Hey all, just some random questions for an early build 69. I am pretty sure the little paper tag on booster check valve is CB for power disc, but what tag would have been used for 4 drum power brakes?
Also, what specs/color was the throttle return spring for a 2-bbl? Anyone with a pic? Thanks!
It's CU for power discs, CG for power drums.
thanks Kurt!
Ok, here is my 1st attempt at the paper booster tag. font is pretty close IMO. I kinda guessed at the size (7/8"x 1 1/4") seem right to me.
I hope to dial in my 2GV spring options and post another pic as soon as I locate a spare coil bracket :sigh:
Here is a pic of the check valve tag I made. How close did I get it?
Kurt, btw, my car came with 4 drum non-power of course. I added the power MC/booster for safety. Still does not stop as well as discs. Oh well.
OK, for the carb springs, I have two candidates (after I found my bracket).
I skinny one and larger one. Which is more correct? Thx
Quote from: KevinW on March 15, 2025, 10:52:00 AMI added the power MC/booster for safety. Still does not stop as well as discs. Oh well.
The drums new are 9.5" inside diameter with a discard diameter of 9.560". (Some sources say 9.590".)
For the drums to work effectively and as designed it is absolutely necessary that you:
• don't exceed the 9.560" allowable inside diameter (so that the shoes don't have to move excessively
• on the front brakes - install the larger (longer and somewhat wider) shoe to the rear and the smaller shoe to the front
• ensure that you have the correct residual pressure valves in the master cylinder outlet ports.
Richard
Quote from: KevinW on March 15, 2025, 12:30:13 PMI have two candidates (after I found my bracket).
I skinny one and larger one. Which is more correct? Thx
My ride has the base 327/210 hp engine which has the small (1-1/4") bore Rochester 2GV 2 Bbl. The return spring on mine is more like the "skinny" one you show.
Richard
Thanks Richard! Skinny spring is what I will use!
On the brakes, I pull off the drums every spring to give them a clean and adjust. I will look into what you posted. thx
For the drums to work effectively and as designed it is absolutely necessary that you:
Upgrade to front disc.
Funny! I have thought about it, but with my Drum only rims, I would have to swap those out too. Unless I got the Right stuff 14" drum to disc kit. Money, Money, Money :)
I don't see a problem using drum brakes on your Camaro as properly maintained, they are okay for normal street driving.
Thx! Yes, I inspect/clean/adjust them every spring. And plan my stops. Twice I had panic stops and the brakes lockup and fade quickly! but I stay as alert as possible!
Another 2GV mystery: I have two 2GV carbs. Exactly the same except the vent cover is slightly different. One has a full cover, the other a cover with a cutout. I looked at the CRG report http://www.camaros.org/carb.shtml and the pics of 68 and 69 had the cutout, but the 67 was not in frame. ps, I have only one carb tag 7029110 CH from 68, but not sure which carb it came off of.
Check out Richard Petty winning at Riverside in 1969. They were still using drum brakes.
https://www.google.com/search?q=nascar+1969+riverside+raceway&sca_esv=c31d1b2737bb79d7&source=hp&ei=XhrXZ6y4DMbHkPIPnqqz0QM&iflsig=ACkRmUkAAAAAZ9cobtWpl42JEVqN5AR_dY-j3CGOy3sT&oq=nascar+1969+river&gs_lp=Egdnd3Mtd2l6IhFuYXNjYXIgMTk2OSByaXZlcioCCAEyBRAhGKABMgUQIRigATIFECEYoAEyBRAhGKABMgUQIRigATIFECEYnwUyBRAhGJ8FMgUQIRifBTIFECEYnwUyBRAhGJ8FSPJjUABYqUZwAHgAkAEAmAGZAaAB7wqqAQQxNC4zuAEByAEA-AEBmAIRoAKjDMICCxAuGIAEGLEDGIMBwgILEAAYgAQYsQMYgwHCAgUQABiABMICERAuGIAEGLEDGNEDGIMBGMcBwgIIEC4YgAQYsQPCAggQLhiABBjUAsICERAuGIAEGLEDGIMBGNQCGIoFwgIOEC4YgAQYsQMY0QMYxwHCAg4QLhiABBixAxiDARiKBcICCBAAGIAEGLEDwgIOEAAYgAQYsQMYgwEYigXCAgQQABgDwgIFEC4YgATCAggQABgWGAoYHsICBhAAGBYYHsICCxAAGIAEGIYDGIoFwgIIEAAYgAQYogTCAgUQABjvBZgDAJIHBDEzLjSgB6CiAQ&sclient=gws-wiz#fpstate=ive&vld=cid:8a5147d4,vid:_DmuONVqSq4,st:0
Quote from: rich69rs on March 15, 2025, 02:14:33 PM
• ensure that you have the correct residual pressure valves in the master cylinder outlet ports.
Richard
Richard, so what does a factory residual pressure valve look like? I pulled the brass seat out of an old drum master cyl (rear port) and there was nothing there! Now I am confused.
I have power drums on my 66 GTO and my 64 corvette. Not as good as disc but they work well for my driving. Had them on my 69 Camaro convertible and they did not seem to work as well. Maybe just not adjusted right.
Quote from: KevinW on March 16, 2025, 03:38:11 PMRichard, so what does a factory residual pressure valve look like? I pulled the brass seat out of an old drum master cyl (rear port) and there was nothing there! Now I am confused.
The residual pressure valve & spring should be behind the seat. Refer to the green highlighted text in the 1st & 2nd attachments and middle picture, left column, 2nd attachment. When you pulled the seat out, it should have been there.
"Another variable at the master cylinder outlets is the use of check valves. They are installed under the tube seats in outlets which are to be connected to drum brakes. The retractor springs in drum brakes tend to force the fluid back into the master cylinder. The function of the check valves is to maintain a line pressure of 8 to 16 psi to keep drum brakes ready for quick responses."Also refer to:
http://www.camaros.org/brakevalve.shtml#rpv
A general FYI - if you ever find yourself in the need of a replacement MC and you try to source one from any parts source - the residual pressure valves may not be there and the folks at the parts house probably won't know if you ask. Consequently, my suggestion would be to rebuild a correct MC as opposed to trying to replace it. Rebuilding it is not difficult at all to do.
Richard
Different master cylinders were used for Camaros with manual and power drum brakes per CRG as there were bleed valves used on the master cylinder for power drum brakes:
http://www.camaros.org/suspen.shtml#Brakecomp
I pulled both seats out of an MD drum master, no valves. Next I will try a 310 BS master.
Quote from: GMAD_Van Nuys on March 17, 2025, 07:05:18 PM
Different master cylinders were used for Camaros with manual and power drum brakes per CRG as there were bleed valves used on the master cylinder for power drum brakes:
http://www.camaros.org/suspen.shtml#Brakecomp
Yes, power assist master cylinders are mounted at an angle with trapped air pockets necessitating the need for bleed valves - but all drum brake master cylinders be they manual or power assist have residual pressure valves.
An interesting sidebar point from CRG report......power assist drum brake master cylinder is "usually" stamped BS, however......
"GM documentation confirms that drum brake master cylinders are BS code and most drum brake master cylinders are coded BS. But a limited number have been observed with the CT code, in both manual and power drum applications. The CT code was used on drum brake applications on Pontiac and Buick vehicles. It is presumed that the CT part was used as a substitute during a parts shortage that and the differences between the BS and CT master cylinders are minor."The power assist drum brake master cylinder in my '69 RS (Norwood 01C) is a "CT" stamped master cylinder.
Richard