Brake problems - opinions required!

MrNorm · Post by **MrNorm** » Thu Mar 24, 05 12:27 pm

Recently completed my brake system, which is good news, but I have a problem! Think it must be a dud master cylinder but I need your opinions.

The whole system is new - calipers, lines, prop valve, linelock, master cylinder etc etc (actually the rear wheel cylinders I reused).
I bench bled the m/c, fitted it and filled the system (brake fluid everywhere, and me with my nice new paint

). Got a number of leaks, unusally for me I must have not tightened a few fittings enough, so after a lot of tweaking they are all dry. Gravity bled whole system twice, and the pedal pretty much still went to the floor. Then I pump bled the system 2 or 3 times, but the pedal is still no good. If you pump the pedal a lot it improves, and the brakes are definitely working, but it is not at all right. Normally this would indicate a faulty m/c to me.

As mentioned, the m/c is new, but it has sat inside the house for many years. All the ports were plugged, and there was still fluid in the orifices! But all I can guess is that the seals have dried up or something. In fact, I nearly disassembled it beofre fitting just to check, but decided not to!

Any thoughts, or am I right in my diagnosis?
A real pain if I need another m/c. I do have a used spare but that has not been used for a similar length of time. If I do get another one I think I might go straight to an aluminium 2 bolt. Saves weight, and less mess without the rubbish 'bail wire' cap??..

Holly · Post by **Holly** » Thu Mar 24, 05 12:34 pm

I'm guessing the fluid level doesn't go down, so M/C will be the likely suspect

Dave-R · Post by **Dave-R** » Thu Mar 24, 05 1:44 pm

Once you get the pedal hard, if you keep your foot on it does it slowly sink?

If so it is the MC for sure. If not it could still be the MC or air but you seem to have ruled out air pretty much anyway.

Derek · Post by **Derek** » Thu Mar 24, 05 7:41 pm

I had this sort of problem, turned out that one of the calipers was not bleeding propaly, so got a friend to push the pedal down and when he released the pedal slowly I pushed the piston back with a piece of wood, did this a few times and it was fine

latil · Post by **latil** » Thu Mar 24, 05 10:38 pm

I trust you've checked the pedal/pushrod is returning fully? Try pumping until hard & get someone to open the bleed , it'll spray but gets things moving ! LWB landrovers suffer coz they have two w/cyls each side on the front & get airlocked and won't bleed

MrNorm · Post by **MrNorm** » Fri Mar 25, 05 3:24 pm

Thanks a lot so far, helpful coments.....

Well, had another quick play this morning. Although the pedal takes a lot of pumping up, I think it is not sinking back once it's pumped up (I'll double check later - there was no detectable difference after a minute or two of holding it).

AND...one of the calipers at least is not releasing properly when you come off the pedal. It is still grabbing quite hard. I've levered it back then pressed the pedal a few times but no change. I'll need to wait until tomorrow when the missus can help on the pedal.
So - maybe I can free that caliper up, or maybe it has rusted internally (the calipers have also been packed away inside for years). We will see!
Could that be the source of the trouble? Could it be stopping the brakes from bleeding properly?

BTW - how much should the calipers be returning by themselves - I thought it should be only a mm or so under the tension of the rubber seals?

Dave-R · Post by **Dave-R** » Fri Mar 25, 05 3:29 pm

Sounds like air in there for sure. Normally the calipers only push back as far as the rotating disc pushes them.

Anonymous · Post by **Anonymous** » Sun Mar 27, 05 2:21 pm

hi mate i get this every week at work, sticky pistons in calipers, only real cure is to strip and clean them, making sure all the crud is removed from the groove where the seals sit, a wire brush on a dremmel or similar tool is a real quick way of doing it , as for bleeding a mighty vac tool is excellent for dragging the fluid through they cost about ?50 but well worth it , i got told off a guy on a course once that the pistons are pulled back from the disc by hydraulic depression, if your seals grooves are grotty it stoppes the piston returning because the build up of crud pushes the seal harder onto the piston. hope this is of some help bye for now trev

Anonymous · Post by **Anonymous** » Sun Mar 27, 05 3:04 pm

Pistons are pulled back by the seals, only by a VERY small amount, the seal rotates slightly in the groove under pedal pressure as the piston moves out, when your foot comes off the pedal the seals unrotate if you will taking the pistons with them a very slight amount, they never actually stop the pads contacting the discs or the pedal would go to the floor every time, neither do they hold them on too tight or the discs and pads would burn out.

Discs can't push the pistons back as they're supposed to be flat

bad wheel bearings, warped discs etc can all give a crap pedal (soft) in certain circumstances

If you've got a sticking piston or pistons it's really going to need stripping and cleaning, no rust on the pistons or peeling chrome, no rust or anything else in the grooves and also check the wiper seal groove for any of the above, and it will need new seals.

The pistons should have some resistance when pushed back in but it should only be the seals and nothing else.

If all is well you should just about be able to see the seal doing it's job, with the caliper off but piped up and bled get someone to VERY gently press the pedal a little, when the pedal is released the piston should return slightly, it's sometimes hard to see but that's what happens[/b]

Anonymous · Post by **Anonymous** » Sun Mar 27, 05 3:11 pm

Forgot to add when checking the seals are working ok DON'T press too hard or too far or the piston will be on the floor and you'll be covered in fluid.

The above is also how discs self adjust as the seal will only ever pull the piston back a tiny amount so as the pads wear the pistons keep on moving out to compensate.

MrNorm · Post by **MrNorm** » Sun Mar 27, 05 4:02 pm

Thanks guys, all useful help. Bin waiting for the missus to be available, hopefully shortly I'll have one more bash at getting the pistons moving back and forth just in case it helps, if not I'll remove the offending caliper and strip it.

Just to reiterate - these are new (rebuilt) calipers, but have been sitting on a shelf for years, I don't think that changes any of the advice.

Slightly complicating doing all this is the fact that my front suspension/discs etc are not installed - the calipers are suspended and have a wooden block in them! Again, doesn't really change anything but it does make them harder to work on!!
I already got to about the limit of safe travel by substituting the brake pad I put in for testing purposes with a thin piece of wood. When the pedal is fully depressed (after a few pumps) the combined width of the block and the thin wood was carefully calculated to extend the pistons to max safe limit

Anonymous · Post by **Anonymous** » Sun Mar 27, 05 4:28 pm

Gavin you say you've about got to the limit of safe travel? does this mean the pistons are a fair way out as that could affect the seals ability to roll the pistons back as they can sometimes have a tendency to tip in the bore which will jam them.

If the part of the piston you can see is clean push them all the way in and block them solidly there preferably with something steel and not wood directly onto the piston as the force on the small surface area will squash wood a little giving you a false soft ish pedal, while pushing them in have the bleed nipple open to allow any air in the caliper to come out, only push them back in if the pistons are clean, oh and if the calipers are off the car make sure the nipples are the highest point, sorry if that bit is obvious but i've seen loads of people doing this with the calipers horizontal and then wondering why they can't bleed them

db · Post by db » Sun Mar 27, 05 9:05 pm

....and dont smother it all in Coppaslip as i've done for years as it rots the rubber seals

You can get some lovely red rubber grease made for t' job (some brake kits come with a little sachet of it)

MrNorm · Post by **MrNorm** » Sun Mar 27, 05 11:05 pm

Wil, when I said the limit of safe travel I meant the piston was coming as far out as it could short of the boot coming out of the piston. I was doing that to get the piston moving in the hope it might free it up.

So, this afternoon I took the caliper off and disassembled it. Wasn't horrible, but then it shouldn't be since it's been rebuilt, any rust should have been minor just from sitting....
Here are some pics below.

It wasn't bad but there was a little surface rust. I cleaned all that off (dremel with wire brush, good tip thanks Trev) and also cleaned the grooves etc. As you can see the caliper bore has seen previous wear but since it's been remanufactured I think it's OK - there is nothing that catches a fingernail. So, cleaned the seals, reassembled, refitted to car and gravity bled.

I'd say the caliper is now better than it was - when you are not pressing the brake pedal you can move the disc pad (still a bit tight, but before it was solid).
I noticed it required quite a lot of force to reinsert the piston past the internal seal (not the dust boot). Enough force that I can't see the rubber tension dragging the piston back really. However, as I said the pad does go from solid to movable once the pedal is released.

However.....brake pedal is still the same. goes to floor but with pumping improves (not hugely but a definite improvement). As best I can tell the pedal does not sink further once pumped up and held.
So, the calipers MIGHT be fixed (??) but even if they are I still have the same problem. didn't get a chance to pump bleed the whole system, but to be honest with the pedal going to the floor it's hard to believe there isn't something else wrong.
If it is still just air in the system it's the worst I've ever come across!!
I guess I could rig up the old EasyBleed but to be honest I've already spent far too much time wiping fluid off the new paint.

Any more thoughts? with all the symptoms I've described, could it be
1) Master Cylinder
2) Calipers
3) Plain old air in the system (and VERY reluctant to leave)
or anything else?

Thanks again....