My mistake. I was thinkng you were working on a '67. Don't change the rotors.

Check your Pm's.

 

I did not have an original '66 mc. I am not sure what year it is for, but I had good braking power before this problem started. Not sure which rod I have. Is it possible to remove the rod without removing the m/c? Can I remove it from under the dash? Also the clevis is in the BOTTOM hole. Would that make any difference? I have never touched it since owning the car, and had ok brakes before this started, except for the pulling which has always been there. Thanks for your help!!!!!!!!! Your thoughts?

 

The master cylinder I put back on the car is for a 67 since I cannot find a 66 mc. I used the same rod.

 

Which rod? The one between the booster and master cylinder, or the one from the back of the booster to the pedal arm?

 

The one from the pedal arm to the booster. I did not know that there were two. I assumed that from your previous post you were referring to the rod out of the booster since it touched the master cylinder, but was not aware that there are two rods. Thanks

 

Danny, did you check run-out on the rotor and trailing arm? Run-out can cause problems with brakes pulling to one side. The disc brake set ups do not like run-out.

 

Here's a photo of the "long" and "short" power brake booster-to-master cylinder pushrods; '67 was the only year that the "long" pushrod was used, due to the "deep" hole in the rear piston.

 

Thanks.....please explain what "run out" is. How do you perform this run out test on the rotor and trailing arm? I am assuming that you check for thickness on the rotor, but what about the trailing arm?

 

Runout is a fancy way of saying the rotor wobbles as it turns. When it wobbles, it knocks the pistons back into the calipers slightly. This, in turn, causes the brake pedal to sink a little low on the first push and be at normal height on the second push. The brakes still work, however.

In my opinion, rotor runout is a red herring in your troubleshooting.

After all you've changed, I'd start to let my mind think about the truly oddball stuff..... for example is there any way you could have reversed the front and rear connections at the proportioning valve? That would give you tremendous rear braking and limited front braking. On the left rear, the corner that doesn't lock up, is there grease getting on the rotor or pad surfaces? That kind of thing...

Jim

 

Agreed.

 

Thanks Jim: There is no proportioning valve on the '66. That started in '67. It is possible that some fluid may have gotten on the pads/rotors, but if so not much. The only thing I have not done is replace the metal lines from the front of the car to the rear, or the short metal lines from the rubber hose to the caliper on the rears. I am certain that I have not mixed, or reversed the lines. However, i might need to inspect the short metal lines that cross over to the right side of the car on the front and rear. Those have not been replaced since I owned the car. The front does not lock up on either side, only the right rear. I have an after market MC and booster, and have ordered a long rod to go between the MC and the booster. Maybe that will do it. (maybe the rod is not depressing the MC enough) I also have new pads on the way. I am going to purchase a micrometer to check the run out or thickness of the rotors before I replace them if necessary. That is about all i can think of to do. Thanks again for your input!

 

Hmmmmm..... didn't know that. So how, then, is F/R proportioning accomplished on a '66? There's got to be sumpthin'......


As I recall, the front-rear line passes by the L.R. caliper junction before it crosses to the R.R. True? If so, and since the R.R. caliper is obviously seeing hydraulic pressure, it won't be the cross over line. You might have a constriction in the line that connects directly to the LR caliper though.

This seems to me like another red herring. You have a good, firm pedal at normal height, yes? If so, you are depressing the MC piston adequately and the length of the rod isn't an issue.

Too, there isn't anything about the master cylinder or its mechanical linkage that could possibly affect a single wheel, like the RR for example.

The new pads you will be trying might help. But if they do, it'd be good to ask "why?". Why are they needed? Are the old pads on 3 out of 4 calipers glazed? If so, why?

In any event, good luck with that experiment.

Jim

 

You have come to all the same conclusions I have.

Front/rear brake bias is handled by different size pistons in the calipers. Same principle as the drums.

 

Will front calipers physically bolt up at the rear? If so, what are the odds that the RR caliper is actually for the front? And that one of the calipers currently installed on the front is actually for the rear?

Jim

 

OK, an update to this situation.

I went over to Danny's last night to help with the brake diagnosis.

First, JohnZ hits another home run with the length of the master cylinder pushrod issue. The old master cylinder (which was some sort of generic replacement, with line openings on both sides of the master cylinder) had a very short opening into the piston bore.

The replacement 1967 to 1970 something master cylinder had a much longer (more depth) opening into the piston bore. We replaced the short 66 pushrod with the longer 67 pushrod.

We also replaced all of the brake pads. Calipers had previously been replaced. One of the pads had very minor fluid contamination on a small part of the surface. Other than that we didn't see anything wrong.

Took the car for a ride. It now seems to stop straight, with no pulling to the right as previously indicated.

However, the car still doesn't seem to have the stopping power it should have. Danny hit the brake pedal hard from 45 - 50 mph, and the car stopped straight, but really didn't slow down like it should have.

I drove the car and the pedal felt solid, with almost no free travel. Danny re-adjusted the rod under the dash to add back in some of the free travel, but is still doesn't feel quite right.

Also, there is a strange clicking noise under the dash (or perhaps from the power booster) when the brake pedal is pushed. We unbolted the master cylinder from the power booster, and the clicking noise is still there. It is like you push the pedal, it travels for a bit, then something "pops" (like something mechanical was binding) and the pedal continues.

We re-bled the brakes (very little, but some air in a couple of the calipers), but that didn't help much, car still doesn't stop like it should. It is almost like the brakes don't have enough clamping force.

Rotors look fine, no glazing or grooves, but they were not resurfaced.

Danny says the car stopped much faster before the master cylinder replacement. It was also pulling to the right then.

He still has the old master cylinder (with line openings on both sides, anybody know what this is?). I suppose we could put it back on.

New master cylinder was bench bled while on the car. It was bolted up to the power booster, the bleeder hoses / fittings were connected, and it was bench bled by depressing the pedal until all of the air was out. Then the lines were connected and the entire system was bled.

All of the brake hoses were also replaced.

OK, any ideas? Do we have a mismatch between a 66 power booster and a 67 and later master cylinder? FYI: The bore size of the new 67 and later master cylinder measured at 1.118 with a vernier caliper (1 1/8, I assume, which is what a non power booster master cylinder should be). Old master cylinder measured 1.024 (I think) bore size.

Where do we go from here?

Reminder, car is a 1966, with power brakes, a 67 and later style master cylinder, no proportioning valve. How is proportioning handled in that situation? Line size? Both front and rear lines coming from the master cylinder looked to be the same size to me.

Calipers are all in their correct locations.

Danny, jump in here and add / correct anything I may have wrong.

 

Changing the bore size of the master cylinder can have a significant effect on the pedal effort.

Using the numbers you measured, the hydraulic line pressure with the new MC will be about 17% less for a given pedal effort.

If the two master cylinders really are 1.0 and 1.125, the reduction in line pressure will be about 21%.

You'd notice that much of a change.

Jim

 

That is interesting Jim. I think I understand that the correct master cylinder for a power brake 66 uses a 1 inch bore, and the manual brake uses a 1 1/8 inch bore. Someone suggested to Danny that he would get better braking with the 1 1/8 bore master cylinder on his power brake car.

Hard for me to say that pedal pressure is different, since I drove the car for the first time last night, and the new (1 1/8) master cylinder was on it them.

Are you suggesting that we should go to a 1 inch bore master cylinder?
Danny still has the old master cylinder, and it looks to be in nice shape.

 

The new longer pushrod (which Danny got from Lonestar) does NOT have the little tip on the backend, or the o ring. The shorter pushrod that we took out does have the small tip on the back end and the o ring.

The longer rod is straight, with a flat surface on the back end, and the rounded surface on the front end.

Is this an issue?

 

Jim is correct. The smaller bore master cylinder will generate more line pressure with the same pedal effort. I don't know about power brakes but if you use a larger master cylinder with manual brakes, you'll notice a higher, harder pedal than if you use a smaller bore master cylinder. There is quite a difference in pedal effort for the same deceleration rate. At least with manual brakes.

The '66 manual brake cylinder is single piston, 1" bore.

 

Yes, Ed good description, however you got the MC issue reversed. The POWER BRAKE MC is 1 1/8 inch piston, and the MANUAL Brake MC is 1" piston diameter. We have the 1 1/8 POWER MC on the car now. I did see what ONE of the clicking noises are after you left, Ed. The Clevis pops when you depress the pedal. I can clearly see it as I hear it, BUT there is another click from inside the booster after you depress the pedal even further. I am wondering about the lines of the MC to the car. I have checked the ASM that clearly states that frt bowl to the front of the car, and the rear bowl to the rear of the car. I am SURE of this, but people keep telling me that the brakes may be better if they were reversed. THANKS TO ALL OF YOU FOR YOUR HELP> I am totally lost on this one..special thanks to ED who is helping me here at my place trying to figure this out!!