Blazer booster to go with Blazer master?

Squag27

Not-quite-so-new-guy
Jun 23, 2021
13
3
West Palm Beach FL
I'm in the middle of swapping out the front and rear brakes for a set from an '01 Blazer and while I know plenty of people have used a RHD Blazer master cylinder, has anyone used the brake booster to go with it? Is it even needed? I basically got the booster for free from the parts car I got the brakes from and I'm just curious if it's worth the hassle of pulling the old one out of my '82 Elco.
 

malibudave

Greasemonkey
Supporting Member
Mar 12, 2010
187
43
Houston, TX
The bolt pattern on the S10 booster is a little shorter that the G-body, so the holes in the firewall and maybe the brake pedal assembly bracket may need to be modified. The s10 push rod will also be about two inches longer than a G-body, so it will have to be shortened.

If you want the best booster, go with a 1990 B-Body 12" dual diaphram booster, but I would also upsize the master cylinder to a 1.125" bore to go along with it. The 1.0" bore master cylinder may make your brake very sensitive to lockup without the ability to modulate your brakes well when using a B-Body booster.


If you add the 1.0" bore to your stock G-Body booster, you should be OK as the g-body booster will take some of the sensitivity out of braking.
 
  • Like
Reactions: 4 users

81cutlass

Comic Book Super Hero
Feb 16, 2009
3,519
113
Western MN
The RHD s10 master requires a 'late' style booster. 78-81 uses a cast iron master and has a small pilot for the master and 84-87 uses a late style booster with a large pilot and aluminum master.

82/83 is a transition years and I am not sure what style you have. To use a RHD s10 master you need a late style booster.

If your car had an aluminum master the S10 style will fit. Not much benefit to swap to the s10 booster.
 
  • Like
Reactions: 1 user

Squag27

Not-quite-so-new-guy
Thread starter
Jun 23, 2021
13
3
West Palm Beach FL
The RHD s10 master requires a 'late' style booster. 78-81 uses a cast iron master and has a small pilot for the master and 84-87 uses a late style booster with a large pilot and aluminum master.

82/83 is a transition years and I am not sure what style you have. To use a RHD s10 master you need a late style booster.

If your car had an aluminum master the S10 style will fit. Not much benefit to swap to the s10 booster.
My '82 does have an aluminum master currently so hopefully I should be all set then,
 

gearheaddrew

Apprentice
Oct 29, 2019
60
33
Bay City MI
The RHD s10 master requires a 'late' style booster. 78-81 uses a cast iron master and has a small pilot for the master and 84-87 uses a late style booster with a large pilot and aluminum master.

82/83 is a transition years and I am not sure what style you have. To use a RHD s10 master you need a late style booster.

If your car had an aluminum master the S10 style will fit. Not much benefit to swap to the s10 booster.
What do you mean by pilot? I bolted the RHD s10 master on my 78 booster. Sounds like I need to get a booster from an s10 or later year Gbody.
 

Streetbu

Know it all, that doesn't
Supporting Member
May 22, 2011
2,644
113
Central NY
Just bolted my RHD master to my '78 booster with no issues... 🤷‍♂️
 
  • Like
Reactions: 1 user

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
3,328
113
Upstate NY
What he means is the bore of the boosters changed in 1980 or 81. It became larger, so the early boosters cannot accept the later style master cylinder. A small bore master cylinder of increased volume for an early, small booster is one from an '80 Riviera. A common change of master cylinder for the later, larger bore booster is an A-body Wagon.

To answer the O's original question, the booster doesn't need to be upgraded for a brake upgrade. The smaller diameter booster, 8" I believe, is dual diaphragm as was standard issue on the HD model with big HP and/or towing capacity. The single diaphragm booster is larger diameter and much more of a pain to work around IMO.
 
Last edited:
  • Agree
  • Like
Reactions: 2 users

Squag27

Not-quite-so-new-guy
Thread starter
Jun 23, 2021
13
3
West Palm Beach FL
Well I haven't gotten the new calipers bled yet but I can at least confirm that the RHD master bolts up just fine to an '82 booster. I didn't bother swapping the boosters based on everyone's suggestions.
 
  • Like
Reactions: 1 user

malibudave

Greasemonkey
Supporting Member
Mar 12, 2010
187
43
Houston, TX
For GM master cylinders, there are strait bore and step bore designs.

For "G-Bodies" and S10s, the strait bore designs came on 1978-1981 "G-Bodies" and 1998-2004 S10s.

For G-Bodies and S10s, the step bore designs were from 1982-88 G-bodies and 1982-1997 for S10s.

Step bore master cylinders have two bore sizes for the front brakes to go along with the LOW drag front calipers that came from the factory. LOW drag calipers retracted the piston down into the bore a little further than a normal caliper Since the calipers are down inside the bore of the caliper a little further than a normal caliper, it needs more fluid volume to get the pad back up against the rotor. The step bore was designed to supply extra volume of fluid to the front calipers and once the internal pressures in the master cylinder exceeded say 100 lbft, then a circuit would switch to the smaller bore for pressure so you can easily stop your car. Rear calipers of GM vehicles were never LOW drag.

Since the volume bore of the step bore master cylinder is about 36mm (1.42"), the housing under the flange is about 1/2", or so, larger than a strait bore master cylinder. Because of this, it will not work on 1981 and earlier boosters because the vacuum booster were not designed to accept the larger housing. It will not work on 1998 and later S10s for the same reason.

A strait bore master cylinder will work on any of classic vacuum boosted GM vehicles, but a step bore master cylinder can only work on vacuum booster designed for step bore master cylinders.

In 1998, the S10s went to a strait, 1.0" bore master cylinder. On the LEFT HAND (regular) drive S10s, the outlets come out on the right side of the master and the outlet sizes are 1/2-20 inverted flare for both outlets. The RIGHT HAND drive 1998 and up S10s, had the same 1.0" bore master cylinder, but the outlets came out on the left side, like the G-body, and had the same outlet sizes as the G-body (1/2-20, rear port to front brakes and 9/16-18, front port to rear brakes).
 
  • Informative
Reactions: 1 users
G-Body Performance Upgrades

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

ContactAdmin@GBodyForum.comfor info on becoming a sponsor