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check your brake pads. If the thickness is low that will cause
an issue with the caliper piston.Have you ever changed the brake
fluid? Do you tow with the Truck?I changed the pad, bled the lines. It is the son’s truck and he said it has been doing it for some time. It does not tow anything but does have something for trailer brakes in it from previous owner.
If the truck has rear drum brakes.Make sure they are adjusted
correctly. this will cause a spongy pedal. If the truck was used
for towing in previous.The rubber lines may be stressed from the
towing and expanding to much. If you pump the brake pedal with the
truck off say 10 times.does the pedal get firm?It sounds like possibly a bad master cylinder
Just to clarify, when you go to stop you can feel the brakes catch and then the pedal kinda free falls a bit and re catches?
yes when the vehicle is almost to a stop the petal falls about a half inch or so and then is good. It is not so much that the brakes go out as the petal just falling at the end.
That often happens when either:
(1) A brake cylinder is rusty and only finally fully applies when the car has stopped.
(2) When a back brake shoe is loose or has rusted-out guides and only finally seats itself when you’ve completely stopped.
(3) A caliper is loose and only fully seats the pads when the car has stopped.
[quote=”grg8888″ post=78718]That often happens when either:
(1) A brake cylinder is rusty and only finally fully applies when the car has stopped.
(2) When a back brake shoe is loose or has rusted-out guides and only finally seats itself when you’ve completely stopped.
(3) A caliper is loose and only fully seats the pads when the car has stopped.[/quote]
True, but I wonder if a bad rear master cylinder piston can do that also, bypassing fluid when it hits the bad part and then catching when it hits the front piston.
Check everything Greg mentioned above, if it all checks out try this. Have a helper stop the truck normally in the driveway and then with the pedal being held down crack the back line going into the master. If no fluid squirts out (and it should its under pressure) than the masters rear circuit has failed and you are basically stopping on the front circuit.
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