Brake problems after rebuild

[derek murray]

Fellas,

Thanks for all the suggestions.

My car does not have a booster. When I rebuilt my rear calipers, brake fluid was used as a lube when reinstalling the new seals and original pistons. I can't remember any pitting of the pistons, but I have a feeling I'll be pulling them apart, anyway, as that was the last bit of work I did. (Everything worked fine before then.) I never did get a chance to road test the brakes at that time as the engine was out of the car. That was 2 years ago.

The master cylinder is a brand new ATE. I replaced the master cylinder a few weeks ago, thinking the original one was bad.... apparently not.

I have "S" brakes up front and bleed each caliper's inner and outer nipples.

[JSV798]

I am having the same problem. Just rebuilt the calipers with new seals to cure sticking pistons when not used for a while. Brakes worked OK, but thought I would refresh the seals. Reading some threads on bleeding I have not had the piece of wood under the pedal so may have damaged the master cylinder seals. But I'm getting air bubbles coming out of the bleed nipples after best part of 2 litres of fluid. Also after shutting off the bleed nipples I can get some resistance by pumping the pedal. If I keep my foot on the pedal it stays solid but as soon as I release the next application it drops to the floor. I'm thinking that there is air in the system but can't understand why I'm not clearing it. Beginning to suspect that it is being sucked in somewhere.

[Jesse16]

Did you ever do the manual old school bleed all the way around with an assistant? Can you push fluid with your foot out each corner and build pressure if the bleeder is closed ?? Push on pedal, open valve and close quickly once fluid comes out. If you cannot build pressure at the pedal, the MC is still the likely culprit.

[JSV798]

I started with a one-man bleeding kit that has a one-way valve which is fitted to the nipple which is then undone followed by pumping the pedal. Problem with this method is you can't see when the bubbles stop. So, tried the old method you suggested with an assistant so I could see what was coming out of the nipples. I was amazed how much air seems to keep coming out. Have now started the whole process again (third time). Have done the rear brakes and seemed to get rid of the bubbles but still little pedal. As it's dual circuit brakes I would have thought I would have some pedal by now but I haven't. Is air being sucked in I wonder.

[DRACO A5OG]

Derek and JSV.

The assembly lube I am talking about is the SILGLIDE, I found it much easier to work with and helps keep corroded areas from getting worse. It is High temp rated. I bet you are leaking ever so slightly from the pistons.

If you look at my pic, the first one showed clearly the corrosion on the seal's line

[Jesse16]

I really can't see how a brake system with a full reservoir over the MC can "suck" in air. I think you should just keep at one corner till no bubbles, them move along. Move the brake pedal slowly vs letting it pop back up after pushing maybe.

[DRACO A5OG]

^^^ +1 Quick Down Slow Up on the pedal.

[Craig]

One thing I do to make sure air is not introduced through the bleeding process is to put a little bit of grease around the outside of the bleeding nipple where the bleeding hose is attached, and a little bit around the threads of the nipple. Just to make sure air does not have a way in.

[JSV798]

Draco and Jesse,
I'm moving on to the front brakes (again) tomorrow and will try the slow pedal up technique. I was getting a lot of air out of the passenger side front caliper so decided to start over; got as far as re-doing the rears and tried to convince myself that no more air bubbles were coming out.
Will report back

[will hung]

Try gravity bleeding. I rebuilt my brake system in 2011, but was never fully satisfied with the brake pedal feel or stopping power. I took my time and gravity bled it last summer and the pedal became rock solid again.

[reddogmotrsprts]

Originally Posted by Jesse16

I really can't see how a brake system with a full reservoir over the MC can "suck" in air. I think you should just keep at one corner till no bubbles, them move along. Move the brake pedal slowly vs letting it pop back up after pushing maybe.

Well, the grommets and fittings on the master are not infallible, and neither is the blue hose. He may have a leak to atmosphere which only comes into play under the vacuum of the pedal return.

Check the brake lines as well, but I'm sticking with the bad master diagnosis, regardless of the fact that you have a new one.

[JSV798]

I have brakes! With an assistant I moved onto bleeding the front brakes using Jesse's technique:

assistant puts foot on pedal
open bleed nipple, fluid and bubbles come out and close while assistant still has foot on pedal
assistant releases pedal slowly.

I put around 2.5 litres of fluid through the system in all

Thanks everyone.

Maybe Derek could try this

[derek murray]

I figured I should update this thread as the problem has been solved.

It turns out the brand new rotors I installed both had a manufacturer's defect. When mounted to the hub the face of the rotor was not perfectly parallel with the face of the hub. This caused one of the brake pads to be pushed too far away from the rotor as the wheel turned. Hence why as soon as the car rolled I would loose brake pressure... seems all so simple now

FWIW, these bad rotors were purchased locally. The replacement rotors bought from our host are working perfectly.

d.

[euro911sc]

Now that is something no one would ever suspect... How did you figure it out?

[DRACO A5OG]

Wow

[derek murray]

Originally Posted by euro911sc

Now that is something no one would ever suspect... How did you figure it out?

I bought a scissor lift this spring so getting the car up on a lift helped me be able to see the pads shifting to the side as I spun the rotor. At first I thought I had messed up putting the bearings into the trailing arm.... or the hub... But as I turned and measured and measured again with the rotors off, it started to make sense.

It's a darn good thing I do this as a hobby and not as my profession. And my wife is extremely happy my "obsessing" is over ...... for now



Sent from my iPad using Tapatalk

[trond]

if the pistons are pushed all the way back with new seals you could have an issue with the seals flexing and pulling the the pistons back again when releasing pedal. I did my calipers last week and I pushed the pistons all the way to contact with disk using compressed air and then connected the brake lines. Or MC is bad. Even new ones can be bad. Mine was

[autojack]

Originally Posted by derek murray

I figured I should update this thread as the problem has been solved.

It turns out the brand new rotors I installed both had a manufacturer's defect. When mounted to the hub the face of the rotor was not perfectly parallel with the face of the hub. This caused one of the brake pads to be pushed too far away from the rotor as the wheel turned. Hence why as soon as the car rolled I would loose brake pressure... seems all so simple now

FWIW, these bad rotors were purchased locally. The replacement rotors bought from our host are working perfectly.

d.

Holy crap, this is the type of thing that will make you craaazy. Nice work figuring it out!