9" Double Diaphragm Brake Booster Differences Between Years

Sweet_Johnny

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I'm looking to replace the power brake booster and master cylinder on my '78 Cutlass Supreme and have found a few options to choose from but am unsure of the differences between them. I've decided to go with the right hand drive S10 master cylinder with a 1" straight bore and a replacement 9" dual diaphragm booster because both of mine leak and I'll be running 2.75" bore calipers on the front. No mods for the rear have been chosen as of yet.

With very little research I found that the booster for 1978 is somehow different than the one listed for '81, and there's a third model listed when I search for 1985. The boosters shown are the same across makes though- Olds or Chevy, Monte or El Camino doesn't seem to matter. I chose '85 for no particular reason but '82 - up are coming up the same.

For '78 I'm seeing Cardone 5471201

For '81: Cardone 5471271

For '85: Cardone 5471243

I know that '78 had different rotors and outer wheel bearings, and that the low drag calipers and metric wheel stud threads came about in '82 but what would that have to do with anything? I could see the '82 and up models having metric threaded booster studs instead of SAE but other than that I can't think of anything unless the rods are different.

I think the last time I replaced a master cylinder was nearly 25 years ago. Can anyone shed some light on this for me please?
 
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Sweet_Johnny

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Guess I found the answer right here on the forum.

 
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gnvair

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I'm not sure what brake set up you are running. I have a 78 with a stock dual diaphragm booster with the 1" bore Buick Riviera master cylinder. I run stock calipers on the front and the Blazer discs on the rear. I also use a disc brake specific proportioning valve. This has worked well for me. Calipers with larger pistons will need a larger bore than 1" or you will have a long pedal travel that will grab close to the floor.
 
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Sweet_Johnny

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I'm not sure what brake set up you are running. I have a 78 with a stock dual diaphragm booster with the 1" bore Buick Riviera master cylinder. I run stock calipers on the front and the Blazer discs on the rear. I also use a disc brake specific proportioning valve. This has worked well for me. Calipers with larger pistons will need a larger bore than 1" or you will have a long pedal travel that will grab close to the floor.
I'm putting together a setup based upon what I've read from you, TURNA, UNGN, malibudave, and a few others over many threads, years, and even multiple forums. From what I've read, the 1" straight bore R.H. drive S10 Blazer master cylinder should work alright with my 2.75" bore single piston Speedway front calipers as long as I keep the drums out back. If I swap those to discs it's my understanding that I'll require a master cylinder bore of 1.25" since disc brake calipers use so much more fluid than drums, and will also therefore require a larger than stock master cylinder reservoir.

The 1" bore is a bit on the small side for an upgrade but Dave swears it's a tried and true setup that works well, especially when paired with braided stainless lines that decrease the pressure loss and ensure the fluid goes to the brakes instead of simply swelling the hoses. I don't know him or any of you guys personally, but it appears that you're all quite knowledgeable and experienced when it comes to the G Body as well as mechanics in general so I'm inclined to believe you. This is especially true when more than one of you agree on something.

The booster I purchased is a new unit for an '85 Monte, SKP brand SK5471243. SKP may be cheap but I read too many bad reviews for Cardone. The master cylinder is Raybestos MC390572, paired with Russell 692100 braided stainless lines and Speedway "Big Bore" Metric calipers, 910-31040. The calipers will get loaded with Power Stop carbon ceramic Z23-154 pads and squeeze upon drilled & slotted rotors from TRQ, part BRA74842. As you undoubtedly know the '78 is special so this necessitates a spindle and bearing swap as well, and I'll list all of those associated part numbers in my build thread when I complete the swap since I'll also be replacing the entire front suspension. I'm hoping to accomplish this task next Sunday and Monday.

I've secured many other parts not worth mentioning here, but do you see anything wrong with the list of parts I have? I researched the heck out of it so I could replace everything but one time, and even purchased all new fasteners and dust shields. Based upon my reading I'm confident that this setup will satisfy but I'm always open to input from people who've already been there.

Everyone is encouraged to chime in- if I'm making mistakes please point them out so I can address them.
 
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