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We backed the truck out to work on the doors and Zach noted the pedal hits the floor... no oil trail visible... oh no? They were just working on Saturday.

knattrass wrote:We backed the truck out to work on the doors and Zach noted the pedal hits the floor... no oil trail visible... oh no? They were just working on Saturday.

Have you rebuilt the entire system, is it the stock system?

I had the same thing happen a few weeks ago. First press of the pedal went to the floor, second press would give me some pressure. Brake fluid level was fine, no leaks anywhere. My NAPA guy told me that's a telltale sign of a failed master cylinder, he said it's bypassing internally. Got a new one from John at MWM, gonna install it this weekend.

Charles/Greg - thanks for the feedback. When we bought the truck the guy said that he had gone thru the brakes, had them relined, etc... We made a decision to only fix what was really needed and spent our resources on restoration not rebuilding. We knew when we installed the lock outs on the front that we had a bad seal. We changed the rear diff oil and had a leak. We figured for now, we'd accept changing the bottom of the bird cage and the M37 on the same schedule.

Zach drove around the block 5 days ago with no issues. The truck sat for 4 days while we worked on the windshield. There were no visible leaks but the next time Zach got in, the pedal went to the floor. Looks like the m/c is original and the rubber boot is torn, but the brake switch was working. If the m/c is blown, would there be enough psi to close the switch? I was thinking that something easy to check would verify the m/c gone bad.

I've never looked at an M37 master cylinder, so I don't know how the switch is activated. What I can tell you, though, is that not all brake light switches are hydraulically activated! In fact, "way back when," most of them were not. They operated something like the light switch on your refrigerator door and the lights came on as soon as you depressed the pedal.

It is a pressure activated switch but I doubt if it requires as much pressure to activate as the brakes themselves need to work.

I had overhauled the brakes (new cups in the wheel cylinders and new rubber in the master...) on mine shortly after I first got her. A few months later after sitting for while the pedal went to the floor when my nephew backed the truck out of the garage...nearly wound up in the neighbors front yard.

Did it right the next time...new wheel cylinders, master cylinder and hoses. Also went with silicone brake fluid... It has lasted several years now....

My old line applies here, "Everything that is left untouched will come back to bite", it's a fact. Rule #1, NEVER believe what a person says about I've overhauled this & that, especially if you are hearing it from a seller. 9.5 times out of 10 all that's been done is just enough to keep the wheels from falling off till it rolls off his property, I've seen a few cases where that even failed. Now if you are dealing with someone you know, this may not apply, although in some cases it still will.

I've had the pleasure & I do mean pleasure of talking with Keith a number times in phone conversations, he has made a good & lasting impression on me & I hope I'll get to shake his hand at some point. Keith, your photos attest to the fact that you & Zach have countless hours invested into it already, believe me I know the prep time required to make a paint job look like that, the 2 of you have done a great job.

My point of view in 1st things 1st is quite different though. The body & paint restoration is on the end of my list of important points. Above all a safe vehicle comes first in my eyes, that means brakes, steering, wiring, etc are top of the list items with me. What has happened in Keith's current brake issue is this; the check valve in the master cylinder has failed. It's function is to prevent system pressure bleed off, pressure bleed off within the cylinder is exactly what you have going on. It is all internal & you will see nothing external going on at all. In the early stages, pumping the pedal a time or 2 will bring the pedal pressure back, as the check valve issue becomes worse, it will eventually lead to more & more pumping & eventually get to the point of no return. Then is when your life & others are at risk. If you were not able to bring it back by pumping a few strokes, other issues could also be factors such as piston cup failure likely caused by rust in the M/C casting bore. Be careful making this repair, a drop or 2 of brake fluid on new, not fully cured paint, well.

Going to the floor was happening to me. Even after a M/C rebuild. I got to the point of worrying about the brakes every time I drove my truck. My answer was the disk brake conversion from Ugly Truckling and Ray Suiter. That ended all my worries. No one can really see the disk conversion so it won't detract from the stock looks. And oh what a piece of mind it brings.

Here is the link to Ugly Trudkling....just click on it:
http://www.uglytruckling.com/

Hi K.
You could just do the master cyl conversion. That is also on the ugly truckling site. It used a 1ton chevy dual resevoir and will work with the all drum set up. The M/C conversion is covered in April 2006 Military Vehicle Magazine also. The safety factor of the dual resivoir can't be overstated if you lose any part of the system with the stock set up you lose all your brakes. Think how fast can you grab the hand brake? With the dual you still have 50 percent of your brakes left. Important for a daily driver.

Was able to get the 3 rusty bolts off and the steel brake line off the m/c and removed it. Tried to remove the brake pedal yoke pin to drop the plunger side of the m/c but that pin was/is rusted a plenty - got it soaked with PB so I keep trying to whack at it. It doesn't need to be removed as the new plunger screws right onto to it... its just one of those things you'd pick at!!

Transfered over the brake switch and fording vent stop cock using the high temp thread sealer (thanks Charles) just got to buy a new short brake line to make the 90 degree bend and re-connect.

Got brave with removing the right front tire, pulled off the drum, noticed only 1 large pan head screw - the other 2 are broken off. Is this a big deal since the wheel bolts up?

Plenty of brake pad fibers and noticed that the drum turned clean about 3/4 revolution and then dragged (obviously an adjustment issue). Will plan on buying the industrial sized brake cleaner can tonight!

Got the flex hose off and wheel cylinder off - those 2 bolts are kind of hidden to get at. Noticed that the cyl had a 90 degree brass block, 2 bronze crush washers, held on by a 3/4" hollow bolt with a hole drilled in the side to complete the 90 degree flow! Seems logical for an elbow?

I'll take some pics tonight of the mess.

knattrass wrote:Was able to get the 3 rusty bolts off and the steel brake line off the m/c and removed it. Tried to remove the brake pedal yoke pin to drop the plunger side of the m/c but that pin was/is rusted a plenty - got it soaked with PB so I keep trying to whack at it. It doesn't need to be removed as the new plunger screws right onto to it... its just one of those things you'd pick at!!

Transfered over the brake switch and fording vent stop cock using the high temp thread sealer (thanks Charles) just got to buy a new short brake line to make the 90 degree bend and re-connect.

Got brave with removing the right front tire, pulled off the drum, noticed only 1 large pan head screw - the other 2 are broken off. Is this a big deal since the wheel bolts up?

Plenty of brake pad fibers and noticed that the drum turned clean about 3/4 revolution and then dragged (obviously an adjustment issue). Will plan on buying the industrial sized brake cleaner can tonight!

Got the flex hose off and wheel cylinder off - those 2 bolts are kind of hidden to get at. Noticed that the cyl had a 90 degree brass block, 2 bronze crush washers, held on by a 3/4" hollow bolt with a hole drilled in the side to complete the 90 degree flow! Seems logical for an elbow?

I'll take some pics tonight of the mess.

You mentioned the drum turned about 3/4 of a round & then started to drag. That isn't an adjustment issue, but is a warped drum.