Brake issue

[MikeB]

I've had this 1969 C10 forever, but I just recently noticed that the brakes take more pedal pressure than usual to stop the truck. Also, even if I stand on the brakes with 100% effort, they will not lock-up. However, the pedal does not go to the floor, nor does pumping the brakes help.

It has 1985 C10 brakes on the front with fairly new Wagner pads. On the back are 11"x2" finned drums (71-72 as I recall) with unknown shoes.

Master cylinder has a 1-1/8" bore, and the combo valve is aftermarket.

More info: I bled the brakes a couple years ago when I replaced the combo valve. Ended up with new clean fluid. I think the problem I'm having just recently started.

Had a friend suggest a 1" master cylinder, but it's always worked fine with the 1-1/8". Any other ideas?

Edit: I just remembered that I got the brake pedal about 1-1/4" closer to the floor by shortening the pushrod by a few turns. Did that a few months ago, but I don't recall having the problem then. But then again...

[Steeveedee]

Is it power brakes?

[mr48chev]

Any driving lately that caused heavy use of the brakes that may have glazed the pads or lining? Towing a trailer that doesn't have brakes, steep grades, lots of stops in traffic?

I'd also check the rear brake for a wheel seal leak as brake lining with gear oil on it or other contaminant can require a lot more pedal pressure. The 77 F2fiddy I have needs rear brake shoes and axle seals when I feel like tearing into it.

[MikeB]

Yes, power brakes with OE-type 11" booster.

No towing or carrying heavy loads.

[weq92f]

.

I'd check the booster vacuum source, check valve and whether it holds vacuum once the source is removed.

If you suspect glazing or other pad/rotor mating issue, perform a fresh pad bedding and rotor seasoning procedure on a safe stretch of road...see if that changes anything.

That procedure is documented Online but it's basically...

Season Rotors:
1)heat the rotors to crazy high temp and let them cool all the way down...twice over the course of a couple days. This involves light stops followed by medium stops, followed by heavy stops then cool down then do it again harder the next day.

Bed PAds
2) Heat up the rotors again with some medium stops, then perform maximum braking from 70 down to 5 without locking up twice in a row. Let cool for 10 minutes while driving. Do a few light to medium stops to put some heat into the system then perform 8 maximum brake events from 70 to 5 without locking up all in a row...then let it cool with 10-20 minutes of driving without using brakes.

1) above heat cycles the new rotor to make it resistant to future warping due to hard braking events or prolonged braking events. This procedure should precede pad bedding.

2) above beds pad material into the surface of the rotor for better braking performance going forward. It's common for the rotor to take a blue hue after this procedure and it's likely you'll smell the familiar brake pad burning aroma.

Hth,

-Kevin

[Rick Bollinger]

Check your rubber hoses. The inside liner can delaminate and block flow. Also if you ran low on fluid or had a little air in your system and hit the brakes hard you may have tripped your valve in the proportioning valve and need to re set that.

[MikeB]

Thanks, guys. I'll look at the easiest things first.

I'll check out the valve. The dash light isn't hooked up (shame on me), but I'll use an ohmmeter.

Front brake hoses are only a couple years old, but I can't remember how old the rear one is.

Hate to get into the bedding and seasoning. It would be hard to find a stretch of road where I could do a 70 to 5 stop! Did that a few times over the years with new pads, but not quite to that extreme.

[MikeB]

OK. Looks like it's the booster that I had rebuilt in the mid-90s. Could not draw a vacuum on it with my lungs or my MityVac. Idle speed goes up when the hose is connected, just like with the usual culprit -- a cracked hose. The check valve seals fine.

Also pressurized it with 10psi air, and I could hear the leak out the back somewhere.

Guess I'll go shopping for a new booster

[jaros44sr]

I’ve got a new one laying here, if interested

[Rust_never_sleeps]

Bad booster will increase effort, but not prevent lockup, so there's at least one additional problem that may have been masked until the booster gave out

[MikeB]

Originally Posted by Rust_never_sleeps

Bad booster will increase effort, but not prevent lockup, so there's at least one additional problem that may have been masked until the booster gave out

I hear what you're saying, but I don't recall ever trying to lock the brakes until this problem. So I think the booster will do the trick. But, yes, there may be an additional problem.

aros44sr--Thanks, but I already ordered one.

[MikeB]

Got my re-man booster installed. Haven't taken the truck out for a drive yet because the passenger door is all apart, but did back it out the driveway and drove it back into the shop. The pedal feel is totally different now. Better than ever. I suspect the old booster had a small crack in the diaphragm that grew over the years. So I've probably been driving around for who knows how long with a leak!

This retainer clip and wave washer were a bear to install! Actually that's a "before" photo. I got the clip back in with a flat washer, but not the wave washer. Not sure if I'm flirting with disaster, but I will get that wave washer installed some day soon. Also looking to use a shoulder bolt if I can find one with the right dimensions.