Brake issue

New to the group but been reading on the forum for long time. This is what I got. 2000 sr5 2wd new to me, 200k on the v6. 16” rims with 255/70/16r Clean little runner and perfect for my 16yr daughter.
Going thru the truck and fixing things that need to be addressed before she gets into it. Normal front brake shake from under sized rotors and braking system, so did the tundra conversion & New brake lines front and rear. Bled the system with dot 3. Have done the conversion before with no issues on other vehicles.
PROBLEM:
Truck drives great for about 15mins no issues no weird noises or problems. After about the 15min mark get a vibration under the seat (feels like from the rearend/ “which is new”) and little shake in front end after you push the brakes. Drive shaft was balanced and new u-joints within the last few months. Sitting at stop sign or light on level ground can take foot off brake pedal and truck won’t move. Little gas and she moves slowly. After more go and stops the vibrations get worse and front end shakes more.
Let the truck cool down and sit it truck runs fine again until the 15min mark.

Do live in AZ and temperature has been crazy here. Think the dot3 is getting too hot and need to go to a dot4 or 5.1? Don’t have crazy big tires or any extra weight on the truck. No lights on the dash so don’t think it’s the ABS pump but just don’t know.

 

Hmm, the timing of everything is weird but do you think you could have a stuck caliper?

 

Sounds like a transmission issue. When I start my car every morning for the last 100k miles or so, I have to put it in R and then D and back to R to get rolling. If I don't, then the whole thing shudders and moves very slowly. Fortunately my issue fixes itself if I do the shifter dance and then never has an issue for the rest of the day.

Your brake fluid won't cause your issue. At least I don't see how it could. When you push on the brakes, the transmission may try and shift down which causes that shudder.

 

All new brake lines x3, rotors, calipers & pads. With 200k I just switch old rubber lines out since I had to bleed the system. Not saying the rotors or calipers can’t be bad being brand new but why when it cools down would it go back to driving/working normal. Truck shifts fine not thinking tranny. It just started after I replaced the front end braking system. Going to get under it tomorrow see if the I can see a brake line pitched or if rear wheel cylinder hanging up.

 

I dunno either.

Check your transmission fluid level anyways. It's free.

 

Have had odd issue before on a classic car, and it happened to be a crimped brake line doing weird things to the rear drums. Thought the posi diff was at fault. Vibration . shaking. Super weird and low probability here, but I throw it out as a possibility. It may be evident from the drum / rotor surface.