14 replies to this topic

[NETTY]

hi there, have a 1989 mini city 998cc. Until yesterday the brake pedal was 'sticking' down but eventually releasing itself. It was intermittent and not doing it allthe time, but can anyone tell me if we have solved the problem by taking the vacuum hose off the servo and reattaching. (now we get a definite spring back from the pedal). This failed the mot ,obviously for safety reasons, but i havent tried her this morning. I just need to ask whether its worth replacing this hose or do as the garage says and try a new servo. The brakes did not fail the mot, just this pedal sticking. After not being on the road for 2 years, we have greased up all the springs etc but its getting so frustrating...has anyone else heard of this problem and have any suggestions please......

[pantera2075]

Replacement servo - complete with master cylinder. Servos are sealed units and can't be worked on inside.

It sounds like you've got 2 or 3 issues that together are causing this problem. It'll be a lot easier and cheaper to replace the whole servo unit instead of individual bits.

[NETTY]

Replacement servo - complete with master cylinder. Servos are sealed units and can't be worked on inside.

It sounds like you've got 2 or 3 issues that together are causing this problem. It'll be a lot easier and cheaper to replace the whole servo unit instead of individual bits.

thanks for advice, would this vacuum hose have anything to do with the problem then??

[NETTY]

Replacement servo - complete with master cylinder. Servos are sealed units and can't be worked on inside.

It sounds like you've got 2 or 3 issues that together are causing this problem. It'll be a lot easier and cheaper to replace the whole servo unit instead of individual bits.

please could you advise the best place to get these parts from please...

[Ethel]

It's more likely to be the other side of the servo.

There's a one way valve in the hose (or its connector, I'm not overly familiar with the specifics of the later Mini servo) that maintains the vacuum in the servo even if there's no vacuum being generated by the inlet manifold when you push the stop pedal. Pushing the pedal closes a passage between the two sides of the servo and opens the rear side to atmospheric pressure to provide the extra push. The problem will be that the vacuum isn't being restored to the back of the diaphragm to release the brakes when you let the pedal up. By removing the hose you restored equilibrium by letting atmospheric pressure in to the front side.

The servo must be serviceable as you can get a service kit for it. I wouldn't be surprised if it's the same one as used on Metros but I've never looked in to it.

Edited by Ethel, 29 August 2008 - 08:08 AM.

[NETTY]

It's more likely to be the other side of the servo.

There's a one way valve in the hose (or its connector, I'm not overly familiar with the specifics of the later Mini servo) that maintains the vacuum in the servo even if there's no vacuum being generated by the inlet manifold when you push the stop pedal. Pushing the pedal closes a passage between the two sides of the servo and opens the rear side to atmospheric pressure to provide the extra push. The problem will be that the vacuum isn't being restored to the back of the diaphragm to release the brakes when you let the pedal up.

The servo must be serviceable as you can get a service kit for it. I wouldn't be surprised if it's the same one as used on Metros but I've never looked in to it.

Hello Ethel, thanks! We took off the vacuum hose and reconnected and seems to be working for now but before we did this the pedal would stick down and was very slow to come back. we have doen this now and the pedal is springing back but I am going to go and try it again in a while, but you think that the servo could do with a service maybe? I am trying to understand the technics of this so please forgive how thick i am !

[NETTY]

By removing the hose you restored equilibrium by letting atmospheric pressure in to the front side.

please explain...sorry

[Ethel]

By removing the hose you restored equilibrium by letting atmospheric pressure in to the front side.

please explain...sorry

Didn't think it was that big a word May be I should have said balance

Inside the metal can is a rubber diaphragm that divides it in to 2 chambers. With the brakes off manifold vacuum is fed to both chambers. When you apply the brakes a simple valve is closed to separate the 2 chambers and another valve lets atmospheric pressure in to the rear chamber - the difference in pressure in the two chambers is what applies the extra push to the brake pedal. If you equalise the pressure in chambers again there'll be no push. Normally, that would be by restoring the manifold vacuum to the rear chamber but pulling the hose off and letting atmospheric pressure in to the front also restores the equilillili-brum brum.

I don't think anything is broken, probably just sticky due to damp and dust.

Edited by Ethel, 29 August 2008 - 08:39 AM.

[emalee]

Just adding my 2p, shoot me down if i'm wrong

but i had a simiular problem with my mini, and it only happened when the clutch pedal was down, when the clutch was released the brake pedal came back up, we sovled it by spraying the pedal box with WD40. it took a few hundred miles to help, but its fine now

might be worth a try if yours is simular

[NETTY]

[hello ethel

i have just been out and tried her and so far so good no sticking...........we ddint have a clue what we were doing but just took the hose off to clean it and put it back on. and its working and hasnt stuck again yet. but im not convinced that two complete amateurs have fixed it so I am going to check again and again !

thanks!

[NETTY]

Just adding my 2p, shoot me down if i'm wrong

but i had a simiular problem with my mini, and it only happened when the clutch pedal was down, when the clutch was released the brake pedal came back up, we sovled it by spraying the pedal box with WD40. it took a few hundred miles to help, but its fine now

might be worth a try if yours is simular

hi thanks emalee

hopefully a few hundred miles will help us..but its only 5 miles to the test centre so fingers crossed for this!

[Dan]

Servos are sealed units and can't be worked on inside.

Yes they can, rebuilding a servo is easy. From the sound of it that's what you need to do. The rebuild kit is available from all Mini specialists. First though, if it sticks again try removing the servo air filter. It probably isn't the problem but you never know. The filter is behind the rubber bellows at the bulkhead end of the servo.

[NETTY]

Servos are sealed units and can't be worked on inside.

Yes they can, rebuilding a servo is easy. From the sound of it that's what you need to do. The rebuild kit is available from all Mini specialists. First though, if it sticks again try removing the servo air filter. It probably isn't the problem but you never know. The filter is behind the rubber bellows at the bulkhead end of the servo.

thankyou dan.i will suggest this to my uncle who rebuilt the mini for us. thanks for advise. i have just tried and shes not sticking now.

[Ethel]

Just adding my 2p, shoot me down if i'm wrong

but i had a simiular problem with my mini, and it only happened when the clutch pedal was down, when the clutch was released the brake pedal came back up, we sovled it by spraying the pedal box with WD40. it took a few hundred miles to help, but its fine now

might be worth a try if yours is similar

That'll be because, with vertical master cylinders, both pedals use the same return spring. the horizontal cylinder's return spring is on the bell crank under the bonnet.

[pantera2075]

Servos are sealed units and can't be worked on inside.

Yes they can, rebuilding a servo is easy. From the sound of it that's what you need to do. The rebuild kit is available from all Mini specialists. First though, if it sticks again try removing the servo air filter. It probably isn't the problem but you never know. The filter is behind the rubber bellows at the bulkhead end of the servo.

I stand corrected!

I've never seen one that looked sevicable tho.