Another brake drum adjusting question

[amaurer]

this might be one of those things where experience trumps theory, but, personally, I don't think the contact pattern would cause pulling of the U-turn style severity.

The reason being that, strictly speaking, frictional force does not depend on the area of contact, only the force applied and the coefficient of friction of the materials. The reason is that, if you have less contact area put are applying the same force then the pressure (force per area) is higher, so everything tends to cancel out; you trade some contact area for higher pressures in the areas you do have (making them wear down faster to boot!).

Thus either your coefficients of friction don't match, or the force applied doesn't match. Both of these may be at play on your vehicle, since you have one side with one *new* wheel cylinder, and you have two different types of shoes. Before you get the shoes rearched, I'd get matching shoes for both sides. Then I'd drive it around town long enough to wear them in well and if the pulling doesn't go away then I'd start looking at the single new cylinder problem and the arching.

Now, in the real world, all sorts of icky "realities" screw up my nice neat hand waving here, so I do expect that the arch of the shoes could cause some pulling. I doubt, however, that its capable of pulling as hard as you describe. Good luck!

(Also, if you stomp the pedal HARD, does it stop straight? I find that if adjustment is my problem then it pulls mostly only under moderate pressure and with a firm stomp it stops straight.)

 

[ducktapeguy]

Just a wild theory, but I'm guessing the reason you're seeing more even wear on the side with the gap is because the brake shoes flex under pressure. So even though the middle of the pad touches the drum first, the force of the wheel cylinders cause the shoes to flex and conform to the wheel drum, exerting more even pressure along the pad. The other side just contacts at the end because that's where all the pressure is applied

I'm also having the same problem. Re-adjusted all the cylinders multiple times, but I'm still getting a slight pull to the right under braking. It's not too bad if you're expecting it, just annoying. I'm hoping you figure it out and that I have the same probem.

 

[Pin_Head]

The brake shoe manufacturer doesn't really matter, as only a handful of companies actually reline shoes and most of them use the same materials. They can use different quality lining materal, but even that doesn't make that much difference. When I used to work at an auto shop doing brake jobs, we used whatever the local Napa shop had on hand, now matter whether it was a "cheapo" job or the "ultra delux" lifetime warranty job. They got whatever the supplier had.

 

[Fallon 40]

It took me all morning but I found a place in Long Beach that will rearc the shoes. The shop that did the drums would not do it since they got rid of their machine. Somthing about when the shoes were made out of asbestos and the EPA / Feds.

After work I'm going to swap the shoes and put them on the other side to see if I get the pull going the other way. That should confirm the needs rearcing idea.
Ken

 

[My wife said no FJ!]

It took me all morning but I found a place in Long Beach that will rearc the shoes. The shop that did the drums would not do it since they got rid of their machine. Somthing about when the shoes were made out of asbestos and the EPA / Feds.

After work I'm going to swap the shoes and put them on the other side to see if I get the pull going the other way. That should confirm the needs rearcing idea.
Ken

Good idea...keep us posted

 

[lostmarbles]

.......... Before you get the shoes rearched, I'd get matching shoes for both sides. ...............................

I think this is the most vital piece of advice amongst these recent posts.

The left and right shoes look to me as though they have originated from different brake-relining shops and that is an absolute "NO NO".

I don't have any preference for any particular brake relining shop - but even when you deal with the one shop, all the linings they give you FOR THE SAME AXLE must come from THE SAME PRODUCTION BATCH.

So even if the shop doesn't put them in boxes with batch numbers on those boxes - the same worker must have put them together using the same lining material on each shoe and must have arced each one to exactly the same radius.

Furthermore, if one drum on an axle has been turned out to a larger radius then the other should have been turned also to match it.

You can't afford to have ANY variation between left and right - Particularly on the front axle!

 

[Fallon 40]

I think this is the most vital piece of advice amongst these recent posts.

The left and right shoes look to me as though they have originated from different brake-relining shops and that is an absolute "NO NO".

Furthermore, if one drum on an axle has been turned out to a larger radius then the other should have been turned also to match it.

You can't afford to have ANY variation between left and right - Particularly on the front axle!

I will place the drum with the larger I.D. on the rear and make sure the four shoes up front are the same.
I'm sure they all came in the same kind of boxes from MAF.

Before this is over I'll be able to do adjust 8 wheel cylinders faster than a NASCAR pit crew!

 

[Pin_Head]

The lining does appear to have a different color, L to R. That would definitely not be good either, so good job to those who picked up on that.

 

[My wife said no FJ!]

Ken, I like your original idea of going left to right with the shoes...and maybe even the drums. I figure if the Cruiser still pulls hard left (you did say left correct?) then that would eliminate these as the 'problem'.

If it pulls right, then I would do it all over again, and swap them to the back, get all matching up front, and test them again.

Personally, I would try to eliminate one scenario at a time...but that's just my 2 cents

 

[lostmarbles]

I will place the drum with the larger I.D. on the rear and make sure the four shoes up front are the same.
I'm sure they all came in the same kind of boxes from MAF....

Ken

If MAF supplied "mismatched" shoes for the same axle it would be their responsibility to remedy the situation at no cost to you.

Also, if your vehicle is like mine, the front and rear drums are not interchangeable. (The fronts are significantly larger.)

 

[Fallon 40]

Ken

Also, if your vehicle is like mine, the front and rear drums are not interchangeable. (The fronts are significantly larger.)

I have a 4/71 FJ40 ( that pulls to the left ! )

I will have to check this. When I had them turned I marked each drum so I would put them back on the exact same way they came off.
I beleive the shoes are all the same from front to rear, or supposed to be. There are some numbers on the side of the shoes, I will see if they are all the same.
Ken

 

[amaurer]

I think your drums are all the same. It wouldn't be possible for you to put "big" front drums like marbles and I have on the rear because they wouldn't ride properly in the groove in the backing plate/dust cover/whatever you call it.

I believe that while the US was getting disk brakes in 79, NZ was getting "upgraded" drums in the front.

On mine the front shoes certainly aren't the same as the rear, not only because of the larger diameter, but because the rears have only a single cylinder. I dunno about yours...

 

[lostmarbles]

Thanks Amaurer - I was going to post this:

"I'm very ignorant about the variations between different years and different models. It sounds like your older forty could well have the same size drums all round (despite the fact that this surprises me). With mine the size difference between front and rear is so significant that you can readily spot it (visually).

"

But you've really cleared it up for me already.

Ken - Would it be sensible for me to suggest you put "all the black shoes on one axle" and "all the gold shoes on the other" with the "best arc fit" shoes going on the front? Is this possible now?

 

[Fallon 40]

Ken - Would it be sensible for me to suggest you put "all the black shoes on one axle" and "all the gold shoes on the other" with the "best arc fit" shoes going on the front? Is this possible now?

That is what I will be doing in 1 1/2 hours from now.
As soon as I get home from work. I have been on here most of today!
Oh well, I gotta figure this out and I know I will with all this help I'm getting.

 

[Pin_Head]

PS I don't think I would bother taking them to a shop to arc them. You could do them in 10 minutes with a file and sanding block. It isn't rocket science. It is the set in the bottom picture that need it.

 

[My wife said no FJ!]

Ken - Would it be sensible for me to suggest you put "all the black shoes on one axle" and "all the gold shoes on the other" with the "best arc fit" shoes going on the front? Is this possible now?

Hi Tom...question...shouldn't Ken first figure out if the Cruiser will pull to the right if he swapped his right front and left front?

I'll be doing my drums myself shortly, and I figured I would have done this first...I mean what if he swaps them, and the Cruiser still pulls left???

 

[lostmarbles]

Hi Tom...question...shouldn't Ken first figure out if the Cruiser will pull to the right if he swapped his right front and left front? ...I'll be doing my drums myself shortly, and I figured I would have done this first...I mean what if he swaps them, and the Cruiser still pulls left???

I tend to think that his problem may have been caused by being given 2 DIFFERENT sets of shoes from MAF (a gold-painted set and a black-painted set). While each set was supposed to go on the same axle, I think Ken may have added shoes from different sets on the same axle. And because they are made to different specifications (which is clear from the photos), I'm sure that would cause severe brake imbalance.

So if this has indeed happened - I think "getting matched shoes on the same axle" over-rides all other considerations at the moment.

It is a shame if he has two drums on the same axle and ONLY ONE is turned oversize. But I could probably live with that situation on the back axle.

Gotta rush off to work now.

 

[My wife said no FJ!]

I completely understand, and agree, but if he swapped them over then he would know for sure...if it pulled right that is.

I just like to eliminate one step at a time...but again, I do agree with the miss-matched sets being a NO NO !!!

 

[rsbcruiser]

Gooder on the even adjustment call. Friction shop, guess I should have said brake shop or automotive machine shop. Some shops (just a few around here) can turn shoes to match the drum diameters. I suppose though that if all shoes are contacting the drums the same, it might not be your problem. Matching diameters is a good idea anyways because you will end up not having to adjust your brakes as much during wear in. more contact means better braking too.

 

[lostmarbles]

I completely understand, and agree, but if he swapped them over then he would know for sure...if it pulled right that is.

I just like to eliminate one step at a time...but again, I do agree with the miss-matched sets being a NO NO !!!

Yeah. Good point.

We're giving him lots of ideas to work with anyway. (And I may indeed be way off the mark with what I am thinking could have happened.)