Brake M/C or Booster problems?

[rastaman]

1973 S3 88...
My brakes seem to be basically functional from what I can tell,(still on jack stands). The problem I am having is that when I try to do a final bleeding of the brakes,(with the motor running) after a couple of bleeds I get no more fluid coming out.
From what I can tell it appears that the master cylinder has not returned to rest position. The pedal does (by spring tension), however it is possible to feel when pressing the pedal that it is not 'activating' anything.

After a short period of time the pedal goes back to feeling normal.(like what ever is sticking returned ). It seems that it is ok, until I attempt to bleed, then something travels too far and sticks.

This truck sat for about 2years. however the MC looks fairly new and has clean fluid. Is it possible for the that the internal parts of the Booster are sticking?:confused:
I am suspecting the MC. As I have never come across a sticking booster.(how ever this is my first LR):)just find it hard to understand why it would with clean fluid always in it.
Any suggestions?

Thanks Guys

ps. I do recall that when I first got the truck and was playing around with the brakes the pedal popped 'up' higher, making me realize that it had been stuck in a half way down position, but the pedal it self is presently not sticking and moves freely.

[Lalo88DK]

While renovating my 1975 SWB Series III, I experienced the same problem, in the end I took off the very okay-looking masterbrake cylinder (on the outside) and found this :eek:

http://i261.photobucket.com/albums/ii66/Volvo960DK/DSC_0003-4-1.jpg

[rastaman]

I took off my M/C there was virtually no rust inside, I depressed the plunger and the inside of the cylinder looks fine and didnt stick at all when being depressed. I pushed in on the brake pedal all the way with the M/C off. it doesnt stick either...

I have re installed the M/C.. now as soon as I can get a third leg to pump the brake, with the motor off, I will see what happens.

Is there anything in the booster that could cause the booster plunger to remain extended after the pedal is released?

I am just thinking that when the pedal is dressed and the brakes bleed, something is being pushed too far and getting stuck.

[LaneRover]

Sorry if this is just a silly question but I noticed that you said your truck is on jack stands. Is there any chance that the brakes aren't completely put together? ie brake springs aren't on the shoes but you threw the drums on just to check the brakes?

I just know that there are times I have figured something out but it took me so long I wish I had someone there to point out the simple step I missed!

Kind of like the friend who called the prop house to say the guns he rented weren't working at all, they wouldn't fire and he needed some answers. They said, "Do you remember that Thompsons fire from an open bolt?" As he said, "Yes, of course I do!" he realized he had forgotten that bit of info and had 4 fully loaded full auto Thompson sub-machine guns on his desk pointed right at him. DOH! Even blanks would have done some serious damage that close . . .

[rastaman]

[QUOTE=LaneRover;70903]Sorry if this is just a silly question but I noticed that you said your truck is on jack stands. Is there any chance that the brakes aren't completely put together? ie brake springs aren't on the shoes but you threw the drums on just to check the brakes?

I just know that there are times I have figured something out but it took me so long I wish I had someone there to point out the simple step I missed!

Kind of like the friend who called the prop house to say the guns he rented weren't working at all, they wouldn't fire and he needed some answers. They said, "Do you remember that Thompsons fire from an open bolt?" As he said, "Yes, of course I do!" he realized he had forgotten that bit of info and had 4 fully loaded full auto Thompson sub-machine guns on his desk pointed right at him. DOH! Even blanks would have done some serious damage that close . . .[/QUOTE

Yeh I know what you mean, however the problem seems to by located from what I can tell in the area of the M/C or booster. I can make a few attempts to bleed and I get fluid out of the rear, then nothing, and the pedal at that point just doesnt feel right, You can push it down but there is no resistance other than the return spring. And if it sits for awhile it feels ok.
Is there some sort of poporting valve going to the rear brakes???

[bobzinak]

I had flexible brake line that had deteriorated inside the hose. particles of rubber that were too big to go through the brake piping, but would float in the line, I found this out when waiting at a long, long stop light, when i released the brake the rubber particles acted as a one way valve and would not release the brake..since it seems that your master cyl. and your pedel are not sticking. the two things that push the fluid back into the master cyl. are the spring inside the master cyl. and the brake shoe return springs. do any of your brakes drag, turn them by hand, it could be you have a sticking wheel cyl. or bad springs, or a bad flexible line.. just my two cents..bobzinak..

[rastaman]

I had flexible brake line that had deteriorated inside the hose. particles of rubber that were too big to go through the brake piping, but would float in the line, I found this out when waiting at a long, long stop light, when i released the brake the rubber particles acted as a one way valve and would not release the brake..since it seems that your master cyl. and your pedel are not sticking. the two things that push the fluid back into the master cyl. are the spring inside the master cyl. and the brake shoe return springs. do any of your brakes drag, turn them by hand, it could be you have a sticking wheel cyl. or bad springs, or a bad flexible line.. just my two cents..bobzinak..

Thanks..I thought of that, the flex brake lines are fairly new...the problem only seems to happen when with the motor running, and after pumping AND BLEEDING the rear brakes. after a couple of bleeds, no more fluid, the wheels spin freely, It is like the plunger in the M/C has bottomed out and stayed there...The pedal returns to top position, however when pressed it seems to only have spring tension on it. After awhile it all seems fine again...tell bleeding is attempted.

[SafeAirOne]

I've had the same thing happen to me---Press the brakes once, all is well; Press the brakes twice and the pedal goes halfway down before it begins pushing fluid.

Master cylinder was bad--The piston was sticking on the return stroke.

[bobzinak]

It seems to me that there is something not right with the MC..buy a rebuild kitand replace the rubber parts..it is easy to do..just be careful when you remove the keeper from the interior spring, you have to bend the tab up to get it to slide off. would recommend doing it indoors so that if it flies off you can find it easy..my choice was in the bathroom, don,t forget to plug the drains..befor you reassemble bend tab down a bit so it will snap into place..there is a small valve in the MC that is on a shaft with the spring on it..as far as testing the vaccuum unit, as I recall you tested it by first starting engine, then turning off engine and step on brake pedel and you should hear the vaccuum being released progressivly as you step on the pedal repeatedly..I have had my rover for along time and have never had one fail or stick. I replaced mine after 35 yrs when I rebuilt my rover, and it worked just the same as the old one..so try the master rebuild first..bobzinak

[bobzinak]

one more thing, the same master is used in the MGB's, there is an excellent sight for lucas/girling info, it called MG GURU.com. so many parts on british cars have alot in common, jags.austin healys mgs etc..the only diference with the mg rebuild kit is the brake fluid tank. I'm sure your not the only one tis has happened to. bobzinak

[rastaman]

It seems to me that there is something not right with the MC..buy a rebuild kitand replace the rubber parts..it is easy to do..just be careful when you remove the keeper from the interior spring, you have to bend the tab up to get it to slide off. would recommend doing it indoors so that if it flies off you can find it easy..my choice was in the bathroom, don,t forget to plug the drains..befor you reassemble bend tab down a bit so it will snap into place..there is a small valve in the MC that is on a shaft with the spring on it..as far as testing the vaccuum unit, as I recall you tested it by first starting engine, then turning off engine and step on brake pedel and you should hear the vaccuum being released progressivly as you step on the pedal repeatedly..I have had my rover for along time and have never had one fail or stick. I replaced mine after 35 yrs when I rebuilt my rover, and it worked just the same as the old one..so try the master rebuild first..bobzinak

Well it looks like a M/C rebuild is in my future...
thanks for all the help from everyone...If this doesnt take care of the problem.....I'll be back


Cheers

[rastaman]

Well I am still having problems. I took the brake tower with booster out, the push rod from the pedal to the booster was frozen solid. I was eventually able to free it and remove the pin, now everything is back together and greased and moving freely.

The problem, when attempting to bleed the brakes after the second bleed, there is no fluid coming out of the master.

Before I invest in a rebuild kit. (this M/C looks totally clean and free movement) Is it possible that the the booster push rod is staying pushed out,(not allowing the M/C piston is unable to return to rest.)

ie a faulty booster, and if so how can I check that the booster is functioning properly. The pedal returns to top position, and is totally free.

The problem seems to happen when bleeding with the engine running.

Need some help guys...
thanks