Peva

I bought my '85 (6 cyl., granny gear 4-speed, short bed) about 4 months ago.

The brakes work fine, except I notice that when the roads are the slightest bit wet, any but fairly light use of the brakes causes the rear wheels to lock up - to the point that I would hate to think of having to stop quickly on a wet road to avoid an accident.

I know that without ABS, you can't have balanced brakes both with and without load, and so it is possible that what I'm noticing is normal (for an unloaded pickup truck without ABS).

I am willing to go to a little bit of trouble and expense to make things safer, so I want to ask some questions and run some ideas by you guys:

(1) Is what I'm observing normal, or is there something wrong with my truck (like maybe the proportioning valve is not working right)?

(2) If this is normal, I would like your opinion on two possible solutions:

--(a) Install a solenoid valve in the rear brake line, with a switch on the dash - the same kind of valve that drag racers use at the track called a line lock valve - but instead of using it like they use it to keep the line pressurized as a brake holder, I would use it to block pressure to the rear brakes when the roads are wet. In other words, with the switch on, I'd only have front brakes - not an ideal solution, but in my opinion, better than what I've got now (on wet roads). If I did this, I'd put a check valve in parallel with it to ensure that when the valve is 'on' (shut), pressure can't build up in the rear brakes (from heat or whatever) and cause drag.

--(b) Is it possible to add ABS (maybe using parts from a later-year junker)? My guess is that it would not be feasible/cheap/easy, but thought I'd ask anyway.

I'm leaning towards the line lock valve, but maybe there's a better solution than what I've thought of so far. (And yes - I realize that driving slow when the roads are wet is part of the solution).

Thanks for any info. and suggestions.

wde3477

In response to your points:

(1) something doesn't sound right. Take a good look at all brakes to see if anything stands out. Perhaps instead of your rear brakes being too aggressive, the front brakes are not aggressive enough, such as if the calipers were frozen on the slides.
Proportioning valve? - maybe - but not a high-failure-rate item.
I'd look for grease or other contamination on the pads/shoes, for good all-around pad contact with the drums/calipers (nice&shiny full width metal contact areas), and even pad wear between the inner and outer disc pads before taking the extreme measures you've suggested.

2(a) - this is a patch and not a fix. Also, concerned about liabilities / responsibilities of a major modification like this to what I consider to be a major safety system.

2(b) - Possible? If you want to bad enough, I suppose. Looking at the sensor ring and pickup in the rear axle, the ABS valve, the controller, and all the related wiring that would have to be swapped and set up. I've got rear-wheel only ABS on mine, and I don't know that it's ever activated except when I intentionally test it.

I'd make doggone sure there's nothing wrong first before even considering the mods. If this were a design problem, I'm sure it would have been brought to light before now.

Also, blacktop roads are just naturally tough in light rains - the oil from the blacktop mixes with water and there's not enough volume of water to wash it off the road. 'Bout as bad as ice.

*edit* One other off-the-wall thing came to mind. It appears that you have a manual tranmission. If the engine is at high RPM's when slowing, there will be significant additional braking at the rear wheels through the engine. Perhaps push the clutch in??

Peva

Thanks, wde.

I will definitely look over the brakes as you suggest - will check calipers and slides. Will be next week end before I can do that. The master cylinder has a small leak - that's getting replaced very soon, but I doubt that's causing this problem.

The previous owner did replace both rear cylinders shortly before I bought it (they were leaking). I will make sure the shoes are not contaminated, and re-check the shoe adjustment. Hmm - I know that the aftermarket sometimes consolidates different size cylinders to a one-size-fits-all. Might check to see what the replacement bore was compared to the original.

Hmm - leaking master cylinder...leaking rear cylinders replaced... Yeah - I'll check the front calipers real good for stuck slides and pistons, and bleed thoroughly to replace the fluid throughout.

Will also consider what you said about engine braking - I didn't think of that.

Thanks again!

wde3477

Another thing came to mind to consider - tires.

Same all the way around? Good tread? Type?-Tires that proclaim long life are typically a harder rubber that doesn't grip/stick as well. Also, maybe it's just me, but the off-brand 'discount' tires don't seem to hold as well.

Not sure if tires would explain the severity of the things you're seeing - just another angle to consider.