When I put the brakes on the pedal goes down further than it should. A quick pump and the pedal applies pressure when it should. In fairly short order when applying brakes again it does the same thing requiring a quick pump. The brakes work fine even without a qiuck pump. And the brake fluid was flushed recently and didn't help.

It feels like there must be an accumulator in the systen and the check valve is not holding. So each time you apply brakes the first thing you do is refil the accumulator. If this is the case does someone know where the thing is and how hard it is to change?

Thanks guys and gals

 

No accumulator in that system. Sounds like you have a sticky caliper. Pressing the pedal once pushes it out a little and pumping pushes it out the rest of the way. Once the pressure is released, the caliper and piston return to the original position. Front calipers are known to blow out the dust seal and corrode the piston and seize. Check all four calipers for proper piston movement and caliper slide movement.

 

You could also have a wheel bearing failed and the spindle/hub TILTS to spread the pads and push the caliper. You close it with the brake pedal and the rotor centers again.

A few revolutions and the tilt starts all over again.

bob gauff

 

Did a little more research with some local Indy guys. The best suggestion from them was that it was a worn master cylinder allowing leakage around the piston. Since there is no wheel noise the wheel bearing was discounted. And with brake application there is no pedal vibration.

If it is the master how difficult is replacement?

What do you think?

Thanks guys.

EZDriver 95 XJ6 2000 Xk8

 

I wouldn't jump to a master cylinder just yet. Check the mentioned items. A wheel bearing that is a little loose will give you a sensation as you described but won't necessarily make noise or vibration. Frozen calipers could exhibit no symptoms just poor fuel economy. The master cylinder is not the easiest job to do and you still have to pull all the wheels to properly bleed the calipers, sooooooo, you may as well pull the wheels now and make sure it is not something else before replacing the master. Just my two cents. Oh yeah, wheel bearings are scheduled to be cleaned and serviced every 60k service.

 

If there is a caliper problem, the car should pull left or right when braking.

Sounds to me you have air in the system. If the brake fluid has not been exchanged for many many years you could have corrosion inside the master cylinder which causes internal leaks.

 

Silly question ...

How much if any of the X308 suspension can be replaced with X300 equivalents?

I have grease nipple envy

 

Brake fluid changed very recently when this problem started. Was well over due then though. If the master is leaking due to corrosion it would bleed down when holding pressure on the pedal and it doesn't. There is no pull left or right when braking which makes me think there is not a caliper hanging up. Air in the system seems to be the most likely thing. But when the fluid was changed it was changed by back flowing from the bottom up.

I seem to remember something in the forum some time back where some check valve in the system can become corroded causing this problem. Searching hasn't found it.

I'll try to do brake bleed again.

EZDriver

 

Back flush?! Hadn't been done in a long time!? I would not have back flushed it. You probably stirred up the bits of little tiny stuff that had gotten comfortable in the master, the pipes, the calipers, etc.. A similar situation occurs when pushing the caliper pistons back in without opening the bleeder at the caliper. I did have a problem on a XJS years ago when pushing the pistons back in without the bleeder open, the master cyl. went bad. That was awkward! I see why you think master now.

 

My term back fllush was incorrect. I think the correct term is vacume flush. But regardless, at this time everything works fine with no pulling one way or the other and no bearing problem. But the pedal will require a second pump. Sometimes it will go quite a ways down before the second pump. And if held there on the initial application with pressure it will continue to slowly go on down almost to the floor. My indy guy and I have concluded it is the master cylinder. After calling my first source for the part I got a price of $665.00 for a new master cylinder. That seems like an incredibly high price for that part. Can anyone recomment a good source for brake parts?

EZDriver

 

$255 rockauto.com

 

Thanks Fredrik. Just looked it up and will get my order in. Thanks for your help. Can't believe the price of some of the OEM parts.

Thanks again.

EZDriver

 

Any little quirks in replacing the master that I should know about? I will bleed the master on the bench before installing it. Anything about bleeding with the ABS in the system. Otherwise I will bleed all wheel calipers using the normal two man system. And from now on flush the system every couple of years.

Thanks

EZDriver

 

What you describe is also a classic symptom of a seized caliper slide pin. Each caliper attaches to two greased pins that slide in the caliper saddle; they each have a small fluted boot protecting it from the elements. If one of those seize up, the caliper cannot re-center itself as the pads wear. It causes the caliper to flex slightly and need a second press of the pedal to get the pads to pinch the rotor.

Something easy to check......I'd hate to see you blow money on a master cylinder and find out it was something like that all along.

Cheers,

 

The problem has gotten worse until now the pedal will sometimes go half to the floor and with continued pressure will slowly go all the way to the floor. A quick pump and the pedal is backup with a hard pedal. At no time do I have uneven brake performance, pulling one way or the other. No loss of fluid. This can only be caused by fluid bypassing in the master. One is on order from Rockauto. I'll keep all posted as to the results.

EZDriver 95 XJ6 2000 XK8

 

Got it. The continued falling of the pedal seals it, that wasn't mentioned before.

Let us know when you have it whipped!

Cheers,

 

The continuing falling of the pedal just started. I even tried to induce this before, but it held firm. But not now. A very progressive failure. However, still driveable if I'm careful. But only when I have to while waiting for the new part. My Indy is waiting to make the switch and I will keep you guys informed.

Thanks guys for your help and patience.

EZDriver