Brake issue with my CUDA

[MOPAR Andy]

Looking for some advise. I am having problems with the brakes on my 71 383 Cuda with power front disc. The car stops ok but the pedal is low, soft and not responsive. I have a 70 challenger and a 72 challenger with similar power brake set ups and they both work great and pedal response is fine. The pedal in the 71 cuda just does not feel the same. I have all new lines and wheel cylinders are fine. I replaced the master with a unit I bought from "Bill Rolik Enterprises" . Bill is a great guy, very knowledgeable and very helpful. I have a friend who is very good with MOPAR braking systems. We went through the whole system and found that the bushing on the brake pedal assembly were worn so we replaced them. I am also trying to figure out the correct term or name for this mechanism that connects the pedal to the booster. Some have called it a "Dog Leg" and some refer to it as a "cantilever" brake pedal assembly. I have attached some photos of the assembly. We also notice that the rod in the assembly has been welded at some point in its life, so not sure if the dimensions and geometry are correct or if it is even the correct piece for this vehicle. The booster appeared to be working fine and vacume was in spec, but I did buy a replacement booster from Rock Auto. We found that the booster that was in the car, had a different push rod than the one I bought as a replacement. The width of the eyelit on the replacement booster push rod, where the rod attaches to the pedal assembly, was wider than the one that was in the car, and based on the width of the pedal assembly in appears the newer push rod is the correct width. I have found that this brake pedal assembly is available in aftermarket reproduction but it appears there are different widths of the assembly depending on year and a lot of them won't be correct. I have a call into Wildcat Wreckers to see if they have a used mechanism.
I was also advised that perhaps the bore of the master is not correct. Apparently based on year and model the bore can be from 15/16 to 1 1/8. I was told a bigger bore will raise the pedal and make it "harder". I ordered the service manuals for the car to hopefully determine what is correct. At this point I am not sure if the master, brake pedal assembly and or booster are correct.
I am learning as I go hope I was clear in explaining the issues. Any thoughts or advise from all my MOPAR brake guru's.
thanks

 

[edison1970]

That looks like the correct linkage. What brake fluid are you using?

 

[Chryco Psycho]

Have you tried extending the length of the pushrod between the booster & master cylinder , if it is too short the pedal will be low , if you extend it too far the brakes will not release you want it to virtually touch will the cylinder bolted up tight .

 

[70chall440]

A few thoughts

• you need the right MC to get the brake "feel" which in essence is a result of line pressure which is a result of MC bore size along with booster support
• if the MC is right (or close enough) it is very possible that your booster is not performing correctly. This might be due to a lack of vacuum, a booster which isn't working properly, etc.
• there is air trapped in the lines. Sometimes they will seem to bleed correctly but still have trapped air some place.
• one or more of your brake cylinders and/or calipers isn't working correctly

 

[MOPAR Andy]

Using DOT 3 fluid. I was able to get an original brake pedal assembly from "Tony's parts. Installed the new assembly and now pedal is even lower and brakes are still soft and not as responsive as my other cars. it appears they welded the rod on the other assembly to help raise the pedal height. Was able to obtain an older original MC with a 1 1/16 bore. It is an American made "True Torque" which is a direct replacement for the BENDIX that would have come with the car originally. We then realized that the MC we had on the car and the True Torque both have a 1 1/16 bore size. So, have not replaced the existing MC with the True Torque. Now thinking of having the True Torque machined and rebuilt to a 1 1/8 bore to increase the pressure. They made a bendix 1 1/8 bore but that was only standard equipment on Hemi cars. The True Torque cost me $140.00 and to have it resized is an additional $240.00. Im hesitant to go further as I should not have to increase the bore size for the brakes to work properly. Good point about the booster and lack of vacuum I tested the vacuum and it was within the correct level and matched the vacuum on my 72 Challenger on which the brakes work and feel great. Neither the new booster or the one that was on the car when I got it have an adjustable push rod so I would have to cut and weld it to increase or decrease the length.
I really appreciate all the help and comments to help resolve my problem

 

[Steve340]

If the pedal is low and soft/spongy generally you have air in the system or the master cylinder is faulty.
Try fitting the new master cylinder and make sure the pushrod clearance is correct.
Leave the bore size alone it will make very little difference.
My factory boosters all had adjustable pushrods fitted - is that your problem?

 

[MOPAR Andy]

Do you know where I can get a correct booster with an adjustable push rod
Thanks

 

[Chryco Psycho]

I thought all boosters had adjustable pushrods , if you slide the rod out the tip should thread into the pushrod , so it should unthread to make it longer , this is the first thing I would try .

 

[moparleo]

Jus to back up a little... Is this the factory brake system on the car or is this a "conversion" meaning it didn't come factory with power front disc brakes ?
Much more involved in a conversion than a master/booster and pedal assembly.

 

[MOPAR Andy]

The booster I have on it is a "cardone" got it from Napa auto parts, the only one I could find. The one that was on the car was not original. I will double check the push rod but pretty sure it is not threaded. Brake system is factory, not a conversion.

 

[moparleo]

OK so is this the first time driving this one and you noticed that the baking was not same as the other factory disc brake cars that you have or was something repaired/changed and then it was different from before ? To diagnose something, the more back round info the better.
The Service Manual is a free download if you want it now.
Chrysler Master Tech Service Conference Library – MyMopar
Resource Library – MyMopar

 

[Steve340]

If the booster is not original with all the lengths of rods/levers/angles etc being taken in to account it is not hard to assume something is off there contributing to your issue.
You have other cars - have a good look and measure and you will probably see the problem.
Take the booster out and compare it to an original.
Failing that get hold of an original booster. They come up for sale on this site or place a wanted add.
I have two cars an E and B body and I raised the pedal height on both cars by lengthening that rod to the pedal.
The factory pedal height was too low for me.
You also may have two problems - the booster issue and a faulty master?

 

[fasjac]

Using DOT 3 fluid. I was able to get an original brake pedal assembly from "Tony's parts. Installed the new assembly and now pedal is even lower and brakes are still soft and not as responsive as my other cars. it appears they welded the rod on the other assembly to help raise the pedal height. Was able to obtain an older original MC with a 1 1/16 bore. It is an American made "True Torque" which is a direct replacement for the BENDIX that would have come with the car originally. We then realized that the MC we had on the car and the True Torque both have a 1 1/16 bore size. So, have not replaced the existing MC with the True Torque. Now thinking of having the True Torque machined and rebuilt to a 1 1/8 bore to increase the pressure. They made a bendix 1 1/8 bore but that was only standard equipment on Hemi cars. The True Torque cost me $140.00 and to have it resized is an additional $240.00. Im hesitant to go further as I should not have to increase the bore size for the brakes to work properly. Good point about the booster and lack of vacuum I tested the vacuum and it was within the correct level and matched the vacuum on my 72 Challenger on which the brakes work and feel great. Neither the new booster or the one that was on the car when I got it have an adjustable push rod so I would have to cut and weld it to increase or decrease the length.
I really appreciate all the help and comments to help resolve my problem

Might want to bench bleed the M/C. Air will cause havoc. I think the 72 had a factory 1 1/32 bore. I use a 1 inch on my 73 with factory booster. Wilwood up front and works great with 11-12”’vac. Something sounds different on the welded push rod.

 

[MOPAR Andy]

already bent bled. think I need find an original booster with an adjustable rod