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Power brake booster

My wife came back from a short trip and asked me to check brake fluid level. She said brake pedal was pulsing.On opening the bonnet,I noticed that the booster was VERY hot. Car has been sitting for four years. Is this something that will go away or do Ineed to replace?

It would be very helpful if you revealed:

Model Year
Odometer Mileage
Whether your car is equipped with ABS
Maintenance history of the car, as it applies to the braking system

Sorry,I entered that info in what I thought was the proper space. It is an 87 Jaguar XJ6VP.The only record we have shows it was in for a scheduled maintenance in the winter of 88. Car now has 127000 mi… Hope this helps.

Do you know whether this vehicle has ABS?
And, how was the brake pedal “pulsing”?

If it does have ABS (rare in 1987, but certainly possible on a luxury car), then a VERY rapid pulsing/vibrating of the brake pedal could indicate that the ABS pump is running when it shouldn’t be. Repairing this problem could involve the very costly replacement of the electronic module that controls the ABS system–IF you can obtain one for an '87 Jag.

On the other hand, if the pulsing is slower, then the problem could simply be warped brake rotors. Replacing the brake rotors will be considerably cheaper than replacing the ABS control module.

Unfortunately, from a distance it is difficult to diagnose this problem because of several factors:

The car may not have been given any maintenance for over 20 years. A lot of damage can be done to many different components of the car if it really went for over 20 years with no maintenance!
And, “sitting” for 4 years did not help anything.

The type of pulsing and the frequency of the pulsing is something that we cannot experience via the 'net.

I would strongly suggest that you get this car to a foreign car specialist who is experienced with the maintenance requirements and the quirks of older Jaguars. These cars tended to be extremely problem-prone when they were new, and the passage of over 20 years–possibly with no maintenance–certainly did not do anything to alter the reality of their poor reliability.

Among the maintenance procedures that you need to have done on this car is a flush of the brake hydraulic system. Because brake fluid is hygroscopic by nature, it absorbs moisture from the air. By this time, the brake fluid in that car is likely highly diluted with water, which makes damage to the caliper pistons and the brake lines very likely. Even if a brake fluid change does not alter the pulsing, it might help to prevent total brake failure in the near future. Just be prepared for the mechanic to tell you that you do need to replace brake lines and other components in the brake hydraulic system.

Of course, the car also should have every other fluid and filter changed, along with the spark plugs and the plug wires. These maintenance procedures can help to improve the way that the car runs, but they are not as vital to safety as brake service is. This car really needs to be gone over with a fine-tooth comb by a qualified mechanic. Be prepared to spend well over $1,000 on all of the maintenance, and possibly a few thousand more if repairs are needed.

I had the car flatbeedded to a shop where they checked it out to the tune of a thousand plus. I did not mention the ABS since I,also,thought it was not available. Have checked back with mechanic and he said to drive it for another week to see if condition improves. He,mechanic,also said that it was not unusal for booster to get very hot in ?hot? weather. Thanks for your input.

VDC’s post is, as always, spot-on and I agree with it completely.

Just as an FYI…when you felt the brake booster did you compare it’s surface temperature to other surfaces next to it? A brake booster is a simple diaphragm in a can that uses vacuum from the engine to assist in braking. There is nothing on it or in it to create heat. However, everything under the hood gets hot when the engine is running on a hot day, and depending on its proximity to the exhaust system and the engine it can get hot.

Thanks, MB.
I should have included the comments that you added.
Sure, the brake booster was hot, but undoubtedly so were all other metal surfaces under the hood!

I assume that the $1,000+ bought you a complete change of all fluids and filters, but I am unclear as to what else might have been done.

Did you have the brake fluid flushed? If not, please be sure to have this done, as it is a definite safety concern, particularly on a car of this age.

Did the mechanic machine the brake rotors, or did he replace rotors?

What exactly was done?

The pulsing is no doubt due to the rotors, but they may not be warped. If the car has been sitting for a long period of time, the rotors will rust less just under the pads. After the first stop or two, when the rust is scrubbed off the rest of the rotor, the part that was under the pad will be a raised section, causing the pulsing. It may wear down in a couple of weeks and the pulsing may go away or at least be reduced to an acceptable level.

All the other hoods I have been under I have not experienced this kind of heat and, yes,I compared it to the surroundings.Plus,my idea of hot is not in the eighties.Along with the fluids,we replaced the dry rotted tires and a couple of electrical parts.It is an ongoing process.

It is really good that you had the car serviced, and hopefully those fluids included the brake fluid.

Regarding the temperature of the brake booster, while it may have seemed unusually hot to you, mountainbike was correct in stating that the booster cannot generate heat on its own, even if it is malfunctioning. As a result, I would suggest that you not worry about the temperature of the booster. The pulsing would have to be related to either the rotors or (possibly) an ABS pump that runs constantly.

Again,thank you for your input.I did not make it clear that there is no ABS system in this car.I was allowed to drive car,yesterday,and did not find any problem with brakes.The idle speed is another story.