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Brake Booster Question

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Sportinlife

Brake Booster Question

I replaced my brake booster and now the brakes are super sensitive. The truck had sat for 9 years and the disks were rusty and the master cylinder and booster were both frozen. The disks have polished up ok, but the brakes are hard to deal with. Question - are valves available to modulate the vacuum to the booster? Should I just replace the disks and calipers?
Thanks a bunch.
Andy

1980 f100 flareside 300 6 and c6. Named Arlene

Gary Lewis

Re: Brake Booster Question

Administrator

Andy - Glad you joined, but you probably missed the email that asked you to go to the New Members Start Here folder, read the guidelines, and then post an introduction.

We ask that of everyone since we hold everyone to the guidelines. So it is important that you have a chance to read them, and if you go to the NMSH folder you'll see them.

So before we answer your question can you assure me that you've read the guidelines?

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Gary Lewis

Re: Brake Booster Question

Administrator

In reply to this post by Sportinlife

Did you replace the master cylinder? You said you replaced the booster but didn't mention the master. c

No, there aren't valves available to modulate the vacuum in the booster that I'm aware of. But if the truck sat for that long I'd bet that the rear brake cylinders are badly rusted and perhaps frozen. That would mean all the braking is being done in the front, and that can get squirrelly.

I'd put the rear end in the air and spin the wheels and gently press on the brake and see if they stop. If so, that means the rear brakes are working. If not then the rear brakes aren't working and you need to pull the drums and check things out.

Gary, AKA "Gary fellow": Profile

Sportinlife

Re: Brake Booster Question

I have since replaced the front disks and calipers. Finding them at a parts store was an adventure, since I have a light duty f100 , with a 4.5 inch bolt circle. The problem remains. I guess I will check and probably replace the rear brakes next. Don't know whether to go with a stock rebuild or explorer disks. I have 10" rear drums.
I replaced the booster and master cylinder, btw.

1980 f100 flareside 300 6 and c6. Named Arlene

Gary Lewis

Re: Brake Booster Question

Administrator

If you've done all that then it is pretty sure that the problem is with the rear brakes. If it was mine I'd just replace the rear wheel cylinders and brake shoes as they are quite capable of stopping the truck. And it shouldn't be very expensive.

Having said that, it is possible that the proportioning valve has gone to one extreme and has blocked off the rear brakes. If that is the case then rebuilding the brakes won't fix the problem. So before rebuilding I'd see if there is any flow to the rear by trying to bleed the rear brakes. If not, then the valve probably has blocked the flow.

You are supposed to get the valve to center up again by standing on the brakes HARD with the engine running to provide boost. You don't have to be moving, just have the engine running and STAND on the brakes. But I've read that it doesn't always work and in that case the valve itself may be bad.

Gary, AKA "Gary fellow": Profile

Sportinlife

Re: Brake Booster Question

Will try resetting the valve. Also I plan on pulling the rear drums tomorrow, so we will see what surprise it has for me.

1980 f100 flareside 300 6 and c6. Named Arlene

Sportinlife

Re: Brake Booster Question

Well, I pulled the rear drums and everything looked fine. No corrosion evident. I looked at the prop. valve and noticed that the reset under the rubber in the front was sticking out. A push with my thumb didn't do anything so I smacked it lightly with a hammer. It moved. A couple more light taps and it appeared to be in the right place. While I had the wheels off, I bled all the old yucky brake fluid out.
Success! While the brakes have more boost than I am used to, they work fine and aren't grabby.
Thanks a bunch!

1980 f100 flareside 300 6 and c6. Named Arlene

BigBrother-84

Re: Brake Booster Question

Good news!

These prop valves act sometimes curiously. Had to change mine, cause the parking dash light was staying on each time I applied the mechanical parking pedal AND the hydraulic one (Big Brother has the two fully operational).
New proportioning valve fixed the problem.

Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.

Gary Lewis

Re: Brake Booster Question

Administrator

In reply to this post by Sportinlife

Excellent! Glad it worked out that easily - and cheaply.

Gary, AKA "Gary fellow": Profile