Wilwood's aluminum tandem master cylinder: a lightweight, dual-circuit upgrade for disc/disc or disc/drum hot rod and truck brake systems. Available alone, or as a complete kit with a bolt-on proportioning valve and bracket.
Highlights:
- Forged/cast aluminum body, about 3 lb, with an 8 oz front reservoir (nearly double the rear) and 1.10" stroke
- Four bores: 7/8", 15/16" (manual, pushrod included), 1", 1-1/8" (booster mount)
- Bare aluminum, black E-coat or ball-burnished finish
- Elongated mounting holes fit 3.22"-3.40" bolt spacing (most GM boosters and firewalls)
Valve kit option: "Kit w/ Valve & Bracket" adds Wilwood's combination adjustable proportioning valve, a mounting bracket that bolts under the master cylinder, and pre-bent stainless lines between them, so it all bolts on as one unit. Need just a valve? See our Wilwood Proportioning Valve listing.
**WHICH BORE SIZE DO I NEED?**
Wilwood builds the 7/8" and 15/16" bores with an integral pushrod for manual (non-boosted) brakes. The 1" and 1-1/8" bores bolt directly to a power brake booster (or can run manual with Wilwood's pushrod kit).
| Your setup |
Starting bore |
| Manual brakes, 4-piston front calipers (Dynalite, Dynapro, Classic Series) |
7/8" |
| Manual brakes, 6-piston front big-brake kit |
15/16" |
| Power booster, 4-piston front or 4-wheel disc with stock-size rotors |
1" |
| Power booster, 6-piston front + 4-piston rear big-brake kits (13"-14" rotors) |
1-1/8" |
Rule of thumb: a smaller bore gives more line pressure with a longer pedal; a larger bore moves more fluid for big multi-piston calipers with a shorter, firmer pedal. This chart is our general starting point, not Wilwood's official spec. Not sure? Email Sales@macsgarage.shop with your calipers and booster setup and we'll confirm before you order.
Residual valves: Per Wilwood, drum brakes need an inline 10 lb residual valve. Disc brakes with the master cylinder mounted below the caliper bleed screws may need a 2 lb residual valve. 4-wheel disc with the reservoir above the calipers usually needs none.
Plumbing: Run the primary outlet to the axle with the most total caliper piston area (usually the front), and use an adjustable proportioning valve to set rear bias.
Fitment notes: Universal; not a direct OE replacement. Fits most classic Chevy/GMC trucks and Impalas with a 2-bolt firewall or booster mount. Pair with a Wilwood pedal or your booster.
Part #: Master cylinder 260-9439 (7/8"), 260-13375 (15/16"), 260-8555 (1"), 260-8556 (1-1/8"); kit w/ valve & L/H bracket 261-13271, 261-13626, 261-13269, 261-13270. Add -BK black, -P ball burnished.
