280z brake questions

[deja]

I have MM rear discs and Silvermine front discs. I am still running the 7/8 MS, which I plan on replacing. After I did the LT1 swap for the second time I seem to have rear brake issues. When I pull into my garage which has a very smooth floor and apply the brakes the front wheels lock and the rears wheels are still turning. I have to really push on the brakes to get the rear wheels to stop. This could be somewhat related to the 1000 rpm idle I have the LT1 set for but I don't think I should have to push that hard to stop the wheels. The pedal seems firm so I don't think I have an air in the lines issue. I read a ton of stuff here about the reaction disc and pushrod adjustment. I decided to try the pushrod adjustment since what I read said there should be 3/8" - 1/2" upward movement of the fluid when I push the brake pedal and I get about 1/8". I took the MS off and found all sorts of crud, even some wetness but can't really say its fluid. The push rod has quit a bit of rust on it and the end part with the nut does not seem to turn, probably because of the rust. So I try to pull the rod out so I can clean it up. It gets pretty far out and then seems to get hung up on something. I thought the reaction disc was on the end of the rod and it would just pull out, am I wrong?

[h4nsm0l3m4n]

I'm not expert, so someone correct me if I'm wrong but I think at least some of your problem is due to the 7/8 master cylinder. Big brakes displace a lot more fluid and therefore lengthen pedal travel so most big brake kits recommend you upgrade to the 15/16ths MC. The bigger MC will reduce pedal travel a bit, maybe fixing your problem. Also if youre running the stock proportioning valve, that may be messing up your front/rear brake bias. Putting in an adjustable one will let you adjust pressure so rear brakes are doing more braking.. although you still want fronts to lock up first.

 

I just swapped my 7/8ths MC for the 15/16ths one and did not see any wetness when I removed it from the booster. The pushrod nut was real tight, but I eventually got it off. The reaction disc is on the end of the rod, but I believe there is a clip or something else on the booster that prevents it from coming out all the way. Remove that and you should be able to pull it out I believe.

[deja]

OH! So to remove the rod I need to pull the booster out of the car in order to get to that clip? I was trying to avoid that, LOL. I guess I will start by getting the 15/16 MS and proceed from there. Getting the MS out would have been a lot easier if I had done it before I put the new engine in. Thanks for your input.

 

I think at least some of your problem is due to the 7/8 master cylinder. Big brakes displace a lot more fluid so most big brake kits recommend you upgrade to the 15/16ths MC. The bigger MC will reduce pedal travel a bit, maybe fixing your problem.

 

I just swapped my 7/8ths MC for the 15/16ths one and did not see any wetness when I removed it from the booster. The pushrod nut was real tight, but I eventually got it off. The reaction disc is on the end of the rod, but I believe there is a clip or something else on the booster that prevents it from coming out all the way. Remove that and you should be able to pull it out I believe.

[johnc]

Testing your garage flow at low speed is useless because you're not getting any weigh transfer. You need to run the car up to a real road speed and test. Don't do anything to your brake system until you go out and do some real testing at 40 and 60 mph.

[deja]

It seems to be fine on the road other than having to push very hard to hold the car at a light. I just don't understand why its acting like it is when I pull into the garage. It never did that until I swapped LT1 engines. The only real difference in the engines is the LT4 cam kit an the RPM adjustment.

I did just notice something I somehow missed however. It looks like this engine is sitting about 1/8' further forward that the old one causing the throttle cable not to allow the throttle plate to fully close. So maybe I am not sitting at 1000 rpm. I have adjusted that. But since I already wanted to swap the MS to the 15/16" I have taken it all out, the new MS will be at the parts store at 4:00.

I did get the rod out and after a ton of penetrating oil got it loose. And the reaction disc was in place so that rules that out. Well it was in place until I dropped the rod and it fell off. I guess I'll epoxy it on before reassembly.

 

 

 

Testing your garage flow at low speed is useless because you're not getting any weigh transfer. You need to run the car up to a real road speed and test. Don't do anything to your brake system until you go out and do some real testing at 40 and 60 mph.

[deja]

Update. I pulled the power booster to get the rod out in order to get the screw in part free. A ton of penetrating oil and it was free. Oh yeah, the reaction disc was in place where it should be. I expoxied it in place just to be safe. I picked up a rebuilt '80 280zx 15/16" master from O'reillys. I did bench bleed it but that turned into a major mess. By the time I managed to get it in the car and the brake lines hooked up I lost all the fluid, I have no plugs for the fittings. Obviously I did not do this right. Fortunately the master I got has bleeders so I was able to bleed it back to itself on the car. I did try to adjust the rod according to the instructions I found here but even screwing the rod all the way in I still only get a small amount of upward movement of fluid, I am so confused. But I had to adjust the freeplay on the pedal quite a lot, probably the difference in the 280Z and 280ZX masters. I have good pressure on the pedal, so I took the car out for a ride. The brakes feel great, but its still an effort to hold the car at a light. I may have to lower the idle RPM a bit to make this thing "streetable".