[packagerjr]

Group,

While in process of a bunch of stuff with my '80, I figured I would migrate to a 1991 M/C while I install the hydroboost (engine is a '91 so staying with that year for posterity's sake). Pros were the clear reservoir, elimination of that stupid wire bale cover retainer, and the ability to have a low level switch.

My new M/C didn't have this large fitting in the secondary (closer to firewall port), so I snagged one out of a yard. I now realize it is actually a proportioning valve. My '80 already has proportioning/metering/warning light valve from the factory.

Two questions:

1. Is the metering function (that delays fluid application to the fronts so the drums can energize) built into the 1991 master cylinder? My WSM makes no mention of such a feature but it is clearly called out in the 1980 WSM. Since I understand the brake systems to be similar minus RABS, I assume the functionality is still needed.
2. For anybody who's made this conversion, would it make sense to find a fitting that could adapt the M/C secondary port to the right size inverted flare? My 80's prop valve also acts as a distribution block, so removing that and trying to replumb looks less fun than the former, unless I just can't find a way to adapt the M/C to inverted flare.

Last but not least is just to stick the old M/C back on, but rather not if I can find a way around the current dilemma.

Thanks.

 

[Hillbilly Heaven]

The delay is built into the master cylinder pistons. One port looking from the top will close before the other. The prop valve was to control pressure not flow. The adapter you are talking about screwed into the master cylinder is just than an adapter. Go to any parts store they have bins full of adapters.

 

[packagerjr]

@Hillbilly Heaven Thanks for confirming the metering delay is built into the M/C. I guess that begs another question - is two metering valves going to be problematic for front disc application? I guess another option is to find another '80 series combo valve, gut it, and install it in place of the functional one I have now, in an attempt to make the braking system more like a 1991 vintage.

The 1991 WSM shows a proportioning valve threaded right into the M/C. Snip isn't great quality but it should show that there is more there than it being just an adapter. The one I pulled had a plastic valve and seat on the M/C side, almost like a reciprocating compressor valve.

 

[Hillbilly Heaven]

It's not metering it's for timing. Metering is done in the prop valve.

 

[BigBlue 94]

That little valve in the rear port keeps a slight pressure built up in the rear lines for the drum brakes. When i went to hydroboost in my 85, with 1988 HB booster and MC, i kept it on the new master. Which meant converting my new stainless line to a new flare fitting.

Did you go with the F350 master or the F-Superduty master? Im running the F350 MC and dually rear wheel cylinders, and thunderbird calipers.

 

[packagerjr]

That little valve in the rear port keeps a slight pressure built up in the rear lines for the drum brakes. When i went to hydroboost in my 85, with 1988 HB booster and MC, i kept it on the new master. Which meant converting my new stainless line to a new flare fitting.

Did you go with the F350 master or the F-Superduty master? Im running the F350 MC and dually rear wheel cylinders, and thunderbird calipers.

On your 85, did you have a frame-mounted proportioning valve originally? Did you remove it as part of your 1988 MC/hydroboost conversion and only go with the valve in the M/C?

Right now I've not committed to much but the plan was to use a 1991 Bronco MC tied to the hydroboost I have. My braking system is stock. I'll be on 35s after it is all said and done and was looking for a little more oomph. But don't have immediate plans to change any of the braking hardware.

 

[BigBlue 94]

On your 85, did you have a frame-mounted proportioning valve originally? Did you remove it as part of your 1988 MC/hydroboost conversion and only go with the valve in the M/C?

Right now I've not committed to much but the plan was to use a 1991 Bronco MC tied to the hydroboost I have. My braking system is stock. I'll be on 35s after it is all said and done and was looking for a little more oomph. But don't have immediate plans to change any of the braking hardware.

Im am running the factory frame mounted prop valve. Now im questioning my previous post though... Oh nope, just looked at a pic and i did indeed use the MC mounted prop valve too.

Mine is not perfect yet, it will lock the brakes completely at 25mph if i push hard. And at about only 50% travel on the pedal.

The 86 and prior trucks can utilize '78 thunderbird front calipers which have a significantly larger piston, which improved braking. Just an FYI for future mods.

 

[packagerjr]

It's not metering it's for timing. Metering is done in the prop valve.

We may be calling the same things different names.

The '80 WSM says one function of the "proportioning" valve is to delay full effectiveness of the front brakes (i.e., metering valve). I have understood this to be that the valve requires the rear generate a certain pressure before allowing full brake line pressure to the fronts. Perhaps the timing you refer to in the new M/C is a replacement for the metering valve function? I have not looked at either the '80 or '91 M/C to see if they are different as a function of stroke. I do know the primary and secondary ports are swapped on the bodies.

Thanks.

 

[Hillbilly Heaven]

Yes you are correct all 3 functions are in that block and people generally call that the prop valve. That is because its main function is the prop valve section.