'72 Z brake booster upgrade

[vtdds71]

I have recently installed the 4-piston front caliper upgrade kit from MSA on my '72 Z, and am finding pedal travel to be way too long, as noted by others. I have ordered a '79-'81 280ZX master cylinder to replace the stock unit, as suggested, but others have said this should not be necessary. One person said the "reaction disc" may have come loose inside my brake booster, and that would cause long pedal travel and grabbing of the brakes. Removal of the booster did not detect any loose parts inside the vacuum chamber, and the booster had otherwise passed all the usual function tests (no loss of vacuum pressure from 19.7" Hg when engine shut off, either with or without brakes applied). I briefly tried to twist the two halves of the booster apart to check inside, but they were really tight, and I didn't want to risk damaging what may be a perfectly good booster. The booster vacuum line check valve seems OK, and I've carefully bled all the lines, especially the MC itself. ALL brake lines have been replaced with stainless steel equipment from Classic Tube, and rear brake cylinders are new.

 

I'm ready to proceed with the larger MC installation, unless I've overlooked something else. Suggestions? Have others found the larger MC will actually give a large improvement, and shorten the pedal travel as hoped? I saw in a previous thread on this site that the actuating rod from the booster has to be lengthened once the larger MC is installed. How much longer should it be? Should I just measure the distance from the outside mounting flange of the MC to the base of the receiving cup inside the MC, and extend the rod by that difference?

 

Thanks for any suggestions you can give me.

[blue72]

It sounds like you are doing the same process of elimination that many have gone through. Kudos for your searching so far. There is an entire Brake/Wheels/Suspension/Chassis section on this website as well.

Perhaps my post from last week will help you as it does indeed sound like the symptoms I had when my reaction disks had fallen out of place (on different boosters).

http://forums.hybridz.org/showthread.php?t=138712

 

The only other possible culprit that I have read about would be installing the calipers on the wrong sides of the vehicle. I'm not sure if that is possible with the MSA kit, but it places the calipers upside down. This makes it impossible to get all of the air out of them, and consequently a soft pedal.

Good luck.

[vtdds71]

It sounds like you are doing the same process of elimination that many have gone through. Kudos for your searching so far. There is an entire Brake/Wheels/Suspension/Chassis section on this website as well.

Perhaps my post from last week will help you as it does indeed sound like the symptoms I had when my reaction disks had fallen out of place (on different boosters).

http://forums.hybridz.org/showthread.php?t=138712

 

The only other possible culprit that I have read about would be installing the calipers on the wrong sides of the vehicle. I'm not sure if that is possible with the MSA kit, but it places the calipers upside down. This makes it impossible to get all of the air out of them, and consequently a soft pedal.

Good luck.

 

Hey Blue 72 - Thanks so much for the great tip. I opened up the booster as suggested, and found the loose reaction disc inside. It's now epoxied onto the back of the actuating rod and ready to reinstall, except I just got a post from a similar thread on Zcar.com in which someone said I will also need to replace the actuating rod with one off a newer booster. He said there's no way to extend the OEM rod enough to adapt it properly to the larger 280ZX MC! Is this true in your experience, or were you able to adjust the original rod length to work correctly? Thanks again, you've saved me hours of frustration, I'm sure!

[blue72]

Well, the rod that I am using is the one that came in the booster I pulled from a '72 240Z in a junkyard. I was also under the assumption that I would have to adjust the length of the rod to make it work with the 280ZX master cylinder. When I removed the rod it had pliers marks on it, and was turned out about three or four threads. I took measurements of its length, but don't have them here with me. I turned it out another 1/2 in. which put it almost at the absolute end of the threads. When I went to reinstall the whole assembly, the rod was way too long, and there was no way the MC and Booster would bolt up.

I wound up wrenching it back down roughly to where it had been previously (3-4 threads). That way the two bolted up, and there was little to no gap between them. My brakes come on at less than an inch of throw now. I was just happy that they work, so I left it at that.

A word of caution though. If the rod is too far out it doesn't allow the valve in the MC to close, and then your brakes lock up, so don't try that bit.

[vtdds71]

Well, the rod that I am using is the one that came in the booster I pulled from a '72 240Z in a junkyard. I was also under the assumption that I would have to adjust the length of the rod to make it work with the 280ZX master cylinder. When I removed the rod it had pliers marks on it, and was turned out about three or four threads. I took measurements of its length, but don't have them here with me. I turned it out another 1/2 in. which put it almost at the absolute end of the threads. When I went to reinstall the whole assembly, the rod was way too long, and there was no way the MC and Booster would bolt up.

I wound up wrenching it back down roughly to where it had been previously (3-4 threads). That way the two bolted up, and there was little to no gap between them. My brakes come on at less than an inch of throw now. I was just happy that they work, so I left it at that.

A word of caution though. If the rod is too far out it doesn't allow the valve in the MC to close, and then your brakes lock up, so don't try that bit.

 

Again, thanks for the further info. The new 280ZX MC arrived from Black Dragon today, so I may just go ahead and swap it for the stock 7/8" unit, although I think the stock unit is pretty new, and in very good condition. I'm going on the assumption that the 15/16" unit does work better in the end with the Toyota caliper upgrade I've installed on my car. If it really doesn't do all that much, I'd just as soon keep the original and return the larger MC for a refund. Just getting to be a pain swapping all these parts around, re-bleeding the system, etc., so it would be nice to just hit the target the next time, and move on to a different issue on the car! Sounds to me like the correct length of the booster pushrod is a variable thing, depending on how much free-play you want in your brake pedal. I agree that a little gap between the pushrod and the MC is essential, but wonder how much to be safe. Maybe some close measuring and experimentation needed here.

 

Thanks again.

[blue72]

Yeah, I left the rod where it is at now because the brakes work well, and I don't feel like taking those four bolts off to readjust it. +/- 1/2 an inch of extra pedal throw won't spoil my day. BTW: If you're looking for a cheaper solution, I purchased my MC from Autozone as a reman for $30. I didn't feel so bad replacing it at that price.