Brake Help - Duff’s Monster Disc Kit

[mpboxer]

Previously, I had power drum all around which stopped good. All new brake lines about two years ago. Upgraded to Duff’s Monster Disc and kept my rear drums.

I’m at a loss. I have good brake pedal when the engine is off. When I start the engine the brake pedal drops about 3” and I have very little travel remaining and the pedal is soft. I was able to drive it and the drums don’t lock up and it stops straight. Definitely not safe or correct though. Too much play in the pedal and way too soft.
Something I noticed also. When bleeding the rear brakes after the brake pedal gets pumped up and the bleeder screw cracks open the pedal drops dramatically (which is good). It doesn’t do that when bleeding the front calipers. The pedal only drops a little bit. Is this normal?

Things I have done:

Brake pedal height before 6 1/4” after 6 3/4
Adjusted shoes
Bench bled MC x3
Adjusted rod to MC x2
Verified bleeders on top of calipers
16 inches of vacuum (which worked fine with previous Toms booster)
Bled brakes for hours (manual and vacuum)
Confirmed brake lines installed correctly to proportioning valve via instructions
Verified no warning light for proportioning valve (therefore I think the piston is centered and I use the plug when bleeding)

Thank you for any insight!
Mike

 

[EPB72]

How did you route your lines from the MC to the Prop valve ..the front res. port should go to the front brakes and the rear to rear with that master cylinder ....a ford master cylinder would be the opposite,,

 

[ngsd]

How did you route your lines from the MC to the Prop valve ..the front res. port should go to the front brakes and the rear to rear with that master cylinder ....a ford master cylinder would be the opposite,,

That is what I said too but the instructions he has says the opposite.

 

[mpboxer]

How did you route your lines from the MC to the Prop valve ..the front res. port should go to the front brakes and the rear to rear with that master cylinder ....a ford master cylinder would be the opposite,,

I followed the instructions I posted. Rear reservoir to the front and front reservoir to the rear.

ngsd and I were talking about that and the instructions seemed weird?

 

[EPB72]

I followed the instructions I posted. Rear reservoir to the front and front reservoir to the rear.

ngsd and I were talking about that and the instructions seemed weird?

Agree weird,, and the kit on there web site shows a ford master cylinder in there kit......and advertise as being all ford .......the MC in your pic is base on a GM style and universal with ports on both sides that are used in most kits being CPP, Summit .Jegs, Speedway , and there front res to front and rear res to back......

 

[mpboxer]

Agree weird,, and the kit on there web site shows a ford master cylinder in there kit......and advertise as being all ford .......the MC in your pic is base on a GM style and universal with ports on both sides that are used in most kits being CPP, Summit .Jegs, Speedway , and there front res to front and rear res to back......

Yeah, I did some research on my MC and it looks like a C3 Corvette one. Kind of annoyed that it’s marketed as “All Ford”. I bet they didn’t update their instructions then. Everything I’m reading with that proportioning valve says to plumb it the way you indicate. I will do that tomorrow and report back.

Ever have to pull the metering valve pin on the front of the prop valve to bleed the front brakes?

 

[DirtDonk]

Yes. In fact that's exactly why there is a pin. When you get away without doing that, it's either because you were lucky or the valve was not working properly to begin with. Since yours is likely new(?) it's probably ok (but still crossing fingers seems a good idea!).
So yes, pull it.

But make sure that the gap between the tip of the booster rod is almost touching the back of the master cylinder piston when you mate the two together. A gap there will increase in size 6-fold at the pedal. You may be dealing with one, or both of those issues.

The hard pedal when the engine is off and the soft pedal when running is how the vacuum booster is supposed to react. One of the tests for a bad booster is to put your foot on the pedal with the engine off, then start the engine to see if the pedal drops. But it should only drop an inch or two at the most on a Bronco I think.

It's not just a master for a C3. That style has become ubiquitous and almost generic after it's decades long run on GM vehicles. Trucks and cars from about the mid-sixties to about the early '80's if I remember. Yours looks like the aluminum version of the aftermarket version of the master. Note the ports on both sides. This was not a feature on any factory unit that I know of. It's for easier multiple fitment.
It's also the master I'd choose to run. I know you were expecting Ford, and if you're trying to keep the stock-ish look under the hood, it's not quite cuttin' it! But it's a good master as long as the rod is adjusted (like on any master and/or booster change) and other stuff is fitted properly.
On that particular master, I can't say it matters which port gets the front and which gets the rear, but I'll sure be interested to hear if it makes a difference here.

Not sure which I'd do first. But probably check the gap on the piston-to-rod interface. Then re-bleed the fronts with the pin pulled (or pushed?) on the proportioning/combination valve. Then change the hose orientation if those others do not pan out.
But if you can, and don't mind, it'd be great if you can do just one of those at a time to ensure you know which one (if any) fixes your issue. With all the new goodies, it could even be a defective part giving you grief. But you don't know until you get all the other stuff dialed in.

Good luck.

Paul

 

[lilthom]

Did you ask Duff’s? They are good at answering these install questions on their products.

 

[billh1289]

Fwiw when I went from manual drums to the monster kit I chased what sounds like the same/similar problem for a while. Ended up finding a very small vacuum leak. Fixing that leak took care of my issue.

 

[mpboxer]

I have brakes! Swapped the MC reservoir lines to the prop valve and bled the snot out of everything again. Waaay better. Don’t know if those instructions are wrong or what. I will definitely be reaching out to Duffs…again.

I’m not trying to chase perfection, but is it normal for the pedal to drop about an inch before the brakes engage? I definitely stop faster and safer.

Oh Paul, the metering valve piston thingy was way too hard to grab with some needles nose until I was almost done bleeding. It seemed like it would pop out more the more the brakes were bled. I eventually was able to grab it with some vice grips and continued bleeding the front.

 

[DirtDonk]

Cool. I think most people find it unnecessary, but when you run into a problem like this it’s definitely something to take into account.
That little valve actually reduces or eliminates fluid flow to the front brakes until a certain pressure is achieved. Hence the low flow with the open bleeder.

 

[DirtDonk]

Regarding the pedal travel, no it doesn’t sound normal. Yes there is often a little bit of pedal travel before it firms up, but with the probably larger than stock master cylinder that amount of travel should be reduced. You automatically have a little extra built in because of the cantankerous design of the angle bracket and Booster. But it should still be very short travel.

But this is why I mentioned previously about the gap between the master and the booster piston. Did you pull that apart to check?

You don’t have to disconnect the hoses to do this. You simply unfasten the master from the booster, pull it apart until you can see the tip of the piston, and either adjust it out a little bit, or take some measurements. You’re comparing the depth of the piston well in the back of the master, to the amount that the rod sticks out from the booster. You want an extremely tiny gap between the two.

If you choose to forgo the precise measuring method for whatever reason (maybe it’s difficult at that angle) then what you can do is adjust the rod out a little bit at a time until when you’re pushing the master cylinder on it touches the piston first and leaves a gap between the master and Booster mounting surfaces.
When you see a gap you turn the rod back in until the gap is gone.

 

[JeffG]

I don't know why these aren't included in the kits, but this is what helped me. I don't know if this does the same thing as pulling the pin, but probably so.

I actually ordered a replacement proportioning valve for another project off eBay and it came with this tool.

https://tomsoffroad.com/parts/66-77-ford-bronco-proportioning-valve-bleeder-tool

 

[mpboxer]

Regarding the pedal travel, no it doesn’t sound normal. Yes there is often a little bit of pedal travel before it firms up, but with the probably larger than stock master cylinder that amount of travel should be reduced. You automatically have a little extra built in because of the cantankerous design of the angle bracket and Booster. But it should still be very short travel.

But this is why I mentioned previously about the gap between the master and the booster piston. Did you pull that apart to check?

You don’t have to disconnect the hoses to do this. You simply unfasten the master from the booster, pull it apart until you can see the tip of the piston, and either adjust it out a little bit, or take some measurements. You’re comparing the depth of the piston well in the back of the master, to the amount that the rod sticks out from the booster. You want an extremely tiny gap between the two.

If you choose to forgo the precise measuring method for whatever reason (maybe it’s difficult at that angle) then what you can do is adjust the rod out a little bit at a time until when you’re pushing the master cylinder on it touches the piston first and leaves a gap between the master and Booster mounting surfaces.
When you see a gap you turn the rod back in until the gap is gone.

That’s good to know about pedal travel, that’s what I was thinking too.

I am confident I adjusted the booster piston correctly, I did it the method you indicated. Turned it out until MC couldn’t sit flush and then brought it in very small increments until the mounting surface was flush.

 

[mpboxer]

Fwiw when I went from manual drums to the monster kit I chased what sounds like the same/similar problem for a while. Ended up finding a very small vacuum leak. Fixing that leak took care of my issue.

Thank you!

 

[mpboxer]

I don't know why these aren't included in the kits, but this is what helped me. I don't know if this does the same thing as pulling the pin, but probably so.

I actually ordered a replacement proportioning valve for another project off eBay and it came with this tool.

https://tomsoffroad.com/parts/66-77-ford-bronco-proportioning-valve-bleeder-tool

Thanks, Duff’s Kit included that. Pulling the pin on the front of the Prop Valve is different. First time I read about it was here on this forum.

 

[R Moses]

I went through the same exact thing you are going through. Dirt Donk (Paul) was the guy that resolved my problem. Even though the bleeders were pointed up I had the calipers on the wrong side. I also tried to reuse the Master Cylinder and found out that the one from the Power drums will not work correctly. Thanks again to Paul (Dirt Donk) and Wildhorses 4x4.

 

[toddz69]

So do you feel they're acceptable now or do they need more tweaking yet?

Todd Z.

 

[mpboxer]

So do you feel they're acceptable now or do they need more tweaking yet?

Todd Z.

Unfortunately no, pedal is hard when engine is off, but something is wrong. There is way too much travel when vacuum assisted. Duff’s is short staffed right now, so I don’t know when I’ll get a call back.

 

[DirtDonk]

Stiff when the engine is not running is standard operating procedure for a vacuum booster. Probably for Hydro boost as well.
But the travel is still what is questionable. Any chance you can shoot a video, or maybe even take some steel photos with a ruler or tape measure in place so we can see how far the pedal goes?