My brakes suck!

[SuperDan]

Ok, so I got my car running in tip top shape now and I just found out that my brakes kinda suck.

I did the Toyota 4x4 calipar swap and what I have noticed is that the pedal has a lot of play in it now, it goes allmost to the floor and then suddenly grabs like crazy at the end. This is kinda lame.

Question: My car is a 78, do i need to remove the stock proportioning valve?

 

 

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Dan, 78 280Z, 383 450hp?, 700R4 allmost there!

http://members.home.net/dporter1/

[MYRON]

SD, Your back! I was beginning to worry...

I did the toyota 4 piston swap as well and

mine feel very solid. Power brakes do not like big cams because the vaccume is not

the same. I bought a vaccume reserve can

from Summit. It makes them feel a little "heavy" but i do have full stopping/lockup power when i stand on them.

It sounds like you have a big cam causing

lack of vaccume or your booster is going bad.

Have you tried to bleed them again?

also check to see if your brake line is

too close to your header causing the fluid to boil. HOW DOES IT RUN??????????????

[John Scott]

SuperD, Sorry to hear about your brakes. I had a caliper piston sticking intermittently in one of my older cars. Sometimes it would grab, other times it wouldn't. Doesn't really sound like your problem. It seems that even if the proportioning valve isn't optimum you'd still have a firm pedal. If there aren't any obvious leaks or pulling to one side or the other, I'd bet you either boiled the fluid, like Myron has suggested, or have an internal leak in the master itself, especially since you have more play suddenly. Does it lock up on front or rear when it does grab? Its always something with these "project" cars. I know you don't want to drive a rod without the binders,... BUT what was the motor like? When does the power come on. Can you ever hook up the tires? If you haven't pushed it that hard yet, we'll try to be patient until you until you figure out the slowing down part.

 

[This message has been edited by John Scott (edited March 16, 2000).]

[SuperDan]

I need to add more info next time before I post

The long travel in the brake pedal was there since I rebiult the braking system. I replaced everthing in it, new wheel cyl, new braided brake cabels, new master cyl, rebuilt 4x4 calipers etc and have bleed the things with Valvoline Dot4 about what seems like a 100 times trying to get the pedal to firm up. Like I said, it has no stopping ability until you get to the very end of the pedal travel ( about 1 inch from the end) and then it becomes super sensitve and goes from nothing to fully locked within a 1/2 inch of travel.

The low vaccume is causing the pedal to be a little heavier now but the problem was there before the cam change.

This happens even when the car is cold and I have the brake lines double heat shielded.

The braking is straight and feels even.

It's hard to describe, its not like the brakes are spongy, it's more like there are no brakes at all for the first 95% of pedal travel then the last 5% is were all the braking happens.

Regarding the engine, the thing is a brute, no other way to describe it. I had alot of problems with idle and drivability with the Holly carb and finally sent it back and got a Carter AFB. It now runs perfect!!!

And yes, there is serious traction problems at any speed below about 50mph.

But it is still very streetable and easy to drive if you keep your right foot light.

But there is no doubt in my mind that im in the 475hp area!

Time for flares and BIG *** tires!!!!!

 

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Dan, 78 280Z, 383 450hp?, 700R4 allmost there!

http://members.home.net/dporter1/

[pparaska]

Dan, it's great to hear the engine is so powerful and sorted out now.

 

About the brakes. Did you change the master cylinder to a different design? The pushrod coming out of the front of the booster had to be shortened or lengthened (I can't remember) when I put a 280ZX M/C on my 73 with the big booster. If there is too much play there, it will act like you say it does.

 

Since you say it isn't spongy, I'd guess that the M/C was bench bled. If you didn't know this is a critical step, as you have to push the piston assembly of the M/C all the way into the body to get all the air out. Bench bleeding is the only way to do this.

 

Keep the shiny side up and don't bug the fuzz with that beast!

 

Pete

[David Spillman]

HI Dan,

I converted to Toyotas/stock rotors last fall and have been unhappy since with braking. BUT A couple of days ago I pulled the master cylinder "replacing w/master/booster from ZX"...it evidently was leaking a little between it and the booster. Sooo I'd check out the master before dumping the brakes like I did. BTW my replacements look awesome "Wilwoods". they're just installed waiting on the aeroquip fittings to make up lines to adapt stock lines with calipers. BTW make sure the rear drums have been snugged up...adjusted out tight,if not already tried.

David

 

[This message has been edited by David Spillman (edited March 17, 2000).]

[MYRON]

When are we going to see some post in the "i'm tellin ya" section of this site

SD???? What tires are you using on your car?

Mine to is around the 475HP mark. With the

improperly installed 700r4 my tires would

spin all the way through 1st gear 1/2 way through 2nd and 3rd would get a NASTY scratch! The factory tires/wheel combo

is about useless for this kind of power.

Mine are yokohama 205/50-16's and do OK.

for now.

Myron

[SuperDan]

Yeah, I bench bleed the MC 3 differnt times thinking that is where the problem is and the MC is a new stock unit for a 78Z so no mods needed to be done.

After looking at the diagram for the stock 78 280 PV I think that may be my problem, it is alot differnt from the 240z unit.

The way I understand it is that in addition to preventing the rear wheels from locking up first it also will (if there is a loss in pressure in the F or R system due to a leak) increase pressure to the opposite system.

Since the front brakes now have a larger internal area I think the valve is bypassing the front brakes and applying more pressure to the rear.

Im going to test this weekend to see if im on the right track.

Im not going to be driving the car hard anymore until a few things are worked out.

1. Get my brakes working!

2. Get my roll cage in.

3. Get some bigger tires.

Number 3 kinda goes with doing my body work since some kind of flares are in my future.

My tires right now are stock 195/70/14 on slot mags, way to small!

 

 

 

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Dan, 78 280Z, 383 450hp?, 700R4 allmost there!

http://members.home.net/dporter1/

[MYRON]

Get some rubber on there SD and you will notice a night and day difference in performance! My first few races were with the factory tires like yours. The yoko's

made a huge difference in the last few

races. I think those are the ones that blew my tranny with all the extra traction. If

I can get my dads crane this weekend i will have mine back on the road by Monday!...

I will be sure to let everyone know how the th350 and 2500rpm stall work out....

Myron

[clint78z]

Super Dan did you ever find a fix my brake are exactly the same. It's like nothing the wham instant lockup. I have 2+2 booster and the larger master cylinder, I had to adjust the pushrod to master cylinder length. It's real dangerous and I have to fix it any suggestions??

[Guest Anonymous]

I am converting to the 4x4 Toyota brakes and 280Z 2+2 Vaccum brake. I also obtained the 2+2 master cylinder (as a precaution) with the 2+2 brake vaccum because between the master cylinder and the vaccum brake cannister is a rod adjusted specificlly for that master brake cylinder and brake vaccum combination. I also have an after market brake propotioning valve for the rear brakes. I switched a vaccum brake on a Datsun 620 pick-up to the original master cylinder and found a brake problem like described. My remedy was to get the adjustment rod from the replacement vaccum to work properly. The brake and vaccum combinations are not apparently identical and easily interchangeable in every application in all the Z models . That is my uneducated opinion

[clint78z]

I have a question in my 76 the master cylinder was the dual type. Then I change to the 81 15/16" master cylinder. Is it me or did the front and rear brake lines have to swap postions the way they hooked into the master cylinder. Might have pulled a dumb dumb ??

[blueovalz]

I think your observation is correct. I also remember using the brakes both ways (swapping front and rear) and not noticing any bias or braking problems.

[alsil]

One thing I have noticed is that mine (I have the 300zx hub/rotor/4runner setup) is really light effort, super sensitive, has a little play, and half way down turns to a rock. if I tap the brakes they lock, if I ease into them, I can get it almost to the part it gets tough without locking them up. 73BOTIZ said he had the smae problem, and he has the same setup. Seems like the booster is overboosting, then it hits bottom and doesn't do any more. Kind of hard to describe. Let's just say I can stop in a HURRY if I need to, and sometimes when I'm not planning on it.

[clint78z]

I have super sensitive feet, and still can't modulate the thing even at 50mph I get nothing then bang it almost puts you head in the steering wheel. I am sure something is wrong I am going to have another look, mabey another shot with the mighty vac.

[Pop N Wood]

SuperDan

 

A couple of guys have posted the fix...you need to adjust the length of the rod that connects the brake pedal to the brakes! The reason you feel no breaks for 95% of the travel is it takes that long for the rod to touch the back of the booster.

 

I had the exact same problem with my 70 when I upgraded to the later model master cylinder. On my 70 the rod is adjustable, sort of one screw inside another. It took an inch or more of lengthing to make the brakes start to work with the first inch of pedal travel.

[Guest Anonymous]

I've read that that lockup problem at the very end of the pedal travel is due to getting the front/rear brake lines coming out of the MC reversed..........might want to check.

[clint78z]

I already used the calipers and adjusted the rod length to just touch the piston socket, on the 280z it is too long when you put it on, and will cause the brake to lock on and not release if not adjusted properly. Something else is up with my little bugger, it is not an obvious track down so I have to go through the whole system again.

[Pop N Wood]

Yeah, Bryan is right. That was the other thing I had to do when replacing the master cylinder.. swap the break lines front to back. The early models and later models are reversed! I remember I got the directions off of the Arizona Z car web site when I was considering their 4 wheel disk set up several years ago.

[Guest Anonymous]

SD, just a suggestion if you haven't figured out your brake problem. If you have verified proper pushrod lenght into the master cylinder and no air in the system, there is an easy way to test where the extra pedal travel is going. Clamp off the all of the 4 flexable brake lines going to your calipers and wheel cylinders. I have special clamps from Snap-On, but you can use small vise-grips (if you use vise-grips be sure to protect the brake lines by placing a piece of rubber hose over the brake line then clamp it off). Once you have all of the lines clamped off check your pedal travel (I am sure it's obvious???? but....this is a stationary test DON'T DRIVE THE CAR IN THIS MANNER). If you still have excessive pedal travel, your problem is in the master cylinder. If your pedal if firm and high, then starting in the rear remove one clamp, re-check pedal. You repeat this for all 4. When the pedal drops you will have narrowed down the problem to a wheel cylinder or caliper. This test will work for any car with a low pedal.