12 replies to this topic

[DaneK]

Hi All,

I have a 1994 Mini Sprite which I've had sat in a garage for around two and a half years and only recently got it MOT'd and back on the road (girlfriend finally graduated Uni). It passed the MOT with flying colours but I've noticed the rear end snakes about under heavy braking:

- It has a type 4 tandem master cylinder with a front-to-rear split dual braking system (later type).

- I've had the back up in the air with my glamorous assistant pressing the brakes and I can't spin the wheels by hand. 

 

Any ideas on how to diagnose/ fix the issue? 

 

Thanks, Dane.

[cal844]

Possibly rear suspension alignment issue?

[Guess-Works.com]

Quite possibly an issue with the master cylinder... or the PDWA

 

basically, it's pumping fluid to the rear cylinders, enough to pass an MOT as the mini is a very light vehicle, but not enough to have an effect on braking in normal use, therefore most of the the braking is being done by the front brakes ( more than normal ) this will have a tendency for the back end wanting to swap with the front end.

[carbon]

+1 for Guesswork's suggestions.

 

As it has been laid up for a while would recommend:

- take rear brake drums off, and clean out the insides.

- if there is any rust on inside of drum where shoes rub, clean off with fine emery paper until spotless

- check for any signs of brake fluid leakage from rear cylinders getting on to brake shoes

- check condition of rear brake shoes, if in doubt replace

Edited by carbon, 10 August 2015 - 04:51 PM.

[DaneK]

Thanks,

Do you have any tips on how I would go about diagnosing if it's either the master cylinder or PDWA? I'd like to try and pinpoint where the issue is rather than preemptively replacing both components.

Dane.

[carbon]

Dane, I can't advise you on the master cylinder or PDWA as I don't have any experience with either of these.

 

My comments about the rear brake drums are based on experience with older minis, which should also hold true for your Sprite.

[Steve220]

Also check subframe mounts/rubbers.

[carbon]

Steve makes good point here.

 

If the front subframe rubbers or other front suspension components are getting a bit slack then you could get instability under heavy braking.

[DaneK]

Thanks fellas,

I've checked the rear drums. No rust/ score marks, plenty of pad left. Brakes re-adjusted to compensate for wear.

Points well taken, I'll do a bit more digging in to front suspension, master cylinder and PDWA.

Dane.

[Spider]

Actually, I would have said it sounds like it has too much rear braking (bias). Again, check the PDWA, and also the size of the rear wheel cylinders.

[nicklouse]

I would be looking at the front brakes. Imbalance on the rear tends to show up with a locked wheel.

If you are not locking up a rear wheel then I would not be looking at the rear brakes.

I would be having a real look at the subframe mounts. FRONT.

Under heavy braking the front creates most of the feel the rear just tends to follow as there is very little load there.

Not saying not to bother checking but if you can't see an obvious issue at the back get looking at the front.

[DaneK]

The best way to describe it is under heavy braking, the rear tries to overtake the front. To me it feels like the rear brakes are doing very little.

[Spider]

Well, in addition to checking the rear brakes as I suggested ^^, is a Trailing Arm(s) bent?  Or worn Trailing Arm Pins & Bearings?