Guest analog74 Posted October 30, 2005 Share Posted October 30, 2005 Hi guys, I'm new to Z's (and small block chevys) but now own a '72 240Z w/ 350 and am having brake trouble. I've searched and read about 50 posts, but still don't know what to try next. When I got the car the brakes were scary - push once and the pedal was soft and barely slowed the car, pump again and brakes were decent, not great. The seller had installed new front calipers, pads and turned rotors. I replaced the master cylinder, rear wheel cylinders (one leaking), brakes shoes, couple of hard lines, rear hoses (with braided steel from MSA) and had drums turned. Have not installed front lines yet. I then bled system in the proper order until no more air came out. Pedal now feels firm, but definitely not rock hard when engine not running. After starting engine, brakes feel the same as before: soft pedal and weak stopping power when first stepping on pedal, get much better but not great with one pump. The motor definitely has a hotter cam in it, so I put a vaccum guage on line going to the booster. The needle vascilates wildly and rapidly between 7 and 14 inches of vaccuum. Is that a problem? How do I know if booster is good? Is this system particularly difficult to bleed? The car is also unmuffled at this point, so I can't listen for an air leak... Any suggestions would be appreciated. Thanks! (this looks like an awesome sight - I was thrilled to find it) Quote Link to comment Share on other sites More sharing options...
DaleMX Posted October 30, 2005 Share Posted October 30, 2005 Sounds like the famous age old reaction disk problem to me. The booster has a rection disk in it that will fall if you pull the rod out of the seated position causing the problem you are discribing above. New and rebuilt boosters come with a paper lock on them to keep that from happining. If you pull the rod the disk will fall. You may be able to reposition the one you have. Quote Link to comment Share on other sites More sharing options...
Guest analog74 Posted October 31, 2005 Share Posted October 31, 2005 Thanks Dale, Can you (or anyone) elaborate? I've never run in to this on other vehicles. I'm replying without the ability to look at my car at the moment, but isn't the booster sealed? Can you explain what I'm looking for and how you reposition the disk? Thanks again. Eric Quote Link to comment Share on other sites More sharing options...
DaleMX Posted November 1, 2005 Share Posted November 1, 2005 Eric, when you pull the booster from the firewall you can see the rod that is connected to the booster. Inside the booster there is a disk that is held in place by contact with that rod. If the rod get's pulled out then the reaction disk will fall out of place. That happened to mine and I didn't try to get it back into place because the booster was just in really bad shape. Another member here had posted a while back about being able to get his disk back in place. Personally if the booster is old I would just get a rebuilt one and be carefull to not drop the disk. FWIW the datsun 280Z service manual had a rebuild procedure for the booster. PM me for more info on that if you want to try it. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 1, 2005 Share Posted November 1, 2005 From what I've seen reaction disk problems usually come around with a title like "I've bled my brakes 5000 times and I still don't have any pedal" or something like that. This could be a reaction disk problem but I'd guess that out of adjustment drums is maybe another alternative. If the rears are way out of adjustment the pedal will be soft and travel will be long. Shoes need to be adjusted so that they lightly drag. If you don't have any drag then they take an excessive amount of pedal movement just to come into contact with the drums. The only booster test I know is to turn the car off and hit the brakes a couple times. Pedal should be normal, normal, normal, slightly harder, rock hard. That basically tells you that the booster is holding vacuum for the first couple pushes on the brake pedal. Quote Link to comment Share on other sites More sharing options...
Guest analog74 Posted November 1, 2005 Share Posted November 1, 2005 Thanks guys, I searched "reaction disc" after Dale mentioned it as a possibility, and I'd have to say I'm not sure other descriptions I read match my problem. I definitely don't have the over-boosted feel. Or Maybe I just panicked and pumped again right away instead of continuing to push until I got that sudden grab because the brakes felt so ineffective. But I'm going to take the booster off as soon as I get a chance and check for the disc because it's got to be in the booster one way or another I think. I am confident I have the rears adjusted out properly and everything is fresh. I didn't put the front calipers on though, so I'm also going to check and make sure the bleeder screws are facing up. I can't remember from bleeding them, but read they are possible to reverse... Thanks again. Quote Link to comment Share on other sites More sharing options...
srgunz Posted November 1, 2005 Share Posted November 1, 2005 This cut away photo will help you understand where that disc is located. It does sound like that is your problem. I am among the many this has happened to. Quote Link to comment Share on other sites More sharing options...
Guest analog74 Posted November 6, 2005 Share Posted November 6, 2005 Okay, I understand where the readtion disc is now, but not how you know whether or not it's in place or how to reposition it if it has fallen. Can't see it, can't feel it, can't hear anything rattling around if I shake it. But, given the fact that I poured about three cups of rusty brake fluid out of it, I think I'll go ahead and order a rebuilt one! (the master cylinder was the first thing I replaced) Hopefully I can get one this week and assemble over the weekend. Quote Link to comment Share on other sites More sharing options...
DaleMX Posted November 7, 2005 Share Posted November 7, 2005 My old one was really messy too, the old brake fluid had crystalized all over the inside of it. Autozone had the best deal in my area. Quote Link to comment Share on other sites More sharing options...
fastzcars Posted November 7, 2005 Share Posted November 7, 2005 I was going to ask that same question. How do you put back the reaction disc? How could you tell if it's out of postion? I only asked because I had to remove the booster from my car and I want to make sure it's back in place when I reinstall it. Quote Link to comment Share on other sites More sharing options...
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