Brake Puzzle.

[Daxklynsmith]

I mentioned recently that the sealing ring between one of the master cylinders and the servo had popped and that I was having difficulty (N/A) on a rebuild seal kit.
(73 3.0 rhd CSA)
Had a look at my 80 635 donor car and although the bore was slightly bigger I had to match it with the servo from the original CS one as the 635 servo was larger..
all seemed to work fine on the short runs I have been doing, did a slightly longer one today, ran it up to around 60mph, checked the brakes a couple of times and then the trouble started.
Brakes would not free up ,all 4 of them.

I didn't open up the 635 one, it looked as if it had never been opened, so no possibility of a seal being the wrong way round..

Anyone have any ideas??

 

[Daxklynsmith]

OK, gather there is different nomenclature.
I'm referring to the brake booster and servo that sit on the LHS.

 

[MMercury]

I mentioned recently that the sealing ring between one of the master cylinders and the servo had popped and that I was having difficulty (N/A) on a rebuild seal kit.
(73 3.0 rhd CSA)
Had a look at my 80 635 donor car and although the bore was slightly bigger I had to match it with the servo from the original CS one as the 635 servo was larger..
all seemed to work fine on the short runs I have been doing, did a slightly longer one today, ran it up to around 60mph, checked the brakes a couple of times and then the trouble started.
Brakes would not free up ,all 4 of them.

I didn't open up the 635 one, it looked as if it had never been opened, so no possibility of a seal being the wrong way round..

Anyone have any ideas??

Here are some off-the-cuff ideas.

I recall you had an issue sourcing a seal. And I thought you borrowed a master -booster/servo/bomba combination from another car and every thing was a-ok. I wonder if the master didn't prematurely meet its demise or if possibly the servo spring collapsed. If the issue were just a seal, I have difficulty understanding how an breached 0-ring between a master and booster/servo/brake bomba - would account for all 4 wheels locking up. In fact, I would expect just the opposite to occur. When the seal was previously blown, did you experience similar lock-up?

If a seal were compromised, you would likely have a vacuum leak and an engine that wants to race. I suppose it possible that a leak on the posterior of the booster/servo might magnify the vacuum effect on the other side of the bladder/diaphragm, although I cant say I have experienced this.

Returning to the issue at foot: brakes that are now dragging or do not release. Why not disconnect any vacuum to the servo/s (plugging vacuum to manifold source) and eliminate them/it as possible culprit/s. If the servo/s is/are deprived of vacuum, then they should not have any effect on the brakes other than to allow for much higher pedal pressure. Parenthetically, I have been told that many of the servos used on rhd cars are similar. I can't cite a specific example, but I wouldn't be surprised if Mercedes, Volvo and even some of BLeyland's finest might be easily adaptable. I don't recall having mentioned this, but I would expect any decent shop that rebuilds hydraulics could find one. I have had masters delivered with the gasket missing, so I would expect there are plenty of extras out there. The Ate masters are grooved to accept an o ring that is actually squared (when examined up close). Nevertheless, I have seen these fitted with slightly larger "round" oil resistant viton "o rings." Because safety is involved, I would advise using only the master cylinder manufacturer's seal. . I am aware of an E3 that successfully sported an Alfa master and booster using a generic viton 0-ring . . . . So when things become unavailable . . . adapt and improvise (draw your own conclusions)

Is the pedal actually depressed and not returning to its original position? If so, could it be that the return spring to the brake pedal has collapsed or fallen off? (Fig 11:33 check out that spring top right hand corner)

What shape is the master cylinder? Even if its new, its internally equipped with a return spring that can conceivably fail. When you bench bleed a master cylinder - substantial effort is required to compress the piston. If you can now easily compress that piston or it fails to return to the uncompressed state, you likely have an answer. Along the same lines, I know of someone who drove through a driving rain storm with an uncovered brake fluid reservoir. His brake pedal attached to his practically new master cylinder became increasingly stiff due to internal rust.

hth

 

[Daxklynsmith]

MMercury, thank you for the reply.
answers in reverse order, when the seal went it went flat to the floor,zero brakes
the only difference between the 635 booster and the original was size, so I am running two boosters of slightly different sizes, however the brake pads were being activated simultaeoneously(sp) so the minor bore difference seems to be evened out.

Car idles normally once warm,
when we took the wheels off yesterday we changed two of the final brake pipes one on each side and bled the sytem and that freed the pads

as soon as I started the car and activated the brakes both fronts locked up and I had to crack the bleed pipe to the booster to release.

I heard what appeared to be a leak when pumping the brakes yesterday before the problem arose,(swish,swish) but that is gone and the brake pedal stays up, even if I pump it with the engine off which normally releases any pressure within the servos.

The hydraulic hoses are old so will check those in case they have collapsed as well as checking for a posterior leak on the booster.
the problem is that the brakes are not releasing pressure so I hope its soluble.

there is a company 3 hours from me that may well have seals so I can see some road time but thanks again for your ideas.

 

[Daxklynsmith]

am now going the route of having the master cylinder and servo rebuilt.
Mine is a rhd, I gather one master cylinder does front and back and one does front only, anyone have any idea which one does front only? the one on top or the one on the bottom?

 

[MarksE9]

Faulty Servo on RHD Car

Hi, I had this problem a long time ago with a MKII Jaguar. The front brakes locked up and only opening the bleed screw would make them release. Turned out to be the servo unit, not the master cylinder and from memory it was a valve in the servo not releasing. I suspect the fault lies with the one you recently fitted so I would start there first. My fix was not expensive being just a rekit with new seals etc.

 

[Daxklynsmith]

Thanks Mark, I think you may be right.
Found a Company one of our other members used over in the UK called pastparts.co.uk, they do a rebuild on the master and servo (£80 and £165 respectively) s I guess thats the way to start and hope that its not something else.
Dick