Disc Brakes . . . Completely Utterly Frustrated

[D Durden]

I need help. I'm at my wits end and pissed at the world right now. Here's the basics.

I have a 1965 Mustang. Years ago I did the Versy/Grenada full disc swap with a '67 booster and m/c. It worked fairly well since 1994. About a year ago, I decided that it was time to rebuild and upgrade the system, so I got a Scott Drake 4-wheel disc booster and m/c. I got Willwood front discs and Right Stuff rears (complete setup). I also run a vacuum pump and reservoir because the cam isn't even close to stock (409 stroker motor).

I have a good mechanic install it. He's done work for lots of my friends for years, and he's done good work for me. He spent time on it, and our result is, basically, if I stand on the pedal till my fatass 230 pound body is lifted off the seat, SOMETIMES the rears will lock up . . . eventually. The car has like zero stopping power. She'll stop at a stop light, eventually, but it takes a while.

The pedal is soft till a couple of inches off the floor, then it's hard as a brick. We disconnected the booster completely, and the pedal gets harder sooner, BUT the braking is still about the same.

About the only thing I can think of is that the Scott Drake master cylinder isn't putting out any power. I'm going to put a gauge on it Monday and see what I get.

Have any of you guys had issues with this related to any of the components I listed? Any ideas at all? About all I have in mind is that the m/c is bad.

Help?

 

[Moosee1955]

Any time you do conversions like yours, weird things can happen. Have a good friend that wasn't trying to diagnose a 65 chevy pickup with conversion. Same deal, pedal goes way too far down. No air, rear shoes adjusted tight, tried different rods for m/c to booster. What about your proportining valve not giving proper eq to rear. Definitely do a 4 wheel pressure test. Is your master cylinder way smaller than original. What do the people that made kit say? The thing that comes to mind about your pedal getting soft then hard is it's running out of travel. Your prob might be like my friends, a misalignment of brake pedal/ pin turnbuckle into booster. Keep us posted, you'll figure it out, Moose.


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[D Durden]

Proportioning valve is new and adjusted. There's just no power going to the brakes, and the pedal goes to the floor before you get any stopping.

I got on Scott Drake's website . . . there's no "contact us" or anything like that. I see no way to report a problem, so I'll have to call Summit, complain there, and then they'll ask me to send the unit back for replacement, of course. Maybe it works, maybe it doesn't.

I tried to buy the "good" stuff i.e. SD, Willwood, and all, but I'm starting to look back fondly on the awesome stopping power of my 4 wheel drum brakes I had in '86.

I've done a lot with this car, and I've struggled through the years, but looking back, I was better off buying a bunch of "no-name" parts instead of the "good" stuff. My Painless wiring harness came with wires mislabeled and 2 were backwards in the harness (headlights). I'm about done with trying to do things "right" with the "right" things. I'd probably do better with just a random assortment of parts.

 

[D Durden]

This is the setup:



Right Stuff Detailing Rear Disc Brake Conversion Kits ZDCRD01
Scott Drake Power Brake Conversion Kits PBC-M1-4WDB


Wilwood 140-13476
Classic Series Front Dynalite Brake Kit 1965-69 Mustang

 

[Moosee1955]

No you don't want drum brakes, I'm 61 I grew driving that garbage. Can't tell you how many scary wheel lockups I had with 4 wheel drum. Have them swap out the master/ booster first. I know this is a stupid question but I'll ask anyway, and forgive me, but 0 air in system, right. Another dumb question and believe it or not it happens. Calipers on proper wheels. I did that once on Datsun 280 z, put r/f on l/f. Bolted right up. Couldn't bleed. Brought 3 best mechanics over. They couldn't figure out. Turns out the bleeders were facing down instead of up. Reversed and problem solved. Again forgive me I know you know, I'm just covering all bases, since your struggling. Moose!


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[D Durden]

No you don't want drum brakes, I'm 61 I grew driving that garbage. Can't tell you how many scary wheel lockups I had with 4 wheel drum. Have them swap out the master/ booster first. I know this is a stupid question but I'll ask anyway, and forgive me, but 0 air in system, right. Another dumb question and believe it or not it happens. Calipers on proper wheels. I did that once on Datsun 280 z, put r/f on l/f. Bolted right up. Couldn't bleed. Brought 3 best mechanics over. They couldn't figure out. Turns out the bleeders were facing down instead of up. Reversed and problem solved. Again forgive me I know you know, I'm just covering all bases, since your struggling. Moose!


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LOL! I had 4 wheel drums the first 7 years I drove the car. I hear ya.

Oh, and yeah, 0 air. They're not "mushy" or anything else that would scream air. All the setup is "right". That's probably the most frustrating thing. I got the right guy, got the right equipment, and did all the little things. And the result? Car is undrivable. We're going to put a pressure gauge on the M/C and see what it's putting out. If it's putting out the right pressure, cripes man, I have no idea what to do after that.

 

[D Durden]

Okay, here’s my latest and greatest.

I called Wilwood, and they were a lot of help. Needless to say, they know brakes. I got expected pressures from them at the caliper (900-1,100 PSI with anything over 1,200 being damaging to the calipers). They also asked about pedal ratios and other things that I hadn’t gotten into, yet. They were good.

I called Scott Drake. Their technical support, after some discussion, told me that, with the vacuum pump I have, the booster is getting TO MUCH vacuum (huh?) when not at idle, but not enough vacuum AT idle. His position was that IF the car varies out of a 16-18 inches of vacuum window, their power booster / master cylinder won’t work. ON THE BRIGHT SIDE, he got me a phone number of the actual manufacturer of their braking units, ABS Brakes.

ABS Brakes was actually pretty good. The unit I have is a dual diaphragm setup, and 15 inches of vacuum is just fine. It’s not great, BUT it should work just fine with the dual setup. After a little talk, we have a plan on what to test, but the culprit right now looks like a faulty brake booster. We’ll see.

 

[tos]

Hey I just noticed that that rear conversion kit you have uses the old GM style calipers. I had an issue with adjusting those things and you might be having the same thing. Look at the gap you have between your pads and disc. When I installed mine there was a huge gap and caused too much travel and this kinda sounds like what yours is doing. These things are supposed to self adjust that gap out of there but mine didn't so I had to do some engineering to get mine right. When I would bleed mine I would watch the caliper clamp up on the disc but as soon as it was released the caliper would completely retract back an leave that big gap again. It sounds liks you are using all the travel on your master cylinder and ill bet its cause of those rear calipers.

 

[tos]

Another additional thought. If your caliper sits like mine then the bleeder screw is not at the highest position so you will have to pull the caliper off the bracket and position it so the bleeder is at 12 oclock to get all the air out. Just be sure when you take the caliper off that you still have it clamping on the disc.

I found this adjustment pdf also

 

[D Durden]

Hey, thanks for the heads up there!

We're going to put a pressure gauge on the calipers and M/C to see what that reads. If we're around 900 PSI, then we'll probably pursue something like you're talking about.

I'll let you know what happens.

 

[tos]

I would almost bet that's at least part of your problem. That caliper was made to fit a thicker disc and the disc generally used with these mustang conversions use a thinner disc. A normal caliper would self adjust when you step on the brakes but this one is a little tricky and doesn't self adjust.

Also if you are doing a pressure test of the rear caliper itself then if what I said is true you will also have a low reading because it cant build enough pressure until those pads squeeze up against the disc.

However if you are hooking the pressure gauge directly to the brake line and only the line and the caliper is completely disconnected you should get an accurate reading

 

[tos]

You probly already know how you are going to check pressure but here's a drawing of how I would do it. The second example should be with gauge installed before it tees off to each caliper to get actual line pressure reading.
I would do it both ways if possible to compare.

 

[bdepedro]

I'm also having trouble with a Right Stuff rear conversion. Same situation, no air in system but soft pedal. I suspect exactly what Tos is saying; that the resting position of the piston is too far away from the disc and is not self adjusting so when I press the brake pedal, the piston has too far to travel and does not have enough pressure in the system to make a strong enough contact with the rotor to stop the car. I'm running stock front discs and a stock booster and mc. I've been told that my problem is that the stock mc is for rear drums and the discs need a larger volume mc to move the pads sufficiently. Can anyone confirm this? or is it an adjustment at the caliper that can be made and still work with the stock mc?

 

[D Durden]

I'm also having trouble with a Right Stuff rear conversion. Same situation, no air in system but soft pedal. I suspect exactly what Tos is saying; that the resting position of the piston is too far away from the disc and is not self adjusting so when I press the brake pedal, the piston has too far to travel and does not have enough pressure in the system to make a strong enough contact with the rotor to stop the car. I'm running stock front discs and a stock booster and mc. I've been told that my problem is that the stock mc is for rear drums and the discs need a larger volume mc to move the pads sufficiently. Can anyone confirm this? or is it an adjustment at the caliper that can be made and still work with the stock mc?

I've heard the same thing i.e. you need a disc / disc setup on the MC. That's what I've got, of course, and it still doesn't work.

I want to believe that's the problem, but, sadly, I can lock the rears just . . . sort of . . . but not the fronts. And I've seen a bunch of great reviews for the Right Stuff brakes, and I even bought the ones specifically for a Versey rear.

We're putting a pressure gauge on the MC and calipers tomorrow. I'll let you guy's know what we find.

This is what I get for doing everything "right" . . . lol!

 

[tos]

I'm also having trouble with a Right Stuff rear conversion. Same situation, no air in system but soft pedal. I suspect exactly what Tos is saying; that the resting position of the piston is too far away from the disc and is not self adjusting so when I press the brake pedal, the piston has too far to travel and does not have enough pressure in the system to make a strong enough contact with the rotor to stop the car. I'm running stock front discs and a stock booster and mc. I've been told that my problem is that the stock mc is for rear drums and the discs need a larger volume mc to move the pads sufficiently. Can anyone confirm this? or is it an adjustment at the caliper that can be made and still work with the stock mc?

That is true, you need Disc, Disc MC. However you still should check that gap first and make adjustments if you can. Once you fix or verify that then if you corrected that gap go ahead and try the MC you have but I think You will need to change it for Disc Disc. Think about the size of a wheel cylinder on drum setup. The pistons a the diameter of a nickel and only move about an 1/8 to 1/4 inch. And the disc caliper piston is 2 to 3 inch diameter. Much larger bore means a lot more fluid and the drum type MC isn't designed to push that kind of volume to the rears.

Now on my rear calipers, I couldn't get them to adjust but it was probly the method I was using. Check out the PDF I attatched on my previous post and try that method. I was able to make mine work though by removing the parking brake lever on the caliper and rotating the cam to take up the slack or gap between the rotor and the disc. That cam has a square end for the lever to lock on to so I moved the lever one notch. I did have to grind a little bit of a notch on the back of the lever because of the lever stop built in to the caliper and to make sure there was a slight clearance between the pads and rotor. It all works great now though including the parking brake. If you go this route just make sure you bleed the brakes after.

 

[tos]

I want to believe that's the problem, but, sadly, I can lock the rears just . . . sort of . . . but not the fronts. And I've seen a bunch of great reviews for the Right Stuff brakes, and I even bought the ones specifically for a Versey rear.

You can still have the issue I'm talking about and be able to "lock them up". You are probly at the end of your MC travel though and are just barely closing that gap. If you have a parking brake installed then you can probly do a quick easy test without a test drive. Pull your parking brake on to where you cant turn your wheels by hand then make sure you have plenty of fluid in the MC. Start the car and pump the brakes a few times then see if its improved any. This will close that gap if there is one and you wont be needing to push the pedal that far. I haven't personally tried this procedure but I believe it will work and it will only take a couple of minutes before you go into hours of hooking up gauges.

 

[bdepedro]

You can still have the issue I'm talking about and be able to "lock them up". You are probly at the end of your MC travel though and are just barely closing that gap. If you have a parking brake installed then you can probly do a quick easy test without a test drive. Pull your parking brake on to where you cant turn your wheels by hand then make sure you have plenty of fluid in the MC. Start the car and pump the brakes a few times then see if its improved any.

I tried that yesterday and did get some improvement but not what it should be. I depressed the parking brake until I could just get my smallest feeler gauge between the disc and the pad and test drove the car. Definitely better but I think the disc/disc mc is necessary. Hopefully that will be my cure but I'll be following this thread to see how things go.

 

[Moosee1955]

It's amazing how a proper sized master cylinder working in tandem with the proper calipers can work. I've got a dumb question, didn't the company you bought all this stuff from, supply the matching master cylinder? It never ceases to amaze me how many times I hear stories like yours. Are these companies just selling parts all willy nilly, or don't they actually test them on a vehicle before adding to catalog. Apparently it's the former, cause I've got a good friend that had same scenario. I posted earlier. Cadillac used to have adjustable rear calipers that you had to know how to adjust. Yours is a combo of caliper/ master cylinder problem. You'll figure it out, keep us posted.


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[bdepedro]

I used the Right Stuff conversion through Summit and went back and was looking through the instructions to see if they say anything about the mc but didn't see anything. I also called their helpline and they said it would be a good idea but didn't indicate it being necessary. I'm definitely going to upgrade it because I'm not even sure its set up for even front discs. Also realized I never changed the distribution block so that could also be part of the problem. Think I'm going to call Wilwood or SSBC and see what they recommend for both.

 

[tos]

I think they are assuming you may already have the proper MC? Or they may have two different conversion kits, one with MC and one without? Or that kit may fit multiple year cars but use different MCs.

Also once you get this gap corrected you'll want to bleed the system the old fashioned way unless you have a pressure bleeder. If you don't have a pressure bleeder then break the bleeder loose and have someone push the pedal to the floor and hold it, then tighten the bleeder. repeat of course till you get no bubbles. Do this first at right rear, then left rear, right front then left front.
Don't pump the brakes and don't use one of those vacuum bleeders just one push on the pedal to the floor for each bleeding is best.