Soft brake pedal, but only when truck running??

Roodaddy · Post by **Roodaddy** » Mon Sep 11, 2006 12:49 am

Hi guys,
I checked through many previous posts about pumping brakes, but I'm not sure if my situation is related.

For reference:
1969 F250, Camper Special, front disc & quite stock 360.

The situation:
When the truck is NOT running I get good pressure against my foot when pressing on the brake. When the truck is running the pedal becomes quite soft. I've had the truck for a year and never known it to be so soft. When I give the pedal a pump during braking the pressure comes up and I can knock the dog off the seat.

Planning to do:
1. Replace all pads and shoes.
2. Adjust & bleed

Should I:
1. be looking at the MC?
2. check out the vacuum line from the engine to the MC?
3. do my planned work above and then check back in?

Thanks (as always)
Bill

P.S. I revived a couple old posts by closing them off as your advice has worked every time so far.

fordman · Post by **fordman** » Mon Sep 11, 2006 12:55 am

can you hear any hissing when you put on the brakes. i'm thinking booster but i can't be sure.

Roodaddy · Post by **Roodaddy** » Mon Sep 11, 2006 1:19 am

Once notably. I don't recall if every time. I'll check again the morning.

Roodaddy · Post by **Roodaddy** » Mon Sep 11, 2006 12:15 pm

Yea there's a noise, but its like "shhhhh" and it's heard insde the cab. Nothing noticable under the hood. I thought that was normal.

Be gentle I'm a Newbie

Thanks
Bill

68F250 · Post by **68F250** » Mon Sep 11, 2006 12:47 pm

Yeah your booster has a leak internally so it's constantly drawing in atmospheric pressure. That's the constant shhhh sound you're hearing. When the booster is working correctly, you should only hear the shhhh sound for the first second when the brakes are applied.

Sabbaticus · Post by **Sabbaticus** » Thu Mar 13, 2008 2:09 pm

Can the booster be repaired or does it need to be replaced? Mine hisses like a an Indiana Jones movie!

Roodaddy · Post by **Roodaddy** » Thu Mar 13, 2008 2:53 pm

I replaced mine.

fordman · Post by **fordman** » Thu Mar 13, 2008 10:45 pm

they can only be replaced by someone with a machine that can take the boosters apart. there is a big spring inside of it that will fly out if its opened wrong. you have to get a new one. or a rebuilt one.

Sabbaticus · Post by **Sabbaticus** » Thu Mar 13, 2008 10:51 pm

Thanks guys.......well now I have an excuse to get that chrome one I saw...................................

fordman · Post by **fordman** » Thu Mar 13, 2008 10:52 pm

oh expensive.

Sabbaticus · Post by **Sabbaticus** » Thu Mar 13, 2008 11:25 pm

all part of the dress up and restoration. Not too bad when one piece at a time.

fordman · Post by **fordman** » Thu Mar 13, 2008 11:41 pm

the oonly one i saw was last nihgt on ebay for 425.00 did you find them for less?

Sabbaticus · Post by **Sabbaticus** » Fri Mar 14, 2008 9:51 am

Found a single diaphram 7" for $129 and a dual 8" for $179

fordman · Post by **fordman** » Fri Mar 14, 2008 8:56 pm

where at?

Sabbaticus · Post by **Sabbaticus** » Fri Mar 14, 2008 11:35 pm

It is a universal.... Which the non chrome version happens to be on my truck.

https://dfbrakes.com/products.asp?id=25

There are several to choose from. Most are GM but there are plenty of universal kits without brackets or Master Cylinder.

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Soft brake pedal, but only when truck running??

Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??

re: Soft brake pedal, but only when truck running??