I've bled the brake lines and still a very soft pedal. Would this be more of a Master Cylinder issue or a bad Caliper issue?
Thank you for your help!

 

If all the air is out, the only way the slave/calliper cylinder can cause soft brakes is if the piston is leaking brake fluid which you will see dripping out. The master cylinder can have worn seals which would result in a soft pedal without loss of fluid. However, check that no fluid is evident around the brake vacuum booster.

Richard

 

I would bleed the system from the master cylinder to the actuator block and then to the calipers ONE LINE AT A TIME to be sure to exclude all air from the system if the pedal is not firm.

 

Was the pedal ever hard and has gone soft? Mine never had a hard pedal or good brakes until I fitted a vacuum brake booster .
Check the vacuum provided by the engine with a gauge and if below 15 in HG fit a booste.
Search for my thread "the route to good brakes" many have done it but wont admit it on here.

 

I'm sure the fluid has never been changed and it's a 27 year old car. Do you think draining the entire system and starting new would help? I don't see any leaking around the master cylinder. Pistnbroke I'll check your thread. Thank you.

 

I watched a YouTube video: Would you recommend changing out all the old fluid with a pressurized brake bleed kit? Any certain brand of brake bleed kit I should order?
To get the old fluid out, do I pressurize the system and then open up all the bleeder valves at the same time into collection jars? Or one at a time?
Since I'm already changing out all rotors and pads, and it's a 27 yr old car, should I also replace all calipers while I'm at it?
Thank you.

 

Of course it can leak inside the booster and not be seen

 

Check pad depth.
New lines between calipers and hard lines will firm the pedal feel as brake lines do break down over time and cause a spongy pedal. Stainless Steel wrapped lines help fight line swelling for a quicker pedal response and more firm feel compared to rubber.
Power bleed the entire system with new fluid (Motive brand is a nice option) as it makes the job easy and generally results in a firmer pedal than other methods.

 

One often overlooked brake issue is frozen caliper slide pins. This can result in some strange symptoms, not least is increased pedal deflection which some describe as a soft pedal.

 

Are we fighting a soft pedal that was hard or just a pedal that was always soft ?

 

I have caliper rebuild kits and new brake hoses ready to do the brakes on my 2003 XKR. The rubber hoses are 20+ years old, and are getting old. If I have to do a panic stop, I'd rather not break a brake hose in the process. Since the system is being drained to rebuild the calipers, new hoses aren't that big of a deal. I like the comfort of knowing that the original system lasted 20+ years, and rebuilding now should last another 20+ years, probably more time than I'll have the car.

 

White out and mustang Bill, I agree, totally overlooked the hoses and they're probably the weakest link, rubber ages and this car was in the hot desert for much of its life. I've replaced hoses on past cars and they were definitely a problem. Good call. Thank you.

 

Why would people not admit it?

 

Are there any clear step by step brake pad install docs or videos? I've seen plenty of videos, but not specifically for the XK8 that explains proper pad installation. For example, there's brake pad lube, but where does that go?

 

It’s a simple process (or else I couldn’t have managed it for the two times I’ve replaced the pads with the ebc redstuff upgraded pads). I believe the shop manual gives all the relevant details.

Regarding any use of “lube”. Use it sparingly. Getting it on the face of the pad or the rotor would be disastrous.

i use it on the pins and the back side of the pads. Just a thin smear and wipe off the excess so just it barely remains.

Z

 

Thank you zray, I appreciate it!