New brakes, new problem. Help please

[Pondrew]

Over the last couple of days (yes it's taken that long, don't ask!) I have changed all discs and pads on my daughter's Mini, so I can be finally happy for her to use the bloody thing. All the discs were massively under minimum thickness, had huge edges on them and the pads were pretty much down to the backing (wear sensors had been disconnected and tied up).

I finished them this afternoon, all looking good, bolts tightened, pad springs renewed, etc, etc. So I took it out for a test drive.

Brake pedal goes to the floor with very little braking effect! I didn't expect the pads and discs to be great out of the box, but there is something amiss with the hydraulics! Feels like someone has changed the fluid for sponge!

I didn't disconnect the brake lines, all calipers were tied up while working on each corner. No fluid leaks anywhere.
The reservoir did overflow as I had to wind all four pistons back a long way, due to how 'used' the old discs and pads were.

The reservoir is still full of brake fluid. I can pump the hydraulic pressure up with the pedal but it just goes away again, instantly!

Any ideas? Could I have got air in the system from the reservoir overflowing? I'm stumped and it is pi*sing me off!

 

[B21]

Air in the system..purge each brake starting at the back…I use an eazy bleeder to help do it with just one bod..

If you are really lucky you’ve got some air in the DCS unit

 

[Pondrew]

Air in the system..purge each brake starting at the back…I use an eazy bleeder to help do it with just one bod..

If you are really lucky you’ve got some air in the DCS unit

I don't understand HOW I got could have got air in the system, though!

Never bled brakes before! Makes me a bit nervous TBH.

 

[smorris_12]

Sounds like the master cylinder. When they get old large amounts of travel or having fluid pumped the wrong way can upset the seals. If it was air in the system I wouldn't expect the pedal to ever get hard as it acts like a perfect spring.

OB side note: what is it with mechanics only ever changing pads no matter the state of the disc? I see this again and again. Are they just lazy? You'd think adding on a set of discs would bring them even more money[1] in and, with it on a ramp and with air tools to hand, it's hardly much more effort.


[1] I boggle at what garages charge for doing brakes. I suppose it's a money spinner and no-one will argue with a safety critical thing.

 

[Pondrew]

Sounds like the master cylinder. When they get old large amounts of travel or having fluid pumped the wrong way can upset the seals.

Is there a way I can ascertain this for sure, myself? I can't even find the master cylinder at present! :roll:

 

[Rockhopper]

Master cylinder is likely directly underneath the reservoir.

 

[Pondrew]

Thanks all for the help.
I think it IS the master cylinder seal (or something wrong with the MC) as it will pump up hard with the engine off and stay like it, but with the engine running it will pump up and then slowly sink with pressure on the pedal.

I have now spent more money on this poxy car than all my others put together in two years! And it still can't be driven.

Four new tyres
Three wheels straightened
One new (used) wheel
discs and pads all round
now this!

 

[pvr]

I have now spent more money on this poxy car than all my others put together in two years! And it still can't be driven.

If you had bought a Jaguar, it would have been the second most expensive intead of the most expensive :evil:

 

[Pondrew]

A little update for anyone interested..

Air in the system..purge each brake starting at the back…

Incorrect....again!

Sounds like the master cylinder. When they get old large amounts of travel or having fluid pumped the wrong way can upset the seals. If it was air in the system I wouldn't expect the pedal to ever get hard as it acts like a perfect spring.

Thanks for this. I think this was exactly the problem. I reckon I turned the seals 'inside out' as it were by forcing fluid the wrong way. After leaving it pumped up with pedal pressure overnight, it was much better the next day. Not great but better. Pedal no longer went to the floor with the engine running.

I took it out again to test it. It was better. Once home I noticed all four discs were extremely hot even though I had only done a few miles around town. I lifted each corner and checked how free each wheel was. All four were binding very slightly.
As the discs are all new, I could see where the pads were touching the discs. It wasn't even on any of them. The nearside rear was discoloured where it was getting too hot (I presume).

So I took all calipers and pads off (again). I removed the caliper slide pins, cleaned them and re-greased (high temp grease). Greased all pistons around the rubber dust boots, sanded the edges of the pad 'wings' to remove any paint and get them totally flat. I then put a tiny bit of grease in the pad sliding clips and re-assembled.

Much better. All discs are now running much cooler and the pads are sitting flat on the disc surfaces. Still need a bit more 'bedding in' but it now stops so I am finally happy to let my learner driver daughter out in the bloody thing.

 

[mr wilks]

No offence intended nut you clearly don't have much experience in this field so why would you choose a daughters runaround to start exploring your mechanical skillset :? this a perfect example of why as a buyer i am always wary of owners who say they carry out the maintenance themselves
Didn't you notice the brakes were shot when you were buying ? rookie error there mr P

 

[Pondrew]

Didn't you notice the brakes were shot when you were buying ? rookie error there mr P

I knew the brakes needed changing, yes. It was tricky telling the wheels were buckled and cracked, though. :roll:
I carried out the exact same brake work on the E89 when I bought it without any issues whatsoever. The brakes on that were (and still are) perfect. Maybe it's a Mini thing, or a brake parts thing, or maybe it's just a crap car. Not sure.

 

[smorris_12]

Buying second hand cars is a lucky bag. They'll be stuff that's fine, stuff the owner is keeping schtum about and stuff they didn't realise had anything wrong with it. Lipped discs and worn pads wouldn't worry me in the slightest (see my earlier comment about mechanics) and there's no way of telling seals that are about to imminently fail, even if you spent hours crawling over it.

There's odd lurking problems that no-one would find unless you absolutely stripped down every last nut and bolt which may show up in a week or not for another 10 years.

 

[Southwestz4]

I always crack the bleed nipple and let excess fluid out to prevent this sort of problem