Guest zfan Posted May 11, 2005 Share Posted May 11, 2005 I recently did the 300xz/240sx rear brake swap along with the 300zx/toyota swap up front. I also swapped out the master cylinder to a 15/16" master cylinder. The problem I am having is I have decent front brakes but nearly no back brakes. I didn't put in a Wilwood preportioning valve as I have no need too yet. I have always heard that I would need it because my back brakes would overpower the fronts. This is the complete opposite and I am baffled. I swapped the brake lines around as the 240 master cylinder and 280 master cylinder are backwards when it comes to front and back brake lines. I am not making alot of vacuum probably 10 to 11" of vacuum and use a vacuum canister and am entertaining the use of a vacuum pump. I do not think this will help with the back brakes though. Anyone got any ideas cause I am stumped! Mike Quote Link to comment Share on other sites More sharing options...
jaime240z Posted May 11, 2005 Share Posted May 11, 2005 Did you bleed the system? When replacing as many parts as you did there is a good chance you got lots of air in the brake lines. Bleed the entire system a few times. Also, be sure to bench bleed your new M/C so you can get ALL of the air out. Did you remember to use to correct bleeding sequence? RR/LR/RF/LF One more thing, make sure the bleeders on the calipers are pointing straight up when bleeding. You may need to remove one of the caliper mounting bolts and pivot the caliper so the bleeders are pointing straight up. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 11, 2005 Share Posted May 11, 2005 Did you take out the stock proportioning valve? It is under the right side in the rear, looks like a T junction but it is actually the prop valve. IIRC you can take it off, unscrew the screw on it and remove the needle thingy inside then put it back in. Or you can just go to the auto parts store and get a new T without the valve and put that in there. FWIW I had Toy fronts and 280ZX rears and I never could get enough rear bias. At one point I went back to stock front brakes, and then the rears were definitely up to the job, but I think the think the Toy calipers were just too much for the rears in my case, and probably yours too. Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted May 11, 2005 Share Posted May 11, 2005 Depending on what year Z you have, the stock proportioning valve is located in the rear like Jon said, or it will be on the firewall like my '73 had. I just gutted it and installed a Wilwood adjustable proportioning valve. !M! Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted May 11, 2005 Share Posted May 11, 2005 A couple of things I forgot to mention that you guys brought up. I power bled it twice and manually twice as well. No I did not gut the stock preportioning valve, I guess I should have but will it increase pressure to the rears as they are VERY WEAK, almost nothing. Yes, I bench bled the new master cylinder. Twice due to the on going problems. The bleeders are all pointed up as well. I just got my 300ZXT CV conversion kit from Ross at Modern Motorsports. I guess I will get started on this just to keep from going batty about the freakin brakes! Mike Quote Link to comment Share on other sites More sharing options...
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