brake pedal goes FLAT..... IT'S BAAAACK!!!!!!!

TxSlick66 · Post by **TxSlick66** » April 1, 2009, 10:00 pm

Also...Do you have the front bowl plumbed to REAR brakes and vice versa? HAd to ask... I see my pic did not post correctly. If you paste the URL in the browser, you can see the pic on my Granada brake installation web page. MAY apply to your Chevy calipers...

Demonknight · Post by **Demonknight** » April 1, 2009, 10:48 pm

and if no ones been a smartass...if the problem happens when you back up hills....don't back up hills

now to read the next two pages

oldtrucks · Post by **oldtrucks** » April 2, 2009, 3:09 am

blackagatha

Have you checked the length of the push rod that operates the master cylinder. I had a similar problem on one of my trucks a long time ago. If this push rod isn't traveling far enough on a duel master cylinder usually the rear brakes aren't receiving enough pressure and causing the pedal to go flat. The up hill thing in reverse kind of has me baffled but that is kind of normal any way. If all else fails try to obtain a pressure guage and check the pressure at each master cylinder outlet.
Some times when we mix and match componets in various systems we create a problem that can be real hard to find and/or correct.
Don't give up there is a solution, might take a while to discover what it is.
I also find that most shops that claim to be experts on brake systems are sadly lacking when it comes to theory and trouble shooting abilities.
I personly don't think you have a problem of air in the system. If you did you would have soft brakes all of the time. I wish I knew where to direct you for the technical information for the master cylinder push rod travel dimentions.

blackagatha · Post by **blackagatha** » April 4, 2009, 3:25 am

no, the rod is definitely long enough. From pulled all the way up (with a light spring) to touching the rod to the MC is like 1/8 inch of travel. I can lock up all fours and make a horrifying scene any day of the week, and yet it does this....

I dont get it...

ICEMAN6166 · Post by **ICEMAN6166** » April 4, 2009, 10:17 am

i think Mike has a good point.

Post by **Greg D** » April 4, 2009, 12:41 pm

I don't know if this will help. When I back up my Uni the brake pedal will depress farther than normal forward braking, it is NO where near as drastic as the problem you have though. About what you would expect for the brakes to self adjust. Everything in my system is new. I however did not use a prop valve and I used a 68 Mustang Disc/Drum MC. Try the Mustang MC?

blackagatha · Post by **blackagatha** » April 6, 2009, 3:28 pm

greg, though not as drastic, it does sound very related.... Ever come up with some Idea why it does that?

I should get under it and adjust the rears, or do the auto adjust a few times and see if its any different. but it seems strikingly odd that it started again after replacing the front pads... it doesnt seem like that should have changed anything???

maybe I made some sort of funky imbalance? idunno.

Post by **Greg D** » April 6, 2009, 5:03 pm

As you know the adjusters work when you back up. I have heard of them not being able to keep adjustment if you almost never back up then when you do it's like the problem you have. Like I said mine isn't bad - I get about 1" extra travel when I back up - that's about it. It's basically just enough to notice it. It has been consistently like this since I installed the new brakes, I can't remember if it did it the first time I drove it though.
You have already tried adjusting your brakes first right? You mention an imbalance in the system which could be caused by the mix of parts. I don't claim rocket science or some sort of epiphany - I may have just go lucky, lol. It'd cost you $20 to try the Mustang MC then you would know.
One other thing - in my experience the Mustang MC seems to work better on straight axle trucks and the one you have seems to work best on Twin Is. Partially just because they are easier to install that way. I helped TeamhaneyF100 put a dual MC on his 65, we used the Mustang MC and I think his would be better with the 70 F 100 (need to get him over to change that this summer). I used the 70 F100 on my 66 and it did seem to work better than Tim's does, both of the trucks just mentioned were drum front swb Slicks.
You could just cap off the rears and have a permanent line lock, you don't need em it doesn't ever snow there right?

blackagatha · Post by **blackagatha** » April 7, 2009, 1:21 am

so, why might the mustang mc be better suited?

The idea of the brakes getting far out of adjustment is definitely possible, I have not checked them out recently. and I guess I can follow how backward may be a different case than forward, if it's clicking.

ha, I would thin the snow would be the TIME TO cap the rears, ha.

Yeah, that sounds like a wee bit of a bad idea.... especially when I go hauling the carcass of another truck home on her!!!

I was mostly thinking imbalance due to brand new brakes up front and older in the rear, but that should have no effect at all I would think. I should take the effort to pop a wheel and have a peek at the shoes before I adjust them down again. I'd hate to kill the drums, but they are cheap. that's the trouble with drums, you cant see the goings on inside....

Gary Seymour · Post by **Gary Seymour** » May 17, 2009, 7:32 pm

Any resolution to this problem yet?