Rear Brake Lockup (356A)

[David Baugh]

Been thinkin' about your issues overnight, Jim.

Before you go any further, make absolutely certain that your leak is not brake fluid. Brake fluid has a distinctive odor compared to gear lube.

Second, you mentioned that you had the splines tightened in your rear drums. As I understand it, that operation involves "crushing" the steel hub to expand it in the aluminum drum. That can change the dimensions slightly. If so, you should have received a pair of 2 mm thickness tubular steel shims. If you did, what did you do with them? They are supposed to be placed over the axle between the bearing spacer and hub, in order to restore the clearance between the drum and the sides of the shoes. If you didn't get those shims, or they've been misplaced, contact Martin. I'm sure he will send you a new pair.

If those shims were installed correctly, and you are still having problems, I suggest that you send an email message to Martin, including a link to this thread.

Dave

[Vic Skirmants]

"I'm wondering if maybe I should unbolt the rear hub and reassemble with some sealant like orange LocTite."
I'm not following what you're referring to as "rear hub". Do you mean the brake drum? If so, I don't understand what the Loctite would accomplish.
Incidentally, when you remove a drum, the small O-ring is no longer compressed, and oil will leak past it.

[Jim Alton]

Been thinkin' about your issues overnight, Jim.

Before you go any further, make absolutely certain that your leak is not brake fluid. Brake fluid has a distinctive odor compared to gear lube.

Second, you mentioned that you had the splines tightened in your rear drums. As I understand it, that operation involves "crushing" the steel hub to expand it in the aluminum drum. That can change the dimensions slightly. If so, you should have received a pair of 2 mm thickness tubular steel shims. If you did, what did you do with them? They are supposed to be placed over the axle between the bearing spacer and hub, in order to restore the clearance between the drum and the sides of the shoes. If you didn't get those shims, or they've been misplaced, contact Martin. I'm sure he will send you a new pair.

If those shims were installed correctly, and you are still having problems, I suggest that you send an email message to Martin, including a link to this thread.

Dave

Actually, one drum got new splines, one drum got "tightened." Martin didn't send me shims but I didn't see 2 mm of new clearance. Frankly, I don't even know which drum's which. Something to look into.

On the other hand, I have a shim in the left front drum because a switch to the later spindles didn't go quite right. That's the drum with asymmetric wear on the shoes. The odd thing about that is I was 100 miles from home when it started scraping.

[Jim Alton]

"I'm wondering if maybe I should unbolt the rear hub and reassemble with some sealant like orange LocTite."
I'm not following what you're referring to as "rear hub". Do you mean the brake drum? If so, I don't understand what the Loctite would accomplish.
Incidentally, when you remove a drum, the small O-ring is no longer compressed, and oil will leak past it.

I wasn't sure what to call it.

I was trying to refer to the joints where the bearing housing pieces sandwich the brake backing plate.

Brake backing plate in green

It's not leaking around the axle or the dowel pin; those surfaces are my best guess for now.

[David Baugh]

The 2mm shim goes between #2 and #3.

The one that was "tightened" is most likely the drum you're having issues with, which requires the shim.

Dave

[David Baugh]

Let me try to clear something up.

You didn't gain "2mm of new clearance", nor would you be able to "see" any change in clearance. If the hub (#2) in the center of the drum (#14) was crushed to tighten it, that would move the drum (#14) closer to the shoes. In essence, you would have "lost" clearance. This appears to be obvious to me, since the inside of the drum is clearly rubbing on the sides of the shoes. And, this is very likely the cause of the "rear brake lockup", which is the subject of your topic.

If you request the 2mm shim from Martin, and install it in the location I mentioned above (between #2 and #3), the clearance will be restored, eliminating the interference (and quite probably) the rear brake lockup.

Using your terminology, "the joints where the bearing housing pieces sandwich the brake backing plate" is sealed by a large O-ring (#8). That should not be the source of a leak, unless the bearing cap (#13) has been distorted by tightening its bolts too tightly without the backing plate in place, or someone installed too many bearing shims (#6). There has already been plenty written on this subject. If the cap has been tweaked, you'll need to buy a new one. Gasket sealer will not do the job.

Dave

[Jim Alton]

The rear brake lockup problem preceded getting the rear drums reworked by Martin Willis so I don’t think that’s the most likely cause.

[David Baugh]

OK. I give up. I thought your previous problem resulted from driving your car with the parking brake engaged.

viewtopic.php?f=1&t=38988&hilit=parking+brake

[Jim Alton]

OK. I give up. I thought your previous problem resulted from driving your car with the parking brake engaged.

viewtopic.php?f=1&t=38988&hilit=parking+brake

My god! Your memory of my 356 adventures is better than mine.

At that point, I had the cast aluminum reproduction drums NLA Parts used to sell on the car. I fixed those problems (circa May 2015) by sending the old, original, forged aluminum drums to Martin Willis for spline repair.

The rear brake grabbing/lockup problem has--to the best of my possibly challenged memory--been around as long as I've had the car.

The Swepco gear oil leak in the left rear apparently came well after May 2015, since this picture shows it dry:

Left Rear Brake 29 April 2015

[Jim Alton]

I tried something all to basic. Since it's seemed the leak was at the junction of the hub (or bearing carrier) halves and the break backing plate I put an 18" breaker bar on a 13 mm ½" drive socket and checked the bolts holding the halves of the hub (or bearing carrier) together.

They all moved about 30°. Could it really be that simple? It's not hard to generate torque with an 18" breaker bar.

[John Lindstrom]

My initial assessment of the condition you described was that there was air in the lines at the front of the car, causing all of the braking force to be sent to the rear brakes only. I had a 62 that did that, my sister borrowed the car one day and did not follow my advice to “drive slow because the brakes are bad”. On my way home from work that evening I saw a car that looked suspiciously like mine off the side of a cliff wedged up against an oak tree.. Yep, fix your brakes before driving your car. Ask me how I know..

[Jim Alton]

My initial assessment of the condition you described was that there was air in the lines at the front of the car, causing all of the braking force to be sent to the rear brakes only. I had a 62 that did that, my sister borrowed the car one day and did not follow my advice to “drive slow because the brakes are bad”. On my way home from work that evening I saw a car that looked suspiciously like mine off the side of a cliff wedged up against an oak tree.. Yep, fix your brakes before driving your car. Ask me how I know..

How would air in the lines at the front of the car cause all of the braking force to be sent to the rear brakes only in a car with single circuit brakes (such as my 356A)?

Was your '62 converted to a double circuit master cylinder?

[John Lindstrom]

Jim it was just a single circuit. I had to pump the brakes like crazy to get the car to stop. I have no idea why it behaved like that. It was such a long time ago that I don’t even remember how I ended up fixing it. It was the darndest thing. I do remember selling the car with a big dent in the side to some guy that was ecstatic to get the car.