Low brake pedal issue on 240Z

[tommott77]

I have slowly been trying to get my recently purchased, though old, V8 conversion Z back on the road. I now have her running the best she has run yet, but have been dogged with brake issues since I took ownership of the car. The front calipers were seized day one when she rolled (or was actually pulled) off the trailer. Since then I have installed new front calipers, a new master cylinder, new brake lines, and now just recently a new rear wheel cylinder (which was leaking) w/ new shoes....and not to mention the millions of times that it has been bled.

 

To this day however I still have an issue with brake pedal and the feel of the pedal. The pedal feels way too low. At this point the car feels like it is stopping as it should, it just feels like the pedal is not grabbing until it is almost on the floor. It really doesn't feel spongy or anything. As I stated almost everything involved in the hydraulic actuation of the brakes has been replaced, save perhaps for the regulator valve and the fail safe pressure switch. Perhaps there is some sort of adjustment in the pedal itself, or the master cylinder that I am missing?

 

The feel of the pedal does not inspire confidence while driving, especially in a near 400hp 2000lb car. Now that the car is running fairly well the time has come to awaken the beast and drive the piss out of it. The only thing holding me back at this point is the brakes. Anybody have any ideas on how to remedy this situation?

Edited March 25, 2012 by tommott77

[280z driver]

Have you checked rear drum adjustment? that as well as the pushrod from the booster to the master can influence pedal feel. If it feels as if it stopping correctly I would learn more towards drum adjustment. That's my .02

[RebekahsZ]

I've been working on my brakes too and have made some progress and learned a lot. Here are my pointers, you can call me if you like 256-366-4685.

 

 

First, did you bleed your master cylinder before going to the wheel cylinders? The master can hold a lot of air. I use plastic tube between the master cyl bleed screws and the reservoirs to recirculate the fluid and vent the air. This technique is really quick. I am always surprised by how much air the master can hold.

 

Second, does repeated pumping of the pedal cause it to become higher and more firm? If not, then I really wouldn't suspect air as the culprit and I would suspect that you have a linkage adjustment problem.

 

For linkage adjustment:

 

1) Your rear wheel brake adjusters may not be working. Remove your brake drums and take a 1/2" drill bit and drill right thru the face of the drum where a rubber plug is currently located. The drum is soft aluminum and it drills really easily. Then take an adjusting tool and tighten your rear brake adjusters until they scrape a good bit when you turn the drum. If you have panasports, RBs or any other "open face" style wheel, you may be able to adjust this way without removing the wheel and tire. You can run your rear drums adjusted a lot tighter than the e-brake adjuster can accomplish. Source: johnc

 

2) If you still have the same problem, get under the dash (actually you may want to do this before #1) and make sure that your linkage is adjusted as maximally as possible. In other words, make sure that your adjustable stopper up near the brake switch is loosened up to allow the pedal to come all the way up. Then adjust your push rod (this is a pain) to ensure that it is pretty much maxed out.

 

3) Now it is time to get wet and nasty. Use a syringe and paper towels to suck the smaller rear brake reservoir dry. Remove the brake line from the master cylinder under the port marked "R." Take out the larger steel fitting that the line screwed into. Take a look with a mirror up inside of the port and you will see a male flare fitting. Carefully pry that out and if you have drum brakes, a little rubber check valve with a spring should fall out. If you have changed your master cylinder, this check valve could be missing. If you need one, I have one that i don't need that I'll mail you for free. There may be a check valve in your old master cylinder if you still have it. If this is the culpret, remember to bleed the master cyl and the rear wheels again. You shouldn't need to bleed the fronts again, the two systems are isolated from one another. Source: Cannonball88

 

4) Think about cutting your metal lines and installing rubber front wheel flex lines into the brake system where it screws into master cylinder. This will allow you to someday change your booster without having to drain and bleed your brakes. It also will make the next step easier.

 

5) You may need to adjust the length of the pushrod that goes between the vacuum booster and the master cyl. (#4) is designed to make this easier too. There are a couple of forum authors who have tried to describe this process, but I'm going to use trial and error (I can't add and subtract).

 

You will find all these tips with the search button, but sometimes it is difficult for me to search because I don't know what specific terms to search. I hope I've made it easier for you. If you go to my content, you will find recent threads with this info. I didn't come up with any of this on my own, rather I got all these tips from other members of hybridZ.

Edited March 25, 2012 by RebekahsZ

[beermanpete]

Another thing to check is the reaction disk in the MasterVac. This can fall out when the master cylinder is off and will cause a low pedal and a senstive pedal feel. Look in the FAQ section on this forum and/or the factory service manual for more info.

[Leon]

I'm with beerman, sounds like the typical reaction disk issue. Is there no brake pressure until it grabs all of a sudden, half-way through its travel? Check the booster for the reaction disk.