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I have a brake question car is 1969 vette L-46


#1

I am starting to diagnose symptoms at the brake pedal. When i start the car in drive way and i hit the pedal it is very soft and goes pretty much to the floor but can barely stop the car. once i do a 2nd and 3rd pump the brake pedal gets firm and stops car like i think it should. Any guesses on where to look first ?
Rubber hose from caliper ?
Caliper cylinder ?
air in lines ?

another issue that may or may not be related is car pulls to the left when i hit the brakes…Fun is huh !?
TIA if anybody comments.
-ALF


#2

@grapeape73 It could be anything from a leak in the hydraulic system to a bad master cylinder. I’d stat with checking the connections at the master cylinder and all four wheels for signs of leakage, and then bleed the brakes to eliminate the possibility of air in the lines.


#3

Mike is on a good path. Obvious leaks is where to start on any brake system. I would then move to pulling the drums to check the wheel cylinders and adjust the brakes. Likely the pulling to one side under braking could be tracked to the wear/lack of adjustment.

Based on your description, I would venture to guess its the master cylinder seals are allowing fluid past and thus not supplying adequate pressure to the rest of the system. Start with the simple and easy (read: less expensive) inspections and fixes first, rather than diving straight to the big ticket items like replacing a master cylinder.


#4

Thanks, I’ll have to break out the FSM and do some reading, was just hoping someone else had exact same symptoms. BTW it’s a C3 vette so Disc on all 4 no drums, and no fluids are making it to ground, will check chassis.
-ALF
P.S. 2 other vehicles need my attention so won’t post updates for a while.


#5

@grapeape73 - My error on the drum/disk statement then. Sticky calipers can cause the pull. With disks at all four corners and no fluid leaks, I would lean towards replacing the master cylinder and any rubber lines.

Best of luck and let us know what you find!


#6

Another item to check on is whether or not any of your rotors are warped. If that is the case, you should feel pulsating action through the pedal or steering wheel. If if this is the case, the pumping action on the brake pads/pistons tends to introduce air into the lines over time and make the brake squishy. As a hack for the problem, some will remove the internal springs from the pistons so the brakes don’t ride on/close to the caliper (the springs are there to apply slight pressure as a way to keep the caliper clear of water/moisture so stopping is more immediate when driving on wet surfaces).

PS - previously owned a '69 Monaco Orange Coupe / L46/4spd. Loved that car!


#7

Typically when the brakes respond to “pumping up” it means either air in hydraulic system or an adjustment issue.
Quick checks to try include taking 4 pairs of vice grips and clamping off all 4 flex hoses as close to the frame end of the hose as possible. Try checking the brake pedal again. If it is now a hard pedal, take one pair of vice grips off at a time and check pedal again. Put vice grips back on and go to next caliper and repeat. You should be able to locate where the issue is. To check the flex hoses for “ballooning” move all 4 vice grips to caliper end of hoses, then go through the removing vice grips and testing procedure.

If the brake pedal is still soft with vice grips applied you very likely have air in system. Bleed brakes at the master cylinder first. If the master cylinder is mounted to brake booster at an angle remove master from car and bench bleed the master cylinder in a bench vice using two lines you either buy or make up yourself that simply loop from the master back into the resevoir. Using a push rod pump the master cylinder slowly and watch the ends of the two lines in the resevoir for bubbles. Keep pumping until bubbles stop. After bubbles stop, leave the lines connected and carefully re-install master cylinder. After master is mounted remove test lines and reinstall original lines to master. Leave lines slightly loose and have someone simply apply brakes. DO NOT PUMP THE PEDAL. Tighten both lines before releasing pedal. Release pedal and wait 10 seconds. Loosen both lines again and have brake pedal pushed down again. Tighten lines before pedal hits floor. After you stop seeing bubbles coming out the connection at the lines stop bleeding. Make sure that the resevoir never runs out of brake fluid.

A bad master cylinder will generally show itself by having the brake pedal slowly going to floor under very light pedal application. This generally happens at stop lights when you are pushing brakes hard enough to hold the car from creeping forward when stopped. A hard application of the brakes will usually give a hard pedal. The reason for this is due to the shape of the seals inside the master. They are cup shaped seals and the hydraulic pressure on a hard application of brakes uses the hydraulic pressure to drive the seals tightly to the bore increasing the quality of the hydraulic seal. Any fluid that leaks past those seals goes right back into the resevoir via the compensating port.


#8

If you are experiencing a soft pedal that pumps up and a distinct pull to the left under braking, I think you should start with the calipers and brake lines on the right side of the car. You’ve got a leak over there that’s allowing air into your braking system. I would expect that a faulty master cylinder would cause general braking problems but not cause the pulling. Warped rotors, while annoying, are probably not the cause of your problems either.

P.S. I previously owned a Le Mans Blue (black interior) '69 L36 (427/390hp), M21 4 speed, low mileage, numbers matching coupe. It was just OK. Nose heavy, sort of slow and really cramped inside.