Nova brakes adequate for 1947 Plymouth?

[kbuhagiar]

Hello, folks,

Hope all out there are doing well on this solemn day of remembrance.

Our 1947 Plymouth Special Deluxe 2-door coupe street rod is equipped with the front disk and rear drum brakes from a 1972 Nova. The MC is a Corvette-style model, with in-line residual valves (2lb front and 10lb rear), bolted to a 8" dual-diaphragm power booster, mounted under the floorboards.

After we purchased the car I noticed some difficulty with the brakes. I found that the power booster was defective and replaced it. A substantial improvement in braking capability has been noted, enough so that my wife can now comfortably drive the car. However, I think the brakes can be better; I have noticed what I suspect to be a bit of brake fade when going down a long hill. To me, this would indicate that perhaps the rear brakes are doing more work than they should, and that the brake system is unbalanced.

Three questions:

1) There is no combination or proportional valve installed on the brake system - could this be an issue, and should I install one?

2) Being as how the MC is the Corvette-style, with both front and rear reservoirs of equal dimensions, would it make a difference how the brake lines are plumbed into the MC (i.e. does it make a difference whether the front circuit is plumbed into the front or rear reservoir)?

3) I have had discussions with some other rodders who have questioned whether the 72 Nova discs are adequate for a car as heavy as the Plymouth (and my initial argument is that, by 1972, the Nova was up to around 3200lbs curb weight) - so, in your esteemed opinions, are the Nova brakes adequate, or should I consider upgrade options?

As always, thank in advance for your assistance and support!

Edited September 11, 2010 by kbuhagiar

[TodFitch]

...I have noticed what I suspect to be a bit of brake fade when going down a long hill. ...

I suspect a bit of failure to downshift when going down a long hill. But then I'm stuck in the past with tiny drum brakes on my 2600 lb vehicle.

Seems like the Nova would be about the same weight as the P15 so I would think that the brakes would be adequate for 1972 standards which are not as good as now. So I am wondering if you are expecting 2010 performance from a 28 year old design.

[p15-1948]

My 48 business coupe has Omega (Nova) drum front and rear. These brakes are adequate for my ride.

But, saying that, I plan to upgrade to discs up front, already have the spindles. Discs will add 7/16 inch width on each side from the drum setup.

I'd think not having a proportioning valve would be a problem. It's been awhile since I did some research on this, but one or the other require quite a bit more pressure to activate, hence the proportioning valve.

You probably need to do a little more research on this issue, good luck upgrading the system.

Mike

[suntennis]

I am not an expert on this, but it my understanding that the purpose of the proportioning valve is to balance the braking of front and rear brakes. One way to test this would be to drive the car like to an empty parking lot and lock up the brakes at about 30mph. If only the front tires skid, then the rear brakes are not helping much. I think the valves on street rods are adjustable. Look through the internet, you should be able to find out how to adjust the valve.

[kbuhagiar]

I am not an expert on this, but it my understanding that the purpose of the proportioning valve is to balance the braking of front and rear brakes. One way to test this would be to drive the car like to an empty parking lot and lock up the brakes at about 30mph. If only the front tires skid, then the rear brakes are not helping much. I think the valves on street rods are adjustable. Look through the internet, you should be able to find out how to adjust the valve.

Good point. I think I'll find an empty parking lot tomorrow and do some testing.

[PatS....]

I plumbed a 74 Nova combination valve into may old 50 Dodge with front disc kit and Cordoba rear end back in the early 90's.

I used the Nova because of the similar weight.

I didn't notice any fade and the back brakes would lock up before the fronts to prevent "dive"

[chopt50wgn]

When running front discs and rear drums it is mandatory to use a proportioning valve. There are companies like Wilwood and others that sell them and can be adjusted for the proper braking.

[Robert Horne]

On my 38 Plymouth Couple, there is no proportion valve. The front wheel cylinders are larger than the rear wheel cylinders, which should put more a little more stopping power on the front, than on the rear, and front and rear shoes are the same size. All 8 shoes are the same size. Each wheel cylinder has a different cup size from front shoe to back shoe. With any brake system of disc front, drum rear, one should have a proportion valve to get the proper balance of a little more stopping power on the front. Good braking is mostly about balance.