Brake question

I have run into an issue with my 99 Durango  that I am having trouble figuring out. Occasionally at start up the front brakes are so sensitive that they go from inactive to fully locked almost immediately. The rear brakes feel like they are in engaged and the rear wheels are driving through the front wheel skid. I feel like the issue gradually goes away after the first few stops, but it is very disconcerting. 

The truck has rear abs only, no fault codes show with the abs system though I have noted that when I test with 4 wheels in the air and press the brakes the rears do take a while to fully stop. Maybe that is how it should be with abs on unloaded wheels!

anyone have any suggestions for where to start? Or does anyone know a good diagnostic brake shop near Atlanta?

Bad compound in the front pads, maybe.  Ford used to have trouble with drums on the rear wheels locking up when it was damp.  Get some heat in them and they settled down.

Certainly possible. The symptom does seem to dissapate with time which could be heat in the brakes. And the pads on it are more aggressive since I do use it for towing. But the pads have been on this for a while and did not have this problem for a few years. So I was also wondering if it might be a booster issue or abs issue. 

I've seen pads develop sensitivity to humidity as they age, in some cases getting more grabby and in some cases getting significantly less grabby. This is the time of year to see it happening.

and this might sound crazy since we are talking about a truck, but is it possible that your tires are also less grippy when they're cold, compounding the issue because more grabby cold brakes plus less grippy cold tires = more tendency to early lock until things warm up a little?

I was gonna ask, how old are your tires?

In the collector car world pretty much every strange brake lockup problem is cured by replacing the 15 year old tires that only have 500 miles on them.

Great question on the tires. They do suck but they have sucked since I bought them.... advice from a friend of a friend and a great sale.... that will teach me. They are 8 years old though. I do need to change them and I am currently waiting for BFG AT's to be available in the desired size for less that $300 each. However. I am still concerned that this happens on warm days on clean pavement at 5 mph and it doesn't feel like the back brakes are slowing the engine at all.

itsarebuild said:

However. I am still concerned that this happens on warm days on clean pavement at 5 mph and it doesn't feel like the back brakes are slowing the engine at all.

Hmmm, OK, thanks for rephrasing the issue. Now I'm thinking your metering valve has stopped metering. The metering valve delays pressure build on the front brakes, basically gives the pressure to the rear a "head start" to overcome all the return spring forces on the drum shoes. Without metering on a disc/drum system, the fronts engage well before the rears, which makes the balance very front-biased and leads to premature front wear.

or maybe your low-speed nitrous system is only spraying the rear axle.