'75 - Bad Master Cylinder or Air in Lines?
 

A friend called last night about his one owner '75. He is going to deliver it to his son next week. Last year he had someone work on the SS brake calipers. He stated there was some minor leaking at that time. (The SS caliper sleeves were installed 20/25 years ago.) Don't know what they did but now he feels the brake pedal is way too low and asked me to look at it tomorrow.

My question, how can I determine if the brakes were not properly bled last year or is the problem associated with a worn out master cylinder?

If the master cylinder is bad, it will more than likely be leaking out of the back end where it attaches to the firewall or booster. There is a seal there with the piston.

You can also check for caliper leaks and brake line leaks by simply looking for brake fluid on the inside of the wheels and tires. Also check the P-Valve/Distribution block on the frame where the hard lines attach...Under the hood, drivers side frame rail. :yesnod:

TiINgot, you have 400+ plus posts here so I assume you know your way around these cars. Im sure youve read what a nightmare these C3's are to bleed. As previously stated here....check under the car and around the rims for visible signs of leakage. If you dont find anything, Id suggest bleeding all 4 calipers again before diving into the master cylinder. Good luck.

How many attempts at bleeding this car was there and how was it bled. Im not a fan of gravity bleeding or the vacuum pumps, manually pumping works but can take 4 or 5 laps around the car if theres a lot of water and air. The power bleeders are the best.

You can pull the carpet back and wipe the fire wall on manual braked cars or pull the vacuum filter/ connector and the rubber grommet and thread a cloth into your booster to look for a leak.

I have bled the brakes on my '73 numerous times over the years and really never had a problem with it. I've used the Motive Power Bleeder with great success in these endeavours.

I've done a few master cylinders as well, bench bleed it, then bench bleed it again, and then some more.

Get a Motive, use common sense, and get to work. It's not Rocket Surgery. Start at the rear passenger wheel, rear drivers wheel, front passenger wheel, and front drivers. Work your way out, and then in. Always worked for me?

Quit dickin around with it and get a Motive Power Bleeder, ORing calipers, and be done with it.

:hide:

Ive read from a brain scientists post that you dont have to bench bleed with a power bleeder, any thoughts

lot more work if you dont
If it leaked last yr it needs to be replaced bleeding is a waste

On my '75 when master cylinder went bad I had no brakes and the brake light lit up on the dash.

I bench bled my master cylinder by hand. Used the power bleeder for
the rest of it.

Thanks for all the replies. All he wanted to do was for me to test drive and give my opinion on the brakes at that time. Last year he had someone replace the calipers with new SS units. He stated the brakes were fine at first but the pedal has been dropping.

FYI, this '75 only has 32,500 miles on it but has never been "detailed". Looks like it has 232,500 miles on it.

My impression it needs to have the brakes bled again. Did not see any leaks but did not have time to get under the car for a good look. Offered to help him bleed the brakes when he was ready.

Side note. He was in a hurry. In 1982 he bought a mostly disassembled '32 Chevy standard coupe. All these years, trips to Hershey etc., he has been collecting parts to restore it to a duel side mount,rumble seat deluxe coupe. 25 years ago I helped him move it from one garage to his new house in two pick-up loads. Now he is retired.

Last year he sent the '32 away for restoration. The morning I went to look at the Vette the shop called and wanted him to drive down so they could teach him how to drive his completed restoration. Vette going to sons house to make room in his garage for the '32. Can't wait to see the '32 completed!

Post a few pics.of the 32, i bet shes a beauty

I agree with that thought to check for caliper leaks and brake line leaks by simply looking for brake fluid on the inside of the wheels and tires. As for me it's the easiest way.



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Usually, if the master cylinder is bad, the pedal will slowly sink right to the floor, because it's bypassing inside. It may do it slowly, but generally, it will end up at the end of its travel.

There are no "minor leaks" on a braking system.... To function properly, it needs to be absolutely leak free.

I did NOT bench bleed last time I emptied my brake system. I did pressure bleeding and it's been working great since.

You were lucky.

Nope. Emptied it twice.

I really do recommend (make it or buy it) a pressure bleeder.