moranj2

I'm trying to diagnose a hard brake pedal issue on a 1971 Cutlass S. I notice that the brake booster makes a groaning (kind of like a cow mooing) sound upon release of the brake pedal when the engine is off. I'm attaching a video recording of the sound.


Other information:

Brakes are disc in front, drum in rear. Engine vacuum is now up to ~14-15

The car's BRAKE light was on when I got it. The rear brake circuit was closed by the proportioning valve. There is no leak, so I'm not sure why the rear circuit was so low on fluid. The pedal felt "normal" under these circumstances.

The brake system has been refilled with fluid and fully bled with good fluid flow at all four cylinders. Proportioning valve has been re-centered and the BRAKE light is out but now the pedal is very hard.

I have verified that the pushrod is in the correct lower hole on the pedal. There is some brake assist noticed when I put my foot down on the brake pedal and then start the engine with my foot on the pedal.

The booster does not appear to be stock and I don't know what brand it is. I'm attaching a photo of it.

Any thoughts appreciated.

Thanks in advance.

jaunty75

The pedal being hard suggests no vacuum assist. The moo-ing sound suggests a booster with a leak. Putting two and two together, I would replace the booster, especially since you know nothing about its history.

Kensey

You won't regret just putting a new one it. I just did on my 72 Delta 88, sooooo much better. It made a weird mow sound when you first pressed it down. It was working, but not 100%

droldsmorland

It could be a bad booster. But first verify the rubber push rod seal between the master cyl and booster is OK. Also look at the vacuum line and its fittings and the one way check valve that barbs into the rubber grommet on the booster, from the carb.

moranj2

Thanks to everyone for the suggestions so far. I haven't really had time to tinker around until today.

I pulled the master cylinder and found that there was significant leakage out the back of the piston bore.





I'm scrapping both the power booster and the master cylinder.

Seems there's all kinds of boosters and masters on the market. Was considering going with a remanufactured combo from Rock Auto:

https://www.rockauto.com/en/moreinfo...sn=443&jsn=443

Anyone with any experience with these? Would be open to suggestions for something better.

Thanks again.

oldcutlass

I bought the same booster separately from Napa and it went out in less than a year. Hopefully they will warranty the part and get me another. Things like this I tend to buy local just because if there is a problem its easier to deal with.

70sgeek

I recently went through the same m/c failure issue, necessitating the replacement of m/c and booster - ultimately went with a brand new Master Power Brakes m/c and 8" booster combo - works beautifully. I don't know that reman parts are necessarily any more failure-prone than new ones but I wasn't worried about retaining stock appearances. I agree though, local buying does have the advantage of local returns ...