1991 Jaguar XJ-S Having problem with "hard" brake pedal. What can be some causes?
Country: United StatesMake: Jaguar
Hello and good evening. When do you experience this pedal feel? Is it all the time? Also does the engine feel normal and running properly?
Your JA Expert,
The pedal is continually hard and the engine is performing well. No variation is detected.
Ok, great. There are 2 areas of focus for this issue. The first being sure that all brakes are in good order. Sometimes brake calipers and sieze and contribute to this feel. That is not the most common issue, but it shouldn't be overlooked. The main focus should be on your vacuum brake booster. This is the unit responsible for power brakes. When you do not have power assist from this unit, you have a very hard pedal. This is the large round component that sits behind the master cylinder. It receives vacuum from the engine and with that vacuum, an internal diaphram, uses that vacuum to assist your foot for power brakes. The first step is to confirm the large hose that goes to the unit has very strong vacuum at it and that it is not broken or collapsed. If it is not damaged and vacuum is present, that brake booster will be to blame and need to be replaced. The master cylinder will not need to be replaced at the same time unless when it is unbolted from the booster, moisture leakage is found at the rear of the master cylinder. Feel free to ask me anything you need to as we continue.
ASE Master Tech w/ 20+ years in the field. Self employed for 9 years. Member of AUTOLAB radio show.