Turn brake-pedal force into the hydraulic pressure your brake circuits rely on with the Dorman - First Stop Brake Master Cylinder (M99031). It installs as a direct-fit replacement for the listed applications, including the 1978-1980 Buick Century and Regal, Chevrolet El Camino, Malibu and Monte Carlo, GMC Caballero, 1977-1980 Oldsmobile Cutlass, 1978-1980 Cutlass Calais and Cutlass Supreme, 1980 Cutlass Cruiser, and 1978-1980 Pontiac Grand Am, Grand LeMans, Grand Prix and LeMans — see the Buyer's Guide tab for the full list.
Built entirely from new materials rather than remanufactured, it's engineered to match the original master cylinder's design, function, and performance on the covered vehicles.
- Cast-iron housing: constructed to match the casting material of the original part for similar performance.
- EPDM rubber components: chosen for resistance to glycol-based brake fluid.
- 100% new: made to meet rigorous SAE International standards.
- Specs: two outlets with a reservoir included; 0.938 in bore diameter; rearward outlet size 1/2-20.
Mounting hardware and a sensor are not included; consult the vehicle service information for the correct fasteners and whether they may be reused. Country of origin: China.
Interchange: 18M70 · 783-36003 · 78336003 · 83-36003 · 8336003 · 83-50003 · 8350003 · M900231 · 100-2208 · 1002208 · M-82003 · M82003 · 11738 · 13-1738 · 131738 · 10-1738 · 101738 · 130.62003 · 131.62003 · MC101253 · 355-47024 · 35547024 · 18003755 · 18005259 · 18006633 · 18009881 · 101253 · M1738 · NM1738 · 2539016 · MC39016 · F101253 · F99031 · MC99031. Manufacturer part number M99031.
This part cross-references / interchanges with the following part numbers:
Frequently Asked Questions
What does this master cylinder do?
It converts the force from your brake pedal into hydraulic pressure and distributes it to the brake circuits through its two outlets.
Does it come with a reservoir, sensor, or mounting hardware?
A reservoir is included. A sensor and mounting hardware are not included; consult the vehicle service information for the correct fasteners and whether they may be reused.
What are its key specifications?
It has a cast-iron housing, a 0.938 in bore diameter, two outlets, and a rearward outlet size of 1/2-20. It is 100% new and made to meet SAE International standards.
Which vehicles does it fit?
It's a direct-fit replacement for listed 1977-1980 Oldsmobile Cutlass and 1978-1980 Buick, Chevrolet, GMC, Oldsmobile, and Pontiac models. See the Buyer's Guide tab for the full list.
What are signs the master cylinder may need replacing?
A sinking or spongy brake pedal or unexplained brake fluid loss can be signs. If a failed master cylinder is the cause, this unit replaces it; diagnose the cause before ordering.