Spongy Brakes

[cubensis]

Hello all, about 3 weeks ago my brakes failed on the motorway. That is to say the pedal went straight down to the floor, after pumping the pedal it would build pressure and break normally. I pulled over on the hard shoulder and i'd either left the handbrake on one click or the drums had ceased on because the rear wheels and drums where very very hot on both sides.

So, I believe once you cook the brake fluid it should be replaced and the system should be bled? I have just had this done at the garage for £75 however it has made no difference to my problem which is?

The problem is the brakes feel very spongy and the brake pedal now goes down lower than it did before, which means I sometimes press on the accelerator when braking. Just like before when I pump the pedal the brakes go really firm. I had the mechanic that changed the brake fluid have a look at the drums and he said they were fine, I was also wondering if there was a weak spot in the brake hose that was causing a bubble somewhere, he said he'd checked this but i'm not totally convinced by the way he answered I think he may have forgot.

Anyway, I was wondering if anyone could shed any light on my spongy brakes? It's a T25 1986 1.9 petrol.

Cheers!

[AdrianC]

So, I believe once you cook the brake fluid it should be replaced and the system should be bled?

More of a case of the brake fluid boiling being a symptom that a change of fluid is LONG overdue. Just bleeding isn't enough - you need to change the fluid completely. Don't forget that the clutch shares the same reservoir.

The problem is the brakes feel very spongy and the brake pedal now goes down lower than it did before, which means I sometimes press on the accelerator when braking. Just like before when I pump the pedal the brakes go really firm.

There's either still some air in there, or something's preventing the rear brakes from adjusting up properly, so the first pump just takes up the slack.

I was also wondering if there was a weak spot in the brake hose that was causing a bubble somewhere

It's unlikely but possible that a flexi is ballooning under pressure.

[cubensis]

Hi, thanks for your reply.

Yea the new brake fluid was pumped in while the old was pushed out, then it was bled.

I asked him to look at the rear drums and he said they all looked fine and performed as they should, maybe air in there but I would have thought this would have been solved by the new brake fluid?

I know it's unlikely but i'm now thinking ballooning brake hose is the most likely cause.

Thanks for your help, maybe i'll take it to another garage for a second opinion.

[California Dreamin]

Hi there,
Several observations:

Spongy brakes are normally down to 'air' in the system.
It is possible that the rear brakes need adjusting and the shoes to drum 'clearance' is excessive but this would normally be easy to diagnose by either: pulling the hand brake on to see if the footbrake is significantly 'higher' or pumping the pedal 2 times in quick succession and again feeling if the pedal height 'bite point' is significantly higher on the second pump.

If he removed the drums then he 'MUST' have checked the wheel cylinders for leaks...so we can hopefully count on his expertise that the brakes themselves are in good condition.

Yes it could be a ballooning flexi pipe but this is pretty rare.

The only other thing that springs to mind is a damaged tandem seal in the master cylinder which can occur after old fashioned brake bleeding (using the full stroke of the brake pedal to bleed brakes) or are you saying he used a pressure bleeder?

Either way mate.....at £75.00 it's down to him to get it right I would have thought.

Martin

[cubensis]

Hello, thanks for your reply.

Yea it sounds like air in the system to me too, although I would have thought the chances of the air staying there when new brake fluid was fed in was slim? To be honest I am not overly familiar with the process but think I can visualise the principles.

So, when you say put the handbrake on; do you mean I should put the hand brake on, and then check if the brake pedal has raised?

When i press the brake the first time it sinks slightly lower than it did previously, as I mentioned I can sometimes rev quite high because I press the accelerator. However I have got into the habit of pumping the brakea second time when stopping, and the second pump becomes much firmer and much more responsive (and the pedal is higher).

Yes I think he did check the master cylinder and he mentioned that this can need replacing when flushing new brake fluid. Does this sound right?

I am not sure which method he used (brake bleeder / full stroke of brake pedal). Is the tandem seal easy to change?

To be honest they have done an okay job the last few times we have took the van there but i'm starting to questions just how thorough they are hence the above question.

Thanks for your time and education as ever - John.

[kevtherev]

if the rear shoes are not adjusted up then you'll have to pump.
as Martin says

[California Dreamin]

1) Yea it sounds like air in the system to me too, although I would have thought the chances of the air staying there when new brake fluid was fed in was slim? To be honest I am not overly familiar with the process but think I can visualise the principles.

2) So, when you say put the handbrake on; do you mean I should put the hand brake on, and then check if the brake pedal has raised?

3) When i press the brake the first time it sinks slightly lower than it did previously, as I mentioned I can sometimes rev quite high because I press the accelerator. However I have got into the habit of pumping the brakea second time when stopping, and the second pump becomes much firmer and much more responsive (and the pedal is higher).

1) Sometimes brakes can be a right pig to bleed and it is not uncommon to have to bleed a second time.
2) Yes..handbrake on...is the footbrake considerably higher and firmer on the first application of the pedal? if so then rear shoe clearance adjustment sounds suspect and needs fettling (manually adjusting and NOT by the hand brake cable but on shoes themselves)
3) Air in the system or rear shoe adjustment....it could be either or both.

Martin