Spongy brakes

[Altrezia]

Hey guys,

My brakes are spongy. I've bled them using the guide in the wiki but it didn't help. They work well but I'd prefer a solid pedal.

Any advice would be welcome.

-al

[Grrrmachine]

Old fluid, cracked pipes or failing seals in the cylinder or caliper.

[Speedtouch]

If you followed the Zone Wiki guide to a tee, maybe that is your problem. It states:

"1. When ready, crack off the bleed screw with a proper brake spanner to reduce the risk of rounding off the bolts.
2. Unscrew one quarter turn
3. Have assistant press AND HOLD the brake pedal
4. Retighten bleed screw
5. Have assistant release brake pedal
Repeat steps 2-5 until fluid seeps from the bleed screw. At this point, retighten the screw fully and move to the next wheel. "

This is a strange way to bleed the brakes! Normally, you undo the bleed nipple, then pump the pedal in and out at least 10 times or so until you see that the fluid coming out is clear and doesn't have air bubbles in it, then tighten the nipple before going onto the next one in a sequence, starting with the one furthest away from the master cylinder and ending up with the one closest to it.

[Altrezia]

Well yes, I did it properly. Did it with an eazi-bleed afterwards too. I flushed the old fluid out and replaced it.

Pipes are OK, so I'll have to check other seals I guess

[G-Bear]

I put new seals in my callipers and gave the pistons a good clean and rub down over the summer. Passed on its retest having failed on the brakes the first time round on its MOT..

[Altrezia]

Mine just passed the MOT without any problems - they did replace both rear cylinders for me, but nothing wrong with the fronts (apparently).

Ho hum.

[milescook]

Depends what you're used - Lotus Elises maybe? From experience some people do find E30 brakes a bit spongy in feel comparison to other or modern cars.

The reason I ask is you say they work well but you'd prefer a solid pedal. People have achieved a rock hard pedal with lots of feel here but changing the M/C, pedal boxes etc.

When do they feel spongey to you - all the time or when everything is warmed up?

[Altrezia]

Yeah, my elise has a rock hard pedal - which is what I've driven daily for bloody years.

I'll take the car for a longer drive ASAP and see how it works.

You do you bleed the brakes with the engine off, right? The pedal was hard until I started the car for the first time after bleeding.

[Speedtouch]

Yes, you usually do it with the engine switched off, unless there is some need for the servo to be operating.

What were the brakes like prior to you bleeding them, and did you use the correct fluid?

[milescook]

Of course the different pads may very vary in feel dependant on tempreature too - did you change your pads in the end?

[Altrezia]

Yes, I'm running some bluestuff now. The brakes were fairly solid before the rear cylinders went on, and after I got it back it was a bit spongy.

I used 'Dot4+' racing fluid.

Thanks again chaps

[Andyboy]

A spongy brake pedal on an E30 - i.e one with too much travel as opposed one that goes to the floor and then pumps up - is caused by a bit of wear in the cross linkage. It's easily rectified by dropping the column undertray and glovebox, slackening the 17mm locknuts on the crosslinkage and turning the crosslink bap with long nosed grips to raise the brake pedal around an inch - this transforms the feel of the brakes but don't overdo it.

[Brianmoooore]

Doesn't this machine have rear drums? Everything in good condition there and adjuster working properly?

[Altrezia]

A spongy brake pedal on an E30 - i.e one with too much travel as opposed one that goes to the floor and then pumps up - is caused by a bit of wear in the cross linkage. It's easily rectified by dropping the column undertray and glovebox, slackening the 17mm locknuts on the crosslinkage and turning the crosslink bap with long nosed grips to raise the brake pedal around an inch - this transforms the feel of the brakes but don't overdo it.

Sounds good. My brakes work very well, just a slack pedal. I don't understand your post though. What is a cross link bap - bar I guess? Will stick my head under and see.

Rear drums, just had new cylinders. Nothing broken to report there.

[Speedtouch]

Yes, crosslink bar - necessary for the RHD conversion to operate the master cylinder on the left-hand side of the car.

[Altrezia]

So I just twist it a bit?

[Brianmoooore]

Cross link bar won't give a spongy pedal - just one that doesn't do anything until it's a long way down, and destroys brake light switches.
Just new cylinders, with the existing shoes and drums reused, and put back exactly as they were? The automatic adjuster can fail to work without anything actually being broken.

[Altrezia]

Only the cyls were changed. Not sure how to adjust drums but happy to give it a go. Garage did the cyls for me so not sure what state things were in other than passing the mot.

[Altrezia]

Quick update - bit more info. I just went to move the car because I had to do another little job, and I tried the brakes again - the pedal goes about 1.5-2 inches before doing anything, but then firms up and is pretty hard. The brakes all seem to work OK, and the pedal does not get near the floor at all.

Still think I need to adjust the rear drums?

[Speedtouch]

They should, in theory, be self-adjusting. However, sometimes, these self-adjusters seize up.

I would be inclined to jack the back of the car up, and get an assistant to press the brake pedal while you rotate the wheels and check if the rear brakes work evenly. If they've passed an MOT recently, they should be OK...

[Brianmoooore]

Quick update - bit more info. I just went to move the car because I had to do another little job, and I tried the brakes again - the pedal goes about 1.5-2 inches before doing anything, but then firms up and is pretty hard. The brakes all seem to work OK, and the pedal does not get near the floor at all.

Still think I need to adjust the rear drums?

That's not a soft pedal then!! Give the wrong symptoms, get the wrong answer.
Back to adjusting the cross link - it goes from a bell crank at the top of the brake pedal, across the car behind the heater box, to another bell crank behind the RH side of the glovebox. It has a normal thread on one end and a reverse thread on the other, so turning it changes its length.
Adjust it so that the brake pedal sits just short of as high as it can go.

[Altrezia]

It's soft compared to my lotus.. that thing only moves about 1 inch in total! ;)

Thing is - before I took it for the MOT and rear cylinders, I swear the pedal was harder.

[miniblob]

Interesting read - I'll be adding that cross-link adjustment to the bottom of my very long list!!!

[TheDutch]

Back to adjusting the cross link - it goes from a bell crank at the top of the brake pedal, across the car behind the heater box, to another bell crank behind the RH side of the glovebox. It has a normal thread on one end and a reverse thread on the other, so turning it changes its length.
Adjust it so that the brake pedal sits just short of as high as it can go.

If this has never been messed about with then would it need doing? It doesn't strike me as something that would deteriorate.

[Altrezia]

I agree. It'll be the last thing I change.

I've re-bled the brakes and it's still no better - certainly longer than I'd expect. Will check the rear adjustment stuff ASAP but I got no time today.

[Brianmoooore]

Back to adjusting the cross link - it goes from a bell crank at the top of the brake pedal, across the car behind the heater box, to another bell crank behind the RH side of the glovebox. It has a normal thread on one end and a reverse thread on the other, so turning it changes its length.
Adjust it so that the brake pedal sits just short of as high as it can go.

If this has never been messed about with then would it need doing? It doesn't strike me as something that would deteriorate.

It's the one thing on an E30 that you can guarantee needs adjustment after many years!
Several heavily loaded joints, all of which will have worn slightly over the years, times the leverage ratio of the brake pedal equals a pedal which has dropped considerably from where it was when it left the factory.
ALL RH drive E30s have either had this rod adjusted or need this rod adjusted, unless they have only covered an extraordinary low mileage .

[Fred555]

Altrezia

PostPosted: Thu Jan 23, 2014 2:08 am


Quick update - bit more info. I just went to move the car because I had to do another little job, and I tried the brakes again - the pedal goes about 1.5-2 inches before doing anything, but then firms up and is pretty hard. The brakes all seem to work OK, and the pedal does not get near the floor at all.

Altrezia - if the pedal doesn't go down to the floor no matter how long or hard you hold it down that generally means the hydraulics are OK with no air in the brake lines & not leaking but is the booster vacuum servo OK?

I suppose compared to the hard pedal feel you get if you pump the pedal till the vacuum is depleted in the servo the servo can make it feel a bit soft compared to the no vacuum left in the servo unassisted feel which is rock hard at the very end but with nothing happening for the first part of travel.

Check if the rubber servo diaphragm has failed and split - can the servo hold vacuum? Is the hose to the servo solid & are its hose clamps secure? - Is the one way valve in the vacuum hose to the brake booster working? Or is vacuum leaking out of the servo because the big rubber "O" ring between the master cylinder and the servo is no longer intact?

[Altrezia]

Thanks Fred - all good info.

I cannot get the pedal to the floor at all. It just feels spongy for the first inch or two compared to how it was before the rear cylinders were done, and compared to my other cars.

[Brianmoooore]

If the sponginess appeared after the rear brake work, the cause is that the brake shoe surfaces are now not perfectly parallel to the friction surface of the rear drums.
The worst case possibility is that the drums or shoes were swapped from their original positions, but it could just be that it's impossible to put everything back in exactly the same place as it was, the adjusters haven't settled properly, or they weren't working properly before, allowing the shoes to wear incorrectly, and now they are.
Hopefully they will bed in again over time.

[Altrezia]

That'd make sense.

I'll whip the drums off when I get a few minuts (I know I keep saying that...!) and make sure everything is A-OK.

How can you tell, visually, if the self-adjustment thingies aren't working?

Thanks again - much appreciated.

[Speedtouch]

It should be fairly obvious just by looking at them; they should have unwound themselves a bit:



If they appear to be stuck in the closed position, or are obviously corroded, then further investigation will be required.

[Altrezia]

Great, thanks. You lot are brill.

[Fred555]

Altrezia

PostPosted: Wed Jan 22, 2014 4:55 am


Yes, I'm running some bluestuff now. The brakes were fairly solid before the rear cylinders went on, and after I got it back it was a bit spongy.

I used 'Dot4+' racing fluid.

Thanks again chaps Smile

Presume the rear cylinders were leaking which is why they were changed (probably like that when you got the car - BTW worn drums = excessive internal diameter can cause otherwise good rear cylinders to leak as the pistons are allowed out too far by the too big drums - if you see what I mean).

So IF the rears were leaking - because the master cylinder is deliberately split into separate circuits for safety against leaks (front to back - I think?) which means the Master Cylinder (MC) chamber that serves the rears would squeeze the fluid out of the first section of the MC but leave the other section intact and able to still pressurise the fronts.

BUT instead of transferring force normally to the divider piston via the pressurised brake fluid only & not by direct contact in the event of a leak one or the other chamber will not press on the other using hydraulic force but instead one will press directly on the other making physical contact within the length of the master cylinder - it is quite hard to explain it would be best if you looked at a cutaway diagram of a master cylinder - so the pedal would feel very different if there was a leak as the MC chambers would be pressing on each other physically directly instead of using hydraulic pressure alone and never making physical contact. Phew what a mouthful.

That might be why the pedal now feels different - leak gone after rear cylinders changed so MC now working normally.

[E30REDD]

I agree. It'll be the last thing I change.

I've re-bled the brakes and it's still no better - certainly longer than I'd expect. Will check the rear adjustment stuff ASAP but I got no time today.

I have the exact same problem as you do.

When the engine is off the brake pedal feels pretty ok. In the beginning it's easy to push down the pedal but the further you push it, the stiffer it gets. When I turn on the engine I can push the pedal even further (can't floor it) and it gets mooshy.

The breaks are working good, it's just that the first 40% of pushing on the brake pedal won't make the car brake much at all, you will barely feel it breaking. If I push it harder it will break just perfectly.

I have bled the system, some air came out the first time I bled it but the pedal was still mooshy. I even bled out all of the brake fluid in the system and replaced it with new brake fluid (DOT 4). The brakes does still feel mushy, no change whatsoever.

I have adjusted the rear brakes (drums) with the star adjuster, which basically pushes the shoes out towards the drum, making the rear brakes to start braking sooner than before. This did only affect my breaking a bit, the breaks works better because the rear brakes are being more used now. Before I adjusted the rear shoes, the car was maybe using 10% of the rear brakes and now it uses 30%. I don't know the exact percentage but you get the point.

However this has not made the brake pedal less mushy and I believe there is some bad sealings in the master cylinder, or could a leaking vacuum hosing be causing those problems?

What is the next step I should check?

[Fred555]

Does either car have ABS? Can you even have ABS with rear drums?

ABS also makes it harder to successfully bleed air out of the brakes - it is best not to drain the fluid out completely letting air in & then bleed air back out again on an ABS equipped car.

The ABS valve unit is what makes it more difficult to get the air out - just flush through with lots of fresh fluid on an ABS car.