gretchen/jason Posted January 1, 2007 Share Posted January 1, 2007 Im using the toyota 4x4 calipers brand new everything works great , also using the zx mastercylinder and stock 280z power booster . Car has a sbc 350 conversion using tokico struts and lowering springs all around , non adjustable struts . Deal is if the road is dry no sand no nothing it stops great . Now if i hit anything at all even a slight amount of sand with very very slight brake pedal effort the fronts lock up and wham no way to stop . I go to slow down to turn a corner if there is any sand snow etc i have to basacilly let off the brake and hope i dont break the rear end loose and go for it . Sucks when coming to a stop light almost hit a truck due to some sand on the road and i couldnt stop . The rear brakes are totaly redone new wheel cylinder pads hardware drums etc and evry so often i set the shoes just incase the become to loose . The only thing i didnt replace is the entire brake line setup and proportining valves . Any ideas Jason 78 280z Quote Link to comment Share on other sites More sharing options...
Pennyman Posted January 1, 2007 Share Posted January 1, 2007 You could try and go back to the 280z MC, that might help. I remember seeing a lot of information on this topic if you search for master cylinder pedal modulation. Haven't done the swap, so not sure exactly, but I'm sure you'll find what you're looking for. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 1, 2007 Share Posted January 1, 2007 The old proportioning valve might have gone bad. I have the Toyota calipers on my car but stuck with the stock 240 master and booster, they are new along with all the rear drum hardware. I have noticed that if I really get on the brakes the fronts will lock up way before the rears but thats how you want it. Wheelman Quote Link to comment Share on other sites More sharing options...
Dat260 Posted January 1, 2007 Share Posted January 1, 2007 I think your problem comes from incompatibility between your zx master cylinder and your rear drums, too much pressure. The ZX MC upgrade is for rear disk brake conversion. I'am with pennyman, go back to your 280z MC and take it from there. Ari Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 1, 2007 Author Share Posted January 1, 2007 Well i upgraded to the zx master cylinder because the stock unit even when i bought a new one for the 78 280z would not stop my car with the toyota calipers . The stock calipers were much worse a couple of times i didnt think id ever stop no matter how hard i slamed the brakes on . so far this is the best except when i hit sand water snow gravel dirt etc anything but dry pavement . heck they grab so good in the front that with 310 ft lbs of torque to the tires actually pushes the ront tires along the ground without them ever turning . kinda like stoping . Jason Quote Link to comment Share on other sites More sharing options...
260DET Posted January 1, 2007 Share Posted January 1, 2007 By fitting the twin piston calipers to the front you have altered the front/rear bias, more piston area on the front than stock. So fit a bias adjuster, or lump it The extra bias to the front makes the brakes feel a lot more effective too, you tend to get more front end dive when the brakes are applied hard. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted January 1, 2007 Share Posted January 1, 2007 You need the bigger MC to flow enough volume to work the front brakes. There was a recent post on this where people with the 4x4 fronts could not get proper front to rear bias. People were complaining of this even with the rear disc upgrades. Try completely removing your bias valve and run the rears straight. I assume you try pumping the brakes, or are the fronts too lock prone even for that? There was another recent thread where a member called zcarnut commented that power boosters are matched to the braking capacities of the car, and that too big of a brake booster will make it hard to modulate the brake feel. Maybe a smaller diameter booster, like off a 160 or 240 would help? I would get some more opinions before I would try the smaller booster because I have never heard of anyone taking that route before. The final option is dual master cylinders and no booster. You probably don't want to go to that extreme for a street car, but it will almost certainly give you enough flexibility to dial in the brakes. Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 1, 2007 Share Posted January 1, 2007 Hmmm.... I have tried several brake upgrades on several 240Zs... I am going with Willwoods for my next car... The systems are not that sensitive to these changes... It will make a difference in FEEL... but the MC and the Booster swaps will not fix this if it is a problem... You have bigger problems... Currently I have: LARGEST late model Toyota Landcruiser calipers Stock 240Z rear drums Stock bias valve and lines Stock MC Stock Booster PORTERFIELD race pads in front Nismo Green shoes in rear Multiple cooling ducts feeding the caliper and the rotor vents Racing slicks Here is a video of my brakes ripping some asphalt at 130MPH... Just look at the nose dive even with a track suspension... I have run everything from stock to full race set ups... and the main limitations of the stock set ups are HEAT RELATED... You CAN bias your brakes with good pad material choices... Modern materials have come a LONGGGGGGG WAYYYYY... you can get any friction and heat range you want... ANYTHING... Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 1, 2007 Author Share Posted January 1, 2007 Where would the bias valve be on a 78 280z ? I know there is a valve on the firewall drivers side . i guess it could be the rears arent getting the proper pressure due to some in line problem . And when i bled the brakes by pressure bleeding it was very hard to get rears to bleed very hard . well the fronts lock up very very easy with sand on the road or some watter when it rains so i feather the pedal . Now on a dry road if i slam the pedal to the floor the rears lock up just before the fronts do stops realy good on a nice day . Are there any other valves or such between the master cylinder and the rears ? I need to figure this out but i must say when it snows i use the parking brake to slow down as its eaiser then trying to keep the front end fom sliding . Thanks for the advice Jason Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted January 1, 2007 Share Posted January 1, 2007 I have had pretty good performance with my setup... s12 4x4 calipers slotted/crossdrilled solid rotors from MSA (should have stuck with solids) rear MSA "high performance" shoes SS braided front lines new 7/8 MC I had problems with the front brakes locking up so I drained all the brake fluid from the lines and let it sit a week or so to let it all drain. I then loaded it with DOT3 fluid and it works great...I'll convert the rears to calipers and get braided lines for it when I can afford too. Before I had my coilovers and stuff in the car when I slammed the brakes the weight shifted forward and the rears would lock up. With my old leaky stock calipers on the car I would push the pedal all the way to the floor and could not lock up a wheel with 215 tires... I think the gunk in the rear brake lines kept them from working as well... also a slightly softer front suspension should help the front brakes from locking up. Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 1, 2007 Author Share Posted January 1, 2007 A softer suspension in the front i could try that ive got tokico non adjustable struts and progressive rate springs very stiff in the front almost no nose dive when i try to stop the car stays "flat " when stoping . Ive thought of getting new springs that are a bit taller as i lowered my z 2 1/2 inches and its a bit low sometimes . Jason Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 1, 2007 Share Posted January 1, 2007 ok I'm out... I am reading your descriptions of your problems and none of it makes any sense... 1. You say that the rears lock first on dry pavement... well.. that is a big problem.. I can heal toe downshift at the braking limit and still not lock the rears... 2. you say that your front wheels lock first in sandy spots... WTF is that...??? if you drive over sand.. expect the unexpected... how would you know which wheels are locking on such a slippery surface... they will all lock up on sand... 3. You sound like someone who has never driven a car without ABS... nice learning curve there ehh???... LOL... Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted January 1, 2007 Share Posted January 1, 2007 I just was at teh gas pump yesterday when it was raining and a first gen Z was flying by and locked up the front wheels coming to a light. Obviously stock suspension because the front wheels were up in the wheelwells under full braking and the rears were not locking up... When I first had my illuminas in my Z set on 5 I would touch the brake pedal and the tires would lock up on medium braking. Set them back to 2f/3r and I can slam the pedal hard and it does really good stopping the car... Having the suspension too hard for the amount of tire can be dangerous when you are braking hard... Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted January 1, 2007 Share Posted January 1, 2007 BJ... I know you're very knowlegable but why disrespect a noob? Some of us may be stoopid but that's no reason to make us feel only an inch tall. ok I'm out... I am reading your descriptions of your problems and none of it makes any sense... 1. You say that the rears lock first on dry pavement... well.. that is a big problem.. I can heal toe downshift at the braking limit and still not lock the rears... 2. you say that your front wheels lock first in sandy spots... WTF is that...??? if you drive over sand.. expect the unexpected... how would you know which wheels are locking on such a slippery surface... they will all lock up on sand... 3. You sound like someone who has never driven a car without ABS... nice learning curve there ehh???... LOL... Quote Link to comment Share on other sites More sharing options...
bjhines Posted January 1, 2007 Share Posted January 1, 2007 sorry... I'm not trying to be harsh.. but at this point... The whole thing has run round and round the maypole... the entire description of the problem is contradictory... I don't think there is any problem except for driver inexperience... if a caliper is sticking.. none of the symptoms have been described.. (pulling to one side, vibration etc..) ABS is a HUGE crutch.. and one that many drivers have never been without... Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted January 1, 2007 Share Posted January 1, 2007 BJ... I meant no disrespect but sometime us noobs don't know WTF we're doing. It's just a fact of life. I'm sorry if I seemed rude but I just hate seeing new guys trashed... especially since I'm one of the dummies and can associate with this lack of experience. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 1, 2007 Share Posted January 1, 2007 Mike, You know sometimes the biggest favor someone can do for us to tell us we're being stupid and to get a clue. Don't be so thin skinned about BJ or any other "older guy" saying something that may sound a little harsh, it might be the thing that gets the guy's attention and makes him realize he's just being dumb. It might even save his life because he stops blaming the equipment for his problem and learns how things work before his lack of experience kills him. Wheelman Quote Link to comment Share on other sites More sharing options...
spotfitz Posted January 1, 2007 Share Posted January 1, 2007 I don't know if this is the case with a 280Z and since my old one isn't here right now I can't check, but... It has been acouple years since I did the ZX master swap on my early 260Z, but I recall having to switch the lines around once the ZX master was installed. Check the side of the master for "F" and "R" and check your lines. Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 1, 2007 Author Share Posted January 1, 2007 All in all id like the fronts to be a little less responsive on any slipery surface rain sand what be it . Ive looked at proportining valve but not sure what to use or if i should redo the entire brake system "lines" . Is weight in the rear a issue ? I had a custom speaker enclosure that all in all added roughly 200 pounds to the rear give or take a few pounds Well ive never owned a car with ABS 31 years old and every car i owned is built befroe 1971 except for my z . My first car was a 69 dodge charger no ABS second car was a 71 dodge charger again NO abs . Never had a car with A/C nor my 3 years of owning a z car in colorado ive never had heat in my ride so its not like i have no experience without ABS .Dont care for it doesnt stop as good to me . Third car is my z . No abs Well ive had a buddy follow me to see what my tires actually do in a very wet road condition i hit the brakes he said the fronts stop but the rears keep turning . I let him drive it slap the brakes on as if to stop quickly rears kept turning fronts locked up as is the opisite on a dry road i hit the brakes to stop hard and wham the rears lock up first untill the rear end lifts up enough to make te fronts skid the fronts do lock up on a dry road but not as quickly as the rears but they do lock up . Ive got a buddy with a 240 z same problem same setup if he turns a corner while braking the front tires skid and the front end goes where it wants . Im trying to see if there is a way to get more bracking to the rears then to the fronts and what should i change in the brake line setup or what bad parts should i look for . I put the stock calipers back on and the problem goes away takes longer to stop but goes away .Should i try a different pad in the front or shoe in the rear . Im using plain stock shoes and ceramic in the front .Been driving my z for 3 years with this problem didnt really bug me till i scratched my rim on a curb a week ago as for snow well thats a common thing i just put studded tires on the front to help hell i can even turn a corner in the snow without studded tires i turn and the wheels turn but car goes straight . But thats another problem i solved . Jason Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 1, 2007 Share Posted January 1, 2007 You need to get rid of the factory bias valve and just use a $50 wilwood unit under the hood where the factory unit is. Adjust as needed. I ran the same brake setup you're using without problems, although I did switch to 280ZX rears with the front Toyota calipers...The bias is the issue. Mike Quote Link to comment Share on other sites More sharing options...
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