HELP , brakes and,upgrades ive done not working right !

[Guest LAYTON]

here is what i have a resurected 71 240z it was a bare shell when i started the car,cut brake lines and a bad master cylinder.

as a built the car i did this combo

80 15/16 master

the toy caliper upgrade with 4 piston and std rotor not vented

and ss lines

and recently the modern motor sport rear caliper brakets and my calipers from my running 240sx with the 300zx rotors

 

my problem is this ive bled at least a gallon of fluid through and my pedal is still very low where it starts to work / and to top it off the system builds pressure in the front calipers so much that after some use they drag and eventually they will lock up needing to be bled off before it will move.

 

i know that i should be able to adjust the lil do-bobber that puches on the cup in the cylinder but ive done that and as i said i have very little pedal.

i had also had the rears working fairly well with the drums but since ive done the rear disc upgrade they barely work at all and from what i been hearing/reading abouth that swap is the tend to be even more if not to much compared to the drums sometimes needing a proportioning valve to fix that so im oppisite ?

keep in mind the car was never working before so ive had nothing to compare to as ive went besides the 280zx i had before that i did vented toy 4x4,s on and ss lines and stock rears with a 15/16 master and the brakes on that car were like droping a aircraft carrier anchor and im not getting the same results yet i must be missing something or have a bad combo somewhere

any ideas ? im super frustrated

[Synlubes]

Were you getting a good full flow of fluid when you blead the system ?

Was it at all 4 wheels and the master cly ?

If not, disconnect lines and clean them out ?

Follow and inspect all brake lines to see if there is a knik in a line ?

Start your bleeding at the master and then work aroud to all 4`s ?

[Guest LAYTON]

ive done that ,that way and i get good flow ,there is deffintely no kinks anywhere i do have good pedal but its way down there but the worst issues are the lack of rears and the fronts building up pressure thats really stumping me the fronts lockking up make me think there is tp much pressure on the m/c cup but with the pedal so low and the rears not working.

im searching for other problem i might have overlooked i do have 2 boosters a 71 and a 72 the 71 im using know with the 15/16 mc

the 72 has a longer stub that presses agianst the m/c cup and the 15/16 m/c has a shallower depth than the 72 7/8 that i have its about a 1/2 inch difference and the plunger on the booster is about the same 1/2 inch longer on the 72 so i cant see why im building pressure or why the rears are not appling much force?

[Synlubes]

Are you using the stock proportioning valve ?

If yes, take it off and apart and clean it ?

Another option, replace the stock pro valve ?

Try again.

[SHO-Z]

I went through a simular problem after a spring change. Was about to pull what little hair I have out. Bleed about a gallon of fluid through the system. I then when looking at the master cylinder I saw the bleeds on the sides of it. One Squirt of air and everthing was great. Evan though you are getting no air at the wheels, you can still have air in the master cylinder.

[VRJoe]

Check the stock porportioning vlave, add a new adjustable porportioning valve in the front line, then adjust the valve down to bring them in to a better balance.

 

Did you bench bleed the master, either way bench bleed it again.

 

Try the vacuum master the matches the master cyl., there have also been reports were the pad fell off the inside of the vacuum assist and caused a similar problem.

 

- Joe

[v8dats]

did u mount the calipers upside down? make sure that the bleeder screws on the calipers are on top and not on the bottom.

i learned this when i was 16 on my z. i bought new calipers,painted them and mounted them with the bleeders on the bottom so when i bled the they wont get dirty.i must have bled everything 10 times before i figured out that there was trapped air on top of the calipers......

check it out and let us know

p.s dont laugh at me i was only 16 8)

[Guest LAYTON]

mine calipers are mounted with the bleeders up ,im gonna try bleeding the system with a power bleeder at a brake place this week if not im gonna go back to the 72 booster and 7/8 master and then see what happens thanks for the ideas and ill report back later this week feel free to add more ideas if you have them i really dont want to put the 7/8's m/c back on there

 

layton

[spotfitz]

I think I remember needing to switch the lines coming from the master cylinder. The lines for the front was in a different location depending on the master cylinder. On my '74 I have the toy front calipers with solid rotor and rear 280 caliper('82, almost like the 240sx) and discs and didn't need an adjustable prop valve.

This may be my memory failing, or the previous owner having them in the wrong place to begin with, but I do remember having to switch lines around.

I just checked an old 15/16 master and it is labeled R on the front(which is the bigger bore section of the cylinder) and F at the rear(being closest to the fire wall).

Now, checking in my not-so trusty Haynes it shows on page 129 the closest to the fire wall as going to the rear brakes in a 240, but as the front brakes in a 260, which is descibed as similar to the 280(on page 238, supplement). Hope it helps.

I now really not looking forward to putting my 260 back together!

[Synlubes]

On the 79-81 ZX master cly, the larger fluid tank (closest to firewall) is for the fronts and the smaller fluid tank is for the rears.

It`s easy enough to follow lines to ck for correct install.

[Guest LAYTON]

i have no idea whats wrong with the 71 master and 15/16 set up i had in there but i put the 72 booster in with the new 7/8 i had and holy sh** i have brakes for days and great pedal i may still go up in master size but ill see how these do for a while!

nice to not have the pressure building also a little more conifidence to finish up a few more things

thanks for all the input guys

layton