14 replies to this topic

[Danyul1275]

Hey guys,

Started having a problem with my brakes that has me a bit confused.
When driving there is a lot of travel in my brake pedal and brake efficiency isn't very good. When stationary the pedal builds pressure and is hard like normal but when driving it goes soft with lots of travel.
There are no leaks from what I can see.
Car is a 81 city, non servo and braided lines have been fitted all round.
Anyone got any idea what could be causing it?

Thanks in advance for any advice

[Swift_General]

You say when stationary the pressure 'builds'. By that do you mean that pumping the pedal brings it up? If so are the brakes adjusted? If an '81 I'm guessing drums all round meaning that lack of adjustment will have an even bigger effect that with discs up front.

Edited by Swift_General, 27 November 2016 - 06:33 PM.

[slidehammer]

I would say if there is no leaks including all the wheel cylinders, then it must be air still in the system. Sometimes it can be hard to shift, especially if the seals in the master cylinder are starting to get hard/worn on the lips so pumping is not as effective at pushing it out of the system. The best way is with a pressure or vacuum bleeder. Something like Gunsons Ezibleed works well. Try that then I would think about rebuilding / replacing the master cylinder.

[bpirie1000]

I would suggest foot on pedal for a ten mins without pumping..... see if it holds pressure.
Then if it hits the floor deaf issue..
Also adjust rears....

If nothing obvious.. try a bleed nipped in the master cylinder before rebuilding it...

Good luck and stock up on brake fluid.......

[Danyul1275]

Cheers for the replies.
Yes when stationary the pressure builds back up, brakes are adjusted up.
This problem has only started recently which is why it's confused me as they were fine before and nothing has been changed between them being okay and the problem starting.
Drums rear discs front

Will have a go bleeding the brakes, I've got an ezibleed kit.

Thanks for the advice

[cal844]

Something leaking or poor adjustment... Check all connections and nipples, remove the rear drums and inspect the wheel cylinders

[AlexMozza]

There is a useful sticky on how to properly adjust drum brakes in the technical section :)

[pdaykin]

Check the tapered washer on the front hub/bearings. If those are worn I've found that can give intermittent pedal feel.

[tiger99]

Yes, anything that causes pad knock - back, ie worn bearings or warped disks, would account precisely for the symptom. If a solid pedal is obtainable while stationary, that strongly suggests that it is not air in the system.

Another thing that changes from stationary to moving is the handbrake. If the rear adjustment AT THE BACKPLATE ADJUSTERS is not as tight as it can reasonably go, ie without heavy rubbing but definitely light contact, all should be well. But if the rears are being held partially on by incorrectly tightening the handbrake cables instead of using the adjusters on the backlplates, then you again introduce lots of extra pedal travel when the handbrake is off. A common problem on various cars, not just Minis, and always due to maintenance error.

But I think that hub bearings and disks are more likely. These creep up on you with the passage of time, and in the case of warped disks, possibly a sustained period of unusually hard use.

Edited by tiger99, 28 November 2016 - 12:58 PM.

[Danyul1275]

Cheers Tiger, will check these out at the weekend weather permitting 

[Cooperman]

As 'Tiger' says, do the following:

 

Back off the handbrake linkage to make the handbrake 'slack'. Jack up the rears and make sure the brake adjusters turn freely (they are prone to seizing up). Back off the adjusters and see if there is any play in the rear wheel bearings. If there is not, adjust the brake shoes until the wheel just locks, then back off the adjuster until the wheel can be turned by hand with a slight resistance. Finally adjust the handbrake cable(s) so that the handbrake operates with a few clicks on the ratchet.

 

Then move onto the front. Jack the car up and see if there is any bearing slack by holding the wheel at the 12 and 6-o'clock position and checking for wheel rock. If there is, remove the wheel(s) and ensure the hub nuts are fully torqued. If wheel rock still exists new wheel bearings are necessary.

 

A warped disc is unlikely, but this can only be checked with a DTI against the disc faces as the hub is rotated. To produce a soft pedal, the warping (run out) would need to be quite significant.

 

Yes, it could be air in the system, but if the problem has developed and fluid level has not gone down it is unlikely. It is worth checking though.

 

God luck with the job.

[Danyul1275]

Brilliant thanks for all the info Cooperman

 

So thankful for this forum 

[Cooperman]

Just one thing. When checking the fronts, make sure any apparent wheel rock is not wear in the swivel hub ball joints. If it is, this will not be a cause of the excesive pedal travel.

[Danyul1275]

Managed to get a chance to have a look over the car finally yesterday, turns out the drive flange bolts on the ns front had worked their way loose! 

 

Good job I stopped driving it once I noticed the problem!

 

Bolts have been replaced now with plenty of threadlock, checked all the other wheels while I was at it.

 

Happy to say brakes are back working as they should, thanks for all the suggestions guys

[tiger99]

Well spotted! That would be the cause of pad knock back which clearly was at the root of the problem.

As you will know, the Mini and a few other classics differ from modern practice in the design of the brake, hub and shaft area. The discs are now generally fitted over the drive flanges and held by a small supposedly non-essential screw. Nothing breaks if the screw is lost. Same for a drum....

However, if it is missing or loose, it is not unheard of for the disc to shift on the studs when the wheel is removed, resulting in muck and rust being dislodged and getting between the mounting faces of the drive flange and disc. So the disc runs a bit wonky (highly technical term!) and you again get pad knock back.

The Mini is arguably better because the interface between drive flange and disc is not disturbed during routine maintenance such as wheel changing. But the fact is that nothing or no-one are perfect. There is always a risk of problems. On any car, after much aggro, I just take great care to clean the mating faces every time they are apart. A good wire brushing, abrasive paper if needed, wipe with clean cloth, and very light film of something like WD40 do the trick. Or something more potent if you want to deter future rusting. I have not had a wonky disk for a long time now. I doubt if the sum total time of such preventive measures has exceeded an hour in 20 years. It takes longer to write about it than do. Some things are quick and clear wins.

I can't remember who taught me about that problem, a long time ago. But someone did and it should be passed on.