Solution for my brake problems: Am I on the right track?

[EvZ]

Hi all,

I have a problem with my brakes. I have read lots of posts on the topic, and I wanted to get some reassurement, that I am on the right track.

For the longest time, I thought my brake booster / Master Vac was toast. It seemed that when I stepped on the brakes, the first half of the brake pedal travel was normal, and the braking itself seemed normal. After about the halfway mark of pedal travel I reached a strong resistance, it felt like I floored the pedal. Strong braking needed a lot of effort all of a sudden. So I thought the brake booster was not doing its job anymore after this point.

I checked various Z forums. I read that if a brake booster is defective, it does not do any boosting at all - either it works or it doesn't. After testing my booster with various methods I found here, I concluded, that the booster is actually ok. The check valve, which allows the vacuum to remain in the booster is also operating normally. The booster is providing power in the first half of brake pedal travel.

The brake lines have all been properly bled and the brake fluid is new and clean.

Ok what now?

I checked the master cylinder (which is brand new btw, the whole car has been restored with mostly new parts before I bought it). It turns out, that someone reversed the front and the rear circuit on the M/C. I am assuming he had the wrong manual, my Z is from 1970, and he probably had a manual for a '72 and later, where the circuits and reservoirs were reversed on the M/C. So I have to get that done.

But even changing the front to the rear (vice versa) circuit will probably not change the feel of the brake pedal, and the dead stop in pedal travel that I am encountering.

Someone suggested, the problem may lie in the adjustment of the rod going through the booster which is attached to the brake pedal. It may now be set up, that the brake pedal travel is moving outside of the bandwidth where the booster supplies power assistance.

Apart from switching the brake circuits back to normal, does this seem to be a reasonable solution to the problem?

Anyone here have another solution? Is there anything I forgot? Am I on the right track?

Cheers, Markus

[Z train]

70-78 MC's were the same configuration.

[spitz17]

EvZ,

I think you will find this thread very helpful:

http://forums.hybridz.org/index.php/topic/69706-reaction-disk-pictures-and-walkthrough/

My own experience:

Valuable hours and sweat have been put into puttering with my brakes in the past. If you undo the MC nuts on the booster, pull the end of MC out of the booster (no need to remove hard lines), let it sit on the side, use a hooking device to pull out the locking plate that keeps the push rod in the booster, and pull the whole push rod out. This may be the solution to all your problems.

There should be a 5mm tall black rubber cylinder attached to the back of the push rod. If this "reaction disk" is missing, then you will never really get your braking right. If the reaction disk is missing, you either have to pull off the entire booster and shake the hell out of it until the "reaction disk" drops out or fabricate a 5mm tall rubber cylinder. I found fabricating easier, as your arms will be very sore after shaking the booster back and forth (it's harder than it sounds).

After all this is done, leave your push rod... I would say with about 5-8mm out (from behind the nut to the end of the threading). Drive the car around and see if it is better, and adjust the push rod accordingly.

[EvZ]

Cool! What a helpful post. Thanx!

Markus

[240260280z]

Some more photos and drawings.

[ZCurves]

You may have seen my posts on the Proportioning Valve. It is an important component that a lot of folks just overlook. If you are going to all of this trouble, it is advisable to take the time and clean this dude out.

[roy-73-240z]

Thanks for starting this thread EvZ!

I'm having the same problem described in the thread that spitz17 posted. This problem is really bothering me do to it being a safety issue.

The guy I bought the car from rebuilt just about everything and pointed out the problem with the brakes. He installed the 4 piston upgrade along with a new 73 master cylinder. When I push on the brakes, the pedal doesn't have any feel to it until approx. 1/2 of the way and then the brakes grab. If you push too hard the 4 piston calipers want to push your head through the windshield. I thought the problem was that I needed the upgraded ZX master (79-81) ,which I bought but haven't installed yet. Info I found on this thread.

http://forums.hybridz.org/index.php?showtopic=38499

I'll look into the reaction disc and let you know what I find. Thanks for the valuable info spitz17 , blue and zcurves.

Let us know what you find EvZ.

[EvZ]

Hi guys,

I'm not really all that mechanically inclined, so I am going to wait for my trusted expert, who is currently on vacation, to come back. I think brakes are nothing to be messed with by an amateur. But since Z's are really rare in Germany, I am really lucky to have someone nearby for all these things.

With the info I gathered here, I am going to have him check all these things. Then I will post the results. Number one focus, after switching front and rear circuits to the right positions, will be the adjustments of the pushrods and the proper placement of the reaction disc. In the process I will also have the proportioning valve checked.

Would it be recommendable to get a freshly rebuilt master vac, in any case for safety reasons? I have a line on one right now without having to send in the old one, and the deposit hassle.

[EvZ]

Well, it's been a while.

I bought a freshly rebuilt Master Vac and had it installed The old Master Vac was not actually broken, the vacuum was all there. I changed it because of the possibility of the reaction disk gone awol.

It didn't change anything so far. Still the same problem. Now we are fiddling with the pushrods. Does anyone know, how much the pushrod has to be adjusted where it connects to the brake pedal in the resting (=brakes off) position?

[beermanpete]

Well, it's been a while.

I bought a freshly rebuilt Master Vac and had it installed The old Master Vac was not actually broken, the vacuum was all there. I changed it because of the possibility of the reaction disk gone awol.

It didn't change anything so far. Still the same problem. Now we are fiddling with the pushrods. Does anyone know, how much the pushrod has to be adjusted where it connects to the brake pedal in the resting (=brakes off) position?

Per the factory service manual for the 1972 model, the push rod length should be adjusted such that the brake pedal is 8 inches (203mm) from the floor.

The factory service manuals are available here:

http://www.xenons30.com/reference.html