Brake problems

[Sarge368]

I am slowly rebuilding a 1973 240z. I was getting leaking from a rear cylinder and a front caliper was not getting any fluid so I replaced both rear cylinders, new brake shoes, new front calipers and pads, and a new master cylinder. I bled the master cylinder first and then bled all four brakes beginning with the right rear using a vacuum bleeder as well as the traditional buddy system.

I have checked over all the lines for leaks and have found nothing. No matter what I do I can not get a good solid brake without pumping them a couple of times. When I depress the brake pedal my brake light comes on. According to the manual this could indicate a pressure differential between my front and rear brakes. I can get my rear brakes to lock up but my front brakes always feel like they are barely working.

Does anyone have an idea of what the problem could be? At this point about the only thing I have not replaced is the master vac, the NP valve and the warning light switch. I am very frustrated at this point as I have moved a lot of brake fluid through the system, replaced a lot of parts, bought a fancy vacuum bleeder that I am not impressed with and still don't have good brakes. I have taken the time to read many, many posts here. I have found some excellent advice but nothing that matches this problem.

I am rebuilding this with my son for him to drive and I won't let him move it until I am positive he has great brakes. Any help would be greatly appreciated.

[Zed Head]

I had a similar problem (almost exactly, actually) when I got my car. The calipers were on the wrong sides. The bolt pattern is interchangeable, but they have to be mounted with the bleed valve on the top. If that's the case, just swap them quickly without letting the master reservoir leak down, give a quick bleed on the fronts only and you'll probably be golden.

[cbuczesk]

I agree with Zed Head. While you're doing the brakes you might want to pull the proportioning valve off the firewall, disassemble it and clean it. They get a lot of gunk in there and stop working properly.

Chuck

[Marty Rogan]

First make sure that your calipers are on the correct side, with the bleeder pointing up as Zed Head said.

Bleed the Master cylinder first. Then make sure the rear drums are adjusted to get all the slack out. You can then use the hand brake a couple of times to get any remaining slack out.

On new calipers it can be really difficult to get air out of them. Try this old racer trick that I learned from someone here:

Make sure you thoroughly bleed the master cylinder first. Then move to the right rear, left rear, right front, and then left front. I also had to crank up the rear drums a bit more.

Once the brakes are bled all around, go to the right front, remove the outer brake pad, open the bleeder screw, then take a pair of lock jaw pliers (Put tape on them so you don't chew up the pitstons) and force the pistons in. Be careful not to push them past the seals. Carefully step on the brake to push the piston back out, but not past the seals. Repeat until all the air is out. Put the pad back in and do this to the inner brake pistons. Then repeat on the left front. I was amazed at how much extra air I forced out of the calipers.

I also recommend SpeedBleeders. With a 25' clear hose I could sit in the driver's seat and bleed the brakes myself.

Hope this helps, good luck!!

Marty

[LeonV]

FWIW, do the left-rear first. It is furthest from the master.

[cbuczesk]

FWIW, do the left-rear first. It is furthest from the master.

Is yours right hand drive? The right rear should be farthest from the master.

Chuck

[LeonV]

Is yours right hand drive? The right rear should be farthest from the master.

Chuck

No. Look at your brake lines. It's not physical distance from the master to the slave that matters, but the length of the lines between the two.

Edit: Refer to figure BR-7 on page BR-5 of the '72 FSM.

Edited May 15, 2012 by LeonV

[cbuczesk]

No. Look at your brake lines. It's not physical distance from the master to the slave that matters, but the length of the lines between the two.

Yep. You're right. I was thinking the lines ran on the left side.

Chuck

[Sarge368]

This is the right front wheel. Thanks for all the advice! I will swap the calipers, clean the proportioning valve and then re-blead as suggested. I appreciate the help and will report back on the progress.

[epsark]

Okay, I have a very similar problem, just the rear not the front. I decided to do the disc brake conversion for the rear with parts (kit from MSA) that I bought from a memeber on this site. Parts and price were great! The installation went fairly well and straight forward, except for the bleeding.

I have read through here and hybridZ (some 30 pages), but no real direction to go with. I have a mini vac that I have used many times, including bleeding the fronts when I replaced the stock calipers because they were shot last year. I started with passenger rear first. No fluid. I then moved to drivers rear. No fuild. I tried this with the mini vac and the buddy system, same result. I have SS lines that are new, and have replaced one of the sections after the split valve (on the drivers side) after it got stripped. This section I believe had been spliced in because there is a female coupler with the line going into the split at the rear. I took the lines apart to try to see if I had any fluid movement. Could hear some gurgling, and a small trickle of fluid. I do mean small. I had my son hold the pedal down until I got the lines back together so I wouldn't lose pressure. Then tried "normal" bleeding again. No fluid. I then remebered to try to bleed the MC, and got plenty of fluid. Then moved to rear again. Eventually I got some fluid from the passenger side, but nothing from the drivers. Again I tried a combination of buddy and mini vac. No fluid on drivers side and gave up trying on passenger again (since I had gotten some fluid), just so I wouldn't be any more frustrated than I am now. I have never had this much trouble with a brake system before.

I find it hard to imagine that the porportioning valve would have suddenly gone, since the brakes worked when I pulled into the garage. I also had plenty of fluid leak out of the old lines. I know it can take a while to bleed, but not 4 hours worth of time. The fronts went much much easier. Is there something I am completely missing? I read something about speedbleeders. I saw them a few years back on ebay, but not recently listed. Should be easier to bleed by myself, so they advertised. Tried with the MC cap on and off in case too much pressure/vacuum. Still nothing. Haven't tried bleeding the front because I just don't see what that would do, but maybe I am wrong. The bleeders are also pointed up, so on the correct sides.

[Lazeum]

I would check how the fluid behaves in the master cylinder when you press the brake pedal. If the pedal goes to the floor, you might be able to see the fluid getting down and up in only one of the 2 tanks. It would help you to target which one is not working properly.

To start filling the lines on mine, I open the bleed valve on one wheel and I pump on the brake pedal slowly. You should see fluid getting down & not coming back up. That would fill the line with air inside but at least it should go thru.

With the buddy method, you should be to finish the job.

Once, I wasn't able to have pressure on brake pedal, it was because the rear drums were not adjusted. It might be that simple to fix.

To bleed brakes now, I ended up building a tool made with a flat piece of steel, a seal bought at the hardware store, a valve I got at auto store, 2 hooks and a chain. I then use a fuel hose & 2 plugs so I can pressurize the brake system by using the pressure from a tire. I don't go over 1 bar (14 psi) to avoid exploding the tank because of too high pressure.

It's a very convenient tool & it works really well.

[Zed Head]

Maybe you have an air bubble in the front that is taking up all of the reservoir travel. Did you take the fronts off or drain the fluid?

Can't remember the details for sure but I think that the front and rear cylinders are stacked one on top of the other in the master cylinder. I remember a discussion a while ago on this topic where it was realized (by me at least, maybe wrongly) that if one half of the system, front or back, fails completely it can take the whole system down. No brakes at all. I think that the back cylinder (front brakes on a 280Z) pressurizes the front cylinder. It bottoms out soon enough that you'll get some pressure on the front cylinder (rear brakes) but not much. I could be wrong, but at the time I thought it through and that seems right. Plus it fit the symptoms my brake problem at the time (a big bubble in the front brakes.)

I think that the early Zs had the rear brake reservoir in the back, so that would be reversed.

The speed bleeders do work really well for flushing a lot of fluid through the lines quickly. Install them and pump away on the brake pedal, but don't forget to keep the reservoir filled.