Spongy Pedal and Poor Brakes

[Mr_Spanners]

I've just finished draining\replacing the brake fluid for some fresh Motul RBF600 in the hope that it might improve the spongy pedal and overall poor brakes.

I've bled the system 3 times (with the help of a mate pressing the pedal!) and the pedal feels firm when pumped up but when driving the pedal travel is excessive and the braking performance is very poor (takes an age to stop!). The new fluid hasn't improved the pedal or braking at all.

The rear pads look fine and the fronts are about 60% worn although they have been on the car for over 10 years!

I'm wondering now whether the seals in the brake master cylinder have gone or whether the front pads are shot??? Maybe it's time a I changed both? What's the general consensus with such a problem? I'd really like the brakes to have a nice bite and firm pedal!

Any comments\suggestions welcome!

~Phil.

[MartG]

Have you dismantled and re-greased the caliper sliders ? ( white lithium grease or red rubber grease )

[widster]

It wouldn't cost you much to change the front pads so i would try that myself.

[Bender Unit]

Keep at it, if you have drained the oil there will be alot of trapped air in the system. I had to do it more times then I care to count when I did mine. Also check and grease all the sliders etc. What state are the calipers in?

Pads can go off, I had this on 1 side.

[Mr_Spanners]

Keep at it, if you have drained the oil there will be alot of trapped air in the system. I had to do it more times then I care to count when I did mine. Also check and grease all the sliders etc. What state are the calipers in?

Pads can go off, I had this on 1 side.

Calipers seem fine - handbrake is perfect (really!) and the car stops in a straight line under full pressure braking (shame the pedal is soft and unresponsive!). I did expect the problem to go away with the fluid change but it's exactly the same as it was. Will try new front pads and grease the sliders first before replacing the master cylinder.

Thanks

~Phil.

[MartG]

Check that none of the brake flexible pipes are expanding when you hit the brakes. You'll need to have the engine running when you test it so that the brake servo works, otherwise you can't apply enough pressure.

[coverco]

I thought you were getting rid of your MK1 Phil, off topic I know but just interested

[Bender Unit]

If it was bad before then it might also be worth doing the brake master cylinder as well?

When bleeding start off with the brake nearest the servo and then work your way around, doing the furthest away last. If you have replaced the fluid there will be alot of air trapped and it sometimes takes alot of passes to get it all out.

Once you think the air is out, pump the pedal hard and repeatedly before taking it out onto the road - it can take a few good pumps to properly seat the brakes and get the full braking force.

[monkeyra]

Just a FYI (which now explains my brake situation), the brake pedal should have about 117mm travel when pushed with a 50kg load... So if you've got long pedal travel (like I have), it's perfectly normal.
Mine feels spongy, but push far enough, and brakes damn well. I've got AP Racing brakes on my ST220, so it's always a bit of a surprise when I go to brake in the tubby

[mr2mk1chick]

It may be that you still have air in the master cylinder bit. try a re-bleed going round in order as described in an earlier post, plus bleeding the master cylinder.
I have also heard of people leavign something heavy on the brake pedal overnight too.

[crazylegs]

the brakes in the mk1 do have a bit of travel but should not be spongy. the mk1 had the best braking performance of its day and still is up there even now. if you want a more pronounced feel then a st185 conversion will give you this or maybe swap for a different master cylinder. i believe a turbo one is a direct fit. Have a look on twobrutal they have an extensive section on brake conversions/mods. be warned though you may well upset the balance.

[Tiger Tim]

I had a lot of trouble with spongy brakes last year but eventually resolved them. I checked the rear pads at one side before I changed the calipers & they were perfect. I assumed the other side were fine & left them in place when doing the calipers at that side. Turned out that the old calipers on one side had been binding & the pads had been roasted & gone off. Changing the rear pads helped sort the problem.
I would put new pads all round - they're cheap

A few things I did. Not sure if they are of any use but here goes:

1. Disconnect the handbrake at the calipers. Screw pistons all the way in & back out 180 degrees to line up with notch on pad.
2. Started engine & left running ( a mechanic told me this helps)
3. Bled from furthest away first( rear passenger,the rear drivers side, then front passenger & finally front drivers)
4. Reconnect handbrake & adjust

It took a while but worked for me

Tim

[ligertigon]

Don't forget to check the vacuum tube to servo and inlet manifold.

[Mr_Spanners]

Thanks for all the advice! I'm going on hols next week but will get the car out of the garage sometime early in March to sort this.... I'll report back!!!

~Phil.

[HighwayStar]

Do you think a set of braided lines might help also ... how many years will the original rubber lines be now from manufacture? I know it was mentioned before but not the solution. Saw an unused set in the for sale section a while ago for £50ish I think (they were SW20 though).
Just a thought if all the bleeding doesn't create a resolution.

R.

[Mr_Spanners]

OK, I've spent a fair few hours on the brakes. Replaced all the pads (front and rear) and also freed up the slider pins which were a little stiff on a couple of the calipers.

Took car out and there's still excessive travel in the brake pedal and the spongy feel and poor braking is still there

Next job is to replace the master cylinder.... can't think what else could be the problem? One thing that is weird is the pedal pumps up solid when the car is stationary and switched off yet the pedal travel is much greater when the car is running - maybe the vacuum to the servo is an issue???

[MartG]

One thing that is weird is the pedal pumps up solid when the car is stationary and switched off yet the pedal travel is much greater when the car is running - maybe the vacuum to the servo is an issue???

Err, no - that's normal. Without the engine running, you don't have servo assistance with the brakes, so the pedal feels a lot harder 'cos you're only applying a fraction of the pressure onto the master cylinder compared to when the servo is assisting you.

If it still feels spongy, before looking at the master cylinder make sure the flexible brake pipes aren't 'ballooning' under pressure. Simplest way to firm them up is to replace them with braided ones e.g. Goodridge

[Mr_Spanners]

One thing that is weird is the pedal pumps up solid when the car is stationary and switched off yet the pedal travel is much greater when the car is running - maybe the vacuum to the servo is an issue???

Err, no - that's normal. Without the engine running, you don't have servo assistance with the brakes, so the pedal feels a lot harder 'cos you're only applying a fraction of the pressure onto the master cylinder compared to when the servo is assisting you.

If it still feels spongy, before looking at the master cylinder make sure the flexible brake pipes aren't 'ballooning' under pressure. Simplest way to firm them up is to replace them with braided ones e.g. Goodridge

But if the pedal pumps up solid with no servo assistance (e.g the engine isn't running) doesn't this suggest the master cylinder is fine??? I'm now wondering where the problem lies.... but will ask a mate over to pump the pedal while I check all the brake lines.

Any other suggestions as to what to check would be welcome!!!

~Phil.

[MartG]

Yes, it doesn't sound like a master cyl issue to me, more like flexi brake lines deforming when you apply greater pressure with the help of the servo

[Mr_Spanners]

Yes, it doesn't sound like a master cyl issue to me, more like flexi brake lines deforming when you apply greater pressure with the help of the servo

Thanks Mart - Will do some more investigating.....

Cheers

~Phil.