70 Duster power to manual brake conversion

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killnine

killnine

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Hi guys,

So I tried to convert my power brakes to manual, and I thought it was going to be at least somewhat straightforward. Of course I was wrong, or did something wrong. I bought a new master cylinder and adjustable brake rod from Doctor Diff, which is listed as "Super duty heim-joint style master cylinder push rod adjusts in length from 6.1" to 6.8" (center of bolt to end of tip). Fits '66-'76 A,B and E bodies equipped with manual brakes.". Well, mine wasn't equipped with manual brakes so I guess that's where the problem starts. Since I had read of people just using a stock manual brake rod, I figured using this would make sense, especially since it is adjustable. I removed the booster and put everything back together, and the rod is at least an inch too long at its shortest adjustment. There's no room for any more padding or adapters at the firewall... the bolts won't handle any more and still be able to have nuts put on them. I tried to put a plastic plate piece from the old booster setup in there and it still wasn't enough. So what am I doing wrong here? If this rod is for a manual brake 70 duster then wouldn't one of its lengths match what I need?
 
Is the brake pedal properly parked against it's stop, and not hanging up on the brake switch?
I know the manual brake pedal looks different from a power brake car. I wonder if the pedal-ratio is the same? And if the top pivot is in the same geographical place?
I have done this conversion a couple of times and had no problems.
BTW
In the manual M/C, the brake rod presses into the back of the piston, and there might even be a small retaining clip (not sure, it's been a long while).It really has to be jammed in there. Then you install the M/C with the rod, and finally hook it to the pedal. This is different from the M/C for a booster. Perhaps your pushrod is just not fully seated.
 
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If you have a manual brake master cylinder, everything will bolt up.

If the push-rod appears to be 1" too long, it is probably not bottomed out inside the master cylinder piston.

Did you install the rubber clip on the end of the push-rod and insert it into the piston? Is the push-rod locked to the piston?

Did you re-adjust the brake light switch? The pedal is much closer to the floor on power brake cars.
 
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DoctorDiff said:
If you have a manual brake master cylinder, everything will bolt up.

If the push-rod appears to be 1" too long, it is probably not bottomed out inside the master cylinder piston.

Did you install the rubber clip on the end of the push-rod and insert it into the piston? Is the push-rod locked to the piston?

Did you re-adjust the brake light switch? The pedal is much closer to the floor on power brake cars.
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I did need to push the rod in further into the MC, but it was still up too high for my liking. I took about a 1/4" off of the threads and the female part and it works well now. Thanks!
 
I pulled my Mc and booster off my 74 and put a manual Mc on and it worked good. Kept my disc brakes. Glad you got it fixed.
 
Charles Johnson said:
I pulled my Mc and booster off my 74 and put a manual Mc on and it worked good. Kept my disc brakes. Glad you got it fixed.
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I'm working on this now. Did you use a stock manual brake push rod? What bore was the new master cylinder?
 
Duster_71 said:
I'm working on this now. Did you use a stock manual brake push rod? What bore was the new master cylinder?
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The MC was from Doctor Diff, the aluminum master cylinder kit. The push rod was the adjustable heim joint from the same. The bore was 15/16 but is available also in 1 1/32. I believe the issue in length is probably due to the difference between a power and manual pedal being different. A stock rod might work better but I have no experience. At least the adjustable had some adjustment available after I trimmed it a bit. And it's a quality piece. I would do it again. If I could weld easily a stock rod would have probably been much cheaper to adapt though.
 
killnine said:
The MC was from Doctor Diff, the aluminum master cylinder kit. The push rod was the adjustable heim joint from the same. The bore was 15/16 but is available also in 1 1/32. I believe the issue in length is probably due to the difference between a power and manual pedal being different. A stock rod might work better but I have no experience. At least the adjustable had some adjustment available after I trimmed it a bit. And it's a quality piece. I would do it again. If I could weld easily a stock rod would have probably been much cheaper to adapt though.
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Power and manual brake pedals are identical. The pedal distance to the floor being different is in the linkage and push rod length with the power brakes. The only differences between a power brake car and a manual brake car are the brake parts themselves, ie- the M/C, power booster, linkage, and push rod. Nothing else is different.
 
72bluNblu said:
Power and manual brake pedals are identical. The pedal distance to the floor being different is in the linkage and push rod length with the power brakes. The only differences between a power brake car and a manual brake car are the brake parts themselves, ie- the M/C, power booster, linkage, and push rod. Nothing else is different.
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72blunblu, I'm trying to confirm that the stock manual brake push rod will properly fit/seat in a 15/16 bore for a cast iron master cylinder. Looks like the 15/16 bore masters were for pwr brakes. I was not really interested in buying other pushrods or master kits.
 
Depends entirely on whether or not the master cylinder was machined for that little rubber retaining ring. I've heard that some are, but all of my 15/16" master cylinders are from dr diff. I am using the stock pushrod with those.
 
OK, so a bit off the original topic, but I've been trying to get my brakes to a safe level and I've reached my sanity point. I'm still plagued by too little pressure to stop the car safely. The front drums were replaced with an SSB disc kit (and the spindles upgraded to be able to do so). The rear is an 8.75 stock a-body length with 10" drums. The rear cylinders were replaced with 7/8 bore just yesterday because I thought the cylinders were leaking. If I clamp the flex hose feeding the rear I get a good solid pedal. I haven't tried driving it like that though so I'm not 100% sure it's solid enough to guarantee the problem is in the rear. When I drive it it will stop it at a slow speed, and I can feel the front working. I've verified the rear drums are adjusted just to the point of almost not being able to get the drums off, and then backed off a few clicks. Strangely, it stops a little better going in reverse. The new rear cylinders made some improvement but not enough. I also put UV dye in the system since I was going crazy trying to find what seems like a leak. I find no evidence of anything leaking. If it's leaking, it's leaking air and not fluid, or it's hidden. I've had the drums off a few times just to verify everything. The pedal push rod when released comes back just enough to be hovering just before pushing in the master. It has plenty of pedal, but just doesn't have the braking power behind it.Every line is new within the last year. I've checked for the UV dye leaks at every point in the system. This power to manual conversion was mainly one of my attempts to fix this, since I thought the booster might be bad. I've had the front wheels off just to look at the front discs and verify everything, and it all looks snug and straight. If anything the pads are too tight against the rotors, because they are slightly touching when I turn the rotor by hand. I hope the SSB kit isn't this bad that I threw away $600 for it, and countless dollars and hours trying to get it to stop.
 
killnine said:
OK, so a bit off the original topic, but I've been trying to get my brakes to a safe level and I've reached my sanity point. I'm still plagued by too little pressure to stop the car safely. The front drums were replaced with an SSB disc kit (and the spindles upgraded to be able to do so). The rear is an 8.75 stock a-body length with 10" drums. The rear cylinders were replaced with 7/8 bore just yesterday because I thought the cylinders were leaking. If I clamp the flex hose feeding the rear I get a good solid pedal. I haven't tried driving it like that though so I'm not 100% sure it's solid enough to guarantee the problem is in the rear. When I drive it it will stop it at a slow speed, and I can feel the front working. I've verified the rear drums are adjusted just to the point of almost not being able to get the drums off, and then backed off a few clicks. Strangely, it stops a little better going in reverse. The new rear cylinders made some improvement but not enough. I also put UV dye in the system since I was going crazy trying to find what seems like a leak. I find no evidence of anything leaking. If it's leaking, it's leaking air and not fluid, or it's hidden. I've had the drums off a few times just to verify everything. The pedal push rod when released comes back just enough to be hovering just before pushing in the master. It has plenty of pedal, but just doesn't have the braking power behind it.Every line is new within the last year. I've checked for the UV dye leaks at every point in the system. This power to manual conversion was mainly one of my attempts to fix this, since I thought the booster might be bad. I've had the front wheels off just to look at the front discs and verify everything, and it all looks snug and straight. If anything the pads are too tight against the rotors, because they are slightly touching when I turn the rotor by hand. I hope the SSB kit isn't this bad that I threw away $600 for it, and countless dollars and hours trying to get it to stop.
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I should add that pumping the pedal does nothing to improve the braking.
 
More info. It has what I believe is a properly working prop valve (72+ type). However, now that I look at the picture of it that I just took, I remember that the two lines from the valve to the MC were not replaced, and although I did not see any UV leaking, that bunch of crud on the one line could be hiding something. I doubt it, but I should probably look into cleaning that off to at least be sure.

normal_20170403_223313.jpg
 
Well, nothing is leaking from the line mentioned. I still can't find a single leak. I guess the next step is to clamp off the back at the flex line again and actually drive it to see if it indeed is a solid pedal when doing so. At least that would confirm 100% that the issue is still in the back. I don't know what would be leaking in the back though unless the flex line, only a year old, is ballooning, or the brake tee with the vent bolt through it is somehow leaking through into the axle housing.
 
So I found the problem. One of the outboard pistons on the driver's side caliper is leaking. And it has probably 10 miles on it since it was installed. And it never had a good pedal. so it's been doing that since install. Of course, I've been off and on trying to fix this for 2 years, so yeah, no warranty. And I don't see any calipers I can just purchase on ssbc's site. Great. Guess I'll call them, or find out how to rebuild calipers.
 
After taking it apart, and removing the pistons, the piston seal on the leaking piston is just slightly too big. It's enough that it very slides over the piston. Another one from a non-leaking piston does not slide over it that easily, but has to be forced along. Obviously a bad seal from the factory and they didn't catch it in QC. Oh well. Boo on you SSBC. I ordered a Dorman D46457 Brake Caliper Repair Kit.
 
killnine said:
After taking it apart, and removing the pistons, the piston seal on the leaking piston is just slightly too big. It's enough that it very slides over the piston. Another one from a non-leaking piston does not slide over it that easily, but has to be forced along. Obviously a bad seal from the factory and they didn't catch it in QC. Oh well. Boo on you SSBC. I ordered a Dorman D46457 Brake Caliper Repair Kit.
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Did that fix your problem??????
 
IT fixed that caliper. I still have bad brakes, but I'm still chasing down minor leaks. The last one I found was a small leak at the transfer tube nut on the other side. Once I get that tightened and bleed it again hopefully things will be better. You wouldn't think a tiny leak like that would cause such a loss of pressure but I guess it makes sense at high pressures.
 
killnine said:
IT fixed that caliper. I still have bad brakes, but I'm still chasing down minor leaks. The last one I found was a small leak at the transfer tube nut on the other side. Once I get that tightened and bleed it again hopefully things will be better. You wouldn't think a tiny leak like that would cause such a loss of pressure but I guess it makes sense at high pressures.
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I do not believe the small leaks you are chasing are the problem I am having the same problem working with wilwood and tring to get in touch with dr diff it could be the 2.6 calipers most people are running the 2.75 calipers cant believe that would make that much difference
 
jmello62 said:
I do not believe the small leaks you are chasing are the problem I am having the same problem working with wilwood and tring to get in touch with dr diff it could be the 2.6 calipers most people are running the 2.75 calipers cant believe that would make that much difference
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I would bet most people are running 2.6" piston calipers. All the stock 73-76 A-body calipers are 2.6's. The only way you'd have 2.75's is if you're using B/E or the F/M/J/R calipers. So you'd have to make a point to get those.

Regardless, that shouldn't cause any problems. The pedal feel would be a little different for a 2.6" piston compared to a 2.75", but both would stop the car just fine and neither should hit the floor if everything is working properly.
 
72bluNblu said:
I would bet most people are running 2.6" piston calipers. All the stock 73-76 A-body calipers are 2.6's. The only way you'd have 2.75's is if you're using B/E or the F/M/J/R calipers. So you'd have to make a point to get those.

Regardless, that shouldn't cause any problems. The pedal feel would be a little different for a 2.6" piston compared to a 2.75", but both would stop the car just fine and neither should hit the floor if everything is working properly.
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I agree but I have a long pedal travel and weak stoping the pedal dose not go to the floor but i can not skid the tires
 
jmello62 said:
I agree but I have a long pedal travel and weak stoping the pedal dose not go to the floor but i can not skid the tires
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That's not a 2.6" vs 2.75" piston problem. Both of those calipers are more than capable of locking up the brakes and stopping the car with any of the stock bore size master cylinders, from 15/16" up to 1-1/32". Probably a wider range than that too, that's just what I know for sure.

You've got something else wrong.
 
72bluNblu said:
That's not a 2.6" vs 2.75" piston problem. Both of those calipers are more than capable of locking up the brakes and stopping the car with any of the stock bore size master cylinders, from 15/16" up to 1-1/32". Probably a wider range than that too, that's just what I know for sure.

You've got something else wrong.
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I sure would like to find it I have not tried replacing pads yet just bought this car not sure if this was always a issue or just started old owner not much help
 
Could be a lot of things. If the pedal is that weak though I would look at air in the lines, contaminated fluid, maybe a bad master cylinder. Leaks can suck air in and make it impossible to bleed the brakes. If the master cylinder wasn't bench bled it could do that too. Could be the wrong size master cylinder, or maybe the wrong push rod. Mismatched parts kind of thing. Does the pedal pump up at all?

Pad contamination usually means you have a good pedal, but don't stop. The hydraulic side works fine but you just don't slow down because there's no friction. Your issue sounds like a hydraulic problem.
 
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