13 replies to this topic

[philip663]

Hey guys. Rebuilt my engine again and have just got it running on the road properly. Running fine with no problems.... bar the brakes. Thought id fixed it but its back to haunt me! 

 

During journeys lasting sometimes 5 minutes, sometimes 15 the brakes would gradually start to stick on. To the point where the car wouldnt roll back if parked on a medium sized hill! 

 

Its just the front brakes that stick on, the back isnt affected. At first i thought the valve on the bulk head was faulty being rusty and old, so i replaced it. No luck there. So i forked out for a new master cylinder. Still no luck so now i am stuck. The only thing left is the calipers? But they have been cleaned, and surely it cant be causing such problems. 

 

The only two things i can think of are, warped disks? I know you shouldnt, but i chucked a cup of water over each disk to see how hot they where. passenger side gave out a lot of steam and hissing. Driver side was a little but not so bad.. which makes me think somethings up with the passenger side causing it to heat the fluid and put the driver side on too? The brakes both stick eaquily, As the car doesn't pull to either side. when the brakes are stuck on there is a littler bit of judder through the steering wheel.. 

 

And the haynes isnt clear on which way the pipes from the master plumb up to the valve on the bulkhead. From the master to the valve i have the pipe closest the servo going to the top left, and furthest from the servo going to the top right, and then underneath the left is going to the front and right to the back, is this correct?

 

 

I really wana get me engine run in, please help =[

 

[lrostoke]

what about the flexi hoses, have you changed those

[philip663]

New braided ones and new copper

[lrostoke]

Just checked Haynes and it describes the port nearest the servo as the primary, so I would imagine that's the fronts.

 

Have you tried cracking off unions at various places starting at the master cylinder to see when the pressure releases.

 

For the brakes to stick on its either pressure build up or piston seizing through rust / bad seals

[tiger99]

Is there free play at the master cylinder when the pedal is released?  There must have been some, otherwise the system would not bleed, but sometimes they stick for various reasons. It is not easy to check on a servo model, but you could try a shim between servo and master cylinder.

 

However, I suspect that the cause is within the calipers as the sticking is unequal on each side.

 

According to the Rover manual (you can buy them cheaply on CD, but I will not say where as there may be copyright violation involved, although the government is changing the law on "dead works" so that may change, but try Googling....) your pipes are connected correctly.

[philip663]

Thanks for the advice, I know the whole front up to the valve is under pressure constantly. Not sure from the master to the valve though, I'd presume so, as the pedal has the correct play in it when the brakes arnt hot. But when they do there thing and get hot, the pedal goes hard, solid, like there's not servo there, or like when the engine if off, but harder.. Maybe I should of meantioned that lol

[Captain Mainwaring]

Thanks for the advice, I know the whole front up to the valve is under pressure constantly. Not sure from the master to the valve though, I'd presume so, as the pedal has the correct play in it when the brakes arnt hot. But when they do there thing and get hot, the pedal goes hard, solid, like there's not servo there, or like when the engine if off, but harder.. Maybe I should of meantioned that lol

 

Nooo, no need to mention all the material facts - it's more fun to guess, especially with braking systems

 

There is an adjustable joint that allows you to set the master cylinder at the end of it's stroke relative to the pedal - if that is adjusted too short, then the ports to the reservoir remain sealed with the pedal up under pressure, and the brakes won't release.

 

As mentioned above, if you crack the union for the fronts at the master cylinder, I'm guessing that you'll get a bit of fluid out under pressure.

 

Drums can stick on if they are adjusted too tight and they over heat, but disks tend to need something to hold them locked on - corrosion will cause dragging, but the symptoms are different.

[Willthewelder]

Are the pads sticking in the carriers?

[philip663]

Thanks for the advice, I know the whole front up to the valve is under pressure constantly. Not sure from the master to the valve though, I'd presume so, as the pedal has the correct play in it when the brakes arnt hot. But when they do there thing and get hot, the pedal goes hard, solid, like there's not servo there, or like when the engine if off, but harder.. Maybe I should of meantioned that lol

 
Nooo, no need to mention all the material facts - it's more fun to guess, especially with braking systems
 
There is an adjustable joint that allows you to set the master cylinder at the end of it's stroke relative to the pedal - if that is adjusted too short, then the ports to the reservoir remain sealed with the pedal up under pressure, and the brakes won't release.
 
As mentioned above, if you crack the union for the fronts at the master cylinder, I'm guessing that you'll get a bit of fluid out under pressure.
 
Drums can stick on if they are adjusted too tight and they over heat, but disks tend to need something to hold them locked on - corrosion will cause dragging, but the symptoms are different.

Hey the servo is adjustable?!? Well this is news, thought the bit on the back of the servo was for adjusting the pedal. I have had the servo in bits and powder coated it, put it back exactly how I got it out. How can I tell if its set up right?

I know as you put the master cylinder on the front of the servo, up until about 10mm before it butts up against the servo the diaphram has resistance on the pushrod of the master. I was under the impression that was normal. Hmm any clues?

Phil

[philip663]

Ok I think if worked it out, my servo applies a constant pressure to my master, only a little, about 5-10mm as I said could this be the problem? I have no idea why the diaphram in the servo is sticking out that little bit more. Is this the route of my problems =D??

[Captain Mainwaring]

Ok I think if worked it out, my servo applies a constant pressure to my master, only a little, about 5-10mm as I said could this be the problem? I have no idea why the diaphram in the servo is sticking out that little bit more. Is this the route of my problems =D??

 

Yes....Look at all the rods and linkages and make sure there is no pressure on the servo actuator rod....

[tiger99]

Seems like you have found the problem.

It also happens on non-servo cars due to a build up of tolerances in the pedal box area. In that case, shims are available to go under the master cylinder, and as they are in two halves, you don't need to undo the dreaded clevis pin to get them in. If anyone needs to fit these, remember to put a splodge of silicone or other sealant where they meet, and use an extra gasket, cut into two halves, so that you don't get any fumes and noise (above what is always there in a Mini!) leaking into the car.

[philip663]

I've taken the pedal off the servo unit, the pedal is applying no pressure when set up, meaning the servo is as far back as it will go. I'm starting to think the servo is at fault since being put back together as I'm sure the diaphram should move back some more but it's solid, won't move any further back. I'll add that it is the later servo from 88>. So as far as I'm aware this servo isn't adjustable? As adjusting the nut at the back only moves the pedal and doesn't do anything to the servo (or at least in my case as I'm not sure it's working correctly).

Thanks for the advice so far, I haven't managed to find any spacers though =[

[Captain Mainwaring]

Washers - but by the sound of it you don't need them.

 

I think you have to force the problem again then let some pressure out of the system and see if it cures it.