If you're like me, you've hated the feel of your stock brakes from day one. In my case, it literally was on day one, driving the SS right off the dealer lot in 1986. I even returned the car and complained, but was told "it's normal". The pedal has an extremely soft feeling, and hits the floor during panic stops. Even then, the SS barely stops, resulting in many unwanted close encounters with disaster.

After a bit of research here on good ol MonteCarloSS.com, I found that GM used a puney 12" single diaphram (aka pancake style) brake booster on all 1986 model Montes.. and on some other years. Later year (87-88) as well as some earlier year Montes got the 9" dual diaphram brake booster, which provides better performance and brake pedal feel. While I still plan on upgrading the remainder of the brake system, I decided to start with a swap out of the single diaphram with a 12" dual diaphram from a B-Body (1990 Caprice). You can use this same procedure to swap in a G-Body 9" Dual Diaphram.

Before we get started, a note about engine vacuum. For the brake booster to operate at peak performance, engine vacuum should be ideally at 18 inches. Booster performance drops off as engine vacuum drops. And typically, engine vacuum can drop off with engine performance upgrades. Use of a vacuum reservoir, or an auxillary vacuum pump can help recover brake booster performance.

Tools required: 15mm deep socket, at least a 12" extension, universal joint, ratchet, needle nose plyers, philips screwdriver, wrench to remove battery cable and an assistant.

Procedure

Disconnect the negative terminal of the battery. You'll be working under the dash, with wrenches in close proximity to the fuse panel and other wireing. Better safe than sorry later.

Take note of the location and configuration of all items in the vicinity of the brake booster. Here, a photo showing the 12" single diaphram booster as installed from the factory.


Next order of business is to remove the dash panel just below the steering column. 4 screws required to remove. This allows access to the pin at the top of the brake pedal.


Using the 15mm socket/ratchet, remove the self locking bolts holding the master cylinder to the brake booster. (Note the orientation of two brackets being held in place by each bolt, one holds the speedometer cable, the other holds a wire harness.) Remove the master cylinder from the booster and let it float, held up by the brake lines. Next remove the vacuum line from the check valve on the brake booster. Also route the various wire harnesses, vacuum and window washer lines to the rear of the brake booster.


The plunger of the brake booster is held in place at the top of the brake pedal by a washer and R-Clip shown below. The round part of the R-Clip should be pointed down. Using a pair of needle nose, grasp the rounded tip of the R-Clip and pull. The clip should easily come off.


Next, using the 15mm deep socket, extensions, universal joint and ratchet, remove the 4 self locking bolts under the dash holding the brake booster in place. Once removed, have an assistant help in the removal of the brake booster, rocking it back and forth while you remove the plunger from the pin at the top of the brake pedal. Care should be taken in the initial separation of the brake booster from the fire wall. There is a thin gasket which can be reused if not mangled during removal. I'm told these gaskets are available from a few vendors. I do not have further information however.


Once removed and placed next to the B-Body dual diaphram brake booster, you can see the obvious difference. Note the pin shown removed from the booter below. This pin is matched to the booster and is placed between the booster and master cylinder. Do not reuse the old pin. You must use the pin which came with the new booster. Below, the original 'pancake style' G-Body 12" single diaphram booster on the left, the new B-Body 12" dual diaphram on the right.


Below, the new B-Body 12" dual diaphram booster on the left, the original 'pancake style' G-Body 12" single diaphram booster on the right.


Reinstallation, like many things, is just the reverse order. Place the gasket on the new booster, insert it into the fire wall. Using an assistant to move the booster back and forth, place the booster plunger back onto the pin at the top of the brake pedal. Once on the pin, place the washer on the pin, and reinsert the R-Clip into the hole in the pin. Then secure the booster to the fire wall using the original 15 mm self locking nuts. Replace the dash panel with the 4 screws. Make sure the booster unique pin is placed in the hole in front of the booster, then position the master cylinder in place. Ensure the two original brackets holding the speedometer cable and wire harness are in place before tightening the two 15 mm self locking nuts for the master cylinder. Re-route the various wire harnesses, vacuum and window wash lines through the clip at the top of the booster.


Secure the vacuum line from the power booster filter to the booster check valve. While you're at it, I recommend replacing that power booster filter. If you're like me, you've not touched it in 25 years. It's about time for a new one. At under $7 a piece from AutoZone (HELP! section P/N 80195), there's no good reason not to replace the filter.

For this swap, I chose to purchase a remanufactured brake booster for a 1990 Chevy Caprice. The Cardone part number (used by most local auto parts stores) is P/N 54-71040. At AutoZone, this lists for $92.99 with a $10 core. Since you're not replacing a like item, the core doesn't apply, so a total of $102.99 for the item, with lifetime warranty. You can also purchase this booster paired with a B-Body Master Cylinder (P/N 50-1040) for $122.99 plus $20 core, or $142.99 total. I don't reocmmend using the B-Body master cylinder with the stock brake system, but this may be a viable option if you've already upgraded. Or, you certainly can go to your local bone yard and find a late 80's B-Body and pull this item. Also note: If you purchase a remanufactured unit, it will come in a rather unattractive gray tone. I spray painted mine with satin finish black Rustoleum.

While I haven't yet had the opportunity to go on a long drive with the new b-body booster, I can tell you the drive way pedal feel is dramatically better. The pedal responds with a firm feel that does not bottom out. I'll report back when I've had a chance to go on a drive. I think no matter what, it's a good first step (of many) in upgrading the stock brake system.

Special thanks to Bob (mmc427ss), PaulB (PB86SS/87LS), and Steve (TPI Monte SS) for their additional guidance prior to this swap.

I hope this helps. It is certainly a good upgrade to consider if you have a single diaphram (pancake style) booster. Good luck!

Is this a worthwhile upgrade for those of us who have the stock G-Body dual-diaphram boosters?

with a 3" bigger diaphragm, i think it would be a good upgrade, especially if you are going to further upgrade the brakes now or in the future

This looks like a good upgrade, I'm going to have to keep it in mind. Lots of B bodies at the local yard. Is there any specifc years, models we shoudl be looking for these on? Did some of the years that had these also get the single diafram?

Paul, please let us know if you see a improvement when you take it for a spin next

I think the b-body booster is a "must have" for any car with brake upgrades, especially if your car has the stock single diaphram unit. As for if it is an improvement over the dual g-body booster, I'm not sure how much, but surely it is. Maybe someone who has done that can share. I think if your brake system is stock with the dual g-body unit, it might not be that noticeable going with the b-body unit. As far as years for the b-body booster, the late 80's style generation worked for a few of us, not sure on specific year ranges unfortunately. I got mine off a junkyard Caprice with the composite headlights, so 88-90'ish I believe. I can concur with Paul C. with what a difference in brake feel it made .

What would you say about a 95 or 96 Caprice booster? A friend of mine is junking his wrecked one, and may not be needing it. Would that be the same as picture? and will it fit?

I would caution against using a later model B-Body (post 1990) booster only because I have not seen it used on a 4th Gen G-Body. Perhaps someone has definite experience one way or another. Since the B-Body went through a generational change in 1991, the configuration may not be compatable.

I did this swap when I changed my brakes to the 2 piston Vette calipers up front & LT1 discs out back, but along with the booster I used the master cylinder as well. I found out the hard way that not all B body master cylinders will work, some of them have metric fittings. If you go looking int he junk yard, you will want to use the one that has a "BW" decal on the master reservoir.

I descided to run passed the yard today & grab one of these. The first Caprice I looked at had a different booster, but was one of the composite headlight cars. I continued looking & came up on a couple wagons. All of them had the correct dual diafram unit pictured. The B body buicks also use them as well. Not sure about the Delta 88's & Parisiennes as I didn't come across any to check, but I would assume they use it as well. If your yard shopping for one, be sure to check those cars too.

I was curious to see the difference compaired with my factory equipped dual 9" car. Install was uneventful & went smoothly. I can say I did notice a difference in pedal feel, & throw. Pedal offers a slightly more confident feel & actually has a slight bit more travel. I would assume it's because the booster is now matched to the B body master I used with the LS1 swap. I actually prefer this as I was never 100% happy with how short the throw on the pedal was before.
Overall, for the $20 it cost me, I'd say it's a worthwhile mod.

I'm going to do the swap soon, after I get the brakes problem fixed. Will it jsut bolt right up with no mods?

B-bodies did come with a few different brake packages. Most are 12" but there were 11" rotors on a B when it was a lighter weight car, such as V6 equipped. Also Hydro boost was used on the Buick and Olds station wagons. When the 11" rotors were used the smaller rear drums, 9 1/2", were used.
Bob

When u say may not be compatible, u mean the 4 bolts lining up to fit and also the 2 bolts to fit the master cylinder? We are sorta stripping a 95 blazer. Im gonna see of the if the booster from it fits, maybe tomorrow if i get to it.

I bought a brand new GM MC for a early to mid 90's b-body and it was definitely different in how it mounted and/or the lines. I didn't keep details but I want to say the line fittings were different sizes, not sure on the physical mounting of it.

I wonder how different the backside clearance is on the single diaphragm g-body unit compared the the b-body unit. The stock single diaphragm booster barely clears the clutch master cylinder (IIRC, the bracket for the master touches the booster). I have the g-body dual unit from my parts car that I plan to install sometime, which will offer much more clearance, but I wonder if the b-body unit would fit.

Vehicles to look for

BUICK ELECTRA ESTATE WAGON (1981 - 1989)
BUICK ELECTRA LIMITED (1981 - 1984)
BUICK ELECTRA PARK AVENUE (1981 - 1984)
BUICK LESABRE 1981
BUICK LESABRE CUSTOM (1982 - 1985)
BUICK LESABRE ESTATE WAGON (1981 - 1990)
BUICK LESABRE LIMITED (1981 - 1985)
CADILLAC BROUGHAM (1987 - 1992)
CADILLAC COMMERCIAL CHASSIS (1981 - 1984)
CADILLAC DEVILLE (1981 - 1984)
CADILLAC FLEETWOOD (1981 - 1984)
CADILLAC FLEETWOOD BROUGHAM (1981 - 1986)
CADILLAC FLEETWOOD FORMAL (1981 - 1984)
CHEVROLET BEL AIR 1981
CHEVROLET CAPRICE (1985 - 1990)
CHEVROLET CAPRICE CLASSIC (1981 - 1990)
CHEVROLET CAPRICE CLASSIC BROUGHAM (1987 - 1990)
CHEVROLET IMPALA (1981 - 1985)
OLDSMOBILE 98 1981
OLDSMOBILE 98 REGENCY (1981 - 1984)
OLDSMOBILE 98 REGENCY BROUGHAM (1982 - 1984)
OLDSMOBILE CUSTOM CRUISER (1981 - 1990)
OLDSMOBILE DELTA 88 (1981 - 1983)
OLDSMOBILE DELTA 88 ROYALE (1981 - 1985)
OLDSMOBILE DELTA 88 ROYALE BROUGHAM (1981 - 1985)
OLDSMOBILE DELTA 88 ROYALE BROUGHAM LS (1984 - 1985)
PONTIAC BONNEVILLE 1981
PONTIAC BONNEVILLE BROUGHAM 1981
PONTIAC BONNEVILLE SAFARI 1981
PONTIAC CATALINA 1981
PONTIAC CATALINA SAFARI 1981
PONTIAC LAURENTIAN 1981
PONTIAC LAURENTIAN SAFARI 1981
PONTIAC PARISIENNE (1981 - 1986)
PONTIAC PARISIENNE BROUGHAM (1982 - 1986)
PONTIAC PARISIENNE SAFARI (1981 - 1982)
PONTIAC SAFARI (1987 - 1989)

Why is it not recommended to use the b body master cylinder on stock brakes?

Im swapping to the b body booster this weekend. Im running ls1 rear disk brakes and c5 corvette front disk brakes. Would swapping to the B body master cylinder help in my application.

What about the proportioning valve?

any tips on how to pick a good booster at the boneyard.

I looked for a composite headlamp older Caprice (late 80's). I forget the exact rationale, besides being the "newest" version that would work.

Several other vehicles use the 12" dual booster, Blazers, fully equipped S10 Blasers and pickups, vans and trucks.

Criteria for the choice of vehicle is:
Looking for a donor vehicle with a curb weight of about 4200-4400. Montes weighs about 3400-3600, booster from say a 5K lb truck may have to much assist.
Also the inlet for vacuum should be about the 10 o'clock location. Inlets can vary depending on vehicle .
Always use the booster pushrod that comes with the donor, it's length is gauged to the booster.
Bob

Late 80's to mid 90 Caprice is always a good donor, try to get one with as low mileage as possible. My donor was an 87 loaded Caprice, garage kept, some Grandma totaled the front end, very low mileage. Of couse I did the swap 12 years ago, picking was much easier then.
Bob

I'm soon to be swapping out the horrid powermaster in GN. I have been reading up on the swap out and was just going to go to advance auto and pick up the Monte dual 9" and MC. Thankfully I found this thread and will be going with the b-body booster and the Monte MC. I don't know if I want to worry about getting the wrong threads on the MC and go through the hassle of exchanging until I get the correct one. Great write up though!

Im glad this thread was bumped! I got a complete LS1 brake swap (Christmas present from the ol lady) that ill be installing soon. Im sure this will help out

Cant figure out how to subscribe to a thread

I pulled my brake booster off a 90-91 s10 and can't remember if I took the pin for that booster. Can someone measure the pin or think I can get one from auto parts store?

Go to the top left of the thread and click the thread options button, on that menu it will say thread notifications. Click that.

HTH

J