Rear brake lock up question? M1009

[porkysplace]

No fudging here. I said I replaced the wheel cylinders earlier, all brake components were replaced except for the proportioning valve and lines (which were all cleaned individually as I said) the only think I did was adjust the brake shoes after putting it all back together as I thought there could have had a little better tolerance. Everything about that parking brake was for sure installed correctly. I took pictures before and after to make sure too. It scouts Honor was installed exactly correctly. I did not get the drums turned or replaced. If I have time I can try to use a dial indicator on it to see if it's out of round. I want to be clear that it's more or less the rear just locks up a little earlier than before. Nothing unsafe per se. The front pads are clean as a whistle, no oil, no nothing. I used a shop manual for everything with pictures just to make sure. I do not mean to come off as hard headed but I am 100% sure of the work I did. There are only two things that changed. Whether or not the proportioning valve is the culprit, or the tight brake shoes adjustment. I can see if I can get the rear drums turned or replaced, although it would be shocking that it would suddenly change what's been happening. You know what I mean?

Well by your own statement you DID NOT REPLACE the rubber lines , brake shoes/pads or drums/rotors so no everything wasn't replaced .

As was already pointed out several out of round / warped drums/rotors brake linings with uneven hardness due to heat or worn out soft rubber brake lines expanding under pressure now that it has good springs and wheel cylinders in the back.

You did half a brake job and don't want to listen to anybody else so why even bother posting the question when your mind is made up on the answer.

 

[Recovry4x4]

Let me add this for thought. Self energizing drum brakes like you have, are more prone to lock up than a disc setup. With enough force or loose terrain, the drums will always lock before the discs, even on perfectly balanced systems and there are variables in weight distribution/shift and coefficient of friction on the stopping materials. Your brakes may be just right now and not just right before proper adjustment.

 

[MarcusOReallyus]

I did not get the drums turned or replaced. If I have time I can try to use a dial indicator on it to see if it's out of round. .... I can see if I can get the rear drums turned or replaced, although it would be shocking that it would suddenly change what's been happening.

You adjusted the shoes tighter and it's locking sooner. That's what I would expect if the drum is out of round.

Unless you're a lot better than most of us, you can't see a few thousandths out of round, so unless you're a lot better than most of us, "they look good" really isn't a sensible thing to say, is it?

 

[o1951]

Somebody needs to take your helmet off and give you a good wonk on the head

I am an old guy. I drove vehicles from 1950's and 1960's when they were new, and did all maintenance on them.I am familiar with all that stuff. The old stuff did not have a flange with wheel studs on end of axle. End of axle had a spline and a big nut. The drum had matching internal splines and was held on by the big nut. The drum had the studs in it, or was threaded for bolts with tapered heads.

1. Single circuit and dual circuit drum brake shoe adjustments are the same.

2. As several people have told you, a good brake job includes replacing rubber hoses and refinishing drums or rotors.

3. As previously posted, I did not have a lot of equipment. The only way I know to check drums is to mount them while I still had backing plate off. I put the drum on, washers over the studs, and the nuts on backwards, so the flat side was against the washers. I torqued nuts to TM value and checked area contacted by shoes for run out, out of round, and taper.
This would let me know if the whole assembly was true. Uneven rust on the contact surface of the axle flange or contact surface of the drum can cause run out, so I wire brushed or wire wheeled contact surfaces clean, and either lightly sprayed with lacquer or wiped with an oily rag to retard future rusting.

If everything is true, and pads/ drums are contaminant free, brakes will come on smoothly and evenly. When I adjust shoes, I tighten them until light drag is felt. Drag should be even as you rotate drums. If you feel tight spots and loose spots, you know drums are way out. If drag is even, then I back off to obtain clearance specified in TM. As I remember, most specified tighten to slight drag, then back off 4 clicks on the star wheel.

 

[The FLU farm]

Are the pads and brake shoes of the some type/aggressiveness? Obviously a "softer acting" pad can change the brake bias towards the rear.
Also, if the rear started acting up after adjusting the shoes, why not back them off a bit and see what happens? Not that I think it'd change anything, but at least it's a no-cost test.

 

[RickTheEngineer]

Well by your own statement you DID NOT REPLACE the rubber lines , brake shoes/pads or drums/rotors so no everything wasn't replaced .

As was already pointed out several out of round / warped drums/rotors brake linings with uneven hardness due to heat or worn out soft rubber brake lines expanding under pressure now that it has good springs and wheel cylinders in the back.

You did half a brake job and don't want to listen to anybody else so why even bother posting the question when your mind is made up on the answer.

I have braided steel lines up front, no rubber hoses. All rubber components were indeed replaced. Also, if you take a look at the multiple times I did mention it earlier on this thread I did replace the pads. Not the drums, shoes or rotors as the problem hadn't existed earlier. I woke up early today and loosened things up a bit in the rear. To the point or very little drag. And the problem appears to be fixed. What I think the problem was is that on some of my trucks they have anywhere from 35"-37" tires, and I think that's why I never experienced a tire lock with the way how I adjust my drums. A couple of hard pushes on the pedal to ensure that the proportioning valve was set correctly yielded braking performance identical to what it had been before. In case this was lost in transit, I kept trying to emphasize that the rear had never really locked up on dry pavement. It was always under very low friction situations that I noticed it would A BIT before the front. I did not know if it was normal with the decreased weight in the rear etc. I broke out a dial indicator and spun the drum and did not see anything that indicated it was out of round on both left and right drum. The right side's shoes were adjusted a little tighter than the left one which confirms so suspicion that that's what was causing the right to lock up a smidge before the left one. Also, to those reading this post, I apologise for any arrogant vibes that may have been given off, perhaps I could have done a better job of explaining things. Such as having steel instead of rubber lines, etc. My mistake.

 

[The FLU farm]

Also, if the rear started acting up after adjusting the shoes, why not back them off a bit and see what happens? Not that I think it'd change anything, but at least it's a no-cost test.

So I was wrong. Again.

 

[RickTheEngineer]

Well, it ended up being the problem! Thanks a lot! Now on loose terrain they all lock up exactly at the same time.

 

[rustystud]

I am just going to add this one last note. As it has been mentioned earlier, if you don't turn the drums and rotors your only doing half a brake job. I will bet you money that your drums are not round nor perpendicular (tapered) . I have never seen any drum with more then a thousand miles that did not have some wear. After 40 years as a mechanic I have seen a lot of brake jobs and no shop would send out a vehicle that had not had the drums and rotors turned. They can cause so much trouble it's ridiculous ! Even if they are "close to being round they still will be tapered as shoes "never" wear evenly. They flop around especially the wider ones like our trucks have. So in the future get you drums and rotors turned ! If you don't your doing a "half ass job" .

 

[Abbylind]

When you replace the shoes they stick out a little further on the leading edge than the old seated shoes. It can cause them to grab a little more and chatter when the brakes are applied. In the old days when they put new material on old shoes you took the drums in too to have them "fitted" to the new shoes. You might sand the leading edge to the new shoes. As for the drums....I bought new drums for a different vehicle, figuring the new drums would be ready to go I installed them without turning the drums...wrong! As they sit on a shelf or the machining process they were both out of round. I quick clean up on the drum lathe rounded them out. YMMV

 

[snowtrac nome]

used drums will achieve a bell shape they should be turned I would still have checked park Brake as described, also the springs should have been replaced they are likely over 20 years old and un told heat and cooling cycles. this comes from a professional mechanic that in his early days did a lot of free work to make things right.

 

[FrankenCub]

Recovery4X4 brings up a good point, besides what everyone else was saying about having the drums turned. Under heavy braking or loose surfaces, the drums on the rear WILL lock up before the fronts every time. The shoes have a greater surface area on the drum to grab than the pads do on a disk, and as you brake hard it unloads the rear making it essentially lighter. All the older vehicles did this, it was the nature of the beast before people started forgetting, or not learning, how to drive. Then came the advent of anti lock brakes, which I hate, to help those control a slide that never learned to do it before. Now someone in a panic stop being used to anti lock brakes has no clue how to handle a slide when a sensor decides to go out and their trusted anti lock no longer works. Maybe the anti lock bit wasn't needed, but relevant to the conversation, rear brakes used to lock up under heavy braking, now they don't. For the most part.

Of the vehicles I get the pleasure to drive, a '31 Model A Ford, '32 Chrysler Speedster, '34 Chevy 3 window, they all have correctly rebuilt brakes and will lock up the rears in hard braking. My '71 GMC 1500 and '84 M1008 will also do the same but also being pick ups they are rear light to begin with so I expect it.

Basically what I'm saying, after turning the drums, still expect the rear to lock under some circumstances even when adjusted by the book. Out of adjustment makes them less likely to lock. It it what it is. Don't loose too much sleep over it.

 

[rustystud]

Recovery4X4 brings up a good point, besides what everyone else was saying about having the drums turned. Under heavy braking or loose surfaces, the drums on the rear WILL lock up before the fronts every time. The shoes have a greater surface area on the drum to grab than the pads do on a disk, and as you brake hard it unloads the rear making it essentially lighter. All the older vehicles did this, it was the nature of the beast before people started forgetting, or not learning, how to drive. Then came the advent of anti lock brakes, which I hate, to help those control a slide that never learned to do it before. Now someone in a panic stop being used to anti lock brakes has no clue how to handle a slide when a sensor decides to go out and their trusted anti lock no longer works. Maybe the anti lock bit wasn't needed, but relevant to the conversation, rear brakes used to lock up under heavy braking, now they don't. For the most part.

Of the vehicles I get the pleasure to drive, a '31 Model A Ford, '32 Chrysler Speedster, '34 Chevy 3 window, they all have correctly rebuilt brakes and will lock up the rears in hard braking. My '71 GMC 1500 and '84 M1008 will also do the same but also being pick ups they are rear light to begin with so I expect it.

Basically what I'm saying, after turning the drums, still expect the rear to lock under some circumstances even when adjusted by the book. Out of adjustment makes them less likely to lock. It it what it is. Don't loose too much sleep over it.

If a truck is loaded properly and has a functioning "proportioning valve" then the fronts will brake harder . In an unloaded truck when braking hard the fronts will still apply harder but as the pressure increases the rears will lock-up. That is why GM and others came up with the rear "load sensing brake valve". The only problem with them was they had a tendency to seize and then no fluid would reach the rear brakes. I took mine off my M1028 and just remember to not slam the brakes in a panic stop.

 

[FrankenCub]

If a truck is loaded properly and has a functioning "proportioning valve" then the fronts will brake harder . In an unloaded truck when braking hard the fronts will still apply harder but as the pressure increases the rears will lock-up. That is why GM and others came up with the rear "load sensing brake valve". The only problem with them was they had a tendency to seize and then no fluid would reach the rear brakes. I took mine off my M1028 and just remember to not slam the brakes in a panic stop.

I completely agree. But even with the above stated the weight still shifts putting more force on the front tires during hard braking or panic stop effectively lessoning the load on the rear tires making them prone to locking up before the front. Maybe the load sensing valve makes enough of a difference with the bigger trucks? I haven't had any hard braking or panic stop with my M1008 being loaded to know for sure. Wasn't the load sensing valve on 3/4 ton and larger pick ups? I don't recall ever seeing them on 1/2 ton or any of the Blazer or Suburban variants. My '78 Blazer Camper Special didn't even have one and it was supposedly built for towing.
The valve on my M1008 actually still works correctly, for the moment lol. I did have an experience with a Chevy 3500 short wheelbase wrecker that the valve quit working when I had a full size van on hook. Didn't work out well for me, or the wrecker, or the car that stopped me.

 

[Recovry4x4]

In reference to that load sensing valve, I think I've had less than stellar luck. It stopped working on my SECM truck. I followed the GM bulletin and eliminated it and the truck stops great. I found out that the ambulance has the same issue. My new V30 had brake issues on It's drive home and I've since ordered everything new except proportioning valve and front steel lines. Guess where that valve will be going?

 

[The FLU farm]

Adjustable proportioning valves are fairly affordable. Without one, the identical front and rear brakes on my Jeep would be a handful - which it can be anyway with an 80-inch wheel base.

 

[rustystud]

In reference to that load sensing valve, I think I've had less than stellar luck. It stopped working on my SECM truck. I followed the GM bulletin and eliminated it and the truck stops great. I found out that the ambulance has the same issue. My new V30 had brake issues on It's drive home and I've since ordered everything new except proportioning valve and front steel lines. Guess where that valve will be going?

I think most people after having a major brake service had those pesky valves removed. I have never found one working properly. I mean it's pretty bad when the manufacturer themselves say to remove them.

 

[rustystud]

I completely agree. But even with the above stated the weight still shifts putting more force on the front tires during hard braking or panic stop effectively lessoning the load on the rear tires making them prone to locking up before the front. Maybe the load sensing valve makes enough of a difference with the bigger trucks? I haven't had any hard braking or panic stop with my M1008 being loaded to know for sure. Wasn't the load sensing valve on 3/4 ton and larger pick ups? I don't recall ever seeing them on 1/2 ton or any of the Blazer or Suburban variants. My '78 Blazer Camper Special didn't even have one and it was supposedly built for towing.
The valve on my M1008 actually still works correctly, for the moment lol. I did have an experience with a Chevy 3500 short wheelbase wrecker that the valve quit working when I had a full size van on hook. Didn't work out well for me, or the wrecker, or the car that stopped me.

As far as I know that load sensing valve only came on the 1 ton trucks or a 3/4 ton with the tow package.