Brakes require pumping to work.

[dmruschell]

This post is about a friend's DeLorean, so I may not have the answers to every question. I will, however, do my best to answer to the best of my knowledge.

He had complained that the brakes on his DeLorean required a pump or two to get the pedal to stiffen up while driving. We had a local tech day this last weekend and replaced his master cylinder with a DMCH cylinder, all of the rubber brake lines, and his front brake pads. We then bled the brake system. I took the car for a test drive, and they did okay at first, but then the bedal went soft and the pedal required pumping to stop correctly. Then, the brakes almost went out completely, but could still stop enough when the pedal was almost to the floor. So, we bled the brakes again.

After bleeding, the brakes were still soft and required pumping. We then bench bled the master and re-bled the entire system with no change in braking performance. There are no leaks in the system.

While replacing one of the front pads, the inner piston on the front passenger caliper took a lot of effort to retract. I was using vice grips, and I couldn't get the piston retracted with them. A more knowledgeable person used a pry bar to get the piston retracted. After bleeding, etc, that wheel was much harder to turn by hand than the driver's side front wheel. I didn't know if that might indicate a bad caliper that may be causing this issue. The brakes don't pull (they did pull to the left before the tech day), so both front calipers should be working equally.

The old master cylinder was leaking a bit into the brake booster, but the booster seems to be functioning.

The only things left to replace are the calipers, brake booster, and hard lines. With no leaks, it would seem that the hard lines are okay. Does anyone have any ideas as to what could be causing this? Thanks in advance!

[DMCMW Dave]

While replacing one of the front pads, the inner piston on the front passenger caliper took a lot of effort to retract. I was using vice grips, and I couldn't get the piston retracted with them. A more knowledgeable person used a pry bar to get the piston retracted. After bleeding, etc, that wheel was much harder to turn by hand than the driver's side front wheel. I didn't know if that might indicate a bad caliper that may be causing this issue.!

That pry bar test indicates a stuck piston. If the front calipers have not been rebuilt, they probably need it.

[dmruschell]

That pry bar test indicates a stuck piston. If the front calipers have not been rebuilt, they probably need it.

Yeah. The old pads were slightly unevenly worn, too, and the brakes would pull to the left, both also indicating a stuck piston on the passenger side. (Though, the brakes don't pull anymore.)

That wouldn't contribute to the brakes needing pumping would it? That's priority #1, but rebuilding/replacing the calipers are on the list to do.

[DMCMW Dave]

Yeah. The old pads were slightly unevenly worn, too, and the brakes would pull to the left, both also indicating a stuck piston on the passenger side. (Though, the brakes don't pull anymore.)

That wouldn't contribute to the brakes needing pumping would it? That's priority #1, but rebuilding/replacing the calipers are on the list to do.

It could. If the rotor is warped slightly it will kick the pad (and piston) back as it rotates. Then when you hit the pedal it make take you an extra hit to actually get the sticky piston to move. This can happen even if the pistons are not sticky, i.e. pad kickback, but it may take more effort to overcome if they are.

I've seen plenty of cars with stuck pistons exhibit no brake pull. Not really sure why, but if you have a stuck piston on each side they will be equally bad and therefore not pull.

[David T]

It could. If the rotor is warped slightly it will kick the pad (and piston) back as it rotates. Then when you hit the pedal it make take you an extra hit to actually get the sticky piston to move. This can happen even if the pistons are not sticky, i.e. pad kickback, but it may take more effort to overcome if they are.

I've seen plenty of cars with stuck pistons exhibit no brake pull. Not really sure why, but if you have a stuck piston on each side they will be equally bad and therefore not pull.

If you can't easily get a piston to retract it can be a bad brake hose or a corroded caliper. Loosen the bleeder and see if it makes any difference. If it doesn't, you need to rebuild ALL of the calipers. if one is corroded they probably all are. If loosening the bleeder and letting fluid out makes it easy to move the piston you should replace all (4) of the brake hoses.

[dmruschell]

If you can't easily get a piston to retract it can be a bad brake hose or a corroded caliper. Loosen the bleeder and see if it makes any difference. If it doesn't, you need to rebuild ALL of the calipers. if one is corroded they probably all are. If loosening the bleeder and letting fluid out makes it easy to move the piston you should replace all (4) of the brake hoses.

In this instance, a new rubber brake hose had just been fitted to the caliper and (of course) we hadn't bled the system yet, so there was lots of air in the lines. So, it's definitely the calipers causing the piston to be stuck.

[PB Co]

I have this same problem. I can lock up the brakes if I have to but I have to give the pedal a small prime for it to feel stiff.

Did I miss a tech day? I never saw an email. My car could use some tech day input.

[dmruschell]

I have this same problem. I can lock up the brakes if I have to but I have to give the pedal a small prime for it to feel stiff.

Did I miss a tech day? I never saw an email. My car could use some tech day input.

Yeah, there was a post in the DMA Google group, which should have been forwarded to the email address associated with the group account, a facebook invite page, and a thread about it on the DMC Today forums (I don't know if there was a thread started here or not).it was at Justin Mettee's place. I think this was the 4th one he's hosted.

I'm planning on starting to host an annual spring tech day so people can take care of issues that may have been discovered at the Spring Social inspections. I'm about a 45 minute drive south of Justin, so the same crowd can come.

Onto your issue.. Have the brakes been bled? How old is the master cylinder? Have the calipers been rebuilt/replaced recently?

[PB Co]

Yeah, there was a post in the DMA Google group, which should have been forwarded to the email address associated with the group account, a facebook invite page, and a thread about it on the DMC Today forums (I don't know if there was a thread started here or not).it was at Justin Mettee's place. I think this was the 4th one he's hosted.

I'm planning on starting to host an annual spring tech day so people can take care of issues that may have been discovered at the Spring Social inspections. I'm about a 45 minute drive south of Justin, so the same crowd can come.

Onto your issue.. Have the brakes been bled? How old is the master cylinder? Have the calipers been rebuilt/replaced recently?

I didn't get any of those notifications. Damn. Only thing I saw was the Oct event on FB.

Bled them twice already. They were so bad when I bought the car. I thought I was going to crash going over the Walt Whitman bridge on my first drive as owner. So it's been a huge improvement over that but I would like more brake confidence. When it was up on the lift the master looked like it had been replaced. The car didn't come with a lot of documentation but I am surprised how much has already been addressed. Problem is, when?

[PB Co]

How many versions of the same club do I have to join to find out about a tech day? Says the guy who just discovered it was last weekend and his only Sat off this month. Come-on! Lol.