Pulsating brake oroblem

[baker53]

I recently purchased a '57 Desoto Firesweep with power brakes. The brakes were nil when I got the car. I installed new steel brake lines, new rubber hoses to drums, new master cylinder, new wheel cylinders, new shoes, and had the drums turned. The car stops fine, but I have an issue whereby upon pressing the brake pedal the brakes engage but as you start slowing down the car seems to surge like the brakes are disengaging and then engaging.

When I have the car on jack stands and have a friend press gently on the brakes I feel smooth brake pressure through 360 degrees of tire rotation. I checked front and back wheels and they all seem to be acting properly. I was thinking perhaps the vacuum booster might be the cause so I disconnected the vacuum hose and tried a test drive. It took a lot of foot pressure on the brake pedal but the car would slow down. I am not sure if the pulsing was gone or not, but I think it was less. I contacted "Dewey Booster" and he does not think the culprit is the booster.

If anyone has any thoughts on this problem I am having, I sure would appreciated hearing from you.

 

[68plymouth383]

Sounds like there's still air in the system. It could also be a defective master cylinder not holding pressure........

I recently purchased a '57 Desoto Firesweep with power brakes. The brakes were nil when I got the car. I installed new steel brake lines, new rubber hoses to drums, new master cylinder, new wheel cylinders, new shoes, and had the drums turned. The car stops fine, but I have an issue whereby upon pressing the brake pedal the brakes engage but as you start slowing down the car seems to surge like the brakes are disengaging and then engaging.

When I have the car on jack stands and have a friend press gently on the brakes I feel smooth brake pressure through 360 degrees of tire rotation. I checked front and back wheels and they all seem to be acting properly. I was thinking perhaps the vacuum booster might be the cause so I disconnected the vacuum hose and tried a test drive. It took a lot of foot pressure on the brake pedal but the car would slow down. I am not sure if the pulsing was gone or not, but I think it was less. I contacted "Dewey Booster" and he does not think the culprit is the booster.

If anyone has any thoughts on this problem I am having, I sure would appreciated hearing from you.

 

[polara66hardtop]

Does the 57' have two cam adjusters on the backing plate for the shoes like the 56'? If so there is a special tool for ensuring correct alignment of both shoes. You won't feel the uneven drag between the shoe and drum on jacks, but you might when driving. The mass of weight being forced to stop can force the drum and shoe into a binding situation, and mimick the problem. This is a problem on all my dodges 41-56. I have never owned a 57. Just one suggestion.

 

[baker53]

Does the 57' have two cam adjusters on the backing plate for the shoes like the 56'? If so there is a special tool for ensuring correct alignment of both shoes. You won't feel the uneven drag between the shoe and drum on jacks, but you might when driving. The mass of weight being forced to stop can force the drum and shoe into a binding situation, and mimick the problem. This is a problem on all my dodges 41-56. I have never owned a 57. Just one suggestion.

Yes, there are two 7/16" hex adjusters on each of the backing plates. Any idea on where I might locate the special tool you are referring to. Thanks so much for your message.

 

[baker53]

polara66hardtop: I just re-read the manual on adjusting the brakes and I see that I did not follow the procedure exactly as written. It states to turn both adjusters to lock the shoes to the drum and then back off on each a little at a time till no drag is felt. When I adjusted them I did one at a time. I will re-adjust them as the manual suggests and give it a try. I did not see any reference to a special tool as you mentioned for the '56 and earlier cars. Thanks again.

 

[polara66hardtop]

I lived in Spring in the 80's. The tool attaches to the spindles,, like a dial Indicator, and rotates 360 degrees, giving you accurate measurement, thus Insuring perfect roundness of the shoes. I have been looking for that mopar tools for 30+ years, to no avail.
Someday I'm going to make one. Glad to help!

 

[baker53]

polara66hardtop: No joy in Mudville today. I verified they were setup as the manual indicated and re-adjusted them per the manual and still have the same issue. Guess I will have to do some more searching. The owner of the booster shop said from what I told him, the booster is OK. I do not feel the pulsing in the pedal so I believe the master cylinder is also OK. I'll keep you posted on what transpires.

 

[polara66hardtop]

my 69' dart did the same thing, and the drums were turned, but were at the end of their useful life. They had been turned but the diameters were way out there. I secured new drums, and the problem went away. Possibly check the diameter, and compare to new specs. Old drums can warp as pressure is applied, and lose their shape. Mainly the front drums are vulnerable, but all four can contribute to the problem. One way to tell is put the adjusters to neutral, and see how far you have to go to make contact. The longer it takes, the more worn the drum is. My factory 55' Desoto book has a picture of that tool used to align the shoes.It probably went to the scrap yard in the 60's. where all good tools go!


I just had a brain fart, and remember there should be four adjusters, two for each shoe. That is why the special tool was needed. The shoes have to make contact on the drum uniformly, hence the dial Indicator tool. I seem to remember my 60' Desoto had the newer brakes. I would make a plan to upgrade to the newer C body brakes, if yours has the old style dual anchor type shoes.

I would also love to have your problem! 57' Desoto's are beyond cool! My first car in 68' was a 60' Hardtop with 383 engine. I paid 75.00 for it. It was called the Batmobile in High school. I still have the Bill of sale and Title to that car. I would Install the 68' disc brakes, and modern 8 3/4 and be done with it. I miss it!

 

[67Monaco]

Are the tires out of round? Is a rim bent?

 

[baker53]

my 69' dart did the same thing, and the drums were turned, but were at the end of their useful life. They had been turned but the diameters were way out there. I secured new drums, and the problem went away. Possibly check the diameter, and compare to new specs. Old drums can warp as pressure is applied, and lose their shape. Mainly the front drums are vulnerable, but all four can contribute to the problem. One way to tell is put the adjusters to neutral, and see how far you have to go to make contact. The longer it takes, the more worn the drum is. My factory 55' Desoto book has a picture of that tool used to align the shoes.It probably went to the scrap yard in the 60's. where all good tools go!


I just had a brain fart, and remember there should be four adjusters, two for each shoe. That is why the special tool was needed. The shoes have to make contact on the drum uniformly, hence the dial Indicator tool. I seem to remember my 60' Desoto had the newer brakes. I would make a plan to upgrade to the newer C body brakes, if yours has the old style dual anchor type shoes.

I would also love to have your problem! 57' Desoto's are beyond cool! My first car in 68' was a 60' Hardtop with 383 engine. I paid 75.00 for it. It was called the Batmobile in High school. I still have the Bill of sale and Title to that car. I would Install the 68' disc brakes, and modern 8 3/4 and be done with it. I miss it!

I will check the drums again as you suggest, but the car had only 38,000 miles on it and the drums looked great except for surface rust which is why I had them turned. The shop indicated they did not have to remove much material and on any of the four drums. I did not see a max diameter on the casting. I'll check around and see what the max diameter allowable is. OK on the '60 Desoto as your first car. The '57 was my third car. I started off with a '38 Ford sedan which was stock, then to a '40 Ford sedan with an Oldsmobile V8, and then the '57 Desoto which I got in '62. I may end up going withe the disc brakes, but theses stop the car great. I just need to get rid of the pulsing. Thanks for your thoughts.

 

[baker53]

Are the tires out of round? Is a rim bent?

The tires and wheels are straight and true. I earlier exchanged the fronts for the rears and no difference was noted.

 

[baker53]

Sounds like there's still air in the system. It could also be a defective master cylinder not holding pressure........

Pressure bled the system and I'm very confident no air is in the system. The pedal is rock hard when applying heavy pressure, so I feel confident the master cylinder is OK.

 

[67Monaco]

Bent axle? If not, then you're back to drums. Could just be hard spot in the drums.

 

[baker53]

Bent axle? If not, then you're back to drums. Could just be hard spot in the drums.

Axles are true; no hard spots showed up while turning.

 

[baker53]

Just for the heck of it, I scribed the brake shoe profile on some card stock and sat it against the turned drum surface. It is a dead nuts fit. When I measured the drums with a three point caliper I got 11.031" which is below the max diameter of 11.060 by about .029"

 

[70bigblockdodge]

I'm still thinking hot spots on drum

 

[baker53]

I'm still thinking hot spots on drum

I'll see about doing a Rockwell hardness test, but I see nothing indicative of hard spot or spots on the drums.

 

[70bigblockdodge]

Hot spots from them getting hot and making them go back out of round and with a single circuit system one slight oor. oposite another oor would be shoving fluid back and forth I would have them checked for roundness again (trued) maybe by a different shop. my 2 cents

 

[polara66hardtop]

I believe you also have two wheel cylinders in each wheel? That pressure consistency is puzzling, which would create that problem. my 56 book also has a third adjustment, that makes sure the shoe is sitting flat on the surface of the drum. . I found a picture of that tool, and will scan it for everyone to see what it looks like. There is nothing in the troubleshooting book that describes pulsating as an issue. Very strange indeed.

 

[baker53]

Hot spots from them getting hot and making them go back out of round and with a single circuit system one slight oor. oposite another oor would be shoving fluid back and forth I would have them checked for roundness again (trued) maybe by a different shop. my 2 cents

I checked the hardness on the front drums and they seems to be OK. I then checked the rear drums and found that both have hard areas and that the left rear was turned to a diameter of 11-1/16" which is just over the .060" maximum diameter. The right rear drum was turned to a diameter of 11-1/8" which is over the max diameter by .065". I am now looking for a pair of rear drums for a '57 Desoto Firesweep. Any leads would be most appreciated. Also, thanks for all the sage advice on this problem. I hope I am getting to the root of the problem.