1 tuff z Posted May 9, 2006 Share Posted May 9, 2006 My brake dilemma… My 73 240z brakes are baffling me. Here are my car basics; john’s cars ls1 mounts, t56 trans, r200 3.9 diff with nismo lsd, Autopower 6 pt roll cage, az rear control arms, mike Kelly front adjustables, ground control coilovers & Tokico illumina struts, mm 13†vented front rotors & pbr calipers, mm rear brackets & 11†solid rotors with 240sx calipers-park brake retained, 15/16’s zx master [early one with the separate reservoirs], stock 73 vacuum booster, removed-factory safety valve [driv side frame rail] & prop valve [firewall], custom ss brake lines for fronts to reroute them away from headers. Ok, here’s what my car is doing. Very sensitive pedal, almost like the old gm over boosted systems, very difficult to modulate, fronts lock very easily. I had a wildwood prop valve inline for the rear brakes, but even with it adjusted for max rear pressure still locked fronts easily, removed prop valve-same pedal feel. Disconnected vacuum, brake pedal is much less sensitive but has greater pedal effort-almost too much for the street but tolerable, easier to modulate brakes and they feel much better, still lock fronts before rears. I’ve bled the brakes and master multiple times, nice firm pedal. I’ve also adjusted the rod between the master & booster based on info I found on hybrid [had it too much at one point [locked the brakes and I couldn’t back the car out of the garage!]. no leaks in the system, vacuum booster doesn't make any noise but I’m thinking that either I have a bad component-like the master or booster or…I need to plumb the prop valve inline with the front brakes. i'm leaning toward prop valve for the fronts. Help! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 9, 2006 Share Posted May 9, 2006 Do not do a prop valve for the front. That is a very bad idea. Sounds to me like the reaction disk is missing. Quote Link to comment Share on other sites More sharing options...
2126 Posted May 9, 2006 Share Posted May 9, 2006 Hi Dave! From the description of brake components, I think you are on the right track about relocating the P-valve. If you can't get the feel you are looking for with the P-valve relocation, you may consider going with a set of new adjustable race type master cylinders. Have you played around with different pad componds? Changing the rear calipers my also be a consideration to increase the rear clamping force. Just some food for thought! Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted May 9, 2006 Share Posted May 9, 2006 I think I would try a more aggressive compound for the rear pads before doing the P-valve on the front. Do you have stainless liness on front and back? I'm sure you do but, didn't see it in the list of mods. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 9, 2006 Share Posted May 9, 2006 Just wanted to reiterate, its a really really bad idea to do the prop valve in the front. The proportioning valves do not give a set percentage of braking reduction. They have a knee in the pressure reduction. So the harder you step on the brakes the less pressure (proportionally) the fronts get once you pass the knee. This means more pressure to the rear, which means lockup, which means spinning off the road. http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 9, 2006 Author Share Posted May 9, 2006 thanks for the added info jon. to add to my posted question, i do have braided flex lines front & rear. ss hardlines in front, stock steel lines for the rears. Quote Link to comment Share on other sites More sharing options...
fastzcars Posted May 9, 2006 Share Posted May 9, 2006 You could have corrosion in the old rear hard lines, it could be restricting flow to the rear's. DON'T put the prop valve in the front. You could also reinstall the stock 240z master cylinder to get more modulation. Since the piston is smaller than the 280zx, you then would have more pedel travel. I installed the 280xz master and didn't like it so I reinstalled the stock one back on, I liked the feel much better. Remember this is a very personal feeling. Everybody's taste on what they like their pedels feel like varies. Quote Link to comment Share on other sites More sharing options...
240playtoy Posted May 9, 2006 Share Posted May 9, 2006 When I replaced my brake system with the 240sx and toyota calipers and the 280zx master, I noticed that my brakes didn't like to activate linearly. I'd press the pedal down and wouldn't get much stopping power then press a little more---front end lockup. It was my reaction disk. It's not that hard to check. Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted May 11, 2006 Share Posted May 11, 2006 All of your descriptions are relative so it's hard to diagnose your problem. Hard to modulate and locks up the fronts easy? Both fronts? Is this easy street driving, agressive street driving, or threshold braking from 130mph? Locking up the fronts first is the right thing, but it should be easy to threshold brake and modulate just before lock up. Especially with an overkill brake system. You've made some serious changes to your system. From your description, I'm not sure what caliper piston sizes you have or brake compounds. You may have quite a bit more clamping force at the front than the rear. If so, you may never get the rears to lock. Still should be easy to modulate. Are you straight plumbed from the MC to calipers? F/R correct? If so, I suspect one or more components is not working correctly. Sticking caliper pistons maybe, improper pad installation, something moving or binding. The booster does strange things when it gives out but not overboosting. If anything, the larger calipers and 15/16 mc should be giving you a longer pedal throw which makes them seem easier to modulate. Again, don't move the prop valve. Changing pad compounds can make all the difference in the world once you solve your problem. Think about getting the fronts working correctly, then worry about bringing more rear force in, after that, you can use your valve. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 11, 2006 Author Share Posted May 11, 2006 finished putting the booster in last evening and took a quick drive-brakes feel much better. it was the reaction disc. pesky little bugger. i had to remove the booster then take it apart. i'll post pics on monday of the dissassembled booster and exactly what the disc looks like and how i dealt with it. i absolutely recommend that if you are installing a new master or booster that you remove the booster and adhere the disc so u won't have to go thru this as i did. hopefully i'll get some drive time this weekend and can see if this effected the front/rear bias and what the overall feel is now. did i mention that i love this website?!?! what would i do without u guys! Quote Link to comment Share on other sites More sharing options...
BlackBeaut Posted May 11, 2006 Share Posted May 11, 2006 It would be awesome to see pics of the booster apart and that damn reaction disk. I'd say it would make a thread worthy of FAQ status! Cheers, Rob Quote Link to comment Share on other sites More sharing options...
240playtoy Posted May 15, 2006 Share Posted May 15, 2006 here are a couple pictures of the parts on either side of the reaction disk, I did not get a picture of the actual disk as it was inside my booster. it is the same diameter as the actuator and ~ an 3 16ths thick and rubber of some sort. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 15, 2006 Author Share Posted May 15, 2006 here's a link to a pic in my gallery [i must b mentally challenged as i can't seem to figure out how to post the pic] showing both the reaction disc and disassembled vacuum booster. reinstalling the reaction disc has solved my overly sensitive brakes and modulation problem. unfortunately i still have too much front brakes-but need to get more drive time-ie-different stopping from various speeds and pedal pressures prior to posting again. anyway for the reaction disc reattachment-my method-clamp the alum plate that the master bolts to in your vice, take two large prybars or screwdrivers on the backside [part that bolts to the firewall] and-after applying some penetrating lube, carefully turn them counter-clockwise about 1/16 turn. mark the alignment position-prior to separating them! i epoxied the disc back in place, cleaned the inside of the booster, inspected all the other parts and reassembled. works great! now looking for another booster to have on hand as a spare. i would absolutely recommend that if you're replacing your master that you remove your booster and as permanently as possible, fix that reaction disc in place! http://album.hybridz.org/showphoto.php?photo=7428&cat=500 Quote Link to comment Share on other sites More sharing options...
BlackBeaut Posted May 15, 2006 Share Posted May 15, 2006 Great pics David! Was that a recon booster unit, if not, how frickin' clean?!! One of these years I'll be sticking a ZX master on mine so it's good to know eactly what I'll be looking for. Cheers, Rob Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 15, 2006 Author Share Posted May 15, 2006 rob, that booster is my original. just 90,000 miles on the odometer. i sand blasted it last fall and gave it a quick rattle can paint job. i was pleasently surprised when i 'cracked' it open to see how clean it was. funny, the nissan shop manual recommends that the booster is maintained annually and [used to?] sell a kit to replace the rubber inner workings. wonder how many actually ever did the maintenance?! Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 19, 2006 Author Share Posted May 19, 2006 hey all, have logged some addn'l driving time on the z. now that the reaction disc [rd] is back in place the modulation, overboost/touchiness issues are solved. normal driving the brakes are great-easy to modulate, nice moderate pedal input pressure required for stops and the car doesn't pull, pulsate or otherwise-feels, brakewise, like a normal daily driver. next issue-fronts locking. either from slow speeds [less than 30] or higher speeds [30-70], i can step harder on the pedal and the fronts will lock-seemingly pretty easy. still need to try a more progressive push on the pedal to see how she reacts with that but as of this point i'm more concerned how the car will [or in it's current state-may not] stop in a panic situation. i haven't tried braking higher than 70, yet... my daily driver cars seem to have a shorter stopping distance that my z does now. do i look for a more or less agressive brake pad compound and do it do it for fronts or rears. i emailed ross from modern-motorsports [using the 'contact us' link in their website] over a week ago and still haven't heard back-he's the one i purchased the brake kit from. i'm hoping someone here can help me sort this one out. Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted May 19, 2006 Share Posted May 19, 2006 What type of pads are you running on the rear? Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 19, 2006 Author Share Posted May 19, 2006 both front & rear are what ross supplied-kvr performance, i believe they are the carbon/kevlar version. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 19, 2006 Share Posted May 19, 2006 I always thought the balance on that 13" front and 11" rear setup would be way off. You'll need to play with different pad compounds front and back, or get dual masters, or get the Extreme rear brake setup. Probably the Extreme rear would get you the best result. Quote Link to comment Share on other sites More sharing options...
1 tuff z Posted May 19, 2006 Author Share Posted May 19, 2006 i hear u jon. i was, however, under the impression that when i purchased the 'complete kit' from mm that it would be just that-a complete kit, which i wouldn't have to do much 'fiddling' with... Quote Link to comment Share on other sites More sharing options...
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