front brake issue

[emso]

I have a 1995 gmc sierra sle 4x4 6.5 diesel. when it rains and the truck's brakes are wet the front brakes will lockup with little pressure on the brake pedal. The rear brakes are fine, only the front brakes will lockup. once the brakes have warmed up they are fine. No issue with the front brakes when their is no rain. What should I look into? Could it be the abs sensor? Could it be the brake pad material swelling up due to moisture? Why only in the rain and when they are cold? again it's the front brakes not the back.
thanks for the help

 

[east302]

I have a 1995 gmc sierra sle 4x4 6.5 diesel. when it rains and the truck's brakes are wet the front brakes will lockup with little pressure on the brake pedal. The rear brakes are fine, only the front brakes will lockup. once the brakes have warmed up they are fine. No issue with the front brakes when their is no rain. What should I look into? Could it be the abs sensor? Could it be the brake pad material swelling up due to moisture? Why only in the rain and when they are cold? again it's the front brakes not the back.
thanks for the help

Both wheels lockup or just one?

Have you duplicated it on jack stands, spraying it with water?

Do calipers slide easily?

 

[emso]

yes both front brakes. This morning the roads where dry and no issue with the brakes. Only does this when it raining. I'll try the jack stand idea. Wonder if it's the abs sensor.

 

[454cid]

Mine lock hard if they're wet or damp. I haven't driven my truck in about 2 months. I'm betting they're terrible right now. I really don't know for sure if its the fronts or rears, Though. I've always kinda thought it was the rears. Which ever it is... it can stop hard from a slow speed. I typically get going a little faster, and then gently apply the brakes to the next stop to get rid of it.

ABS removes brake pressure not adds to it. It's not your ABS unless you can't stop when you should be able to.

 

[emso]

Hasn't rained in a while. I guess I'll just need to be careful when their wet and cold.

 

[Coveman]

That happens on a couple of my cars after I wash them. First brake application is grabby, then back to normal

 

[Schurkey]

First Guess: Contaminated brake pads.

 

[Gibson]

Yeah,, under certain conditions the rear drums can be grabby until they warm up.
Part of it is caused by atmospheric conditions,, relating to the amount of humidity in the air vs the dewpoint, where water vapor condenses into liquid,
So,, you pull into your parking place with warm/hot brakes,, as the shoes/drums cool down the moisture in the air condenses on their surfaces,, and the next time you apply the brakes they act grabby, or lock up,, until all the moisture is evaporated.
It's really a common thing, it's something that is part of the reality of drum brakes.
It was a very big issue with early airplanes, and is one of the reasons that some aircraft started using discs as far back as the 1930s,,
Oh,, having the brake shoes not adjusted-out properly makes it worse, the increased shoe travel adds to the "locking" action.

 

[Hipster]

First Guess: Contaminated brake pads.

Ditto, Oil/fluid contamination, or trying to drive off rotor rust if it was excessive will make them grabby.