Hard Brake Pedal that prob has something to do with the prop valve?

Hi all, started getting a hard break pedal kinda out of the blue. Brakes seem to grab fine, just hard to press.
Did the simple tests for the master cylinder, that seems ok.
Had the mechanic bleed the system, but prob not the bleeder on the LPV. (He prob didn't even realize it had one)
So, here's the thing. Got a load of firewood a while back. And the brake pedal felt normal, great even. Unloaded the firewood and it (brake pedal feel) stayed good for several weeks. Left the truck outside in the cold overnight once, and the pedal got hard again.
Loaded up with some wood pellets for mom's pellet stove. Brake pedal again went back to normal and continued after I unloaded. Stayed again for a few weeks, now it's back to hard pedal.
Clearly, this has GOTTA have something to do with the LPV, but I've usually heard of it causing spongy brakes, not stiff. Couldn't find a replacement LPV on Rock Auto either. May have to get a Toyota part because my truck is 20 yrs old?
Anyone else think I'm on the right track, or could offer any guidance?
Thanks in advance.

 

Welcome to TacomaWorld
You could try adjusting the actuator rod up if it's not too rusty.
The LPV can be deleted and plumb rear brake lines to a manual proportioning valve under the hood.

 

It could be a problem with your booster or hoses in that system.

 

I know you are looking for a "replace this part" answer but this can turn into a parts cannon type thing pretty fast. As mentioned above, check the brake booster first. Forgive the remedial explanation as I do no know what you know of things mechanical... bleed the vacuum off the booster then with a slight foot pressure on the brake pedal, start the engine and see if the pedal falls slightly. Shut of the engine and press the pedal normally, you should get 2 maybe 2 1/2 applications before the pedal gets hard. When the pedal is hard press hard on the brake pedal then let off, now with a slight pedal pressure see if the pedal falls to the floor slowly. If it does the brake master cylinder is bad. The next item to check is the rear brake adjustment. Should be a slight drag or very close to it. The rear brake return springs on 1st gen Tacomas have a tendency to not do their job after the years. The springs are responsible for the correct operation of the rear brake auto adjusters in conjunction with the operation of the parking brake. The load proportioning valve has a bleed port on it and many do not know it is there. If there is any air in the system it will be lodged their, the highest point in the system. I have never tested a LPV, if it is questionable, I just replace it. If the truck is stock height and the mechanism is free in operation then this is one of those times where you replace the part with a know good one and eliminate that from the problem.

 

Thanks Glamisman,
Yeah, thats the test I did for the master cyl. Passed ok.
Good tip about the bleed port & the air being trapped there. As I stated my mechanic bled the brakes, replaced brake fluid actually.
My guess is he prob didnt even know about the LPV & bleeder as it's kinda obscured by the spare tire.
I gotta do the rear brakes anyways, but have to replace the inner (backing plates, I think they are called) as well, as mine are deteriorating.
Kinda a decent sized job, since the axles would prob need to be pulled as well to do that. I was thinking on maybe Spring '21 for that project

 

Well, update, FYI.
I tried to adjust the rod, as it does look adjustable, but it broke. I guess 20 yrs of rust will do that. (soaked for a couple days in WD 40)
Tied it up about 2" higher with a coat hanger, and the brake pedal does seem much better, and the rear brakes don't lock up........easily.
I have a 1.5"-2" lift (add-a-leaf) in the rear, but I never had to mess with it for the 15 yrs the lift has been on. Dunno.
Anyway, it's a temp fix, but gotta look for a new rod now, preferably one slightly longer. I remember they used to make them, along with ext brackets for lifted trucks, hope they still do
Thanks for the input for assist.

 

I see this a lot with lifted Tacos and no pivot extensions. I just guessed you left out the info about being lifted.
Glad to help, sorry the adj threads broke. Can't say I didn't warn you.
Happy holidays
Love the coat hanger fix
Very resourceful on your part