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Brake Master Cylinder Bore Sizing

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Romel

Re: Brake Master Cylinder Bore Sizing

I am talking about the proportioning valve, the rear load sensing valve is out of play, it doesnt matter to it if the brakes applied quick or slowly. To my knowledge it is just a mechanical valve, partially open when empty, fully open when loaded truck.
The proportioning valve is supose to let the pressure to the rear brakes untill it touches the drum, then move the pressure to the front brakes. Seems this mechanism inside is sticking or not reacting right. Once the rears are blocked u do not have much power to the front, basically sliding like on the ice, fronts not braking much, no matter how hard u push the pedal.

1986 XLT Lariat F250 6.9 IDI, supercab, sidewinder, psd intercooler, hydroboost

Gary Lewis

Re: Brake Master Cylinder Bore Sizing

Administrator

With that description I would agree - it is the proportioning valve.

What's your plan? How are you going to fix it?

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

Romel

Re: Brake Master Cylinder Bore Sizing

I have no clue, I cant dig into it as I need the truck every day. I might take it apart during the spring and see what is inside, some springs, seals. I am scared to open it as if something breaks I am off the road for long.

1986 XLT Lariat F250 6.9 IDI, supercab, sidewinder, psd intercooler, hydroboost

Gary Lewis

Re: Brake Master Cylinder Bore Sizing

Administrator

Perhaps one of us here in the States can find one for your truck and send it to you? But, we'd need to find it specific to your truck, as shown here (Driveline/Brakes) on the Proportioning Valve tab. Can you tell us which one your truck needs? Or, maybe better, more about your truck, such as GVW and whether 2wd or 4wd?

Gary, AKA "Gary fellow": Profile

Ford F834

Re: Brake Master Cylinder Bore Sizing

Administrator

Gary, according to the chart in the MPC Jan needs E4TZ-2B257–F. For F250 4wd over 8500 gvwr and 6.9/7.3 or 7.5 engine. This also happens to be the one used for ALL F150 1984 and up. This being the case, I have a used one for him from a 1985 F150. Only problem is, I’m a worthless 💩turd💩 these days when it comes to finding time to mail stuff. 😢😔. I just need to get it to him.

SHORT BED 4-DOOR DIESEL: 1986 F350 4x4 under construction-- 7.3 IDIT ZF5+GVOD

STRAIGHT SIX 4X4: 1981 F150 2wd to 4x4-- 300 I6 close ratio diesel T19, hydroboost brakes, Saginaw steering

BIG F: 1995 F-Superduty under construction— converting to 6.9L IDI diesel ZF5+DNE2

Gary Lewis

Re: Brake Master Cylinder Bore Sizing

Administrator

Cool! I was hoping he would need that one, but didn't know if he has 4wd or not so couldn't tell.

Have you taken one apart? Surely there are seals involved, but can they be cleaned and re-used?

Gary, AKA "Gary fellow": Profile

Ford F834

Re: Brake Master Cylinder Bore Sizing

Administrator

I’ve nrver opened one. But Jan’s description of rust poorige in the MC makes me think a hydraulic shuttle could be sticking in its bore if the valve works that way. I’d like to have a look in one myself.

Gary Lewis

Re: Brake Master Cylinder Bore Sizing

Administrator

There's a procedure in the shop manual to dislodge the shuttle if it sticks one way or the other, so it is obvious that bad brake fluid can cause problems. Jan's is apparently not stuck at either end, but in the middle.

If he had a spare he could try cleaning it with a cleaner, or disassembling it.

Gary, AKA "Gary fellow": Profile

Romel

Re: Brake Master Cylinder Bore Sizing

It is hard to do anything on the truck these days as it rains and rains and the truck does not fit in the garage. I am in the process of moving from one location to the other and I am using the truck daily, plus it gets dark at 5pm.

1986 XLT Lariat F250 6.9 IDI, supercab, sidewinder, psd intercooler, hydroboost

Gary Lewis

Re: Brake Master Cylinder Bore Sizing

Administrator

Please be careful on those wet roads!

Gary, AKA "Gary fellow": Profile