Lack Luster Brakes

[carfreak6970]

So the car in question is a 70 charger. It has 10" drums all around that were rebuilt with new springs and cylinders a couple years about (about 1500 miles ago), new hard and soft lines, new master cylinder, with a repro disk brake booster. I bled all the air out of the lines and verified that there are no leaks in the system. However my issue is under heavy braking I can not get the wheels to lock up (from a 10-15mph roll). So the pedal does not go to the floor, but it does stop before it gets to the floor, it is solid.

so here are a couple ideas I have that may be the reason for my subpar braking:

So the car was always a power brake car so I don't believe there is an issue with the brake pedal length, but to be sure is there a way to determine if I have the correct power brake pedal?

This is the second brake booster on this car. I adjusted the push rod length that protrudes into the master cylinder. I believe I left about a .015" gap between the tip of the push rod and the corresponding cup in the master cylinder. Is that too much or not enough? I thought it was enough from what I found online. Like stated above, the brake pedal is solid but could it be that the master cylinder/booster doesn't have enough travel?

I did feel the wheels after the test drive and they did feel like they were really warm? could it be that the push rod is to far extended into the master cylinder to the point the brakes are dragging and they are getting hot to the power that they are losing their effectiveness?

The last idea I got was maybe the adjusters are not locking into place due to that lever not contacting the star part of the adjusters. So after a couple stops the adjusters work themselves in? I did go in reverse a couple times and slam on the brakes (which I thought was a way to help adjust the brakes out?) and it did seem to improve the braking, but it was at the end of my drive and didn't get to test anything further.

Am I on the right track? is there ways I could prove if any one of these ideas is causing the problem of lack luster braking?

thank you

 

[Kendog 170]

Have you tried manually adjusting all four corners?

 

[carfreak6970]

Have you tried manually adjusting all four corners?

So when I installed the booster a year or two ago I did. I may have done it last year as well (have to look at the maintenance log). When thinking in the shower this morning I thought the easiest place to start was at all the wheels to see where they are adjusted at, remove drums and wheels to see if that adjuster is working properly and insure that the brakes were assembled properly. From there adjust the brakes and put on the ground and try another trial drive and see what happens.

 

[Professor Fate]

So the car was always a power brake car so I don't believe there is an issue with the brake pedal length, but to be sure is there a way to determine if I have the correct power brake pedal?

There is NO DIFFERENCE in power/manual/drum/disc pedals.

This is the second brake booster on this car. I adjusted the push rod length that protrudes into the master cylinder. I believe I left about a .015" gap between the tip of the push rod and the corresponding cup in the master cylinder. Is that too much or not enough? I thought it was enough from what I found online. Like stated above, the brake pedal is solid but could it be that the master cylinder/booster doesn't have enough travel?

Get the Factory Service Manual for free over at MyMopar.com . It has the spec and procedure for setting the push rod length correctly, as well as anything else you need to know about your car- right from the folks who designed it. Not from an anonymous internet source.

I did feel the wheels after the test drive and they did feel like they were really warm? could it be that the push rod is to far extended into the master cylinder to the point the brakes are dragging and they are getting hot to the power that they are losing their effectiveness?

Possible. See above. Drums normally will be warm after use.

The last idea I got was maybe the adjusters are not locking into place due to that lever not contacting the star part of the adjusters. So after a couple stops the adjusters work themselves in? I did go in reverse a couple times and slam on the brakes (which I thought was a way to help adjust the brakes out?) and it did seem to improve the braking, but it was at the end of my drive and didn't get to test anything further.

Brake adjusters are side specific. Make sure you have them assembled correctly and on the proper side.
They only adjust in reverse, and could take quite a bit more than one trip down the driveway, dependent on how far out of whack the original adjustment was. Manually set the adjusters so you just begin to feel a light drag when you rotate the wheel, then go about letting the self-adjusters do their thing.
Several things you did not mention that could be contributing to your issue:
What size master cylinder are you using? Did you use a proper drum/drum master with both residual valves still in place?
What size wheel cylinders did you put in?
There are multiple sizes of both; parts sources are getting notorious for incorrect part number listings. The FSM and part catalogs will tell you what was originally on the car.
When you say you installed a "repro disk brake booster", is this an actual replacement part or an aftermarket "Fitzall" unit that is non-factory?

 

[carfreak6970]

There is NO DIFFERENCE in power/manual/drum/disc pedals.

Get the Factory Service Manual for free over at MyMopar.com . It has the spec and procedure for setting the push rod length correctly, as well as anything else you need to know about your car- right from the folks who designed it. Not from an anonymous internet source.

Possible. See above. Drums normally will be warm after use.

Brake adjusters are side specific. Make sure you have them assembled correctly and on the proper side.
They only adjust in reverse, and could take quite a bit more than one trip down the driveway, dependent on how far out of whack the original adjustment was. Manually set the adjusters so you just begin to feel a light drag when you rotate the wheel, then go about letting the self-adjusters do their thing.
Several things you did not mention that could be contributing to your issue:
What size master cylinder are you using? Did you use a proper drum/drum master with both residual valves still in place?
What size wheel cylinders did you put in?
There are multiple sizes of both; parts sources are getting notorious for incorrect part number listings. The FSM and part catalogs will tell you what was originally on the car.
When you say you installed a "repro disk brake booster", is this an actual replacement part or an aftermarket "Fitzall" unit that is non-factory?

I am not to sure on the wheel cylinder sizes. I guess I can try to measure those. But I know the master cylinder is the 1" bore like the FSM states it should have. It is drum drum master cylinder, but I did not remove any residual valves. I looked through the brake section in the 70 charger FSM and was not able to locate anything regarding where to adjust the length of the booster push rod too.

The booster is a reproduction of the disc brake power booster.

 

[Professor Fate]

I am not to sure on the wheel cylinder sizes. I guess I can try to measure those. But I know the master cylinder is the 1" bore like the FSM states it should have. It is drum drum master cylinder, but I did not remove any residual valves. I looked through the brake section in the 70 charger FSM and was not able to locate anything regarding where to adjust the length of the booster push rod too.

The booster is a reproduction of the disc brake power booster.

I don't have a '70 FSM, but my '68 manual states the pushrod should be adjusted to .910-.920 above the mounting surface with the filter housing attached.
The '68 manual also shows a different booster being used in drum applications vs disc (Midland-Ross vs Bendix). Don't think it should make a difference, but the factory did change them for a reason.

 

[AJ/FormS]

Here's something to consider;
New brakeshoes never match used drums. That is to say, if you lay a new shoe into an old drum, and manage to not hang it up on the ridge, it will rock up and down the friction surface. This means that the shoe is only contacting the friction surface over a tiny patch. It will take thousands of miles to break-in.
If it's a bad enough mismatch, you'll get extra pedal travel, as the shoes force the normally round drums, into an oval shape, at which time the pedal will get harder and braking will improve, but it may take both feet on the pedal to achieve.
If you machine the drums to restore them to round, this changes nothing, because the shoes are still only contacting in a tiny patch.
The proper procedure to cure this situation, is to take your shoes and drums to an old-school brake shop, and have the new shoes ground to match the radius of the old reground drums. If the drums are excessively worn, then the shoes will have to be excessively ground, reducing their lifespan.

 

[carfreak6970]

I don't have a '70 FSM, but my '68 manual states the pushrod should be adjusted to .910-.920 above the mounting surface with the filter housing attached.
The '68 manual also shows a different booster being used in drum applications vs disc (Midland-Ross vs Bendix). Don't think it should make a difference, but the factory did change them for a reason.

Interesting... There is nothing like that in the 70 Service manual. I guess if I ever take off the master cylinder Ill take that measurement

Here's something to consider;
New brakeshoes never match used drums. That is to say, if you lay a new shoe into an old drum, and manage to not hang it up on the ridge, it will rock up and down the friction surface. This means that the shoe is only contacting the friction surface over a tiny patch. It will take thousands of miles to break-in.
If it's a bad enough mismatch, you'll get extra pedal travel, as the shoes force the normally round drums, into an oval shape, at which time the pedal will get harder and braking will improve, but it may take both feet on the pedal to achieve.
If you machine the drums to restore them to round, this changes nothing, because the shoes are still only contacting in a tiny patch.
The proper procedure to cure this situation, is to take your shoes and drums to an old-school brake shop, and have the new shoes ground to match the radius of the old reground drums. If the drums are excessively worn, then the shoes will have to be excessively ground, reducing their lifespan.

Oh God... I didnt even think of that... I guess that would be very easy to determine if I am taking the drums off anyway. Thanks for the idea.

 

[Kendog 170]

Here's something to consider;
New brakeshoes never match used drums. That is to say, if you lay a new shoe into an old drum, and manage to not hang it up on the ridge, it will rock up and down the friction surface. This means that the shoe is only contacting the friction surface over a tiny patch. It will take thousands of miles to break-in.
If it's a bad enough mismatch, you'll get extra pedal travel, as the shoes force the normally round drums, into an oval shape, at which time the pedal will get harder and braking will improve, but it may take both feet on the pedal to achieve.
If you machine the drums to restore them to round, this changes nothing, because the shoes are still only contacting in a tiny patch.
The proper procedure to cure this situation, is to take your shoes and drums to an old-school brake shop, and have the new shoes ground to match the radius of the old reground drums. If the drums are excessively worn, then the shoes will have to be excessively ground, reducing their lifespan.

Well with now1500 miles on it. It can't hurt to try an adjustment 1st.

 

[carfreak6970]

So I made some time last night to look into the charger and found a couple interesting things. First off, like I vaguely remember, the adjusting lever was not contacting the star on the adjuster. I am chalking this up to mismatched parts from the original components mixed with todays revised design of moving the star closer towards the center of the adjuster.

So even if I would have adjusted the front, eventually they would have just "unwound" them selves and I would be back at my initial issue. Speaking of adjusting, I believe I got the adjusters on the wrong sides. Since if you were to use a brake spoon and push up from the back side of the backing plate that would loosen the adjuster and not tighten it.

The other lovely issue I found is that I have a leak in the left front.

I guess this isnt a good picture but you can see how shiny the pad is. I think at one point or another the wheel cylinder leaked. So I have new adjuster kits on order as well as new front cylinders and shoes. Hopefully they will be here Saturday so before the holiday weekend is out this will be on the road.

The inspection of the rears showed a good wear pattern and everything appeared to work the way it should. So it looks like I really only had rear brakes working on this car.

Ill get these issues addressed and see if that cures my lack luster brakes.

 

[carfreak6970]

So this past holiday weekend I got some time to work on the brakes. I replaced both front wheel cylinders, brake pads and installed new adjuster kits. I adjusted the brakes and took it for a ride. They were better but not great. Towards the end of the drive once I came to a complete stop at a stop sign I did notice smoke and and brake burning smell that eventually went away and did not come back. When I got back home I did the speed up to 15 mph and slam the brakes, reverse and repeat. Initially it wasnt stopping that great but by the 5 to 6th time it was consistently nose diving and locking the brakes up, which is what I wanted. So I am guessing a combination of breaking the brakes in and improper adjustment caused the smoke.

Last night when the weather and time was cooperating I repeated the drive to make sure everything stayed the same. Thankfully it did!! Stopped great when I took it on the loop, took it downtown and it acted fine, and even drove it to work today with no issues! so I would say that this issue is closed.

Besides the brake booster over boosting the brakes (using a disc brake booster), which wont be an issue when I get to installing those disc brakes. And noticed the Ammeter jumping way to much. Ill have to check some grounds and connections for that one.