I have my truck that has a problem have not yet figured out. When I test drive it the brakes seem to catch, give out, then catch just fine. It does not vibrate as if it were a rotor issue and this only happens when you initially hit the brakes. I have replaced the calipers, pads and master cylinder. The rotors seem new but vehicle has sat around for couple years. Brake lines are also fine and rear brakes perform nominally. Any ideas on this issue? 2000 ford f150 2wd disc in front drums in back has 141k on it and Sat around for about 2 years. Needed to change brakes because they were sticky.
No ideas until you tell us what truck this is, disk front/drum rear or disk/disk, the miles on it, how long it has been sitting and any other detail you think would be useful. Also what you mean by “give out”.
give us some details on the truck- make, model, year, mileage.
also, give some idea on the (recent?) brake repairs. Why were they done? Who did them? are they competent to do brakes?
Giving out as in let go
Not helpful… Details about your truck? Year? Brand? Model? Mileage? Engine? Transmission? Brake style? How long its been sitting? C’mon, help us help you.
I did look at the edit
Possibly failing brake hoses or the booster. I lean to the booster.
I had the same problem before I replaced the booster.
You didn’t say you had replaced the booster in your first post. Anything else you forgot to mention?
Is this truck equipped with ABS or does it have a proportional valve?
Is it worse when it’s wet outside, or it’s raining?
Does it ever get better, after you’ve gotten the brakes warmed up?
If yes, the problem might be the rear shoes and drums
It might be oil or grease or something is getting on the friction parts and that’s reducing the braking force until it gets wiped off after the initial application of the brake pedal. Are you losing brake fluid? A leaking rear wheel cylinder could cause something like that. It doesn’t take much brake fluid on the inside of the drum to make the shoes slip.
As posted above, the rubber brake hoses that attach to the calipers and wheel cylinders are always suspect w/this sort of symptoms too. The hoses can look fine from the outside, but inside they can collapse after you apply the brakes, and weird symptoms can crop up. Usually the symptom for that is the brakes seem to lock up or be very grabby. Might be worth it to take a flyer and replace all the rubber brake hoses. Could be just what the doctor ordered. Best of luck.