Swoopy

Hello all.
Driving the 71 Cutlass S (Swoopy) again and having a blast!
have a 350 stock with headers and a holly 600.
Rebuilt the holly long ago (recently cleaned with new float needles) and have had issues with gunk bypassing the filter and clogging the float needle, so getting a new filter and perhaps re-doing the lines. Flooded 3 times recently, twice at busy intersections and one on a side road. easy fix, but it did embarrass the boy!
Yup all 42 year old stuff. Garage kept last 26 years.
Decided to do a check as it was still running rough and slight miss.
Timing, dwell, set idle and check for leaks.
Adjusted a few to get in spec and it still had a slight miss and backfire that sounded like metal contact.
So turned it off to think and grab a beer...hmmmn
As I turned it off ...sisssssss...with volume than decreasing.
Check for vacuum and noted it was the brake booster.
disconected the booster and wala smooth as silk. I am amazed at the quality of the OLDS!
researched threads and noted that it may be the cup between MC and booster.
After a long post, here's the rub. How does one replace the rubber diaphram inside? Can it be done? it's only a diaphram and a MC seal right?
I have another 70 brake booster and MC so that may be a choice, but that has been sitting for years.
Thanks for the input.
hey Rob, still can't get the old pics of Swoopy from the X, Still working her.

Olds64

Rob, I've never heard of rebuilding a vacuum brake booster. I'm sure it can be done (since rebuilt units are available from the auto parts store). Check out Fusicks and Kanter for rebuilt/new units and rebuild kits. If there are kits available I'm sure Fusicks and Kanter carry them.

FWIW, I bought a rebuilt vacuum booster and master cylinder from a local auto parts store. It worked ok for about a year and then the master cylinder started to leak. I got a warranty replacement from the auto parts store and it's leaking again (after another year). When I return home I plan on getting my money back from the auto parts store (I still have the receipts and I don't think anymore are available through their distributor anyways). I will end up putting one on my 71 98 from Fusicks or Kanter. It might cost a bit more but they have good products and their customer service is top notch.

MDchanic

Full rebuild instructions for the booster are in the CSM, but if you already have a spare I'd try that first - they don't fail very often, so it's probably fine.

- Eric

brown7373

I had to replace the booster on my 72 shortly after I bought it in 2006. It started as a hiss when I shut it off, but otherwise, all was good. It progressed to a major vacuum leak so bad the car ran rough and was terrible at idle. I could see where the master cylinder was leaking (or had leaked) out the back, probably damaging the rubber in the booster. I sent it to Steve Gregorie for a rebuild and correct cad plating. Not a big deal if you have access to the rebuild parts and have the right tools.

droldsmorland

The hissing sound is likely the rubber seal between the booster & master cylinder.

Swoopy

Olds64- Thanks for the heads up on the poor quality units.
MDchanic- I'll give the swap a try since it is no cost and rarely go bad, cool.
Brown7373-I'll think about the Re-do from Steve Gregorie as other posts have recommended his work at a reasonable cost for a fine job.
Droldsmorland- I think that too. I believe Joe stated there is a cup seal to replace in other MC thread and that I could leave the MC attached and try to squeeze it in place.
Thanks all.
Oh and the reference to Rob. He asked about my handle and my reply was that a menacing owl was on the trunk prior to paint. The x has the photos and is difficult to get to.

joe_padavano

Just to clarify, you can leave the M/C brake lines attached, unbolt the M/C from the booster, and pull it forward far enough to change the seal without needing to bleed the brakes.

Lady72nRob71

Hey Swoop - long time no hear!
Glad you remembered those lost pics, cause I almost did.
It is time you get a police artist involved...

That seal can be changed and they are available somewhere.
Many people send their original boosters in for rebuild and replate and the rubber guts are replaced in the process. I had mine rebuilt and it looks and works like new.

Hope it goes well for ya!

Swoopy

Status report.
It was the MC seal to booster.
Thanks Joe as I did not have to disconnect or bleed brakes.
The seal had a tear by cup and there was some rust. A little elbow grease, WD40 and 2000 girt to clean and it was good.
MDchanic I removed the MC cup seal off the 70 MC and placed on 71. Worked like a charm.
I'm happy happy as Phil the master Duck would say!
The 70 olds it came from is sure different. The proportioning value is attached to the MC whereas the 71 was on the frame.
A few pics as I did not find any besides the corvette one Joe posted. I didn't findla many cup seals but a few MC repair kits.
Shot pics of the 70 MC and the cup seal.
Thanks again all.
Rob, I'll keep working her to get my pics, although its the least of my worries. But damn, give the man his history! I have many photos of the Frankenstein creation.
Thanks again all.
Oh my estimate of cup seal: 1 and 11/16 wide, 13/16 deep with a 1/8 top ring that sits in the MC.

Olds64

That's awsome that you got it fixed!

MDchanic

There you go!

Another example of an expensive repair avoided by replacing an easy-to-change part.

Glad you got it fixed!

- Eric

joe_padavano

1967-70 disc brake cars used a separate metering valve bolted below the M/C and the same distribution block as was used on drum brake cars. This was done to minimize the assembly line changes for what was then a somewhat rare option (disc brakes). Starting with the 1971 model year, disc brakes were becoming much more common, so GM decided to combine the proportioning valve function and the distribution block function into a single combination valve mounted to the frame. This reduced parts count and assembly touch labor costs, in addition to avoiding a whole bunch of line connections and potential leak points. The two designs are equivalent in function.

Swoopy

Joe my hats off to ya, good stuff. Very logic of GM.
Yup, drove around today, great breaks!
Easy pedal effort.
Ah, its nice to get so many thumbs up.
These olds attract attention.
Had a float needle clog at an intersection, prior. Under the hood several people asked if I needed help and I acknowledged their gallantry and said I got it just a clog needle. One gent said no big deal no worry, happens all the time. Good to have so many kind people about. Even the city cop pulled behind lights flashing and gave me a thumbs up.
Totally different view then driving the B2300, much more enjoyable.
Only a few months more before winter and salt hits the road, yuck.
Until than low humidity, great air, and good olds times.

joe_padavano

Glad that worked for you. One of the reasons I like to work on cars is the instant gratification. You have a car that doesn't work, you fix it, and it works, usually within a weekend. You feel like you've accomplished something. It's a far cry from my day job where I'm working on programs that might fly within five or ten years.