Odd rear brake issue

[eurotrash]

So, after acquiring my wife’s ‘73,  I had found that the rear brakes weren’t even close to being adjusted properly. They were in fact probably not doing much of anything that all. And the wheel cylinders were leaking something fierce. 
 

I proceeded to adjust the brakes to the proper “whisper” distance and then installed new wheel cylinders. And in doing so, I discovered why the shoes were set so far off the drum.. the car randomly has the driver rear grab and lock up the wheel! No pedal involved, but something just causes it to grab. 
 

.. put the car in reverse and the brake pops free and is fine until it randomly grabs again. Might be 10ft, might be 10 miles. 

 

its a bit baffling, as I have had the system completely apart, cleaned and lubricated the hand brake lever on the rear shoes, etc.  I can’t figure it out. The lever was tight, but not like, stuck. Nor was it floppy loose.  Short of hammering on the rivets to make them super loose, to be sure there is no binding and that they are 100% able to be pulled in by the spring system, I don’t know what’s left or why anything can just randomly shift.

 

The hand brake was 12 clicks before engagement, and now I have taken it completely out of play by removing the nuts. 
 

maybe the drum is warped…? 
 

 

[dlacey]

If you think its the drum condition, try swapping the drum to the other side & see if problem follows?
The position of the lining on the brake show is important to manage the geometry of brake drum operations and the 'self-servo' or 'spragging' effect... some aftermarket brake shoes have the linings too long or in the 'wrong place' around the shoe surface (check brake shoes are correct). Filing a 45 degree chamfer on the leading edge of the friction material is a common method to reduce brake grab..maybe worth a try?

[John76]

The spring "hook" should be pointing out.

Looks like the spring is catching on the edge of the plate when the brake is applied, causing it to stick.

 

 

[eurotrash]

I have the spring pointing outward in the hand brake side, where it could bind with the lever. But again, you don’t have to hit the brakes AT ALL, to make the issue happen. Just the action of rolling produces the shift and bind. 
 

I have filed the friction material ends to a 45* angle and swapped the drums side to side. I will take a drive and report back. 

[eurotrash]

Welp. I couldn’t get the issue to resurface during the drive. Seems it may be gone?!? 

[Mike Self]

After taking the parking brake linkage out of play as you have done, short of linings that are loose on their backing (I've seen that happen several times in the past year or so), I'd suspect that something in the brake shoe department is shifting--on a random basis.  Have you checked the "bitch spring" at the bottom of the shoes to make sure it's not relaxed or even cracked.  It's a very strong spring, and if it's too weak to position the shoe bottoms, they're gonna flop around and self energize.  

 

The other thing I found when (recently) installing new shoes and drums, the new shoes required a lot of grinding/sanding/filing down to be able to install the drums.  And more recently, brake shoes that had delaminated and shed small pieces of friction lining that was flopping around inside the drums and periodically wedging themselves between shoe and drum.

 

mike

[John76]

2 hours ago, Mike Self said:

brake shoes that had delaminated

Yikes!  Not good...what brand did this?

I recently replaced the front pads on my daughter's Honda with Raybestos pads that cracked in half during the first 100 miles.

OEM Honda brake parts from now on!!

[TobyB]

Did the leaking brake cylinders soak the shoes?

 

That will tend to make the shoes sticky.

 

t

 

[jgerock]

What brand are those shoes? Perhaps they aren’t arched (made) correctly.

 

The rubbing (contact) points on the shoes to the backing plates need some brake paste.

 

Speaking of weird rear brakes, I recall having my rear brakes lock up after washing the car at Vintage 2009 and letting it sit overnight.  It let out a loud pop after I applied lots of power in reverse.  Never happened again thankfully.  I usually drive my vehicles and drag the brakes after washing them.

[TobyB]

That was probably rust- which will bond the shoe to the drum if you give it half a chance.

 

t

 

[cda951]

On 3/26/2024 at 4:15 AM, jgerock said:

What brand are those shoes? Perhaps they aren’t arched (made) correctly.

 

The rubbing (contact) points on the shoes to the backing plates need some brake paste.

 

Speaking of weird rear brakes, I recall having my rear brakes lock up after washing the car at Vintage 2009 and letting it sit overnight.  It let out a loud pop after I applied lots of power in reverse.  Never happened again thankfully.  I usually drive my vehicles and drag the brakes after washing them.

 

This is an ongoing thing at my shop. I often remind the helper/porter guys to do a quick "wipe" of the brakes after washing a customer car, because said "pop" is disconcerting to a customer driving off the lot. Much more prevalent on modern cars with large wheels and very exposed disc brakes.

 

By the same token, if a BMW 02 (with the large opening for the clutch fork in the transmission bellhousing) is parked at a curb during a heavy rainstorm, the clutch disc will often stick to the flywheel and pressure plate thanks to rust, so some slippage will be required to free it up. I had to do this sometimes back when mine was regularly street-parked. Same thing happened to my girlfriend's Z3 Coupe a few months ago---another wet winter here in SoCal. Luckily I was parked at the back end of the block in that case and wasn't between two cars, could slip the clutch in reverse to pop it loose  .

Edited March 28 by cda951

[eurotrash]

Got her out for Karie’s bday and dang it! It grabbed again… may just have to order new shoes for it and eliminate that possibility

[Mike Self]

6 hours ago, eurotrash said:

may just have to order new shoes for it and eliminate that possibility

Do a post mortem on the old shoes to see if the linings are loose, delaminating or simply not centered properly on the shoes... inquiring minds want to know.

 

mike