Brake issue-how can this happen?

Similar problem with my o/t 67 Pontiac. Except the brakes didn't drag, pushrod adjustment was correct. Bad master cylinder, we surmised that the piston was not completely retracting. My problem was a high pedal together with the rear brakes locking up way too quickly.

How we found out was while trying to bleed the brakes after installing a proportioning valve as this was all subsequent to adding power brakes to the car. We were unable to get them to bleed correctly. As a last ditch try we got a rebuilt master cylinder and that fixed the problem.

 

I might have missed the part where you disengaged the E brake. My bad.

 

You should hardly have to shift at all. It's not like the peanut motors you get today, it is a torquer. You should be able to idle down to 5 MPH in high gear and pull away without a buck. Even take off in 2nd and skip low entirely.

In other words, you don't need low gear except starting from a dead stop. You can do most of your driving in high gear, when going slow shift down to 2nd, you don't need low unless you are starting from a dead stop.

Low is not synchro so if you do want to shift into low when moving you will need to double clutch or synchronize the tranny speed by ear.

One other thing. If you look under the hood you can see the shift linkage. It may be a good idea to clean, lubricate, and replace worn bushings and possibly adjust the linkage. It should shift very easy although slow. You don't whip it from gear to gear like a Mustang or a Honda. You pick a gear and leave it there like a tractor lol.

 

Perhaps a stupid response but would the car not shudder trying to get it going in first gear if the brakes were essentially locked on? Just wonder if the two issues are related.

 

Most prevalent items with mopar brakes dragging,

improper minor adjustment (check the write up at P15 D 25 on the main page under the works in progress tab)

plugged relief port in the MC, Shine a light and make sure you can see two hole in the bottom of the reservoir. One about the size of a pencil lead the other infront of it a bit smaller, Clean both with a piece of wire or drill bit.

Improper free play at the top of the pedal.

Early 40's cars had a stepped wheel cylinder bigger bore on one end, and smaller on the other thes must be installed correctly. These are non self energizing brakes.

The later cars had dual whee cylinders one for each shoe.

Another thing to check is the filler cap on the MC as it provides a vent, the vent must be free. Also do not over fill the MC, if there is no place for fluid to return, the brakes will drag/lock

http://www40.addr.com/~merc583/mopar/framesets/wipbrakeframeset.html

You can make a simple adjustment gauge by following the prototype that an be found on the Graham-Paige Club wesite under their technical section.

You may want to consider an upgrade to disc, there are a number of options one of whichis made by Hamber olddaddy check it out at www.rustyhope.com.

 

I'm not eliminating a bad MC entirerly...but I have to lean on the misadjustment of the rod at this point.

 

I did check that even B4 leaving...I made sure it was all the way in. PO said he and his PO used it often just for the sake of keeping it moving so it wouldn't freeze up.

 

Yeah she had torque...the brakes were dragging for most of that 4 miles best I can guess and she kept pulling...the temp gauge stayed on the low 1/3 end the whole time! Not too shabby for an old 87hp flathead 6.

When I did get the shifting right she slipped right on in...it just didn't seem to want to go from the front range to the back without alittle coersion...as I recall the PO saying it was a cable setup. I have to do some reseach on that! Same PO said the heater didn't work because the control cable was frozen..but we flipped the fan to low on that model 50 unit and heat was coming out...guess he never tried it.

 

There's no stupid responces here....and that is a good possibility given the brake situation, but maybe the motor mount too as was said earlier...or both!

 

i say you have two problems with your master cylinder, first the rod is not adjusted with free play that would allow the line pressure to release, second the master is bypassing internally, the pressure builds as you repeatedly apply the brakes because the master can't return all the way to allow the line pressure to release, so the pedal gets hard, then for the pedal to regain free play after sitting for awhile the pressure has to drop and that could only happen in your case if the fluid bypasses the rubber cups inside the master, I'm going to guess the guy you bought the car from was not able to adjust the brakes properly and had to much pedal free play, so he tried to fix that by lengthen the pedal/master push rod, i bet $10 thats what is going on.

 

Agree....Go with pedal pushrod adjustment first......Most issues are generally more simple to fix than we first believe.

4TTRUK

 

LOOKED UP your braking system in an old motors repair manual I have. covers 1935-1952. looks like 40 plymouth used lockheed style brakes and according to the manual your freeplay s/b 3/8 of inch. by the way this adj. of brake pedal rod is real easy, especially if everthing is newer. I would check this first. it is the most likely culprit and the easiest to check and or fix.

 

Thanks for the look up, that will come in handy!

 

My money is on the plugged return vent in the master cylinder.
Check that first BEFORE you mess with the push rod adjustment.
In fact, that's probably the last thing I would check.
Jack it up and spin the wheels, listen for the brake shoes dragging.
These are tricky to adjust properly. Do it by the book.

 

This is not a modern car you are driving... keep up all that unneeded downshifting and you'll be replacing transmissions at regular intervals...IMHO.