helitool master cylinder upgrade

[Matthew Ziegler]

I just did the chevy mastercylinder upgrade in my m37, I'm having a tough time getting a good pedal, also the truck originally had a brake pedal return spring which is difficult to utilize with the new master, anyone have any experience with this modification? when It's adjusted for good responsive braking, the front calipers tend to drag after a mile or two. After backing off on the adjustment on the pedal to master rod it takes a lot of leg effort to slow the truck down. I also installed an adjustable proportioning valve to the rear brakes from wilwood.

[Gordon Maney]

Do you know for a fact you don't have a residual valve in the front brake circuit?

[Matthew Ziegler]

master

I can't say that for certain, what's a good way to tell?

[Gordon Maney]

What was the application for the Chevy master cylinder? Was it for a vehicle with drums front and rear?

[Charles Talbert]

If the M/C you used is the 1 that Ray recommends for the upgrade; it has no residual check valve. Since you mentioned front calipers, I'm assuming you installed front disc. If this is correct, you likely have the push rod adjusted to tight against the M/C piston causing drag at the front pads. The piston must fully release in order to prevent drag. Normally this system works well with a good pedal after proper bleeding. If you still have drums on the rear, the shoe to drum clearance may be adjusted too wide or uneven, and you will need a check valve with a 10# rating in the rear circuit as close to the M/C as possible. If you don't have a booster in the system, it will require lots of foot pressure, even with a good solid pedal for a decent stop. The addition of vacuum boosters in an otherwise original truck will make a DRASTIC improvement in braking ability. Bleeding the system with a pressure bleeder is also a good idea, gets out every bit of air. Getting a proper pedal pull back spring in place is also a must, be sure the pedal is pulled all the way up when in the released position. The location of the spring bracket on the frame must move behind the new M/C. The use of a link along with the spring to get back to the proper length and spring tension is also necessary. We typically make a link from .125" diameter welding rod to incorporate the needed extra lengh.

[Matthew Ziegler]

brakes

Thanks Charles, one more question, is the 10# check valve a residual pressure valve? asked the guys at my local speedshop and they said they're the same thing, I'd rather check to be safe. also picked up some cool a/n stainless brakelines you can get fittings to adapt them to any pipe or flare size and they aren't very expensive,

[Gordon Maney]

A residual valve is a check valve.

[Charles Talbert]

Typically they do the same thing, however numerous types of check valves exist, some not being suitable for use in a brake system; so don't let someone sell you something you don't want. As long as you get the correct type that install in-line, it should work fine. Suitable types are offered by Wilwood and others that are designed specifically for brake system use. These are what we typically use when a residual pressure valve is needed.

[Gordon Maney]

Typically they do the same thing, however numerous types of check valves exist, some not being suitable for use in a brake system; so don't let someone sell you something you don't want. As long as you get the correct type that install in-line, it should work fine. Suitable types are offered by Wilwood and others that are designed specifically for brake system use. These are what we typically use when a residual pressure valve is needed.

Thank you Charles. A residual valve is not just a check valve, it also maintains a low pressure in the circuit, just a few psi, to keep out air and water.

[jrodjared]

What was the application for the Chevy master cylinder? Was it for a vehicle with drums front and rear?

I just posted a thread regarding this and then discovered this one. Would this upgrade work for a drum/drum setup? That's the part I can't seem to figure out. Don't see why it wouldn't?

[Charles Talbert]

I just posted a thread regarding this and then discovered this one. Would this upgrade work for a drum/drum setup? That's the part I can't seem to figure out. Don't see why it wouldn't?

It will work fine in a drum/drum application, but since there is no residual pressure valve incorporated into the M/C; you will have to install the 10# residual pressure check valves in both circuits as close as possible to the M/C in order to get proper braking action and response.

Just for the record, it is also necessary to have very slight residual pressure in an all disc system, but the valves are preset for only 2# of residual pressure for disc system use. Reason for this is that the M/C is mounted so low in these trucks, practically level with wheel cylinders or calipers, depending on whether you have a drum or disc system. In the event you are relocating the M/C up on the firewall or some other higher than standard mounting location, the 2# valve can likely be ommitted.

[jrodjared]

Cool, thanks for the info Charles!