Brake Sensitivity, Sudden Stops

[HotWheelsBurban]

Drum brake systems make a lot of dust in their normal operation. Unless you pull the drums off regularly, this dust stays in there and can make any or all of the many parts that make it properly function stick. This will cause the"grabbing" you're noticing.
What I recommended to people back in my parts house days, was when servicing the drum brakes, is to replace all the springs and attaching parts as well as replacing the shoes. You'll also need to lubricate the wear points with hi temp brake lubricant. Even when everything has been properly serviced and lubricated on a drum brake system, the dust I mentioned will accumulate over time. My Burb's rear brakes were serviced by a mechanic friend 4 years ago. He replaced both wheel cylinders (they were leaking), and I believe that he reassembled everything correctly. But after a bazillion stops in 4 years, I'm sure it's dirty as hell in there. Something else my Burb does, especially if it's humid or damp, is the first few stops on the initial driving, it screeches like there's no linings left. The wear surfaces in the drums get a little rust glazing on them, that takes a few stops to get rid of. I've noticed this on other vehicles in greater Houston too, when it's damp. Part of it may be the lining compound or the temperature of the drum once it gets warmed up after a few stops.

 

[someotherguy]

Forgot to ask, Does a 95 have rear ABS?
If so that adds another layer to the problem

All GMT400's have rear ABS. '95 added front to the package (on pickups; SUV's had it since '92)

Richard

 

[stutaeng]

Your experience is common, especially in cold/damp weather.
Cold drums/shoes are quite "grabby", much more so than discs.
Once the shoes "drag" a bit they warm up and smooth out.
The effect is multiplied if the rears are out of adjustment.

I was not aware of this. My only truck with drums is my '00 GMT400 K3500. I have not encountered this, that I can recall? How cold are talking there? I know I've driven in the wet/damp plenty of times, and cold, well we get down to below freezing frequently in the winter. I remember driving daily for a week in the winter, while my other truck was down...

Admittedly, I have not removed the drums on the rear of that truck. I'm scared to do drums, LOL. And the truck stops very well, so not messing with mine. But that's good to know.

 

[Gibson]

"I know exactly where you're coming from on that.
Here in the PNW it rains much more than just about anywhere else, and I've experienced that situation on many occasions, with my '97 K2500 Sub,, especially stopping at the end of my long dirt driveway when leaving in the morning.
So, a friend of mine has been a service manager at a Chey dealer for years, and I discussed it with him.
Here's what happens; After driving awhile, the brakes are warm/hot, and dry.
Then, you park and as the brakes cool-down the moisture in the wet air quickly condenses on the drum and shoe surfaces and forms a very thin layer of rust on the bare metal.
Then, the next time you go to use the brakes it's as though the brake shoes, instead of rubbing on clean metal, are grabbing onto a rough surface, and they lock, or try too, and they act that way until they warm-up and and that tiny layer of rust is cleaned/wiped off.
When the brakes are adjusted "just right" their needs to be a little drag so that after a fairly short distance the drums and shoes are clean and dry.
But yes, it can also be a sign of worn components,, no guarantees."

In response to the post by HotWheelsBurban, I'm quoting myself from a post I made a few months ago.
He's right, when the weather gets wet the drums get some rust, and until the shoes drag that off they will grab.

 

[CrustyJunker]

Had a Buick that did this. First stop post-rain pretty much locked them up. Lots of stares leaving a parking lot.

 

[thinger2]

"I know exactly where you're coming from on that.
Here in the PNW it rains much more than just about anywhere else, and I've experienced that situation on many occasions, with my '97 K2500 Sub,, especially stopping at the end of my long dirt driveway when leaving in the morning.
So, a friend of mine has been a service manager at a Chey dealer for years, and I discussed it with him.
Here's what happens; After driving awhile, the brakes are warm/hot, and dry.
Then, you park and as the brakes cool-down the moisture in the wet air quickly condenses on the drum and shoe surfaces and forms a very thin layer of rust on the bare metal.
Then, the next time you go to use the brakes it's as though the brake shoes, instead of rubbing on clean metal, are grabbing onto a rough surface, and they lock, or try too, and they act that way until they warm-up and and that tiny layer of rust is cleaned/wiped off.
When the brakes are adjusted "just right" their needs to be a little drag so that after a fairly short distance the drums and shoes are clean and dry.
But yes, it can also be a sign of worn components,, no guarantees."

In response to the post by HotWheelsBurban, I'm quoting myself from a post I made a few months ago.
He's right, when the weather gets wet the drums get some rust, and until the shoes drag that off they will grab.

Yep. Im also in the PNW and have a dirt alley.
Whenever I leave I have the choice between driving a short distance through a small but rocker deep pond at the end and soaking the brakes, or I can go the long way past 2 construction sites and pick up some nails and drywall screws in the tires.
(seriously, if you are in construction, dont chuck open containers of hardware or toolbelts in the bed of your truck and wonder why you have flat tires all the damn time)
I choose the pond because I have BFG All Terrains that are only about a year old.
I always have to remember to dry the brakes out before I pull up to the stop at the end of the block or she just rolls right on through it
I have the opposite problem on the way back in.
The brakes get soaked in the pond but the distance to the back of the shop is too short for them to dry out again.
Not to mention I have to inspect my brakes a couple of times every winter because rolling hot drums and rotors through knee deep ice water and then parking it is pretty rough on the linings and the whole system in general.
But brakes are a hell of a lot cheaper than a set of BFG KO2s

 

[CrustyJunker]

Eek, that's the worst! I'm thankful brakes in these trucks don't have a million moving parts and operate decent enough when dunked through conditions like that. Drums will be drums, but If the fronts had extra pins, spring clips, etc. I could see that being a major headache multiple times a year.

 

[thinger2]

All GMT400's have rear ABS. '95 added front to the package (on pickups; SUV's had it since '92)

Richard

That I didnt know. The forum is amazing just for the knowledge you get from it.
Thanks!

 

[thinger2]

Eek, that's the worst! I'm thankful brakes in these trucks don't have a million moving parts and operate decent enough when dunked through conditions like that. Drums will be drums, but If the fronts had extra pins, spring clips, etc. I could see that being a major headache multiple times a year.

The brakes on these are not real good to begin with.
They entire system needs to be maintained on regular basis.
And the front to back balance is almost an art form.
That said, I have totalled 3 cars with this truck.
Dont just pull out in front of a GMT400
in your Subaru and expect to not get hurt.
A brand new Caddilac, Toast
A Jaguar Xj6 Toast.
The Subaru, bent in half.
The ******** combined and bent my bumper a bit and broke one of my fog lights.
You have to drive a GMT400 the same way you would drive a 24 foot U-Hual
Except the U-Hual has better brakes

 

[Frank Enstein]

When you inspect the drums wash them out with HOT low pressure water. If the water turns milky the wheel cylinder is leaking. Wash down with brake cleaner after.

Check the backing plate wear pads for grooves from the shoes. The wear pads need to be smooth and flat and lightly lubricated with a high temp brake lube. Be sure to keep the lube off the friction area.

The shoes should be smoothed slightly where they contact the backing plate. A wire wheel or sandpaper will work. Just smooth them a bit but don't make them shorter.

Replace the springs. All of them. They are very inexpensive to do and you are in there anyway. The same goes for the self adjusters.

If you need new shoes get ceramic if you can. They generally last longer, grip a little better, and are easy on the drums.

Get the drums turned or replace them if you put on new shoes. I paint the outside of my brake drums after cleaning them well. The wheels don't rust to them as badly and they look a bit nicer.

I use Rustoleum professional gloss black. The best I've tried from a rattle can. Looks like powdercoating! It doesn't need to be high heat. It will smell a little the first few times you work the brakes hard. Kind of like cooking oil.

When you adjust them be careful to not overtighten them. If you tighten them too much you will ruin the shoes in short order. And to get the drums off is a pain. Been there, done that.

Use the parking brake often and stop the truck with the brakes when you back up rather than putting the trans in drive and they should stay well adjusted.

Sorry for the long post but I untie these knots everyday at my day job and I wanted to be clear.

 

[Supercharged111]

When I went shoe shopping I didn't see any ceramic. They were all organic IIRC except for the semi metallic Powerstops.