[jmar]

Is there a factory brake guru out there? I have a '69 Camaro SS. I am quite sure it was originally a SB 350 with Muncie 4 spd. It has front disc brakes that are GM factory from what I can tell so far. The brake pedal also has the chrome bezel and pad that says "Disc Brake".

Now the car has a BB 396 compliments of 2 owners ago. Unfortunately, the guy I bought it from owned it for less than a year and didn't know much about the car (he said). Believe it or not, he told me that the guy he bought it from told him all about the mods he did and had receipts for everything, ... but the guy I bought the car from threw everything away!!! Arghhhh! I can tell it's a 396 from a '67-8 Chevelle according to the engine block code, and the alternator is mounted on the driver's side. It has an Edelbrock 750 cfm electric choke, RPM Performer dual plane intake, 1-7/8" headers, 2-1/2" aluminized flowmaster exhaust, trick air shocks in rear, slapper bars, and Garbriels.

So, anyway, my problem is that the "go" is real good, but the "whoa" needs some tuning. When I am going 35-40 mph and have to hit the brakes, things get very touchy. The car will nose dive, the rear comes up as expected, the rear brakes lock up, and the car makes a big screeching noise and often slips sideways... not the coolest demonstration of stopping power!

So, I have basically 2 questions at this point in time: 1) If the car still has SB front coil springs, then maybe I am nosediving too much given I now have a BB, so maybe this unweights the car more than the SB springs can handle; and, 2) I don't seem to have a brake pressure proportioning valve installed; the car should have one given it has disc front, drum rears.

I have a GM assembly manual. It seems to indicate that a V-8 engine installation with disc fronts had a proportioning valve mounted on the frame rail at about the location just under the driver's door. I don't see anything under there.

Does anyone know what the factory brake setup should be on this car? (It has power brakes; disc front/drum rear.) Is there a proportioning valve that is actually part of a "combination valve" mounted to the master cylinder?

Do you think an aftermarket adjustable proportioning valve would let me adjust the pressure to the rears to eliminate the early lockup of the rear drums in "panic" braking?

Do you think that installing BB front springs will help significantly? (I know an old racer's trick is to use light coils in front, even 6 cylinder coils, to help weight transfer during launch. But I need better "whoa".)

Thanks for reading this long post. Hope this generates some feedback and interest amongst Camaro enthusiasts!

Thanks.
Jim

[1st & 2nd GENGuy]

The location you described is where my proportioning valve was. I replaced mine with an aftermarket adjustable (put it by the master cylinder) when I put rear discs on.

I would change the springs.

Make sure your back brake shoes are adjusted correctly.

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68SS ZZ4, 4sp T-10, 12 bolt, getting painted

78Z28, 330hp vortec, TH350, 10 bolt (just finished)

[davidpozzi]

Get an adjustable proportioning valve and get stiffer front springs. Adjust the valve by starting with the rear too high in pressure. Then make repeated stops gradually reducing the rear pressure. When the fronts start to lock first you are done. This way you will have the max amount of rear braking to help get you stopped. You may want to reduce the rear pressure further after driving under various conditions, like rain, etc.

Small blocks with air, and Big Blocks got the under the frame proportioning valve origonally.

[jmar]

Thanks for the great information. I now have a couple more follow up questions:
My car now sits level and looks good with my P22560R15 tires on 15" Rally rims.
If I go to stiffer springs, will this raise the front, or will the right height be the same, only stiffer. Only stiffer is what I want. What spring rate should I look for? What's a good source for 69 Camaro BB springs?

Also, David, you said the SB w/AC and BB cars came with proportioning valves... what about SB w/o AC but with front disc brakes? Any info on that factory combo?

Thanks again.
Jim

[1st & 2nd GENGuy]

New springs will probally change your height. I believe all disc/drum combinations had proportioning valves.

By the way proportioning vavles (good adjustable ones) are not cheap.

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68SS ZZ4, 4sp T-10, 12 bolt, getting painted

78Z28, 330hp vortec, TH350, 10 bolt (just finished)

[This message has been edited by 1st & 2nd GENGuy (edited 02-19-2000).]

[snakedr]

jmar,
69 Camaro with ss, z28 or big block should be equipped with 1 metering block, this is below the master cyl and contains the brake warnig light switch. 1 residual pressure valve below master cylinder and almost against the power booster(this has a switch that should be depressed during bleeding)this delays pressure to front brakes to allow the drums to over come spring tension for even brake application. 1 proportioning valve on frame rail. First genaration cars do not have combination metering blocks and proportioning valves. With all that said you are not configured correctly for all that weight. After market prop valve may be a good start. Shop carefully I have seen prices from $50-200 for the same p/n valve.

[Art Rasmussen]

It is not a good idea to use an adjustable proportioning valve alone with a disc drum setup.
A combination valve is the safest way to go. These valves have both a proportioning valve AND a hold off valve.
The need for these two valves arises from the differences in the way that discs and drums work.
The discs need more pressure to operate which is why the rear brakes will lock up without a proportioning valve to restrict their pressure.
At the same time the caliper's pads are always in contact with the rotor (unless you have some VERY expensive racing calipers) while the shoes in the rear drums are retracted by the springs. Consequently the calipers begin to apply pressure to the rotor immediately while the drums have to overcome this spring pressure first. In slippery conditions this can cause the front brakes to lock up first and so the hold off valve delays the application of the front brakes to compensate.
Art Rasmussen
Art Rasmussen Design and Fabrication, Inc. WWW.HOTRODDINGTODAY.COM

[davidpozzi]

Hi to Art Rasmussen, I like your stuff! Any here in Central California?

All disc brake cars had the proportioning valve mounted on the frame too.
Art is right about the hold back or metering valve. The metering valve holds back delivery of pressure to the front discs until about 30 to 40 lbs is reached, there is a rubber diaphram on the end of the valve that you depress when pressure bleeding the brakes. This disables the metering function and allows the low pressure bleeder to send fluid to the front calipers.

The early camaros had the brake light switch, metering valve, and proportioning valves all separate. Around 1970 they combined these three valves into one "combination valve" It also functioned as a T fitting for the front brake lines. You could run the old separate type brake light switch, metering valve, and an adjustable proportioning valve, without trouble.
I have seen some four speed front disc Camaros without the Metering valve, I believe it is needed more with the automatic transmission Camaros, during choke operation the fast idle (2200 rpm factory spec fast idle cam) would be driving the rear wheels, even while braking. With an automatic trans and front discs the fronts would tend to grab and lock with out the metering valve.

If you go with the Combination valve, you must get the right one for your car or you will have an incorrect proportioning valve setting for your car. Any other mods such as heavier engine, different wheel size/type, alignment, suspension geometry, spring rate, type or size caliper or rotor, will change the needed proportioning. You want to avoid rear lock up as it will cause you to spin out under very hard braking. All factory systems favor front brake bias, so if you brake too hard (to the point of lock up) you will plow straight ahead and not spin into an oncoming lane and have a head on collision.

This thinking also was incorporated into the front suspension design of the 60's. The front end was actually designed to plow or understeer under sudden swerves etc, and keep you in your lane. All in the interest of "Safety"!

[jmar]

Thank you all very much for the detailed information on various 1st gen Camaro braking setups. I now have a lot more information to work with.
I will trace out and identify my brake system using the information that has been posted. I already searched the frame rail under the driver's side and can not find a proportioning valve! I will search by the master cylinder and try to identify the metering valve and hold off valve. Everything looks stock from what I can tell so far, so I should be able to find things. I'll post my findings once I have this job figured out so others can benefit from what I find.
What do you think about an adjustable proportioning valve that has a pressure gage attached? Gimmick? Useful? Where would such a valve be mounted? Up by the master cylinder?
Anyway, I look forward to investigating further. Anything anyone else can think of will be appreciated.
And, just to ask again, does anyone know what the coil spring rating should be for a '69BB Camaro? Who has good springs?
Thanks.
Jim
Jim

[ppalomaki]

I just took a proportioning valve off of a 67 with factory air. It is the one that goes on the driver's side at the back end of the subframe. Is this the same valve that was used on big block cars? I don't know what its worth but I am willing to sell it for a fair price.

[penguinjohn]

does anyone have any pictures that detail the differences between these blocks? i have a metering block but no proportioning valve on the frame and am considering an adjustable proportioning valve. should this be located before or after the metering block? for reference purposes, i am in the same position as jmar (68 bb disc/drum). if anyone has a picture or two that they could post to help me out, i would really appreciate it. thanks.

[davidpozzi]

Use the adjustable prop valve put it in the rear line where it comes out of the brake warning switch block.
If you put it before the block the brake warning light will come on due to unequal pressure seen by the switch.

The factory proportioning valve is brass and rectangular, about 3/4 X 3/4 X 1 1/4.

I don't know about the differences between prop valves used on small block cars and big block ones, I'd suspect they are the same.
Make sure you have good shocks.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer



[This message has been edited by davidpozzi (edited 01-16-2001).]