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what is the correct process to bleed brakes

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Old 11-25-2012, 10:28 PM
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Default what is the correct process to bleed brakes

I purchased a 1997 XK8 with 90,000 miles on it. The car has been terribly neglected by the previous owners and in need of a lot of work, all of which has been completed except for new brakes. I replaced the front and rear brakes and replaced the fluid with brake fluid purchased at the local Jaguar dealership. I've obviously done it wrong as the brake pedal now is excessively soft.
The procedure I used to replace the fluid was
  1. drain the reservoir
  2. refill with new brake fluid
  3. bleed the calipers starting with the farthest from the reservoir (right rear) and moving towards the left front
I've bled the system twice now with no improvement. I've read about pumps and accumulators but don't see that this car has those - other than a hydraulic block located behind the front left headlight.
 
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Old 11-25-2012, 10:36 PM
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Originally Posted by PattertiXK8
I purchased a 1997 XK8 with 90,000 miles on it. The car has been terribly neglected by the previous owners and in need of a lot of work, all of which has been completed except for new brakes. I replaced the front and rear brakes and replaced the fluid with brake fluid purchased at the local Jaguar dealership. I've obviously done it wrong as the brake pedal now is excessively soft.


The procedure I used to replace the fluid was
  1. drain the reservoir
  2. refill with new brake fluid
  3. bleed the calipers starting with the farthest from the reservoir (right rear) and moving towards the left front
I've bled the system twice now with no improvement. I've read about pumps and accumulators but don't see that this car has those - other than a hydraulic block located behind the front left headlight.

You said you 'replaced the front and rear brakes'. Can you describe exactly what you replaced or serviced?
 
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Old 11-25-2012, 10:53 PM
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Sounds like there's still air in the system. Here's the bleed procedure from JTIS:

1. Fill fluid reservoir to the 'MAX' (maximum) mark

Make sure the brake-fluid level does not fall below the fluid reservoir 'MIN' (minimum) mark when bleeding the brake system.

2. Prepare the LH front brake-caliper for bleeding
a) Remove dust cap
b) Connect bleed pipe and fluid container to bleed nipple

3. Bleed the brake:
a) Apply pressure to brake pedal
b) Open bleed nipple
c) Fully depress brake pedal
d) Close bleed nipple
e) Release brake pedal
f) Wait two seconds to allow system to prime
g) Repeat procedure until air-free brake fluid is expelled from the caliper
h) Tighten Front Caliper bleed nipple to 4-6 Nm

5. Following the procedure above, bleed the brakes in the order shown
a) Left-Hand Front
b) Right-Hand Front
c) Left-Hand Rear
d) Right-Hand Rear

Graham
 
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Old 11-26-2012, 07:52 AM
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Here is a trick for bleeding late model brake systems that you can't get that last bit of air out of. Most, if not all, cars now have dual diagonal brake circuits. So:

Start the bleeding process on the front or rear as the OEM specifies. For instance, if you do the RF first,then go to the diagonal caliper at the LR and finish off that ckt. Then back to the LF and RR in sequence.

The above trick has worked for me when I just couldn't get that last bit of sponge out of the brake pedal. Hope this helps.
 
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Old 11-26-2012, 09:26 PM
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Responding to the posts:
I replaced the pads only. Didn't replace or rebuld the calipers.
Graham - the process you describe is what I did but not in the sequence you describe.
Tarheal - This sequence makes some sense. I'll give it a try.

Thanks for the help guys
 
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Old 11-26-2012, 09:39 PM
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Originally Posted by PattertiXK8
Responding to the posts:
I replaced the pads only. Didn't replace or rebuld the calipers.
If you did not resurface or replace the disks it may not be a bleeding issue. The new pads may not fit flat against the disks and therefore they feel mushy. It is best to resurface or replace the disks, but given enough wear, the new pads may bed-in to match the old disks and probably get somewhat firmer.
 
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Old 11-27-2012, 01:19 AM
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When I have had the odd problem I have done it with the ignition on so the abs pump is working to help....... normaly does the trick
 
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