buZy Posted January 19, 2007 Share Posted January 19, 2007 In good faith to Hybridz I did a long search but didn't find much. Still trying to figure out why my rears won't 'lock up' like the fronts do under hard braking. They feel like they almost dont work at all. But reading the oem serive maunal I found this, a rear proportional valve located on the rear brake line. On my car it looks 35 years old so my thought is how can it be still in good working condition. Corroded shut, not letting enough fluid pass through? It is allowing some to pass as the rears still do bleed fluid. Either way I am going to take a chance and replace it with something as it can't cost much money. I am running out of ideas to fix this problem. My question is should I replace it with an exact oem or join the lines together and run a stardard aftermarket adjustable bias valve inside the car? Have any of you guys had much experience with these before? Sorry for rambling on and on but this issue is driving me crazy! Thanks, Brian Stock rears new shoes and adjusted. Fronts toyota calipers oem rotors new pads New 71 oem master Brian Quote Link to comment Share on other sites More sharing options...
johnc Posted January 19, 2007 Share Posted January 19, 2007 The adjusters might be frozen. Get a shop manual and look at the procedures for checking the rear drum brake adjusting mechanism. Quote Link to comment Share on other sites More sharing options...
buZy Posted January 19, 2007 Author Share Posted January 19, 2007 Hey John thanks for the reply. Checked the adjusters and they are not frozen. When I replaced the shoes I took them apart and lubricated them. If fact I replaced the entire wheel cylinders with new oem parts on both wheels. Putting it all back together working the parking brake did adjust wheel cylinders but a short while after the clicking noise went away. The parking brake may also need adjustment it feels soft though most its motion till the last few clicks. So I have been manually adjusting checking them every few hunderd miles. But it appears no matter how tight I fit the drums to the pads the brakes still have little engagement. During road testing under extreme braking the fronts do produce considerable heat. Very hot to the touch. The rears barely any real heating experienced. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 19, 2007 Share Posted January 19, 2007 I think your fronts are just too powerful in comparison to the rears. If you can bleed the rears then you have plenty of fluid movement. A restricted brake hose is pretty obvious. You'll open the bleeder with pressure on the brake pedal and little or nothing will come out. You can install an adjustable prop valve, but if it is all the way open and you still don't have enough rear brake pressure, then you have a problem. You might look at the possibility of installing the larger prop valve and also installing larger wheel cylinders. I think Dan Baldwin was looking into that at one point. He might be able to direct you a bit, maybe PM him about it. The other solution is dual masters, but unless you buy something like John Coffey's bolt in dual master adapter it is not going to be a straightforward installation. Quote Link to comment Share on other sites More sharing options...
buZy Posted January 20, 2007 Author Share Posted January 20, 2007 Hey Jon thank you for the advise. I have learned so much from this site time and time again. Dual masters would be cool though probably not needed on the street. Saw Johns conversion you were talking about. Wow! Nice quality parts indeed! My old brakes are so not worthy haha! Ok for now I will search for pinched lines and try a adj prop valve. Hope luck is on my side this time. Quote Link to comment Share on other sites More sharing options...
MONGO510 Posted January 20, 2007 Share Posted January 20, 2007 Are the rear cylinders frozen? I have seen a lot of seized cylinders on the early Z's. Quote Link to comment Share on other sites More sharing options...
buZy Posted January 20, 2007 Author Share Posted January 20, 2007 Are the rear cylinders frozen? I have seen a lot of seized cylinders on the early Z's. No they are not frozen. New nissan oem parts only about a year or two old. The fluid is always kept clean and with less than 1500 miles total. Quote Link to comment Share on other sites More sharing options...
2ManyZs Posted January 20, 2007 Share Posted January 20, 2007 If you aren't sure of the e-brake, it may be that it isn't adjusting the rear brakes tight enough. I've never trusted the e-brake to adjust the shoes, I've always drilled out the hole in the drum to 1/2 inch so I could easily adjust them and actually see what I was doing. If you're not sure, take a ride around the block and pull the e-brake up one click, hit the brakes a couple times and see if the rears try to lock up or get hotter, if they do, the shoes aren't adjusted tight enough and should be done by hand. If one click doesn't change anything, try two clicks on the e-brake (since it might be so far out of adjustment). Another thing is, what kind of shoes are you running in the rear? The shoe compound might be part of the problem as well if nothing else is wrong. Quote Link to comment Share on other sites More sharing options...
buZy Posted January 20, 2007 Author Share Posted January 20, 2007 Have been adjusting the brakes by hand. Tight or loose to the drum it does not seem to matter. Not sure of the exact pad material, typical auto parts store replacements. Here is what I am also wondering about basic brake dynamics. Do the front calipers (Toyota 4 wheel drive pickup truck 79-85) use more fluid capacity than the stock ones? If so, it would be using more fluid to the fronts and then not enough pressure the rears? If that is the case then using a prop valve on the front line might help? Maybe not as it might be all about pressure and not really fluid capacity. Like Jon said my fronts are just to powerful compared to the rears. I trust his word and wealth of racing knowledge. So I guess it is time to start experimenting with proportioning the rear line. It would be cool to get these brakes working properly. Really dont want to spend the money on a 4 wheel disc upgrade. This is the lightest setup possible and would work fine for the street. Again, Thank you everyone for your input. Brian Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted February 11, 2008 Share Posted February 11, 2008 Any updates on this Buzy? I just got my car going and I'm having the same issue. I too have the Toyota Calipers up front and stock drums with new pads in the rear. I had my car up on jack stand this weekend repairing the trans, and after testing the trans, I couln't stop the rear wheels with full peddle! Fronts work well, rears are bled, but I should probably re-bleed. No leaks, I'm stuck too. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 11, 2008 Share Posted February 11, 2008 Any updates on this Buzy? I just got my car going and I'm having the same issue. I too have the Toyota Calipers up front and stock drums with new pads in the rear. I had my car up on jack stand this weekend repairing the trans, and after testing the trans, I couln't stop the rear wheels with full peddle! Fronts work well, rears are bled, but I should probably re-bleed. No leaks, I'm stuck too. That is not a bias problem, your rear brakes aren't doing anything. That's a blocked or pinched brake line or some other failure in the system, or that full pedal just squirted a whole bunch of brake fluid inside the drums. Check the soft brake lines and wheel cylinders for leaks and bleed them again. If barely any fluid comes out then its a line blockage. Happens sometimes when cars are stored long term. I've managed on one or two occasions to blow them out by quickly stomping on the brake pedal, but usually that just lets a bunch of crap loose in the lines and it then takes out the rear wheel cylinders... Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted February 12, 2008 Share Posted February 12, 2008 Thanks JM. I'll re-bleed them this weekend and see whats what. They probably need adjusted as well, but I'm not really all that knoledgeable on Drum brake adjusting so I probalby didn't do it right when I changed the pads. And I don't have an E-brake as of right now either. If all else fails I can do the maxima disks in the back to compliment the front, I think that's the swap that went well with the toyota fronts and the bigger MC. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 12, 2008 Share Posted February 12, 2008 It may be possible to have the shoes so far out of adjustment that they don't do anything, I didn't realize you had just replaced the shoes. Quote Link to comment Share on other sites More sharing options...
boodlefoof Posted February 12, 2008 Share Posted February 12, 2008 While it sounds like you guys do have some real problems with lack of rear pressure, just a word of caution... Whatever you do, don't adjust front/rear pressure such that the rear brakes will lock up before the fronts. That is a no fun situation. Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted February 13, 2008 Share Posted February 13, 2008 It may be possible to have the shoes so far out of adjustment that they don't do anything, I didn't realize you had just replaced the shoes. I put the pads on probably between 1-2 years ago, but I only started driving it a month or so ago. I'll check the adjustment and bleed this weekend, unless it doesn't warm up, man it is freaking cold out! Quote Link to comment Share on other sites More sharing options...
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