Regarding power boosters, some have written that they are the same between drum and disk brakes. From the many boosters I have removed from 68-72 cars, all the drum boosters used a longer master cylinder pushrod than the disk units, making it impossible to mount a disk master to a drum booster. Does anyone know of a year for certain where the disk master will accomodate the longer pushrod? I could put some of these drum boosters to good use if I could find a disk master cylinder to fit!

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
TC member #493
Never forget Earnhardt!

Depends upon the year - As I understand it 1969/early 70 and earlier use the short pushrod and late/1970 and newer use the long pushrod. Doesn't matter disc or drum. a 69 Disc brake master cylinder uses the short pushrod and a 71 Disc brake master cylinder uses the long pushrod. The pushrods just pull out and I bought a new one from Master power brakes, my booster had a long rod and I needed a short for my disc brake 69. The disc master cylinder for the short pushrod has an Oval cap with 2 bails to hold it down, the Disc master cylinder for the long pushrod has a rectangular cap with a single bail to hold it down.

You should be able to use either booster and swap along for short according to what you need for your master cylinder

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Tom Donaldson
71' GMC Sprint

Bob,
what is that infomation based on? I have sold 4 disk brake conversions in the last month (one 70, one 71, two 72s) and dozens of 69-72 setups over the years. None ever had the master for the longer pushrod, whether round dual bail or square single bail cylinders. All of these disk boosters had the shorter rod, while the drum units had the longer one. I have yet to see a "long rod" disk master cylinder of these years, so I will still assume GM had things different between drums and disks to keep someone from putting on the wrong kind of master. Has anyone ever seen a "long rod" disk master cylinder, maybe on the 67/8 cars? For now I guess I will just shorten the rods in my drum boosters to match the disk ones.

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
TC member #493
Never forget Earnhardt!

FWIW
My 67 Elky power drum car had a long rod. Got a MC for long rod discs - I think it was a 'newer' (72+ ?) full size Chevy.
Phocks

Dave, I got my hands on a brand new never been used 1972 Chevrolet Parts and Accessories Catalog, effective August 1972. I will post the diff in the boosters as soon as I get a chance to read up. Next on the agenda will be the diff in steering shafts! My other parts book was printed in April of 83 and a ton of stuff isn't even listed in that book as parts were discontinued over the years.

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Never be afraid to try something new.
An amatuer built the Arc,
Professionals built the Titanic.
Team Chevelle Gold #33
ACES Member #02913
Chevelle Club of Michigan
Rode shotgun in the ONLY Z16 convertible made.

thanks Tom, this has been bugging me for a long time! I believe I have had some "long rod" disk masters from the 73 up cars, but by then most cars came with disks standard so there may have not been a need for two different rods. I am really trying to figure out for the 68-72 what years or setup used each booster.

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
TC member #493
Never forget Earnhardt!

Dave,
I think I have a spare short rod if you need one. I'll have to check. E-mail me if you need it.

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Tom Donaldson
71' GMC Sprint

I got my disc brake setup off a 71 Grand Prix and it had the long pushrod with a disc brake master cylinder. I still have the master cylinder and long pushrod, but didn't use it because I wanted the double bail M/C that was correct for my 69.

Tom,
was the Grand Prix booster the same externally and functionally as the A body booster? I am just wondering if because the Prix is considered a larger car maybe that is why it had the different setup. I still havent found an original chevelle disk booster with the longer rod, but it is good to know that I should be able to get a 71 GP master to use on the drum boosters I have.

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
TC member #493
Never forget Earnhardt!

Ok, the GM parts book shows a different part number for disc and drum brakes for 68 to 72. They also show a bunch of diff rods which is probably the only difference. I would think a Grand Prix would use the same booster as a Chevelle, someone with a Hollender catalog could answer that one.

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Never be afraid to try something new.
An amatuer built the Arc,
Professionals built the Titanic.
Team Chevelle Gold #33
ACES Member #02913
Chevelle Club of Michigan
Rode shotgun in the ONLY Z16 convertible made.

Sorry, it hiccup'd.

[This message has been edited by Bob M (edited 03-01-2001).]

Ok guys, I'm not an expert so don't shoot me, but this is what I have found out. Disk Brake master cylinders from 67 to 70 had the recessed hole for the long rod from the booster. 71 and on used the short rod. There is a big difference in master cylinder appearance from 67 to 70 depending on year and whether or not it was for disk or drum brakes.
Master cylinders for 67 to 68 disk brakes are tall and thin with an oval cover held on by two bails going from side to side.
Master cylinders for 69 to 70 disk brakes are short and wide with an oval cover held on by two bails going from side to side.
Master cylinders for 71 to 72 disk brakes use the short rod, and have a rectangular cover that is held on by one bail going from front to rear.
Master cylinders for 67 to 72 drum brake cars are tall and thin, have an oval cover that is held on by one bail going from front to rear. They also use the long rod.
One thing to note, just because you find a particuliar combination on a car does not mean that it is the way it came from the factory. A lot of things get changed over 30 years. A lot of boosters and master cylinders are taken from other GM cars such as Old Cutlas, etc. They do not necessarily have the same configurations as Chevelles. Assembly plants did not always use the correct parts depending on shortages, model year changeovers, etc.



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Bob Murray 66 Malibu
Greenfield, Indiana (Indianapolis)
http://www.chevelles.com/showroom/bobm_SC1 (http://www.chevelles.com/showroom/bobm_66malibu)
TC Gold #49
Aces #01941
NCOA #20838

[This message has been edited by Bob M (edited 03-01-2001).]