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Author
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Topic: Brake problems
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-24-2002 08:37 AM
   
I've got a 67 with power disk brakes that I've replaced the master cylinder, booster, both front calipers, rear wheel cylinders, hoses etc. Aboout the only thing that hasn't been replaced is the hard lines and the stock proportioning valve. The car stops ok but if you need to stop quick, no matter how hard you press on the brakes you can't get the brakes to lock up the wheels. I realize that you never want to lock the wheels but what I'm saying is I don't think I'm getting the brake pressure that I should. Could it be the proportioning valve ? bad master cylinder ? Where should I start looking. The pedal is firm not spongy.Any ideas? ------------------
67convertible 289/auto
65fastback 302/4sp
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V8 Thumper
Gearhead Posts: 3529
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 06-24-2002 08:51 AM
Is that p/valve adjustable? Jeez, with all new hardware, I would think (hope) that it's making sufficient hydraulic pressure... are your rear brake shoe adjusters free and working properly?
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-24-2002 08:57 AM
The proportioning valve is the stock non-adjustable type. I haven't checked anything yet but I can start with the rear brakes to make sure they are adjusted properly. I've never owned a car (new or otherwise) where the "automatic" adjusters worked properly.------------------
67convertible 289/auto
65fastback 302/4sp
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-26-2002 08:09 AM
I've bled the system and adjusted the rear brakes but no luck. I put a vacuum gauge on the booster and it holds vacuum just fine. I just don't seem to get the clamping pressure that I should when braking. I mean even standing on the brakes I can't lock it up. I friend of mine asked me if I had put the correct master cylinder on it when I replaced it. I think it was the right one but I can't say for 100% sure that it is. It bolted up with no problem is all I remember. Even though the m/c is only about 5 years old, I'm thinking about replacing it again and making sure I get the correct one. What about the proportioning valve ? Is there anything to check on those ?------------------
67convertible 289/auto
65fastback 302/4sp
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V8 Thumper
Gearhead Posts: 3529
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 06-26-2002 08:26 AM
The p/valve in my '65 GT (front disc/rear drum) was LOADED with crap (don't ask what the m/c looked like  ). Contaminants in a hydraulic system are BAD...Was your car originally optioned with a power brake booster? I believe the booster requires a different length pushrod, it could be something as simple as that... Are you running an aggressive cam/manifold/carb package? How much Hg" does it pull at idle?
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-26-2002 08:31 AM
Yes, the car originally came with the power booster disk brake setup.
The cam is just a little more than stock with an Edelbrock performer intake and an Autolite 4100 carb.
The last time I checked it was pulling around 15" Hg as well as I can remember.
So can I rebuild the p/v ? Take it off and let it soak in brake cleaner ?------------------
67convertible 289/auto
65fastback 302/4sp
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V8 Thumper
Gearhead Posts: 3529
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 06-26-2002 08:39 AM
That's not too much cam by any means, 15" should be just fine. Yes, you can rebuild your p/valve provided that:The bores aren't pitted
~and~
That you can find a seal kit! Locating seals might me tough, being that many of those p/valves have been out of production since the mid-70's. Is it leaking? that's usually a good indication of problems. Is your brake fluid semi-clear, or is it dark and murky?
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-26-2002 09:04 AM
No, the p/v is not leaking and the fluid is clean and clear.
One thing that I have always noticed is that there is always a small drip of brake fluid on the bottom of the master cylinder. The strange part is that it doesn't look like it came from the brake lines.
When I originally bought the car the old master cylinder had nothing but sludge in it.
Where might I start looking for a seal kit for the p/v ?------------------
67convertible 289/auto
65fastback 302/4sp
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-26-2002 03:49 PM
One thing I noticed when bleeding the brakes it that the fluid would squirt out of the large(front brake) reservoir when pressing and releasing the brake pedal. I didn't notice it doing that when bleeding the small(rear brake) reservoir. Could something be clogged in the master cylinder or proportioning valve ?------------------
67convertible 289/auto
65fastback 302/4sp
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Moneymaker
Administrator Posts: 19751
From: Lyons, IL, USA
Registered: May 99
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posted 06-26-2002 06:56 PM
The booster has nothing to do with the hydraulic pressure, so let's get that out of the way.
If you do not have access to a high pressure guage it will be difficult do diagnose the problem. Based on my experiance and the simptoms, I would tend to agree that you have a plugged or in operative p/v.  ------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 06-27-2002 08:10 AM
So where might I find an overhaul kit for the p/v ? Or should I just take it apart and clean it good ?------------------
67convertible 289/auto
65fastback 302/4sp [This message has been edited by Robert K (edited 06-27-2002).]
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V8 Thumper
Gearhead Posts: 3529
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 06-27-2002 08:22 AM
Dis-assembly and cleaning would be a good place to start, that may tell you what's wrong with it. Call around to a few parts houses, maybe even a few brake shops and check availability on your particular p/v. You could also try an industrial hydraulics shop, but you'd need to provide seal numbers or measurements; they likely wouldn't have part numbers for (almost) 40 year old cars.You could always go to an aftermarket p/v... $50 for a good one (adjustable)
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Moneymaker
Administrator Posts: 19751
From: Lyons, IL, USA
Registered: May 99
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posted 06-27-2002 09:19 AM
As Todd says, take it apart, clean it, flush it, and try to air check it. It's probably just gummed up. ------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 07-08-2002 09:15 AM
I took the p/v off and cleaned it the best I could. I couldn't get the plunger out of it. Theres really not much to it. It didn't seem to be clogged. Then I removed the master cylinder and bench bled it and adjusted the pushrod per the specs in the shop manual. Re-installed everything and it still doesn't feel like it has the pressure it should. I haven't bled the system yet after re-installing everything so it is possible that after I bleed it it will be OK but I'm not holding my breath. Is there anything else I should try ? ------------------
67convertible 289/auto
65fastback 302/4sp [This message has been edited by Robert K (edited 07-08-2002).]
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Jeff
Gearhead Posts: 280
From: Moore, OK USA
Registered: Mar 2001
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posted 07-08-2002 03:14 PM
There's some speed you can lock up the brakes, so try it at 15mph, then 25mph, etc. The faster you go the harder it becomes to lock them up. The brake pads used can impact braking performance.
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SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
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posted 07-08-2002 07:15 PM
The Car Craft magazine this month has an article about a very similar problem. They did a 4 wheel disc conversion and didn't like the stopping power. In their case it turned out the booster wasn't large enough. They determined that by checking the psi at the master and found only 600 psi. Getting a larger booster solved their problem.------------------
'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics
MCA Member # 47773
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Brad Harrington
Journeyman Posts: 3
From: Everett, WA, USA
Registered: Jul 2002
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posted 07-08-2002 07:15 PM
Hi Robert:
Are your sure you didn't install your front brake calipers upside down? I once did that and had the same problem you are having.1969 M code Mach 1
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Brad Harrington
Journeyman Posts: 3
From: Everett, WA, USA
Registered: Jul 2002
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posted 07-08-2002 07:26 PM
Hi Robert: When I say " upside down I mean did you put the left caliper on the right and the right on the left?
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fastford34
Gearhead Posts: 392
From: penna
Registered: May 2002
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posted 07-08-2002 08:00 PM
Robert,if i read your post right,i think the large resorvoir is for the rear drum brakes & the small one is for the front discs,this is due to needing more fluid to activate drum brakes than disc brakes.hope i am right & this helps you.
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SteveLaRiviere
Administrator Posts: 33988
From: Saco, Maine
Registered: May 99
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posted 07-08-2002 08:05 PM
quote:
Originally posted by fastford34:
Robert,if i read your post right,i think the large resorvoir is for the rear drum brakes & the small one is for the front discs,this is due to needing more fluid to activate drum brakes than disc brakes.hope i am right & this helps you.
Just the opposite. The large reservoir is for the front disc. The disc calipers' pistons take more fluid to activate due to their larger bores. ------------------
'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics
MCA Member # 47773
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fastford34
Gearhead Posts: 392
From: penna
Registered: May 2002
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posted 07-08-2002 08:17 PM
thank you for the correction. as usual i had it bass ackwards! 
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 07-09-2002 09:30 AM
Since it was raining yesterday, I thought I would read the shop manual (what an idea). To make a long story short, when I hook up the wire to the top of the p/v, the "brake" light comes on inside the car. According to the manual, this means that the p/v needs to be centered. I am going to try centering the plunger in the p/v tonight and see if it makes any difference.
The brake booster is the same size as the original one I replaced. I don't think I have the calipers backwards but I'll double check. I'll keep everyone posted as to the results. Thanks for everyone's input so far.------------------
67convertible 289/auto
65fastback 302/4sp
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 07-10-2002 08:36 AM
I went through the process to center the p/v plunger so the "brake" light would go out inside the car. I could never get it to go out so I don't know if the plunger is stuck or what the problem is. I took off the rear drums and inspected everything. No leaks or even evidence of leaks. Replaced drums and readjusted shoes until tire spins about 1/2 to 1 turn. Inspected front rotors and calipers. No leaks. No grease on pads or shoes.
One thing I did notice was that with the engine on, in park or drive with my foot firmly on the brake, the pedal wants to drift ever so slowly toward the floor after holding the brake for about 10 seconds. It never goes all the way to the floor.I'm thinking new master cylinder/booster and definitely new p/v. The only place I could find that sells the exact replacement is Mustangs Unlimited. All the other vendors had the non OEM type where you have to re-bend the brake lines.
Any thoughts ? ------------------
67convertible 289/auto
65fastback 302/4sp
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 07-10-2002 05:48 PM
I have ordered a new proportioning valve from Stainless Steel Brakes. I just remembered that I have an extra master cylinder for the 67 in a box in the garage. I'm going to swap m/c's and see what happens.------------------
67convertible 289/auto
65fastback 302/4sp
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 08-12-2002 11:43 AM
Installed different m/c and new p/v(distribution block). Brakes seem better but still not what I was expecting. I can lock the brakes (rear) at higher speeds, say around 40 and higher. Less than 40 and they won't lock up. Didn't ever get the fronts to lock. When I was bleeding the front system after installing the new parts I heard a small pop sound. It was that stupid differential valve in the p/v that turns the "BRAKE" light on inside the car. So I followed the shop manual instructions on centering it by opening up the outlet port of the opposite system on the p/v (the rear in this case) and pressing the brake pedal. Didn't work. I played with this for quite some time and was not able to get the valve centered again. I was so disgusted I disconnected the light and went for a drive. Did not see any difference the valve made either centered or not.
Any ideas on how to get the differential valve centered again so I can hook up the light ?------------------
67convertible 289/auto
65fastback 302/4sp
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Hemikiller
Gearhead Posts: 395
From: Clinton, CT
Registered: Feb 2002
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posted 08-12-2002 12:42 PM
The differential valve should center itself when the front and rear systems have the proper pressure. If the light stays on all the time, you may still have air in the lines, or some other problem. Alex's recommendation of a pressure check at each wheel may be in order. Might be time to bring it to a trusted garage for a second opinion before you get really frustrated....
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lyle29464
Gearhead Posts: 827
From: Mt. Pleasant S.C.
Registered: Mar 2000
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posted 08-12-2002 09:40 PM
I would revisit the plunger. I had a problem like that once.
Lyle
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 08-13-2002 08:05 AM
You mean the master cylinder ? Do you think I still have a problem with it ?------------------
67convertible 289/auto
65fastback 302/4sp
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lyle29464
Gearhead Posts: 827
From: Mt. Pleasant S.C.
Registered: Mar 2000
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posted 08-13-2002 02:08 PM
If the plunger is not getting a full stroke It will give you problems like you have. This could be the wrong rod or a change in the hanger or a deference of how the master cylinder fits the fire wall.If you lost any of the stroke even 1/4 to 3/8 it will show up big time at the wheels. I had a car that the dash had sagged down a bit and it made the stroke shorter i.e. very poor brakes------------------
Lyle
69 rag top
93 explorer
98 f 150
several boats
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Robert K
Gearhead Posts: 514
From: Nashville, TN
Registered: Apr 2000
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posted 08-13-2002 02:40 PM
That's interesting.....
The pedal does seem like its bottoming out when it's pressed all the way down. Like it hits a stop or something. No matter how hard you press it won't go any farther. (It's not on the floor either) It does have the adjustable push rod that I adjusted per the shop manual.... Hmmmmmmm.......------------------
67convertible 289/auto
65fastback 302/4sp [This message has been edited by Robert K (edited 08-13-2002).]
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lyle29464
Gearhead Posts: 827
From: Mt. Pleasant S.C.
Registered: Mar 2000
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posted 08-13-2002 09:45 PM
I think your getting close
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