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Brake over-pressure worry
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Author:  mollymoke [ Sun Nov 18, 2007 6:10 am ]
Post subject:  Brake over-pressure worry
Hi all,

My newly found Mini K has an aftermarket style plastic bottle brake master-cyl. which was fitted 2003.

But what I'm finding is that when I've braked a few times the brakes feel like they are over-adjusted, and they bind, and get hot if you keep driving.
I've checked and it is all wheels (was thinking the hand brake cable was stuck). If I stop for 5 minutes or so it settles down, but quickly builds up again.

So my questions are:
Is the problem related to the master cylinder 'pre-load' valve, or some non return valve, or just an inappropriate master Cyl?

Of course I'm tempted to find the correct Cyl. and replace it, but will that fix the problem?
Author:  drmini in aust [ Sun Nov 18, 2007 7:38 am ]
Post subject: 
It sounds like the restrictor valve in the MC is faulty, acting as a non-return valve. I'd strip it and replace the valve. A $10 seal kit includes a new one.
The current plastic tank 0.7" bore MC is the brake right one for a K.
Author:  9YaTaH [ Sun Nov 18, 2007 7:40 am ]
Post subject:  Re: Brake over-pressure worry
mollymoke wrote:
Hi all,

My newly found Mini K has an aftermarket style plastic bottle brake master-cyl. which was fitted 2003.

But what I'm finding is that when I've braked a few times the brakes feel like they are over-adjusted, and they bind, and get hot if you keep driving.
I've checked and it is all wheels (was thinking the hand brake cable was stuck). If I stop for 5 minutes or so it settles down, but quickly builds up again.

So my questions are:
Is the problem related to the master cylinder 'pre-load' valve, or some non return valve, or just an inappropriate master Cyl?

Of course I'm tempted to find the correct Cyl. and replace it, but will that fix the problem?


If the shoes are brand new/oversize that will give the same symptoms...maybe pull the drums to see what is going on..they may just need to be backed-off :?:
Author:  TheMiniMan [ Sun Nov 18, 2007 9:23 am ]
Post subject: 
I would make sure that the mastyer cyl piston is returning properly first, sometimes if the spring is weak or broken or the wrong one then the piston assy won`t return fully & therfor doesn`t come back to clear the recovery hole inside the cyl to the resovoir. If some dork has fitted the wrong type seals inside it & they`re tight in the bore then that will cause it to not return fully too & be very slow to do so even if it did.

This can also be caused by the wrong type/length master cyl pushrod.

it also can be caused by crap/grit/poo jammed in the "Slow return Valve" or it can be the wrong one or it can be buggered (as DR Kev suggested)

However---> ("""IF""") ALL 4 brake hoses are stuffed & swollen & perished & all yukky-poo, then that can cause a similar symptom.

Mick, i see no reason why oversize shoes would cause brake grabbing "IF" they`re set up correctly & not over adjusted ---> & as the punter says, leave it for 5 mins & the problem is gone again, so i doubt it`s an oversize shoe problem

I also doubt that all 4 wheels have sticky cyls, but i spose it`s a possibility also, just highly doubt that all 4 wheels happen to get all sticky at once.

so my bet is that it`s master cyl related problem also

Have you got a brake booster/servo fitted????
Author:  9YaTaH [ Sun Nov 18, 2007 10:44 am ]
Post subject:  Shoes
TheMiniMan wrote:
Mick, i see no reason why oversize shoes would cause brake grabbing "IF" they`re set up correctly & not over adjusted ---> & as the punter says, leave it for 5 mins & the problem is gone again, so i doubt it`s an oversize shoe problem


Matt...we have all seen it...you get new shoes and they may have high spots or are very tight in the drum when near completely backed off.

Ifn the brakes are "dragging" then they will certainly heat up the hubs and bind - so...wait till they cool down and hey presto they roll again.

Just my 5c
Author:  simon k [ Sun Nov 18, 2007 7:53 pm ]
Post subject:  Re: Shoes
9YaTaH wrote:
TheMiniMan wrote:
Mick, i see no reason why oversize shoes would cause brake grabbing "IF" they`re set up correctly & not over adjusted ---> & as the punter says, leave it for 5 mins & the problem is gone again, so i doubt it`s an oversize shoe problem


Matt...we have all seen it...you get new shoes and they may have high spots or are very tight in the drum when near completely backed off.

Ifn the brakes are "dragging" then they will certainly heat up the hubs and bind - so...wait till they cool down and hey presto they roll again.

Just my 5c


nah.... you're smoking something Mick... the brake material doesn't expand under heat!
Author:  9YaTaH [ Sun Nov 18, 2007 8:08 pm ]
Post subject:  Re: Shoes
simon k wrote:
nah.... you're smoking something Mick... the brake material doesn't expand under heat!


Grasshopper....you have much to rearn 8)

If the new linings are a little too fat/have high spots...they are in contact with the drum inner surface...and guess what :?: Friction = heat :roll:

Whenever you fit new shoes, adjust and inspect frequently when bedding in.

Feel your hubs/hub caps after each "spirited" run....coz you are heating up the grease in your hubs as well :idea: :D
Author:  Morris 1100 [ Sun Nov 18, 2007 8:16 pm ]
Post subject:  Re: Shoes
9YaTaH wrote:
simon k wrote:
nah.... you're smoking something Mick... the brake material doesn't expand under heat!


Grasshopper....you have much to rearn 8)

If the new linings are a little too fat/have high spots...they are in contact with the drum inner surface...and guess what :?: Friction = heat :roll:

Whenever you fit new shoes, adjust and inspect frequently when bedding in.

Feel your hubs/hub caps after each "spirited" run....coz you are heating up the grease in your hubs as well :idea: :D
When the brake drum heats up it will expand... away from the linings. :D
Author:  simon k [ Sun Nov 18, 2007 10:45 pm ]
Post subject:  Re: Shoes
9YaTaH wrote:
simon k wrote:
nah.... you're smoking something Mick... the brake material doesn't expand under heat!


Grasshopper....you have much to rearn 8)

If the new linings are a little too fat/have high spots...they are in contact with the drum inner surface...and guess what :?: Friction = heat :roll:

Whenever you fit new shoes, adjust and inspect frequently when bedding in.

Feel your hubs/hub caps after each "spirited" run....coz you are heating up the grease in your hubs as well :idea: :D


uh huh..... I adjust and inspect my rear shoes before each motorkhana ;)

I'd still be bloody worried if my brake shoes expanded when they got hot tho!

wouldn't that sh1t you.... you put all that effort into adjusting them properly, then you go out and get them hot and the suckers start locking up on you cos they got fatter? :lol:
Author:  drmini in aust [ Mon Nov 19, 2007 5:04 am ]
Post subject: 
Only time I ever find brake shoes tight is when people have tried to fit oversize linings into a standard drum.
If the shoes match the drum diameter (std, + 1/32", or + 1/16") there should be no problem.
I do put a chamfer on the ends, as many brake bonding shops don't seem to bother with now.
Author:  mollymoke [ Mon Nov 19, 2007 7:23 am ]
Post subject:  Brake Preasure
Ok thanks for the advice, and no I don't think shoes expand.
I'm assuming it must be the master-Cyl, it has done very few miles since it was replaced ('a couple of Classic Adelaide runs only, so the PO tells me and the fluid is still 'very' clean) and most of the hoses look good.
I'll find the correct type and replace it, update you then.

Chris
Author:  feralsprint [ Mon Nov 19, 2007 8:29 am ]
Post subject: 
Last year I had to do the brakes on the wifes Mazda, needed a new mastercylinder and as they couldn't get one in a hurry had the old one rebuilt and sleeved, picked up the cylinder and a new bottle of fluid from the brake place and fitted it all up(one caliper rebuilt as well) bled it all up with the new fluid and away she went, got a call a bit later that the brakes had locked on. Went a got the car home by releasing the pressure from the system by cracking one of the unions on the lines open and then started to have a look, the new fluid had like a vaselien substance floating in it, dropped the MC back off and took it back to the brake shop and they said it was fluid contaimation, lucky for me that being a tight ass I had saved the old fluid from taking it the first time in a jar and had the new bottle they had supplied, nothing in either, I can only guess what they had used to reasemble the cylinder but they swore black and blue it was our fault untill I shoved the 2 containers of braake fluid under there nose then it wss oh we are sorry turns out the stuff was clogging the return valve up and another revuild and complete flush was required

Jon
Author:  9YaTaH [ Mon Nov 19, 2007 6:06 pm ]
Post subject:  Re: Brake Preasure
mollymoke wrote:
Ok thanks for the advice, and no I don't think shoes expand.
I'm assuming it must be the master-Cyl, it has done very few miles since it was replaced ('a couple of Classic Adelaide runs only, so the PO tells me and the fluid is still 'very' clean) and most of the hoses look good.
I'll find the correct type and replace it, update you then.

Chris


I don't think they expand either, don't ever remember saying that...however...I know for sure that sometimes new brake shoes can drag, heat up the whole hub etc and "bind".

The other thing is, that the drums wear a high spot in the centre and are no longer round...thats why you need to check them for concentricity :shock:

Nothing like the smell of burning brakes in the morning :D
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