Mysterious P15 braking problem

[46Chris]

Getting my '47 Special Deluxe sedan ready to advertise, and my extremely capable mechanic has run into a head scratcher with the brakes so I offered to post the question here.  

 

For some history and context, he replaced the rubber hoses (one was collapsed) and put in a new master cylinder.  He has adjusted the brakes in the rear and bled the fronts over and over again.  Shoes and hardware look great. Front brakes are non adjustable. The front left is grabbing more than the right.  He reports that it’s manageable gradually braking but if you stomp on the pedal in a panic brake situation it will throw you right into the oncoming lane.

 

Would love for this mystery to be solved, rather than tell a new owner to avoid any hard braking at their peril.

[Sam Buchanan]

Two items I would  check first:

 

1) Proper adjustment. This can be tricky but the procedures have been discussed extensively on this forum. Here is a tech article:

https://p15-d24.com/page/p15d24/tech/brakes.html

 

Need clarification on your statement "Front brakes are non adjustable".

 

2) Pull the drums to make sure there isn't a wheel cylinder leaking on one side and putting fluid on the shoes. Maybe he has already done that.

 

Edited July 12 by Sam Buchanan

[46Chris]

Thanks Sam, I'm going to print out the tech article for my mechanic.   Will make sure there isn't a wheel cylinder leaking.  As to his statement about non-adjustable (since I was copying from his text to me, into the post) I believe sharing the tech article will offer some additional perspective. 

 

There are a few Ammco 1750 brake gauges on ebay, starting at $400.  Is a major adjustment accomplished by this tool a factor here, providing a leaky wheel cylinder isn't the culprit?   If so, I could buy one to use and then re-sell it.

 

 

Edited July 12 by 46Chris

[bacelaw]

48 minutes ago, 46Chris said:

Thanks Sam, I'm going to print out the tech article for my mechanic.   Will make sure there isn't a wheel cylinder leaking.  As to his statement about non-adjustable (since I was copying from his text to me, into the post) I believe sharing the tech article will offer some additional perspective. 

 

There are a few Ammco 1750 brake gauges on ebay, starting at $400.  Is a major adjustment accomplished by this tool a factor here, providing a leaky wheel cylinder isn't the culprit?   If so, I could buy one to use and then re-sell it.

 

 

 

Search YouTube for Keith's Garage - he shows how to fabricate your own brake tool and I find it superior to the Aamco tool (I have both). 

 

One other random tip:  make sure the brake pedal rod, where it enters the master cylinder, is properly adjusted.  If it's not, you'll never get the brakes adjusted properly...

[Plymouthy Adams]

the above gives some means to check the brakes for contact patch, but the real problems seems to be your mechanic does not understand this particular braking system, not sure I would put much trust in his abilities and when you are driving, your very safety is at risk as is others sharing the highway.  While you can get a lot of information here, workmanship is still 'key' to a successful brake repair.

[46Chris]

12 minutes ago, Plymouthy Adams said:

the above gives some means to check the brakes for contact patch, but the real problems seems to be your mechanic does not understand this particular braking system, not sure I would put much trust in his abilities and when you are driving, your very safety is at risk as is others sharing the highway.  While you can get a lot of information here, workmanship is still 'key' to a successful brake repair.

I'm grateful to this community for sharing key information that will help my mechanic to understand and fix the problem.  

[Tom Skinner]

Chris,

In your post you say your mechanic bled the front brakes over and over again. Refer to your service manual to confirm: One should start bleeding brakes at the wheel furthest away from the Master Cylinder first followed by the next closest, etc,. finishing with the one closest to the Master Cylinder. Another fact is if your front Wheels have two Brake Cylinders the Lower Brake Cylinders should be Bled First. Andy Bernbaum Sells the tool for $95 refered to above for Shoe Adjustments, in addition to that I agree with Sam a Cylinder might be leaking or a Shoe was made wet with brake fluid during the job effecting the "grabbing Brake Shoe Side". These Brakes require either a seasoned mechanic or one with experience on our old buses read (an older mechanic) its not a rush job sort of thingy. Good Luck!

Tom

[46Chris]

42 minutes ago, bacelaw said:

 

Search YouTube for Keith's Garage - he shows how to fabricate your own brake tool and I find it superior to the Aamco tool (I have both). 

 

One other random tip:  make sure the brake pedal rod, where it enters the master cylinder, is properly adjusted.  If it's not, you'll never get the brakes adjusted properly...

I watched Keith's two videos - the tool was fabricated for him, and I wasn't able to find out where to get one.   Possible I could rent yours?

[Tom Skinner]

Chris,

One more piece of advice - don't take this the wrong way - One should endeavor to learn how to work on their own car (in the case of our old Mopars) as one could become upside down in one quickly paying someone else to do the work. In addition to saving tons of money - the Pride of owning your car magnifies as you Master it Mechanically.

Any Suit can grab his wallet and get some mechanic to wrestle with his car - but the owner that fixes his own car is grabbing the right "W" - namely a Wrench not a Wallet.

Just MHO. (No offense to us guys getting too old to turn Wrenches LOL)

Tom

[46Chris]

11 minutes ago, Tom Skinner said:

Chris,

In your post you say your mechanic bled the front brakes over and over again. Refer to your service manual to confirm: One should start bleeding brakes at the wheel furthest away from the Master Cylinder first followed by the next closest, etc,. finishing with the one closest to the Master Cylinder. Another fact is if your front Wheels have two Brake Cylinders the Lower Brake Cylinders should be Bled First. Andy Bernbaum Sells the tool for $95 refered to above for Shoe Adjustments, in addition to that I agree with Sam a Cylinder might be leaking or a Shoe was made wet with brake fluid during the job effecting the "grabbing Brake Shoe Side". These Brakes require either a seasoned mechanic or one with experience on our old buses read (an older mechanic) its not a rush job sort of thingy. Good Luck!

Tom

Yes, in the tech article Sam B initially shared I saw the bleed sequence.  I did provide my mechanic with the manual, but printing out the tech article and some of the additional responses from the group here, will help him a great deal.  Very smart, younger man who runs a very busy 2 man shop up here in the northwoods of WI.  And I'll check out Andy's shoe adjustment tool, thanks for that.

[Tom Skinner]

The Tool is available through ebay or Andy see above for $95

[46Chris]

Just now, Tom Skinner said:

Chris,

One more piece of advice - don't take this the wrong way - One should endeavor to learn how to work on their own car (in the case of our old Mopars) as one could become upside down in one quickly paying someone else to do the work. In addition to saving tons of money - the Pride of owning your car magnifies as you Master it Mechanically.

Any Suit can grab his wallet and get some mechanic to wrestle with his car - but the owner that fixes his own car is grabbing the right "W" - namely a Wrench not a Wallet.

Just MHO. (No offense to us guys getting too old to turn Wrenches LOL)

Tom

Well taken,  I'm older, and unfortunately have lost the desire to be an expert.  It's why I've realized I need to sell the old cars I have, much as I love them.

[Sam Buchanan]

40 minutes ago, 46Chris said:

I watched Keith's two videos - the tool was fabricated for him, and I wasn't able to find out where to get one.   Possible I could rent yours?

 

Here is the post detailing how I made an adjustment tool, maybe this will be useful for your mechanic:

 

https://p15-d24.com/topic/50182-brake-adjustment-tool-updated/

 

However, if the proper procedure is used (per the tech article) it should be possible to achieve satisfactory brake performance without using the tool. The tool just allows us to get closer to optimum performance. But brakes that aggressively pull to one side indicate a serious issue, either mechanically or grossly out of adjustment.

Edited July 12 by Sam Buchanan

[Plymouthy Adams]

while the old mopar brakes when in top shape are some of the best there was AT THE TIME....technology marches forward and better safer systems come along even if morphing at a slow rate.  Is it good that your mechanic could learn from this....yes....would I still trust him...likely not.  The bold statement of no means to adjust means he did not truly study the design staring him in the face, zero access to older manual, no internet, no desire to be proactive and learn.  He could well have read many articles in shorter time than for anyone depending on a forum member to respond....sorry I just don't support shops that are not only inept to repair but not keen it seems to seek out any knowledge on their own.  His non-adjustable comment is a total deal breaker.

[soth122003]

Something else to consider about the grabbing brake. It was likely that the shoe had brake fluid on it and the leaky cylinder was fixed or replaced, but the shoe was just leaned off. If so, the shoe has absorbed the fluid and while it may look good, it will always be a problem. The seeped in fluid will rise to the top and create a grabby brake. If the leak went un-noticed for any amount of time, couple of days to a couple of months, no amount of cleaning the shoe will restore it to optimum condition. IMHO. 

 

Best bet if this is the case, replace the shoes. They're fairly cheap and they come as a set so you'll have new shoes on both sides no worries about uneven wear.

 

Joe Lee

[46Chris]

1 hour ago, soth122003 said:

Something else to consider about the grabbing brake. It was likely that the shoe had brake fluid on it and the leaky cylinder was fixed or replaced, but the shoe was just leaned off. If so, the shoe has absorbed the fluid and while it may look good, it will always be a problem. The seeped in fluid will rise to the top and create a grabby brake. If the leak went un-noticed for any amount of time, couple of days to a couple of months, no amount of cleaning the shoe will restore it to optimum condition. IMHO. 

 

Best bet if this is the case, replace the shoes. They're fairly cheap and they come as a set so you'll have new shoes on both sides no worries about uneven wear.

 

Joe Lee

Joe, that's a good thought.  I visited the mechanic this morning to drop off the tech post and additional contributions from the community.  He had bled from longest to shortest, made sure the rod going into the master had the right travel, and had adjusted all shoes so that each shoe barely scraped the drum.  it's entirely possible that the prior owner (long deceased) had not replaced shoes when he worked on the brakes, even though we can see clean wheel cylinders and new lines.  He had not replaced the master and one flex line was collapsed, so it's possible he did not replace what may have looked like good shoes even if a wheel cylinder had been leaking and replaced.

[desoto1939]

I had similar issue with the front left brake pulling hard to the left.  There was no grease or leaking brake fluid on the front left or right shoe linings.  We replaced all brakes hoses rebuilt the two single cylinder cylinders and adjusted brakes shoes as per specs. Measured the pressure in the hoses going to each brake show and drum.

 

We still had pulling to the left.  Then my very experience mechanic took all four front shoes off the car and then took a skim cut on each line approx 5-10 thousands off each shoe. Installed the shoes and the issue was resolved. He feels that there might have been something in the lining or it hardened up and glazed.

My two front drums were also cut down by him in 2020 might have been some material leftover from cutting drum, but he did not feel this was the issue.

The car has been stopping fine and have a great brake.

 

Very small issue can cause major problems.

 

Rich hartung

Desoto1939@aol.com

[DonaldSmith]

Hmmmm. I have the problem where, after the car isn't driven for a few months, the brakes pull hard left.  After a series of panic stops for a few miles in the neighborhood, the brakes straighten out.  (Pedal travel seems far, so I'll do at least the minor adjustment.) 

 

So, before I rip into things, I'll pull the right front drum and take a hard look at the surface of the shoes. 

(Maybe hit them with some coarse sandpaper? Some guys even stick sandpaper in the drum to arc the shoes as they drive.).    

 

Why do these cars always seem to pull hard left?  (This is a description of the brakes, and is not as political statement,)  

[Los_Control]

1 hour ago, DonaldSmith said:

Why do these cars always seem to pull hard left? 

If you are young and dumb you can correct that. I was 15 years old and had a 1963 Rambler .... it was a big job for me to replace the clutch in it.

I had no $$ left to fix the brakes .... So I just pinched off the brake line going to the left front wheel ... so it obviously pulled to the right.

 

The old hippie I sold the car to for $100 just laughed, at least it pulls you into the ditch and not oncoming traffic.

Just saying, we can adjust such things.

 

In your case, I probably would want to completely disassemble the brakes and use a wire wheel to clean the backing plates, I would clean every moving part and probably paint .... not needed though .... then properly grease all pivot points.

If everything else is correct they should work fine .... @soth122003 had a great point, any brake fluid on the shoes they need replaced .... grease and such from your hands you can clean off. .... not brake fluid though.

[Sam Buchanan]

1 hour ago, DonaldSmith said:

Hmmmm. I have the problem where, after the car isn't driven for a few months, the brakes pull hard left.  After a series of panic stops for a few miles in the neighborhood, the brakes straighten out.  (Pedal travel seems far, so I'll do at least the minor adjustment.) 

 

So, before I rip into things, I'll pull the right front drum and take a hard look at the surface of the shoes. 

(Maybe hit them with some coarse sandpaper? Some guys even stick sandpaper in the drum to arc the shoes as they drive.).    

 

I think the brakes will pull toward the side that has the contaminated shoes, the fluid-soaked shoes will grab the drum instead of engaging smoothly.

 

Sandpaper in the drum while driving??!!??  😬

Edited July 12 by Sam Buchanan

[Tom Skinner]

Sam,

On the homemade Brake Adjusting Tool using the 3/4" - 16 Nut I have a couple quick questions:

1. What size Threaded Rod and how Long?

2. What size Angle Metal and How Long?

I am going to make my own for my car since $95 or $450 seems a bit ridiculous to pay for one.

Thank you in advance for the information.

Tom 

[Sam Buchanan]

42 minutes ago, Tom Skinner said:

Sam,

On the homemade Brake Adjusting Tool using the 3/4" - 16 Nut I have a couple quick questions:

1. What size Threaded Rod and how Long?

 

Doesn't matter, use whatever you have, 1/4", 5/16", 3/8", etc. Make it long enough to position the angle.

 

42 minutes ago, Tom Skinner said:

2. What size Angle Metal and How Long?

 

Once again, use whatever you have, 1/2", 3/4", whatever, it is just a pointer.

 

Mine was built out of material I had in the scrap box. As long as the tool is rigid it will serve the purpose. Hope this helps.

 

42 minutes ago, Tom Skinner said:

I am going to make my own for my car since $95 or $450 seems a bit ridiculous to pay for one.

Thank you in advance for the information.

Tom 

 

 

[Tom Skinner]

Sam,

Thank you !!!!!!!!!!

[chris 48 P15]

i found this tool worked better for me at adjusting the brakes 

also refacing the drums will do a lot to improve braking

[Sam Buchanan]

3 hours ago, chris 48 P15 said:

i found this tool worked better for me at adjusting the brakes 

also refacing the drums will do a lot to improve braking

 

I'm glad you were able to improve your brakes but that tool isn't capable of getting the shoes concentric with the axle. Having the shoes the same "diameter" as the ID of the drum will not provide good shoe/drum contact if one shoe, or a portion of a shoe, is closer to the drum than the other. There are actually four adjustments on each brake, each shoe has a minor and major adjustment. This complexity is what throws many folks who are not familiar with these brakes.

 

The tool we have been discussing allows us to set each shoe the same distance from the axle which provides even contact of both shoes with the drum, and this is similar to the procedure used back in the day to assure concentricity.

Edited July 14 by Sam Buchanan