Jaguar brakes have long been considered some of the best in the world, and the Jaguar brake booster is partly to thank for that designation. By providing enough assist to easily operate the brakes, yet not too much, which would result in a mushy pedal feel, the Jaguar brake booster is an ideal combination of sport and luxury-not unlike your Jaguar itself. Operating off engine vacuum, the Jaguar brake booster requires no additional power to operate. It does require a running engine, but the Jaguar brake booster also incorporates a trick little check valve to ensure that you still get two or three full-boost stops in the event your engine stalls. This feature was particularly important for the Jaguar brake booster units fitted to older Jags. If you're working on a Jaguar that has a hard brake pedal and very little stopping ability, check the vacuum lines running to the Jaguar brake booster first. Ensure that they're airtight and free of cracks. If you have a vacuum pump, apply vacuum to the Jaguar brake booster through the check valve connection. If the Jaguar brake booster holds vacuum, your problem is elsewhere-look for a leak where the Jaguar brake booster vacuum tubing connects to the intake manifold. More often than not, you'll find that your Jaguar brake booster isn't holding vacuum due to an internal leak. A large rubber diaphragm makes up one of the critical components of the Jaguar brake booster, and this diaphragm is prone to dry rotting as it ages. Order a new Jaguar brake booster from our selection to set things right again.