1969 Z-28 pressure valve
 

do all 1969 Z-28's have the brake pressure valve on drivers side frame rail?

no

can u elaborate on that - and why please?

----I can understand your response!....Bill S

i understand the comment - and have looked for why that is, so I was looking to get better educated on this as i have a different understanding - but data is king in this industry.

appreciate the background if you can share WHY, not all 69Z's would not have this valve?

My January Z never had one

"The '67 Chassis Service Manual says it was used on Camaros with air conditioning, and the '69 manual says it was used on Camaros with 12-bolt rear axles; usage varied, and no precise pattern of options or equipment has been observed that would dictate its presence. "

Source: CRG https://www.camaros.org/brakevalve.shtml
Author: John Hinckley

:biggthumpup:

Don't forget, all the brake valves in the CRG report can be rebuilt. Kits available from Muscle Car Research: https://www.musclecarresearch.com/

I documented my rebuilds here: https://www.camaros.net/threads/1969...valves.483596/

My jL8 Z28 doesn't have one

The pressure regulator valve under the master had two functions. It delays the engagement of the front disc, so the car did not nose dive when brakes were applied and also provided 30-40 psi to the rear wheel cylinders. The ensured the rear drum shoes engaged prior to the front calipers.This applies to front disc, rear drum configuration.

Updated:
From CRG/ John Hinckley Brake valve report
Rear brake line pressure regulator mounted on subframe function:
"The valve limits the amount of hydraulic pressure, at a controlled rate, to the rear wheels in proportion to the amount of pressure to the front wheels. This action prevents the rear brakes from locking up before the full effective braking effort is produced by the front disc brakes."

Valve usage is not consistent between Norwood and Van Nuys either. There is no completely logical pattern based on CRG data collection. Chevrolet literature says one thing and data says something else.

Ask Mike Gibbons. Is it even necessary. 🤷

Steve,

The November 69 Chevrolet Service News quoted in John Z's CRG report was specifically about the 70 Nova with Disc Brakes. CSN called it a Pressure Regulating Valve. It prevented the rear brakes from locking up.

Eddie,

The Pressure Regulating Valve (3982304) was used on all 70 Novas with Disc/Drum brakes. The valve was on the subframe from the first part of 70 production. Later production is was under the master cylinder.

While researching this I noticed that the Camaro valve (3908326) looks just like 3982304. Parts books states that it was for:

67 with AC, (not sure why)
67-69 396 Except 4 Wheel Disc Brake,
68-69 350 Except 4 Wheel Disc Brake,
68-69 327 w/4-Speed Except 4 Wheel Disc Brake,

This would indicate that the cars came standard with Disc/Drum should get it. This was safety feature after all. Not only did the Nova get it in 70, but so did the Chevelle w/Disc Brakes. There were two Chevelle designs.

JL8 Z's wouldn't need it. 12 bolts axles generally went on cars with front disc bakes. Maybe the 302 in the Z did not necessitate such lockup protection. Other than that, it is a mystery why there is no completely logical pattern based on CRG data collection.

Greg.

There's more under this link:
https://www.camaros.org/suspen.shtml#valve
Some JL8 cars have the valve, btw.

Thank you guys, I see not definitive pattern for this - and unfortunately no real pattern either.

Recognize this was not my thread but Georges, i appreciate hearing the input and thoughts etc.

I was under the impression this was a pretty clear answer, especially for the 69Z cars, all had 12 bolts, boosters and masters with distribution valves and dump valves.

Obviously not.

Thanks again.....



I got it - there is conflicting info on what is right or wrong or no real definitive pattern for the application.

My 69 Z built late June does have the valve mounted on the subframe. Hope this helps!! Greg, my 70 L34 Nova does not have the valve on the subframe and is a January built car. I take it that the early Novas go up to November or December??

Precisely, Willow Run made several production changes at the end of 1969. Not having it on the subframe in January makes sense. What build week in January? I can compare with the database.

Greg

A topic that I have wondered about for a long time.
I was working with the understanding that all 69 Z28 & BB cars had them.
12 bolt applications makes sense- as does not required on JL8 cars.

However, my NOR 02B X77 does not have one- and have always wondered why.
Was thinking perhaps someone had replaced the subframe at some point in its early life.
Though it did appear to be quite unmolested & original when I completely disassembled & rebuilt the car in 2020.

Not to change the subject, but I realize that some cars came with the pressure release valve and some cars did not. My car is a 03D build and it has the valve. Did all the sub-frames coming down the assembly line have the hole for the provision for the valve.

^^
1968 LOS Z28
Subframe has provision No Valve:
I would hazard a guess that ALL sub frames were spec to have provisions i.e. holes for locating tang and self tapping screw for install of valve as needed.

From the usage info on CRG:
As noted above, the 69 NOR Z28's did not use it until mid-year, in the late January / early February timeframe.

Greg, my Nova was built on the 3rd week of January 1970.

Thanks, That is firmly after the change over.

Greg

My 69 Z and my 69 SS survivor nova did not have the valve. My 69 Z/28 still retains the original brake line from the booster to the rear end bracket. Both cars were November of 68 builds.

Salvatore,

As mentioned earlier, the pressure valve was introduced in 70 on the Nova. So wouldn't be on your 69.

Greg

For sure Greg. You know me as Sam.