Question about brakes.

[stony]

Ok guys. I have an issue and want to confirm my fix before spending money.

 

I have the stock 260 master cylinder and booster installed. Up front I have 240SX calipers and on the back I have the wilwood setup for an 8.8 rear-end. Before I tore the car apart I had drums on the back and 300ZXTT large calipers up front. This setup worked great with the stock master and booster. But now I’m getting nice air free fluid out of the master and all calipers but brake is spongy and takes 3 pumps before I get the brakes to stop the car.

 

First pump nothing, second pump slight stopping, 3rd pump locks up the brakes but still goes almost all the way to the floor. If I hold it they don’t release. I’m thinking after reading the stickies my master cylinder is no longer up to the task. I want to upgrade to the wilwood 1 inch. Just want to confirm I’m not missing something simple. All stock brake lines are removed and replumbed with hard line and braided hoses. all stock valving on the firewall is removed and i plan on installing a wilwood porportioning valve once i get the brakes a little closer to operational

 

any inputs.

 

 

[robbs70z]

Do the master cylinder out of an '81 280zx. It has a 15/16 bore. That's what I am using and I have AZ Brakes front and rear. Pedal is high and firm. Also get an adjustable prop valve for the rears to get the brake bias dialed in

[Cannonball89]

I'm assuming that you bench bled the master cylinder? If not, try that first.

 

A stock master cylinder will be a little squishier with big disk brakes, but it will still stop you without having to pump up the pedal 2 or 3 times.

[NewZed]

Sounds like an air bubble in a caliper or two. You can get bubble free flow because the fluid passes under the bubble on the way out. If you can hold it and they don't release that's a sign that pistons in the master cylinder have a good seal. The pump-up action is a sign of an air bubble, being compressed.

 

One more sign of an air bubble is if a large volume of fluid leaves the reservoir when you're pumping the brakes. If the piston is slipping, the fluid is left behind, while compressing an air bubble takes fluid to replace the volume. Have a friend watch the reservoir or set a mirror up.

Edited April 24, 2012 by NewZed

[stony]

I did bench bleed the MC.

 

I did notice that it seems like there is fluid squirting into the reservoir when I press the pedal from the bottom??? Almost like fluid is bypassing. Bad MC?

 

 

 

[stony]

Here is what I’m talking about. Is it supposed to squirt fluid like that in the forward res? The rear one doesn’t do that. I’ve never seen/noticed that before.

 

 

[beermanpete]

Here is what I’m talking about. Is it supposed to squirt fluid like that in the forward res? The rear one doesn’t do that. I’ve never seen/noticed that before.

 

Yes, this is normal. The filter screen is missing which prevents the fluid from squirting out like that. Your other reservoir probably still has the filter screen in place.

Edited April 27, 2012 by beermanpete

[stony]

Dang thought i had it ;>

 

So in general for my application, the stock master should work to slow down during drag racing. Everything i have read is talking road racing. I really don't want to upgrade if i don't need. to. The rear willwood calipers have dual bleeders. I'm assuming you only have to bleed from the top and the only reason there are 2 is because they are interchangeable. or do i need to bleed from the bottom also?

[RebekahsZ]

I had same problem with my swap. 1. Make sure rear check valve is removed from master cylinder first and foremost. 2. Bleed rear calipers with them in your hand with a block of wood in place of the rotor. When you think you have all the air out twist caliper in your hand a few degrees and bleed some more. Dont get pinched Rinse and repeat-sorry shampoo joke-I live in a house full of women. No matter where the bleeder is located you still have trapped air.

[stony]

GOT IT@!!!!! i'm such a dumbass. The rear end has been together for a while with the wheels on. When i looked under the car i had very easy access to the bleeders on both calipers so i never took the wheels off.

 

I was under the rearend tonight doing final look thru and clamping some stuff up securely when i noticed there are 4 bleeders on the wilwood calipers!!!! 2 upper and 2 lower. on thew uppers there is one on the inbd side i could see with the wheel on and one on the outbd side i couldn't see!!! bled both side and brakes work like a champ now!!! glad i didn't buy a MC ;>

[Cannonball89]

Yes, this is normal. The filter screen is missing which prevents the fluid from squirting out like that. Your other reservoir probably still has the filter screen in place.

 

No, Fluid squirting up out of the resevoir when pumping the pedal is an almost definite indication of air being in the system somewhere.

 

 

GOT IT@!!!!! i'm such a dumbass. The rear end has been together for a while with the wheels on. When i looked under the car i had very easy access to the bleeders on both calipers so i never took the wheels off. I was under the rearend tonight doing final look thru and clamping some stuff up securely when i noticed there are 4 bleeders on the wilwood calipers!!!! 2 upper and 2 lower. on thew uppers there is one on the inbd side i could see with the wheel on and one on the outbd side i couldn't see!!! bled both side and brakes work like a champ now!!! glad i didn't buy a MC ;>

 

Glad you got it fixed.

[beermanpete]

No, Fluid squirting up out of the resevoir when pumping the pedal is an almost definite indication of air being in the system somewhere.

 

Not true. There is a small opening connecting the master cylinder to the reservoir. When you press the brake pedal and the piston starts moving it pushes a bit of fluid through this opening into the reservoir. After the piston has moved far enough to go past the opening it closes the opening and begins applying pressure to the brake calipers.

 

The opening is small enough that the fluid moves with enough velocity to cause a little stream of fluid to squirt out the top. In the Z there is suppose to be a filter screen in the reservoir that diffuses the stream so you don't see the squirt. In all the older American cars I have worked on (that don't have the filter) I always had to keep the lid on the master when bleeding the brakes to prevent the brake fluid from squirting out of the master and making a mess and ruining the paint.

[Cannonball89]

Not true. There is a small opening connecting the master cylinder to the reservoir. When you press the brake pedal and the piston starts moving it pushes a bit of fluid through this opening into the reservoir. After the piston has moved far enough to go past the opening it closes the opening and begins applying pressure to the brake calipers.

 

The opening is small enough that the fluid moves with enough velocity to cause a little stream of fluid to squirt out the top. In the Z there is suppose to be a filter screen in the reservoir that diffuses the stream so you don't see the squirt. In all the older American cars I have worked on (that don't have the filter) I always had to keep the lid on the master when bleeding the brakes to prevent the brake fluid from squirting out of the master and making a mess and ruining the paint.

 

Oh ok. A Ford mechanic told me that the Mustang master cylinder will stop squirting fluid out when bled properly. I guess I've never taken the filter screens out of my Z master cylinder when pumping the pedal. Anyway I guess the squirting in my dad's Mustang is normal then? I don't know. We are having a really hard time bleeding his brakes.