[1st65]

I just bought a 65 GP with a 421 from my father in-law . It has the 8 lug drums and the brakes seem soft and not able to stop the car when in drive . Is this an old fluid issue or is the master cylinder going bad ? Brake pads are in great shape . If it is a fluid issue what type of brake fluid should I use to replace the old stuff .

[Stuart]

Could be a failing master cylinder, but I think the first step should be flushing and bleeding the fluid. Unless you know some other type is in there now, it most likely has DOT3 fluid. Also, check to see if the brakes shoes are adjusted properly; they're supposed to be self adjusting but the adjusters may be nonfunctional or missing.

[1st65]

Thanks for the help I’m new to this .

[salem1912]

You came to the right spot. Like Stuart said start with the basic stuff. How does the fluid look, adjust up the shoe's. Will if pump up with a few quick pumps of the pedal? Also you can go down to specific information on big car help section. Welcome to PY and post up some pictures!
https://forums.maxperformanceinc.com...play.php?f=428

[limejudge69]

Don't overlook internally failed rubber brake hoses. They are not as easy to diagnose as the more common issues (master cyl/wheel cyl etc) but are common on older vehicles

[mgarblik]

Does your Grand Prix have manual brakes or power brakes? That makes a big difference in how the brakes "feel", even when working correctly.

[BILL BOWMAN1]

Like Stewart said, start with the easy stuff. Fresh juice and a good bleed. Then I would say the master if that doesn’t help.

[1st65]

It has power brakes and will have some pictures as soon as it gets down to Georgia it’s been sitting in my father in laws garage for 25 years. It’s all original and I know they didn’t make a 65 convertible but that’s what it is . Everything on it is GP . Should have it this week .

[stevep]

Wheel cylinders may be bad too.

If it has been sitting that long, replace the master cylinder, 4 wheel cylinders and the 3 hoses.

[stevep]

Originally Posted by 1st65

It has power brakes and will have some pictures as soon as it gets down to Georgia it’s been sitting in my father in laws garage for 25 years. It’s all original and I know they didn’t make a 65 convertible but that’s what it is . Everything on it is GP . Should have it this week .

I think that I may have seen this car at a POCI convention.

Does the VIN start with 25267?

[geeteeohguy]

Originally Posted by stevep

Wheel cylinders may be bad too.

If it has been sitting that long, replace the master cylinder, 4 wheel cylinders and the 3 hoses.

THIS^^^. If it's been sitting that long, it will need all of the above. Not expensive. I did the '61 Chevy and the '66 GTO with parts from Rock Auto. Not expensive.

[mgarblik]

As a way to help you diagnose the brakes....... when the hydraulics are good and the shoes adjusted properly, the brake pedal will be very hard with the engine not running and the vacuum out of the power booster. Should only drop about 1" when you push the pedal hard. If it drops low or continues to drop with steady pressure you have a leak or a failing master cylinder. As mentioned, all the parts are available and cheap.

As for what the car actually is, most likely a Catalina convertible. It was common for owners to change out the grilles, and taillight panel and make many full size Pontiac's "Grand Prix". I have a friend with a 66 Bonneville convertible, "Grand Prix". I have seen dozens of them. VIN will tell you right away or the title.

[1965gp]

Agree on wheel cylinders - even after a year or two they seem to need to be replaced.

[1st65]

The vin does start with 25267 . I will check out rock auto

[mgarblik]

Catalina convertible, a great car. Should be pretty easy to sort out the brakes and then have some fun with the car. Lots of people can help you here if needed.

[1st65]

3 hoses not 4 ? Does anyone have a parts list on what I need to buy for the brakes ? Like part #’s . Thanks everyone for the help hopefully I get the car this week so I can start on the brakes .

[salem1912]

Yep three, older cars only had one for the rear.

[mgarblik]

Originally Posted by 1st65

3 hoses not 4 ? Does anyone have a parts list on what I need to buy for the brakes ? Like part #’s . Thanks everyone for the help hopefully I get the car this week so I can start on the brakes .

Rock Auto.com has a great on-line catalog system IMO for the kinds of stuff you need. Just plug in year make and model and everything they have available is listed, some with pictures. They also list the parts by price and quality level so you can get what you want. Heck my NAPA store uses the Rock Auto site for look-up all the time because the NAPA corporate software is terrible.

[stevep]

Originally Posted by 1st65

3 hoses not 4 ? Does anyone have a parts list on what I need to buy for the brakes ? Like part #’s . Thanks everyone for the help hopefully I get the car this week so I can start on the brakes .

If you are doing all the hydraulics, flush the metal lines out and use Silicone brake fluid.
I do it to my customer.s and my cars.