Installed new 4 piston calipers on rear, 6 piston calipers on front, with complete new brake line to a new master cylinder and SS flex lines to the calipers. I did this about 8 years ago, but it has not been driven much since installation. When I went out for a test drive today, the brake pedal kept getting harder and harder to push and the vehicle struggled to move forward. By the time I got back to the house, they were completely jammed up. If I give it a day, they are released and the wheels spin freely. This is happening on all four corners, not one or two. This tells me the common denominator is the MC.
I took out the master cylinder and checked for trap valves and there were none. I exercised the main piston and it moved freely in and out of the chamber. Some of the SS flex hoses have a sharp bend, but not what I would consider a kink in the line.
Because of the size of calipers I put on the vehicle, should I run larger than 3/16 line?
Because of minimal usage, could the pistons in the calipers be seized?
Just to add to Mustangmans post…
Once the brakes are locking up, crack open a bleeder valve to see if A) the caliper releases and B) is the fluid under pressure?? (like you are bleeding the brakes).
If you installed a MC like Wilwood etc, it is possible the actuator rod to either the booster or the MC is too long applying pressure to the brakes…
Also, are you running a booster, if so hydraulic or vacuum? if vacuum, have you also installed a bigger performance camshaft with a tight LSA, low vacuum??
Basically if the pedal is solid and doesn’t move, that means the fluid has nowhere to go, if you clamp off all the brake lines on a properly working brake system, the pedal with only move about a 1/2"ish, same thing if the actuator rod is to long and already applying the brakes and the fluid is pushing the caliper pistons out and then you depress the brake pedal, the fluid has nowhere to go therefor giving you a rock hard pedal…
I didn’t mix fluids, it was new installation front to back and I bought all the same DOT 3.
Due to limited locations to mount an MC setup, I purchased an under dash kit, unfortunately Wilwood doesn’t have that kind of setup. So piston length should be good, plus I have good brake travel until they lock up.
I lifted up the front end and the wheels spun easily, since the MC has been removed. I tested the piston in the MC and it moves freely and easily.
I’m running a vacuum booster with a vacuum pump.
I don’t think i have either of these installed: combo valve or a bias control adjustment.
Ok, so my MC is universal and has outlet ports on both sides. When the piston is facing my body, I used the left side ports. Is there a chance the left and right ports are used for different things? Long shot, I know but thought I’d ask.
Universal parts don’t always work universally. Contact Wilwood and ask if that particular MC will work with their calipers. Have the Wilwood and MC part numbers when you call them. You’ll need the manufacturer ID for them too.
To me, it sounds like something is stopping the fluid from returning.
But, there appears a small flow allowed so that over time, it can relax the brakes.
This is where I would be focusing initially. It may not look kinked from the outside due to the SS jacket. Try to get some relief so there is no sharp bend at all. Maybe just unbolt the hardlines for a test run to see if it acts differently when the hoses are not bent.
Just had another thought- after 8 years like that, the hoses may have taken a set with the kink and may not fully return to their original round shape even when relaxed. Might need to massage that bend area a bit…
I just took the lines off each caliper and blew air through the brake lines from front to back no problem. I’m thinking moe and more its the MC. I also checked the hardlines and no kinking or damage. I rerouted the SS flex lines to be more straight.
Perhaps the booster pin should be adjusted backwards to allow the fluid to release back into the MC. This is the most plausible explanation I’ve come up with yet. The adjustment was never played with from the vendor, but who’s to say some nine year old in Shenyang just put this together like the picture on the wall shows???
Yes. It appears that the master cylinder piston extends 1/2" beyond the mounting flange, the pushrod in the booster should be recessed the same amount (plus 0.010").
If the master cylinder piston is not fully retracted at rest, the piston seals will block the reservoir fluid return holes. As the fluid in the brake calipers expand with heat, the brakes will self-apply if fluid is not allowed to return to the reservoir.
Replacement brake boosters will sometimes include a gauge for the installer to verify/adjust the pushrod inside the booster. You will have to make your own measurements.
That is exactly what I was thinking and getting at in my 1st post about the actuator rod being out of adjustment, and your pictures and Nevada confirmed it… Even though the pedal free play from the pedal to the booster is correct didn’t mean the rod is correct between the booster and the master cylinder…
Thanks so much guys, I took the long way round but I think I got there. I’m letting the brake fluid self bleed for the night and then I’ll do a good bleed tomorrow. Hopefully just some fine adjustments.
I’ll look and see if I can find a tool for the setup I have.
Normally, that booster pin has 2 nuts on it and can be adjusted in/out as needed. Then just lock the nuts to set the position. The tool I have is shaped like an H with a rod that slides through the center beam of the H with a lock screw to set position. Loosen screw, place tool over master and slide pin until it touches the master piston. Tighten screw. Now flip the tool over and place it over the booster. The adjust the booster pin until it barely touches the tool pin. I like to leave a small gap.
How that underdash unit works, I have no experience. I would think the adjustment rod is for pedal engagement to the booster but you have it in your hand and hopefully have some instructions? At a minimum, perhaps you can tell if there is contact between them as you’re assembling the master and booster together to verify if that is the problem?
Twin Turbo, I’ve bought that tool off amazon. After the adjustment, the pedal had slop in it before it engaged the piston. I think I backed it off too much. If the top of the pedal has further travel, then the piston should have more room to back off. That’s my theory and I’ll (dis)prove it Thursday night when the tool arrives.
Cool. In a traditional setup and hopefully same here, there are two interfaces; the pedal to booster and the booster to master. The pedal can be sloppy and still have the booster pin too far out, holding the master piston from retracting fully. The tool should help eliminate the booster to master pin clearance as an issue. Good luck! Would love to see the set up and car at some point.
This is a really cool arrangement if you get it to work. I built a car many years ago (still have it) with the intention of minimizing everything in the engine bay. So, manual brakes, all lines hidden in frame rails (brakes, trans etc), heater delete and so on. Just an engine sitting there. Was fun to do. Would absolutely have done this if I knew they existed to remove the brake mechanism from the bay as well. Plus, power brakes would be nice. Too much engine, too much gearing, too little brakes…it’s hard to hold it back when shifted into gear, the tires squawk briefly even standing on the brakes
