Pedal feel after disc conversion
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Senior User
Joined: Jun 2002
Posts: 344
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From: Lancaster, So Carolina
Pedal feel after disc conversion
Flush with victory after a toysteer conversion, we moved into more modern brakes.
I stuck with the stock 5x5 1/2 wheels so used 1980s vintage front ventilated rotors, big GM calipers. Leery about being overboosted with stock pedal arm leverage, I did not go boosted at all. Mid Fifty sold me a 68-72 Mustang dual master cylinder, bracket etc. We used a proportioning valve from a 69ish Econoline.
After many bleeds, we still get a softish pedal. It bites about 1.5 in down like the stock master, but mushes down to about 2 in from the floorboard with pretty constant resistance (and good braking).
I guess Im used to the rock hard stock master. Any chance the new master isnt cutting it? or pads need to seat or something?
Im all ears
I stuck with the stock 5x5 1/2 wheels so used 1980s vintage front ventilated rotors, big GM calipers. Leery about being overboosted with stock pedal arm leverage, I did not go boosted at all. Mid Fifty sold me a 68-72 Mustang dual master cylinder, bracket etc. We used a proportioning valve from a 69ish Econoline.
After many bleeds, we still get a softish pedal. It bites about 1.5 in down like the stock master, but mushes down to about 2 in from the floorboard with pretty constant resistance (and good braking).
I guess Im used to the rock hard stock master. Any chance the new master isnt cutting it? or pads need to seat or something?
Im all ears
Elder User
Joined: May 2006
Posts: 907
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From: Kansas City, Mo
Brakes
Jay, You didn't say if the rear was disc. During the 60's was the change over to disc. Several vehicles had a choice of drum or disc. Also master cylinders are different for drum/drum, disc/drum and disc/disc front /back combinations. Make sure you have the correct m/c. I would have installed a power booster. I don't know anyone who didn't upgrade to pwr boost with disc/disc. Did you bleed with pressure kit or by pedal only? Was porportioning valve for a disc/disc,disc/drum or what you have? Keep m/c fluid full. Hope this helps. Have a great day,chuck
Last edited by 49fordpickumup; May 1, 2007 at 05:35 PM.
Fleet Mechanic
Joined: Mar 2005
Posts: 1,511
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From: peyton, colorado
Assuming the flex lines are in good shape, bled properly, etc you may be describing a "long pedal". A long pedal has a long travel to actuate the brakes, then has a firm pedal once they bite. It's usually caused by a mc that is too small, so it makes up for the small diameter piston with longer travel. Is the mustang mc a drum/drum or a disc/drum? Do you know what diameter the pistion is? You mentioned BIG Gm calipers, how big? Did you rebuild the rear drums at the same time? Improperly adjusted shoes will also give you a long pedal. You may want to jack the truck, and slowly apply the brakes while you turn the front and rear wheels, to see if one end is grabbing before the other. Maybe you can isolate it to front or rear. Keep in touch. -Rusty
Elder User
Joined: Dec 2003
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From: New Mexico
It might mean some more time spent with the proportioning valve too. There should be a slight lock-up first forward then rear---(so the rear doesn't fishtail too soon) As for the feel, it is the brake drum set up that to grab and the disc set up that operates more in a linear fashion. I'd also think about seating the discs and drums in before further adjustment. Those are brand new surfaces that are getting used to mating
Fleet Mechanic
Joined: May 2006
Posts: 1,696
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From: S.W. Florida
I shall now display my brake ignorance for all to see and ridicule. The bed boards are out of my truck, and attached to the Ford 9" rear (drums) axle is what I assume is the proportioning valve. The strange part is, and I am certainly no brake expert, is that it has a length of 5/16 hose exiting it, vented to atmosphere. I have never seen a "vented" P.V.???? I have Cordoba front clip with Chrysler discs, and I too have what I consider excessive pedal travel. Stops great, rear shoes are correctly adjusted. Just 5-6" of pedal travel b-4 good braking.
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Lead Driver
Joined: Aug 2002
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From: Saskatoon SK Canada
I assume you mean the junction block the brake hose it attached. The hose is just for axle ventilation similar to a road draft tube.
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Senior User
Joined: Jun 2002
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From: Lancaster, So Carolina
Fact check:
Calipers from 89 Caddilac
Proportioning valve from Ch**y van about same era, had disc/drum
I stuck with rear drums-only about 2000 mi on completely new cyl, hoses, shoes, drums
Mid Fifty item 5914 Master cyl "Designed for all drum applications AND disc front/drum rear"
I will go thru another bleed after driving some more to chase out any more air if its there. After that, I suspect the M/C is either the wrong one or not working right.
Calipers from 89 Caddilac
Proportioning valve from Ch**y van about same era, had disc/drum
I stuck with rear drums-only about 2000 mi on completely new cyl, hoses, shoes, drums
Mid Fifty item 5914 Master cyl "Designed for all drum applications AND disc front/drum rear"
I will go thru another bleed after driving some more to chase out any more air if its there. After that, I suspect the M/C is either the wrong one or not working right.
Posting Guru
Joined: Aug 2005
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I did the Granada front disc conversion on my 65 Mustang and used a 67 master cylinder and a prop valve off of a Fairmont of 80ish vintage and it worked great after plumbing in for prop valve and repositioning soft lines.
Some calipers can be installed on the wrong side of vehicle and the bleeder is not the highest point on the caliper and therefore you can bleed brakes til cows come home and you won't get all the air out. I don't know if yours are like that or not, but it is something to check.
Some calipers can be installed on the wrong side of vehicle and the bleeder is not the highest point on the caliper and therefore you can bleed brakes til cows come home and you won't get all the air out. I don't know if yours are like that or not, but it is something to check.
Lead Driver
Joined: Aug 2006
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From: Brentwood, TN
If the calipers are higher than the MC then fluid will bleed back (actually just the pressure reduces) and require more brake pedal to get the pressure back into the lines. There are devices, like a proportioning valve, that act to hold pressure in the lines so that you don't have to push the pedal so hard every time you actuate the brakes. I don't recall the technical name for these inline devices but you can get the scoop on them from any of the brake suppliers.
Fleet Mechanic
Joined: Mar 2005
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From: peyton, colorado
Charlie, good point! Those are residual valves, or residual pressure valves. They're a one way valve to prevent just what you're talking about. Available from pretty much all the vendors. You need a different pressure for disc and drum, but the psi you need escapes me. They just plumb into the line.
Hotshot
Joined: Oct 2004
Posts: 15,882
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From: Durham NC
Yes, unless the proportioning valve has them built in (doubtful in this case) you need a residual valve plumbed into the the front and rear line after the proportioning valve with an underfloor MC. A 2# valve (usually designated by red color) goes in the line to the front brakes, a 10# valve (blue) in the rear brake line for disk/drum applications.
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Senior User
Joined: Jun 2002
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From: Lancaster, So Carolina
Guys, sounds like you nailed this one. I will put on the 2/10 backflow valves and probably an adjustable proportioning valve. (The rears are locking up a little bit early unloaded)
I wont condemn the master until all the new valvling is in.
I wont condemn the master until all the new valvling is in.