Miles Posted October 1, 2011 Share Posted October 1, 2011 (edited) Car: 72 240Z Brake Configuration: Front: MM Toyota caliper 300ZX vented rotors. Set up is two years old Rear: MM 240SX caliper 300ZX solid rotors. New calipers to replace two year old leaking units New rebuilt 280Z booster. Reaction disk verified in-place. Push rod adjusted to just contact the MC piston socket so there is a just noticible contact when the MC is pushed into the booster. New Wilwood 1 inch master cylinder. Bench bled before installing. Wilwood proportioning valve plumbed into the rear brakes where the "residual pressure valve" (aka proportioning valve) used to be in back. New porterfeild R4S pads front and back Bleeding: Used a power bleeder to bleed all four calipers. Re-bled MC bleeder screws after it was on the car before bleeding the system. Bled the system twice and saw no bubbles after initial bleeding the first time. Differential pressure switch has not been activated. Research: Researching the archives indicates that long pedal travel and spongy brakes are a common complaint with the above setup. Problem: With the engine off, the pedal is spongy about first third of travel and then gets solid about even with the gas pedal. I noticed that this morning after the car sat over night that the pedal was initially hard as rock and high with no play until I pumped the brakes a few times and then they became spongy again and the travel become long again. Brakes do not pump up. They are just spongy the first third of travel an then hard with a little spongyness. Makes me think that there is a leak in the system. I am going through the whole system today looking for leaks at fittings and caliper pistons and rechecking theMC push rod adjustment. Why would the pedal firm up over night and then go spongy again after a few pumps? Edited October 1, 2011 by Miles Quote Link to comment Share on other sites More sharing options...
Miles Posted October 2, 2011 Author Share Posted October 2, 2011 Re-bled MC and calipers. Pedal came up firm after bleeding, but after four or five stops I was mashing the gas pedal with every stop and the pedal was mushy. The left front wheel locked twice so there must be a problem with the right front caliper. I am suspecting that the new Wilwood MC may be bad out of the box. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 2, 2011 Author Share Posted October 2, 2011 Air is some how entering the rear brake section of the master cylinder. After a short drive or just pumping the brakes I get a lot of air out of the rear brake section bleeder on the MC. The lines between the MC and the brake differential pressure switch are tight and dry. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted October 2, 2011 Share Posted October 2, 2011 I just got finished doing a Maxima rear disc swap into my 240z. I thought I had all the air out of the system but my pedal was still spongy, then I took one bolt out of my calipers and rotated them to make sure that the bleeder nipple was as high up as possible. Re-bled them and got lots more air out of it immediately and my pedal firmed up. Had to use a piece of wood to simulate the shoes and the rotor, but that was no bid deal. I never would have guessed that the attitude of the caliper would make such a big difference, but it sure did. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 2, 2011 Author Share Posted October 2, 2011 I rotated the calipers also so the nipple was vertical. I discovered last night that rear section of the MC is sucking air. I can bleed the air out of the rear section. After closing the bleed nipple and a few pumps of the brake pedal the pedal goes soft and I find air in the rear section of the MC. Today I'll run some tests on the MC to see if it is leaking internally or if there is a bad fitting in the pipe that connects to the differential pressure switch below the MC. Quote Link to comment Share on other sites More sharing options...
Miles Posted October 14, 2011 Author Share Posted October 14, 2011 Problem solved. The 280ZX MC was leaking internally in addition to leaking fittings at the output ports. Quote Link to comment Share on other sites More sharing options...
spitz17 Posted October 14, 2011 Share Posted October 14, 2011 How did you find out the 280ZX MC was leaking internally, and did you buy a new one? If so, from where? Thanks! Quote Link to comment Share on other sites More sharing options...
Miles Posted October 14, 2011 Author Share Posted October 14, 2011 (edited) How did you find out the 280ZX MC was leaking internally, and did you buy a new one? If so, from where? Thanks! The master cylinder would not hold pressure. It would sink to the floor during hard stops. I tried all of the usual places to buy a replacement, but found out none of the rebuilders or after market companies were supporting the 280ZX master cylinder. I did find that RockAuto can send your defective MC to Cardone for rebuild for about $40. I tried the RockAuto service, but it took four weeks to get my MC back and then it still would not hold pressure. Don't waste your time chasing a 280ZX MC. It is extinct. The autoparts stores advertise that they have them, but the truth is none of the rebuilders supply this MC anymore. The solution is to go to a one inch Wilwood tandom MC (p/n 260-8794) and a 280Z booster combination. Others have started doing this swap. See thread: http://forums.hybridz.org/index.php/topic/100010-brake-booster-and-master-cylinder-upgrade/page__gopid__961481 If you have the Modern Motorsports Toyota vented front and 240SX rear disk brake kits installed the combination of the one inch Wilwood MC and 280Z booster works better than the 280ZX MC swap. I had the 280ZX MC and stock 240Z booster set up for two years and always felt that a larger MC and larger booster was needed. The other advantage of the Wilwood MC is that you can get one from Summit, Jegs, etc. or your local speed shop. Edited October 14, 2011 by Miles Quote Link to comment Share on other sites More sharing options...
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