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!