Do I have a Residual Valve in Master Cylinder

[Sean D 31]

Hello everyone,

 

Was wondering if anyone can give me some advice.  I purchased the following master cylinder: http://www.mustangsunlimited.com/itemdy00.asp?T1=F71248+01 and do not know if it has a residual valve or not. Since the description says for power breaks, I doubt it does. Is there a way to check to determine if it has one or not?

Here is my current setup:

No customization and all is stock power brakes with single piston front disks and drum rear brakes...bendix power booster, and the right 69 pedal, distribution block and proportioning valve: https://www.npdlink.com/store/products/distribution_block_and_proportioning_valve_assy_exact-186692-0.html

I have replaced the MC with the one indicated above, replaced front brake lines, re-did the entire rear drums including slave cylinder, pads and drums, as well as new front calipers.

 

Here is my problem: with the car off the breaks are hard without having to pump the pedal, which would indicate no air in the system...btw I had gone through a gallon of fluid to ensure no air.  When I turn the car on the pedal drops multiple inches and half way to the floor. When driving I slam on the breaks and no wheel lock up, just slowly come to a stop. While troubleshooting, and car running I plugged the rear port at the MC and break pedal drops, but when I plug the front at the MC the breaks are hard with the car running. Will a 10lb residual valve on the rear line between the MC and distribution block help this?

 

Also, not sure what size bore the MC is and mustang unlimited could not tell me. Anyone know or have a guess? 

 

[Rsmach1 71]

With the car off in a power brake car the pedal is typically hard, this doesn't mean there is no air in the system. Your symptoms indicate there is indeed air somewhere. Did you thoroughly bench bleed the M/C ? Another VERY COMMON mistake when replacing calipers is to install them on the wrong sides, this leads to the caliper having an air pocket that can not be bled out, when the caliper "appears" to be on correctly.

 

 

You would think having the bleeder facing straight up would be correct, but in the case with these calipers the bleeder should be at an angle. check em and let us know if you still have an issue.

[Rsmach1 71]

Oh yeah for your other questions the M/C bore should be 1" for that M/C and the residual pressure valve should already be in the M/C. Adding another one will NOT help.

[Sean D 31]

Oh yeah for your other questions the M/C bore should be 1" for that M/C and the residual pressure valve should already be in the M/C. Adding another one will NOT help.

Why do you think that the residual is in the MC? I read that most do not come with and especially when the description from MU states power disk.

[Rsmach1 71]

The valve should be in the front port of the M/C (for the rear brakes), there's really no reason to have one for the front disc's unless the M/C sits low in the car.

 

The problem you've described of excessive pedal travel is typical of air in the system.

 

Did you check the caliper orientation?