properly .
There is nil braking effort happening at the rear on the first prod then on the second pump it fills the rear up and becomes firm .
Many systems of this age have little braking effort on the rear add in a old proportioning valve and it can give strange indications of what is and whats not working .
Get it checked on a brake tester .
There is nil braking effort happening at the rear on the first prod then on the second pump it fills the rear up and becomes firm .
Many systems of this age have little braking effort on the rear add in a old proportioning valve and it can give strange indications of what is and whats not working .
Get it checked on a brake tester .
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