zack_280 Posted February 3, 2012 Share Posted February 3, 2012 (edited) As stated in the title my rear brakes are locking up before the fronts. I have a 15/16 master cylinder with the AZC big brake kit. All the hard lines are stock. I'm not sure why my rear brakes would be locking up. I assume that the new discs just lock up with less pressure than the old drums. But it could be that the stock proportioning valve is not properly proportioning. After considering the problem and potential solutions I am leaning toward the third option below. I am considering replacing the stock proportioning valve and hope that that fixes it, but I feel like that's probably not the problem and it will probably waste a bunch of my time. Solution two is to install a proportioning valve after the stock valve. After looking at the plumbing this looks like I would have to replace the hard line running to the rear of the car and that would be a royal PITA. Solution three is to delete the existing proportioning valve and switch and replace them with a Wilwood proportioning valve (link below). I realize that I would have to replace a few hard lines, but at least I don't have to run a new hard line to the rear of the car. I would just have to run a few hard lines from the master cylinder to the new valve and from the new valve to the driver side front caliper and to the existing hard lines that go to the rear and to the passenger side front caliper. Can anyone think of a reason that this might not be a good idea? http://wilwood.com/M...temno=260-11179 Here's a picture to help with what I am talking about. The Wilwood valve would replace items 2 and 6. Edited February 3, 2012 by zack_280 Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 3, 2012 Share Posted February 3, 2012 What does AZC say to use? It seems they should be have already figured this out. Anyhow, I suggest option 3. Quote Link to comment Share on other sites More sharing options...
luseboy Posted February 3, 2012 Share Posted February 3, 2012 An adjustable proportioning valve is what you need. from azc's rear install page: " Be sure to use one of our cockpit adjustable proportioning valves to set the brake bias. Here's a typical installation of the adjustable proportioning valve along with the hydraulic line lock for the parking brake function. The stock proportioning valve has been retained and the rear brake line has been brought from it along side the trans tunnel to the new valves and then out through the floor to the splitter over differential. " This will solve your problems, you just have to screw the proportioning valve in (acctually out technically, it's counterintuitive) enough so that the fronts lock before the rears. Quote Link to comment Share on other sites More sharing options...
zack_280 Posted February 3, 2012 Author Share Posted February 3, 2012 (edited) Thanks for the feedback. luseboy, I was planning on adding the proportioning valve. I know AZC says to use it and I have the one that they sell. I just didnt' install it b/c I don't have the proper tools (flaring tool and tubing bender) and it was going to be difficult to replace the entire rear brake line. I figured I'd see if there was actually a bias issue first. There is, but I think rather than going through the hassle of using the prop valve I have and replacing the rear line, I'd rather get the Wilwood unit I mentioned above. The reason I wasn't too sure about that option is because I seem to recall someone on here saying not to remove the stock proportioning valve. But I don't see why it would be a problem. Edited February 3, 2012 by zack_280 Quote Link to comment Share on other sites More sharing options...
johnc Posted February 3, 2012 Share Posted February 3, 2012 You should not run two proportioning valves. If you install the Wilwood adjustable valve then you should remove the OEM valve. Quote Link to comment Share on other sites More sharing options...
zack_280 Posted February 3, 2012 Author Share Posted February 3, 2012 Thanks, John. Now I just need to find all of the fittings and place my order with Summit. Quote Link to comment Share on other sites More sharing options...
wrcbonk Posted February 3, 2012 Share Posted February 3, 2012 If you haven't already, go to Sears and by a Craftsman 10 mm line wrench so you don't strip your line nuts like I did. Quote Link to comment Share on other sites More sharing options...
luseboy Posted February 3, 2012 Share Posted February 3, 2012 Ah i see what you were thinking there, makes sense. I believe you could also install the wilwood prop. Valve in the engine bay, that way the amount of flaring would be minimal. I hear good things about the rigid flaring tool, they go for about 70 bucks, i plan on getting one for when i install all new lines/fittings/etc in my car. You honestly probably wont need a bender unless you use stainless line. There's a place called fed hil that make really nice lines, i will be using them for all my lines. The stock fittings are all 10mm x 1.0 (iirc). Definitley get a line wrench! All my fittings stripped super easily using a normal wrench. The stock line is 3/16". I hope this helps, im kinda just throwing out everything i've read haha. Quote Link to comment Share on other sites More sharing options...
takayuki Posted February 4, 2012 Share Posted February 4, 2012 Here a simple bolt on solution http://www.datsunstore.com/product_info.php/pName/brake-proportioning-valve-adjustable-kit-7383/cName/brake-and-clutch-z-brake-parts Quote Link to comment Share on other sites More sharing options...
tightywhitey185 Posted February 4, 2012 Share Posted February 4, 2012 Wait wait.....So im running the willwood prop valve.I should totally remove the stock prop valve? Quote Link to comment Share on other sites More sharing options...
zack_280 Posted February 4, 2012 Author Share Posted February 4, 2012 Thanks. I just bought some straight steel line sections of line that already have the fittings on them. They were pretty cheap at Summit, but now I need a 3/8 24 to 10mmX1 adapter. Not having much luck there. At least the lines only cost about $5 each and I only needed 3. I figured I'd buy them and then try to find fittings and if I can't then I'll try to get some copper-nickel alloy lines and borrow a flaring tool or something. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 4, 2012 Share Posted February 4, 2012 Wait wait.....So im running the willwood prop valve.I should totally remove the stock prop valve? Yes. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 4, 2012 Share Posted February 4, 2012 Thanks. I just bought some straight steel line sections of line that already have the fittings on them. They were pretty cheap at Summit, but now I need a 3/8 24 to 10mmX1 adapter. Not having much luck there. At least the lines only cost about $5 each and I only needed 3. I figured I'd buy them and then try to find fittings and if I can't then I'll try to get some copper-nickel alloy lines and borrow a flaring tool or something. Adapters are tough to find. We bought one pre-made steel line with the 3/8-24 fittings, cut one end off and swapped one of the fittings with one from a metric line. We re-flared the ends thus giving us 2 lines, each with a metric fitting at one end and an SAE fitting at the other end. Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted February 5, 2012 Share Posted February 5, 2012 Adapters are tough to find. We bought one pre-made steel line with the 3/8-24 fittings, cut one end off and swapped one of the fittings with one from a metric line. We re-flared the ends thus giving us 2 lines, each with a metric fitting at one end and an SAE fitting at the other end. For those looking for adapters, I have tirelessly scoured the web in search of those hard to find adapters to fit adjustable proportioning valves to our cars. After finding these adapters, I did what the Beer man did, made custom lines with one metric end and the other to fit the valve. But for those looking for adapters, here is what I have found (mostly this sites archives): http://www.flyinmiata.com/index.php?deptid=&parentid=&stocknumber=14-76255 http://www.brakequip.com/mfthread.html Quote Link to comment Share on other sites More sharing options...
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