milesz Posted May 7, 2012 Share Posted May 7, 2012 I have too much brakes in front (toyota 4x4 conversion and 79 280zx brake booster) and it seems like none in the rear (stock drums). I think I need to add a prop valve but not sure how to do that or what kind to get. Any help will be welcome. Thanks Quote Link to comment Share on other sites More sharing options...
beermanpete Posted May 7, 2012 Share Posted May 7, 2012 Using an adjustable prop. valve should help. Generally the new valve is installed in the cockpit, in a location the drive can reach while driving. It can be installed under the hood as well. We have the Wilwood valve in our car. There are other brands. They all do the same thing. Summit, Jegs, and other mail order companies have them. Here is the Wilwood valve at Summit: http://www.summitracing.com/parts/SUM-G3905/ To install the new valve you need to remove the original valve. It not recommended to have 2 prop valves installed. In the early cars the valve is located under the car near the rear axle. Starting in '73 it is on the firewall just to the right (passenger side) of the brake master. In the 73 and newer cars the front brake line connects to the prop valve too so it has to be reconnected properly with a union. Quote Link to comment Share on other sites More sharing options...
SUNNY Z Posted May 8, 2012 Share Posted May 8, 2012 Just adding a proportioning valve to the rear won't solve your issue. Proportioning valves are used to keep the rear from locking up before the fronts, and sending you into a spin / crash. Sounds to me like you need to service your drums. (I'm told) that a properly serviced set of rear drums will do a good amount of braking. However, Simply upgrading the fronts and leaving the rears alone is not a good idea. I went with a BMW setup up front, and 240sx in the rear. I have a similar problem, but its not THAT noticeable. When I stand on the brakes, my fronts lock up, but the rears don't. This is with the prop valve all the way open. Truth be told, I need more rear brake, and then tone it back down with the prop valve. There's tons of info on this stuff in this section, but sometimes you have to do a little digging. Pull your rear brakes apart, and see whats going on in there - at least thats where i'd start. That may not be the end-all solution however. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted May 8, 2012 Share Posted May 8, 2012 What you want to do is increase the amount of torque applied at the rear wheels. You can do that by trying a more aggressive pad material, increasing rotor diameter, or increasing the force of the caliper. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 8, 2012 Share Posted May 8, 2012 You might try ceramic pads in rear and semi metallics in front. Ceramics bite better cold and semis don't bite as well cold but resist fade. If you don't track the car (road race) fade isn't a regular issue. Street cars mainly worry about good performance cold. That is what we perceive most of the time. Race pads aren't any better until you get them hot. Quote Link to comment Share on other sites More sharing options...
Miles Posted May 8, 2012 Share Posted May 8, 2012 (edited) I have too much brakes in front (toyota 4x4 conversion and 79 280zx brake booster) and it seems like none in the rear (stock drums). I think I need to add a prop valve but not sure how to do that or what kind to get. Any help will be welcome. Thanks Do you mean that you have a 79 280Zx brake master cylinder? Sunny is right. the Toyota front stock rear is unbalanced such that the rear brakes aren't doing much. You can try to get your rear brakes working better, but in the end your brakes will be unbalanced. Do not install a proportioning valve unless your rear brakes are locking up before the fronts. It is a waste of time and money and adds unecessary complexity to the brake system. You might be better off putting stock calipers on the front and installing Porterfield R4S pads and shoes. Do not use the Porterfield R4 pads/shoes as they are for racing only Edited May 8, 2012 by Miles Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 8, 2012 Share Posted May 8, 2012 Have you removed the stock proportion valve? I removed mine, drilled the guts out of it and replaced it; then my plumbing was all still stock, just no pressure reduction to the rear brakes. If you then get rear wheel lock up, you can put in a cockpit proportion valve. Quote Link to comment Share on other sites More sharing options...
VKLR Posted May 9, 2012 Share Posted May 9, 2012 Have you removed the stock proportion valve? I removed mine, drilled the guts out of it and replaced it; then my plumbing was all still stock, just no pressure reduction to the rear brakes. If you then get rear wheel lock up, you can put in a cockpit proportion valve. I agree with the above suggestion. Quote Link to comment Share on other sites More sharing options...
SUNNY Z Posted May 9, 2012 Share Posted May 9, 2012 I agree with the above suggestion. That seems unnecessary. I would just go to NAPA and buy two male-male brake fitting unions. Simplifies the system, and cleans up the engine bay. I used one when I installed my prop valve. See it chilling there below the valve? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 9, 2012 Share Posted May 9, 2012 Oh yeah, looks simple and great. The prop valve on a 240z (that's what I got experience with) is under the axles in the back of the car. Your solution looks much simpler. It was a PITA putting the prop valve INSIDE the cockpit, and in all honesty, once I get it set, I probably won't adjust it, so your solution looks great. Quote Link to comment Share on other sites More sharing options...
zero Posted May 9, 2012 Share Posted May 9, 2012 I did pretty much exactly the same thing as Sunny Quote Link to comment Share on other sites More sharing options...
VKLR Posted May 10, 2012 Share Posted May 10, 2012 The valve on my 75 started leaking. I went to the local Z-car grave yard and got a couple of later model blocks without the valve. I guess they were stock there were a few with them on there. Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted May 10, 2012 Share Posted May 10, 2012 (edited) Since we don't know what year the OP's car is, I would not recommend to them to remove the guts of the stock prop valve. Doing this with the early S30 (up to '72) means that you are only affecting the rear brakes (though changing overall balance). Gutting a later prop valve, ('73+) means that the front and rear brake systems are no longer independent, and if there is a brake line failure at either end of the car, will lose brake fluid from both reservoirs. Edited May 11, 2012 by Six_Shooter Quote Link to comment Share on other sites More sharing options...
johnc Posted May 10, 2012 Share Posted May 10, 2012 IMHO, putting a prop valve in the cockpit of a car isn't a good idea unless is a race car driven by someone who knows how to brake. I've seen a few drivers immediately back off on rear brake when they get a little rear lockup in one corner. Lap times dropped a bit because braking was affected on all subsequent corners where rear lockup wasn't a problem. Its an even dumber idea in a street driven car where I've had customer cars come in with the rear brakes turned down as far as the prop valve adjuster allows. When asked, the owner said, "Well, it was raining about 6 months ago and I turned the rear brakes down because I was afraid they would lock up. I guess I forgot to turn them back up." Again, that's just my opinion. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 10, 2012 Share Posted May 10, 2012 I represent that remark. Quote Link to comment Share on other sites More sharing options...
codyethridge Posted February 4, 2013 Share Posted February 4, 2013 Thanx for the info guys.. i think i understand a little better Quote Link to comment Share on other sites More sharing options...
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