Guest Zelicious Posted June 26, 2005 Share Posted June 26, 2005 Hello all. i have a massive brake problem. system on a 240z....toyo brake conversion...new master cylinder, new proportioning valve, master cylinder bled then right rear, left rear, right front then left front. i did all work above because the front brakes would gradually tighten within first 10 minutes of driving to the point of completely locking up and making the car immobile. after completing all the above work i took the car out and yes you guessed it the brakes did the exact same thing again with the binding up( he shakes his fist at the brakes in an angry fashion). i bled the master on the side of the road to release the pressure in brake system so i could get the car home. this bleeding of master caused the brakes to loosen up. obviously the pressure of the hydraulics is building well, but is not releasing thus causing a build up of pressure and eventual binding of the pads on the rotors...I JUST CANT FIGURE OUT WHY??!!?? the brake conversion was done by prior owner so i dont know how well or what parts he used....was thinking about going back to original datsun calipers at this point. any help would be GREATLY appreciated..hope i gave enough info for you guys...sorry about length of post Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 26, 2005 Share Posted June 26, 2005 I think I may know what the problem is. If I'm right the rod from the brake pedal that pushes on the back of the master cylinder is adjusted out too far. When this happens the pressure is never fully released, because the little hole between the reservoir and the piston inside the master cylinder never opens up. So the longer you drive the more heat goes into the brakes, which makes the fluid expand which essentially pushes on the brakes a little harder and a little harder until you're trying to drive with the brakes on. I had this exact problem on my clutch, which in the clutch showed up as a normal working clutch, and as we drove it started slipping more and more and more, because the clutch fluid was expanding more and more and more.There should be 1/8" or 3/16" free play between the pedal starting to move and the pin engaging the back of the master cylinder. Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted June 26, 2005 Share Posted June 26, 2005 Are the calipers new or rebuilt? Sounds like the pistons are sticking. Someone correct me if I'm wrong. Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 26, 2005 Share Posted June 26, 2005 unfortunately i dont know the history of the calipers on the car right now just that they are toyota calipers. i am going to check out the rod length thing to see if this is the problem. forgot to mention that this only affects the front brakes as i am able to pull up the e brake with no problem. THANKS FOR THE HELP SO FAR! Quote Link to comment Share on other sites More sharing options...
skipzoomie Posted June 27, 2005 Share Posted June 27, 2005 JAMIE T hit it right on the head. All of the junk that forms in calipers over the years will make them stick. Another problem is old brake hoses. The insides will deteriorate and block the return of the brake fluid when the pedal is released. That may be your problem as the brakes release when you relieve the pressure at the bleeder valve. A stuck caliper piston will be stuck regardless of the pressure. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted June 27, 2005 Share Posted June 27, 2005 I am with Jon and vote for the Master cylinder rod. It is not letting all the fluid back into the master and leaving a bit of pressure at the calipers. Easy test is to open the bleeder valves on the calipers when they lock up and release the pressure. IF that frees up the brakes, then check the adj. on the rod.... Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted June 27, 2005 Share Posted June 27, 2005 Master cylinder pushrod is my bet. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 27, 2005 Share Posted June 27, 2005 Make it 3 votes for Jon... Quote Link to comment Share on other sites More sharing options...
PeterZ Posted June 27, 2005 Share Posted June 27, 2005 Make that 4 votes. You will know when you have enough clearance for the pushord when you can push the caliper pistons back into the bore and the displaced fluid backfills the reservior. Your piston is blocking off the transfer port and there's only one place for the pressure of heated brake fluid to go. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted June 27, 2005 Share Posted June 27, 2005 5 Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 27, 2005 Share Posted June 27, 2005 have not had a chance to get under the hood yet....raining here now and the mosquitos almost carried me off last night as i was checking it out. anyway i do appreciate all the input, hopefully it is just the rod that needs adjustment, because then i would not have to adjust my budget anymore! i will post once i adjust the rod so you peeps will have bragging rights on your evaluation prowess! thanks again. dave Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 27, 2005 Share Posted June 27, 2005 just got some more info...there is supposed to be a mounting flange between vacuum servo and master cylinder...shows this part in my haynes manual. unfortunately there is not one on my vacuum servo unit! also it looks like a hard to find part.....would it be possible that one of you out there could measure the thickness of this part so that i could fab one up myself....it seems that if it is thick enough it may be causing the problem with my brakes, therefore eliminating the need to adjust the rod . any thoughts on this?? thanks again! dave Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 27, 2005 Share Posted June 27, 2005 Well that would be a problem. That spacer is about 10mm thick. You might still be able to adjust it out from inside the car without having to make anything. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 27, 2005 Share Posted June 27, 2005 Wait just a minute. On my 240 there is a spacer that has the mounting holes on the sides, and that spacer has studs on top and bottom. I don't think you can bolt up the master without the spacer. I wonder if your PO used a different master and had to get rid of the spacer because it wouldn't bolt up with it on. Any pics? Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 27, 2005 Share Posted June 27, 2005 have to confess...i will post pics when my 17year old daughter gets home. she is my modern technology advisor and handles all these little details for me because I HAVE NO CLUE HOW TO WORK THIS HI_TECH STUFF. Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 27, 2005 Share Posted June 27, 2005 My daughter uploaded the pics to her account on an image hosting site. Since they are large, she will post links to them. http://img.photobucket.com/albums/v205/stealmeastar/240zbrakes003.jpg http://img.photobucket.com/albums/v205/stealmeastar/240zbrakes002.jpg http://img.photobucket.com/albums/v205/stealmeastar/240zbrakes001.jpg a picture is worth a thousand words. thanks for the help Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 28, 2005 Share Posted June 28, 2005 I just happened to have an old booster and master sitting right here. Took a pic for you. There is a lot of threaded end where the pedal attaches to the pin. I'm still thinking you might be able to adjust it out there. Quote Link to comment Share on other sites More sharing options...
Guest Zelicious Posted June 28, 2005 Share Posted June 28, 2005 well spacer is obviously missing so i went under dash and backed off rod that attaches to brake peddle by 4 turns took her out and same result as before...locked up brakes...this time though i bled the caliper and you could here the brake disengaging. by the looks of it i believe previous owner used used parts from a junkyard to do conversion( why try to save money on brakes??!!).so my question is now this...should i just replace calipers with new( cost from autozone is around $35-$40 each) and which calipers do i have? my rotor is not solid so does that mean i have to get a later model toyota caliper then the 79-85 years. the stamp on the side of my caliper is S12-8. actually replacing the calipers at this point is a forgone conclusion as well as brake lines. since i have already replaced master and proportioning valve i might as well complete the job right and avoid any further problems with braking due to old parts and stinginess. i just want to make sure i order the right calipers from the get go so i can put this headache to rest! after all, when all is said and done stopping is THE MOST important part of going. Quote Link to comment Share on other sites More sharing options...
PeterZ Posted June 28, 2005 Share Posted June 28, 2005 I suggest you also need to adjust the pushrod lenght at the booster by removing the master cylinder. The pushrod end should have threads and a hex area for adjusting. If the pushrod length is too long because you're missing the spacer, no amount of underdash adjustment will help. Maybe you can make a master-to-booster shim that uses as much of the master cylinder mounting threads as possible to creats more space between the pushrod and the master. Again, when this is right you can test the effects by being able to push the caliper piston into the bore (and pushing the brake fluid into the reservoir). You probably can't do that now with your current adjustment. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 28, 2005 Share Posted June 28, 2005 Oops, yeah I think Peter is right. There is the adjustment between the pedal and the booster, then there is a second rod between the reaction disc and the back of the master. So you would have to take the master off the booster, pull the pin and look at it. Maybe you can adjust it there, maybe you can modify it, maybe you'll have to get a spacer. The reaction disk is a little rubber disk. If it falls out of it's little spot you'll be chasing all kinds of other problems, so make sure you put it back in if it falls out when you're messing around in there. Isn't this convenient? http://www.classiczcars.com/photopost/showphoto.php?photo=15854 Quote Link to comment Share on other sites More sharing options...
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