Brake help

[elvimto]

The system was doing fine then by mistake I loosened up the caliper joining bolts and thought since I did that i would replace the seals i had a spare caliper so I put in new seals and filled the system up. The brakes have been bleed now when i drive the car and you hit the brakes as in emergancy they seem to work fine but if you are stopping for traffic or a stop sign sort of slow stopping the pedal gets very harder to push. I got back to the garage and with the engine at idle depressing the brake pedal I can hear an air noise or vacuum noise down by the brake pedal up under the dash. Any ideas what this could be? am I looking at removing the booster ? Thanks in advance for your help.

Stuart

[73stagman]

Sounds like you may have a damaged booster diaphragm. You can get a kit from james paddocks (in the UK) for around £50. This means the booster does have to come out.
However.... the booster does have a "filter" of sorts down by the brake pedal but in my head that should not be "hissing" when the engine is running because the engine vacuum is separated from the pedal by the diaphragm.

[dasadrew]

Hi Stuart,

I'm afraid I don't have experience (yet!) of a running Stag, but it is normal that brake servos would make a slight rushing air sound when you apply the brakes as this is the way a servo works (lets air into the back of the servo so that the vacuum applied to the front part can suck the diaphragm forward to give you your servo assistance). The rear part is also initially under vacuum and, as you close off the rear chamber from the vacuum side, this can also cause a slight whisping sound.

Are the seals you used on the caliper really genuine brake seals of the correct dimension and material and not the nearest AutoZone available "O" rings? It seems like an amazing coincidence that you replaced the caliper seals, have a braking problem and it's the servo that has gone stateside?

It's not clear from your post if the caliper in now is a used one you had lying around, or the original with new seals?

Drew

[73stagman]

Hi Stuart,

I'm afraid I don't have experience (yet!) of a running Stag, but it is normal that brake servos would make a slight rushing air sound when you apply the brakes as this is the way a servo works (lets air into the back of the servo so that the vacuum applied to the front part can suck the diaphragm forward to give you your servo assistance). The rear part is also initially under vacuum and, as you close off the rear chamber from the vacuum side, this can also cause a slight whisping sound.

Are the seals you used on the caliper really genuine brake seals of the correct dimension and material and not the nearest AutoZone available "O" rings? It seems like an amazing coincidence that you replaced the caliper seals, have a braking problem and it's the servo that has gone stateside?

It's not clear from your post if the caliper in now is a used one you had lying around, or the original with new seals?

Drew

Would the air be "hissing" once the pedal has stopped moving Drew? It isnt clear from Stuarts post that it is only happening when the pedal is moving but you might be right that the air he can hear is when the pedal is moving and filling in the pedal side of the chamber.
The wrong seals in the caliper though wouldnt make the pedal hard would they? They might leak and then the opposite would be true.

[dasadrew]

Would the air be "hissing" once the pedal has stopped moving Drew? It isnt clear from Stuarts post that it is only happening when the pedal is moving but you might be right that the air he can hear is when the pedal is moving and filling in the pedal side of the chamber.
The wrong seals in the caliper though wouldnt make the pedal hard would they? They might leak and then the opposite would be true.

The hissing shouldn't continue - it should be a slight "gasp" as the pedal is moved. My own experience is that, when you are looking for a fault you'll hear all sorts of unusual and expensive sounding noises which have been there all the time.

On the seals, I'm thinking that, if they have "ballooned" or were the slightly wrong dimension, they may be blocking the passageway and will only let fluid through at a high pressure. This would explain the bad brakes at slow speed gentle braking, but OK when applied hard. I remember cleaning up a "normal" 'O' ring once (can't remember why!) in some thinners or whatever. I came down next morning and it was about 5 times its original size!! Since then I'm very careful if I'm using 'O' rings in contact with anything other than water!

Additionally, if there were a servo problem, I can't understand why the problem wouldn't occur during heavy braking. When my servo went on the Escort, it was the opposite; braking on a dual carriageway was frightening, but stopping the car rolling on a slight incline was no problem.

[73stagman]

All true if the o ring has been exposed to mineral oil at all even for a bit of a wipe with grease to help seat it it will blow up like a balloon. With the two caliper parts tight together there would be nowhere else for it to go but into the passageway and blocking the passageway.

More info required on the hissing noise me thinks but you are sounding to be more and more right the servo issue is not consistent with no servo at all which would be the case with a blown diaphragm

[Giles]

As the guys have suggested above likely to be work you have done but i have known bleeding to cause master cylinder issues due to it going through far greater travel than normal. Could it also cause servo issues? just a thought, unless it was vacuum or pressure bled of course.

[elvimto]

Should have said the kit came from a US supplier of Stag parts dependable, the caliper was a spare that had been refurbished but I replaced the seals from the kit. I blew air through the caliper ports all clear and assembled so i believe that can be ruled out. I did use a vacuum bleed pump the hand held type to start with then went back to the normal pedal bleeding. The only time you can hear the hissing or air is when the pedal is depressed, when the pedal is up no noise. The pedal does not feel spongy which to me would suggest air in the system it just gets hard as in its losing vacuum assist. When you brake hard the brakes seem to function as they should but as I said on long slow braking the pedal starts to feel hard and you have to use more force on the pedal. I will look for the filter and get under the dash and check for vacuum leaks. It could be possible that when you are at say 30 mph and you hit the brake there is plenty vacuum assist but if you are at slower speed and use the brake vacuum assist goes away due to a leak off somewhere, do you think that could be possible?

Cheers Stuart

[73stagman]

does the hissing carry on for as long as you hold the pedal down...? It would only hiss as you press the pedal down to apply the brakes any air noise should then stop.

[73stagman]

I think the filter is just a piece of foam around the push rod going into the booster. I dont know if it can be replaced or cleaned easily or not. I know its not shown as a spare part on Rimmer bros web pages

[martin]

Hiya Stuart, I would be inclined to replace the whole servo, separating the two halves can be difficult and risky, it's just likely to spring apart and punch you in the face. There's also the issue of getting it to re-seal after repair. The price difference is not huge. The filter is not an issue, if you can hear a hissing, it's working. Good luck, Martin.

[elvimto]

does the hissing carry on for as long as you hold the pedal down...? It would only hiss as you press the pedal down to apply the brakes any air noise should then stop.

You can hear the hissing as long as you have the pedal depressed and it stops when back in the up position does this help any?

cheers Stuart

[73stagman]

I think you can hear the engine vacuum through a split diaphragm but others may tell me I'm wrong.

[73stagman]

By the way.
I have my servo in pieces at the moment. I have to replace the diaphragm and seals just because the car has been standing still for thirty or more years and I didnt want to risk a failure. The servo was really easy to take apart. The internal spring isnt that strong. I just used a drift and tapped lightly to turn the master cylinder side away from the pedal side which was held in a vice using the four studs sat into a suitably drilled plate held in a vice. As I felt the thing come apart I just held the outer half down and kept tapping.. It just sprung apart easily.
Putting it back together could be a bit more tricky but we will wait and see!

[elvimto]

I have a spare servo that i bought a while back that I forgot all about is there a way to bench test this ? If I hook up the vacuum line to the check valve and start up the car would this tell me if the unit is good? It really does not look hard to repair but the cost of the kit is 160 US we have 2 companies here that will do this repair I would have to call them. Is the concensus that the servo has failed I never had a servo go bad before.

cheers Stuart