S12+8 and 240sx brake issue

[WizardBlack]

Hello, I have an issue and just want to confirm what the problem is.

 

Previous Changes: Starting with my "new" '77 280Z, I installed stainless braided lines. Still not happy, I install a new booster and new 7/8" master cylinder along with rotors and pads for the front. Now the fronts definitely lock hard but the rears aren't doing much. After doing all the improvements, I notice fluid leaking from one of the rear drums (must be a busted cylinder). I leave it be since I don't drive it.

 

Current Changes: While down for turbo install and megasquirt, I tear into the rear brakes to find both cylinders blown and the rear drums soaked in fluid. I spring for the rear caliper conversion brackets and buy 240SX rear calipers, pads and rotors from a parts store (Autozone loaded calipers and the 300zx rotors as per the sticky thread). While I am there, I also get the non-vented toyota 4x4 front calipers and pads. The front rotors are new so I leave 'em be. (maybe 5 miles on them) To top things off, I get a set of speed bleeders to make life easier.

 

After installing all this, here is how my setup looks:

 

"new/rebuilt" Toyota calipers with new pads and rotors

"new/rebuilt" 240SX calipers with new pads and rotors

Speed Bleeders

stainless braided lines

"new/rebuilt" 7/8" master cylinder and new booster

everything else is left as is

 

When trying to bleed, they all seem to need the bleed fitting pretty loose to get them going then they start to bleed ok with it barely cracked. The rears bled pretty much normally and grab when you press the brake pedal. The fronts just seem to "ooze" a little brake fluid out when you press the pedal. After bleeding both fronts this way, when someone presses on the brake pedal, the front pads move in towards the rotors but never get there. Likewise, when you let off the pedal, the springs in the caliper pull the pads back out to reset.

 

I understand I have a 7/8" master cylinder but should they not at least grab the rotors? They only close about half the gap between the front pads and the rotor. I'm pretty sure the MC and booster are fine since I had them working with essentially new stock front brakes and no rear brakes. Is there a factory prop valve somewhere I need to remove? I have a wilwood adjustable prop valve that I haven't installed yet. (One thing at a time, etc.) Perhaps the combination of no proportioning (or stock) valve and smaller MC?

[riverz]

When I did mine I had to bleed my master cyl only with the bleed port on the side of the master cyl a couple of times to get them to work right. good luck

[Zmanco]

The master cylinder should be bench bled before installation. If you try riverz' suggestion and it still doesn't solve it, then that's probably your next step. It was for me

 

BTW, with 4 wheel discs, the factory prop valve is not going to help your braking performance. As for adding an adjustable prop valve, it's likely with your setup that you'll find that the fronts still lock up first without one. I had to go to a rear pad with higher coefficient of friction in order to be able to get a good front/rear balance.

 

Lastly, make sure you have the correct toyota 4x4 calipers for the solid rotors. You probably do, but if you had the vented ones, then even a 15/16" MC isn't going to solve the issue of the pads not hitting the rotor.

[WizardBlack]

Yeah, I am sure I have the correct caliper. If you get the wrong one, it won't fit with the solid rotor. You also clearly have a massive rotor gap.

 

I dunno if I explained it very well, but the master cylinder and all that was changed a while back. I bench bled it for a solid 10 minutes. Note also, that I can get fluid out coming out of the fronts when bleeding and they move when you press the pedal; just not very much.

 

Where is the stock prop valve if I can remove it? I have no original electronics in the car so I don't need the little switch thing just below the MC either if it can be removed as well, etc.

[Zmanco]

The prop valve is on the firewall on my 73, but I'm not sure where it is on a 77. It shouldn't be too hard to follow the rear brake lines to find it.

 

It sounds like there is air trapped in the front calipers. I hope you don't mind me making a very basic suggestion, but double check to be sure you have the calipers on the proper sides. A while ago a guy had the same issue and had them swapped resulting the air collecting above the nipples. No amount of bleeding was going to solve that.

[WizardBlack]

The prop valve is on the firewall on my 73, but I'm not sure where it is on a 77. It shouldn't be too hard to follow the rear brake lines to find it.

 

It sounds like there is air trapped in the front calipers. I hope you don't mind me making a very basic suggestion, but double check to be sure you have the calipers on the proper sides. A while ago a guy had the same issue and had them swapped resulting the air collecting above the nipples. No amount of bleeding was going to solve that.

 

No worries. Yeah, I have them left-to-right properly. I think what happened is removing the stock front calipers to swap to Toyota calipers resulted in air getting up into the master cylinder. I guess it's my own mistake for not thinking of that. Likewise, with that pressure regulating thing (with the switch on it), it probably passes air between the front and rear circuits. I already started bleeding air from the MC and it was loaded. :-/ I'll letcha know if it doesn't fix the issue.

[Zmanco]

FWIW, when I installed my 240sx calipers in the rear, the only way I could get all the air out was to unbolt them and shake them and then bleed them. I suspect some air bubbles were trapped/stuck around the piston.

 

Once all the air is out, bleeding is easy. It's just getting it out the first time Good luck!

[WizardBlack]

FWIW, when I installed my 240sx calipers in the rear, the only way I could get all the air out was to unbolt them and shake them and then bleed them. I suspect some air bubbles were trapped/stuck around the piston.

 

Once all the air is out, bleeding is easy. It's just getting it out the first time Good luck!

I wonder if I've not got something similar. I had a rubber mallet out to tap around the calipers.

 

It seemed like when I crack the speed bleeder and push the pedal down the first time it gushes out. After that, I only get a dribble which clearly isn't enough. Maybe I need to pull em off and do the jiggle shake.

 

As a side note, I went back and rebled the master cylinder (rear reservoir first, then front) (didn't notice any bubbles) and then rebled the brakes. The pedal seemed stiff like a newer car (fairly short travel then it mostly stops and won't drop further without a LOT of pedal force) after doing the rear calipers. As soon as I started to bleed the fronts they got squishy again. It seems like the normal brake pressure to decelerate in traffic would put the pedal just about on the floor; like it has a lot of travel and is greatly overpowered. The reason I say overpowered is that I had someone spin the front rotors and soon as I press the pedal, they stop. Even though I probably don't have 5~10 pounds of force on the brake pedal and it hasn't travelled but one inch yet.

Are the brakes just like that on the datsun? I want the pedal to drop about 1.5" inches or so when I press the brakes pretty firm and then travel maybe another .5~1" before wheel lockup like an Mitsu Evo 8 would do (with braided lines) or STi, etc. Am I gonna need a different MC design, etc. or do some of you have that type of brake performance? Do I still have wretched air in there somewhere?

[Zmanco]

As a side note, I went back and rebled the master cylinder (rear reservoir first, then front) (didn't notice any bubbles) and then rebled the brakes. The pedal seemed stiff like a newer car (fairly short travel then it mostly stops and won't drop further without a LOT of pedal force) after doing the rear calipers.

So after you finished bleeding the rears things felt good?

 

As soon as I started to bleed the fronts they got squishy again. It seems like the normal brake pressure to decelerate in traffic would put the pedal just about on the floor; like it has a lot of travel and is greatly overpowered. The reason I say overpowered is that I had someone spin the front rotors and soon as I press the pedal, they stop. Even though I probably don't have 5~10 pounds of force on the brake pedal and it hasn't travelled but one inch yet.

Did this occur (pedal squishy and going to the floor) ONLY when the bleed valve is open? Otherwise, what changed from the situation above?

 

Are the brakes just like that on the datsun? I want the pedal to drop about 1.5" inches or so when I press the brakes pretty firm and then travel maybe another .5~1" before wheel lockup like an Mitsu Evo 8 would do (with braided lines) or STi, etc. Am I gonna need a different MC design, etc. or do some of you have that type of brake performance? Do I still have wretched air in there somewhere?

Two things:

 

1) it sounds like you still have air in the system somewhere.

 

2) with a 7/8" MC you are going to have a longer pedal than with 15/16" unit. When I did my swap I initially left the stock 7/8" MC in but didn't like the longer pedal travel. It wasn't so long that it was unsafe, I just didn't like it.

 

But in general, once you have the system sorted out, you should have brake feel similar to what you describe for the Evo.

[johnc]

This might be an odd suggestion, but check the master cylinder pushrod at the booster and also check to make sure the reaction disc hasn't fallen out.

[WizardBlack]

This might be an odd suggestion, but check the master cylinder pushrod at the booster and also check to make sure the reaction disc hasn't fallen out.

 

I changed the MC and booster not long ago, and I was aware of the reaction disc issue at the time, but I am not sure if I recall seeing it per se. From what angle would you see it, etc.? I remember reading about it was was a tad confusing on how you'd see it or what it attaches to. (I'll do some searching again, too. It's been a while)

I also made sure to adjust the pushrod on the MC to the same length as the old one as per a set of vernier calipers (unless, of course, the old MC rod was off... heh).

[WizardBlack]

So after you finished bleeding the rears things felt good?

 

Did this occur (pedal squishy and going to the floor) ONLY when the bleed valve is open? Otherwise, what changed from the situation above?

 

Two things:

 

1) it sounds like you still have air in the system somewhere.

 

2) with a 7/8" MC you are going to have a longer pedal than with 15/16" unit. When I did my swap I initially left the stock 7/8" MC in but didn't like the longer pedal travel. It wasn't so long that it was unsafe, I just didn't like it.

 

But in general, once you have the system sorted out, you should have brake feel similar to what you describe for the Evo.

 

The pedal started to feel more and more squishy as soon as I pressed the brake pedal after cracking the first front caliper to be bled. As in, on the first downstroke of the pedal I knew something was wrong because it went too far and too fast. In other words, they got nice and hard (though not quite Evo-like) after first bleeding both circuits of the MC and then doing both of the rears and it went downhill within a few pumps on the first front caliper. For the record, you bleed in this order: MC rear reservoir, MC front reservoir, LR, RR, RF, LF, no? (I will note here that while normally bleeders and speed bleeders just barely need "cracked" to bleed them, I found that the front speed bleeders had to be turned a tad more (a total of probably 45 degrees from tight) to actually get them to start bleeding) While watching the hose connected to the front caliper, the first push of the pedal ejected a normal amount of fluid but after that first push (which is, again, also when it started to get really squishy) it would barely dribble out even with some rather violent/hard jabs of the brake pedal. Maybe I just need to go back to standard bleeders and find a cohort?

 

EDIT: It sounds like I have the front bleeder too loose and it's sucking air in on the upstroke, doesn't it? That'd explain the first massive gush and overly easy pedal pressure on the first pump (fitting too loose) and the consequential squishiness only getting worse (constantly drawing more air in).

[J__]

ok so is ur pedal supersoft ? i assume thats the problem. i had the exact same problem when i did the full swap. wasnt reaction disk, wasnt mc, wasnt calipers. but there was just air in the system. took me 2 weeks to figure out.

 

the rear 240 calipers when installed on the Z, you have to swap the left and right to get them to fit (at least i had to on my 280z) and i dunno if it was the swap or just the different mounting position than the car it was made for, the bleeder valve is not sitting at 12 o'clock, maybe at 11 or 10. because of that there is air still there that u can never get out if u bleed with it bolted down. you have to loosen the bottom bolt, tilt the caliper so the nipple is 12 o'clock and bleed some more (stick a piece of wood or something between the caliper while u do this since the rotor isnt there anymore). You should get a few good squirts of air out and hopefully, voila, hard as rock pedal.

 

try that. that was the case in my situation. took ages to figure out and countless sets of mc/brake calipers, etc. pain in the ass

[WizardBlack]

ok so is ur pedal supersoft ? i assume thats the problem. i had the exact same problem when i did the full swap. wasnt reaction disk, wasnt mc, wasnt calipers. but there was just air in the system. took me 2 weeks to figure out.

 

the rear 240 calipers when installed on the Z, you have to swap the left and right to get them to fit (at least i had to on my 280z) and i dunno if it was the swap or just the different mounting position than the car it was made for, the bleeder valve is not sitting at 12 o'clock, maybe at 11 or 10. because of that there is air still there that u can never get out if u bleed with it bolted down. you have to loosen the bottom bolt, tilt the caliper so the nipple is 12 o'clock and bleed some more (stick a piece of wood or something between the caliper while u do this since the rotor isnt there anymore). You should get a few good squirts of air out and hopefully, voila, hard as rock pedal.

 

try that. that was the case in my situation. took ages to figure out and countless sets of mc/brake calipers, etc. pain in the ass

 

 

Ah, very interesting. I will give that a try. I know the other poster mentioned taking them off and 'shaking them', too. Sounds like another example of the same problem. If this works for me as well it aught to be stuck into the sticky since everyone is gonna have the same issue. Do you also have the toyo brakes?

 

BTW, you might look at my "member's projects" thread and confirm if my caliper orientation is the same as yours?

[WizardBlack]

I removed the upper bolts holding the 240SX rear calipers in place, pivoted them forward so the bleeder fitting was pointed straight up. Now I have a brake pedal that finally gets hard after pressing it in about 1.5". I'd say it's about like an OEM EVO/STi pedal (with rubber brake lines). It does ramp up in pressure from "off the pedal" up to that point, but it's not linear; it moves fairly easy until it hits that spot. I wonder if that might be the smaller MC? Or do I still have some air in it somewhere?

[Zmanco]

I think you're saying that the pedal moves easily most of the way, and then gets firm very quickly without much more movement? To me, that's the sign of a well prepared brake system. Only if it still feels a bit mushy as the pressure builds would I think there was still air in it.

[J__]

i just looked at ur build pics, nice and clean! im not sure if i have the toyo ones, i think i have nabisco? nabco? lol i cant remember, cars at home, im 3000miles from it =*(

 

anyway as far as the postioning, its the same as mine, but either you removed the wrong bolt or it was a typo... i had to remove the bottom bolt, not the top, and tilt the caliper UP until the nipple was 12 oclock.

 

heres a picture, u can kind of see the nipple is on the bottom since i had to reverse the Left and right side due to the positioning of the ebrake. so technically you even have to raise the caliper so the nipple is pointing beyond 12 o clock, even 2o clock.

 

 

the 1.5" sounds about right. mines got a little less throw. i think its about 3/4" before it becomes rock hard. And yes, it's not linear, its just like 20% resistance then BAM 90% solid feel. How hard i brake just depends on how much pressure i put on the brakes, not how much the pedal moves like normal cars.... my friend hates it but i love it haha kinda gives a sense of security? i have the bigger mc though.

[WizardBlack]

I think you're saying that the pedal moves easily most of the way, and then gets firm very quickly without much more movement? To me, that's the sign of a well prepared brake system. Only if it still feels a bit mushy as the pressure builds would I think there was still air in it.

Hmm, yeah I guess so. I'd think that having all stainless braided lines would eliminate a lot of the "takeup". My stock STi has about 1.25 inches of takeup before it gets hard (with rubber lines). The Datsun has 1.5 inches of takeup but it does get harder when it "hits". I now feel like I could literally stand on the pedal whereas before it'd practically hit the floor if you really pressed hard on it. Maybe I just need a bigger MC to eliminate some of the takeup, then.

 

As I side note, I didn't point out that I used a vac bleeder to get the last bit out of the rear brakes.

[WizardBlack]

i just looked at ur build pics, nice and clean! im not sure if i have the toyo ones, i think i have nabisco? nabco? lol i cant remember, cars at home, im 3000miles from it =*(

 

anyway as far as the postioning, its the same as mine, but either you removed the wrong bolt or it was a typo... i had to remove the bottom bolt, not the top, and tilt the caliper UP until the nipple was 12 oclock.

 

heres a picture, u can kind of see the nipple is on the bottom since i had to reverse the Left and right side due to the positioning of the ebrake. so technically you even have to raise the caliper so the nipple is pointing beyond 12 o clock, even 2o clock.

 

 

the 1.5" sounds about right. mines got a little less throw. i think its about 3/4" before it becomes rock hard. And yes, it's not linear, its just like 20% resistance then BAM 90% solid feel. How hard i brake just depends on how much pressure i put on the brakes, not how much the pedal moves like normal cars.... my friend hates it but i love it haha kinda gives a sense of security? i have the bigger mc though.

 

You have different calipers than I do. Mine has the bleeder at a different point. It's already ALMOST at the top. You described the pedal pressure very well. I'm betting I just need that 15/16" MC now. I hate to swap just for a 1/16" bigger MC, though. Doesn't seem like it'd be that much.

By Toyo I meant Toyota 4x4 brakes. I dunno the "brand" stamped on it, but it's the S12+8 non-vented calipers.

[J__]

yes i have the s12+8 calipers. mine is vented however.