Well, my brake system flush has hit a snag.
1999 XJ8L US
Background info: Bought the car from a guy who claimed he knew all about cars, and I'm discovering that was not the case. He did some brake work, as the pads look very new and I was awarded a bonus set of pads upon cleaning the spare tire compartment (win!). Brake pedal had a lot of movement before any pressure was achieved. He claimed "These cars are known for that, you can have it adjusted if you don't like it." I prefer my brakes to work on physics rather than hope, so a system flush was in order. Draining the reservoir and front brakes yielded chocolate milk colored brake fluid.

Arriving at the left rear: no movement. I disconnected the hose from the back of the caliper and still no fluid with my wife standing on the pedal.
I moved over to the right rear, which yielded more delicious chocolate milk, to isolate/diagnose.

A quick search online yielded a potential clue to air in the ABS module, which upon activation would push through the module. What say the experts here? I only have a code reader, so not able to activate through OBD, would need to do it via skid.

 

Try disconnecting the brake hose from the steel brake line (vs the caliper side) and gently depress the brake pedal to see if there’s fluid coming out of the pipe. I’ve encountered a few internally collapsed brake hoses on these cars so maybe that’s all it is. If there’s still nothing coming out, then you’ll need to trace the left rear fluid supply line coming out the top of the ABS block. I’ve never seen in any of our scanners an option to activate the ABS pump on these cars before.

 

As an aside, I've encountered two hoses blocked but only one way in the past. Not on cars, but bike hoses are exactly the same so they can do odd things when they fail. Took me a while to workout why those brakes stuck on a bit.

 

https://www.jaguarforums.com/forum/x...brakes-232097/

This old thread gives the procedure from the Jag workshop manuals, there's no mention of activating the ABS pump at any stage.

 

Spongy pedal? Can you press it to the floor? Does it come up and shorten travel with a few pumps of the pedal? I doubt trapped air in the ABS pump, more likely the calipers.

If a Front caliper is allowed to empty, no amount of pressurized bleeding will get it filled 'in situe' - they are located in such away as to trap a very small amount of air.
Removing the caliper and rotating it so the bleed nipple points 12 o'clock, there will be bubbles.

Rusty coloured fluid means a complete flush and fill, as others have suggested replace the hoses from the hard lines to the calipers, a cool upgrade are BF Goodridge steel braided hoses, a firmer pedal instantly....

I wonder if the rust taint is coming from the master cylinder, if it's been replaced by a part stored open enough moisture is pulled in by the fluid to rust internally, I've seen this happen.

 

Brake pedal doesn't get any resistance until about half pressed while driving. Master cylinder looks to be original. Fluid wasn't rusty colored, more of a muddy brown in the catch canister.

 

While tracing, I identified the issue, but I'm not sure where to proceed for repair. When I disconnect the brake line from the ABS block, I get little/no flow from that port. I've tried a few times with pressure on the pedal. For comparison I disconnected the front left hose from the ABS block, knowing I had no issues bleeding that wheel; it spurted with minimal pressure on the brake pedal.

I have no codes indicating an ABS error. Is this an ABS module fix? Other?

 

The issue will likely reside inside the hydraulic block itself. I’ve never taken one apart on these so I can’t give you any guidance there.

 

I have encourted few cases where abs hydraulic unit has air trapped in and therefore soft and spongy pedal. Or barely any brakes after tohorgly system bleed. If there is no way to bleed system with computer. Then you can do the following: Drive the car and brake hard to make abs valves move. Do this several times and bleed from every wheel again. More slippery road, the better.

 

Thank you, this was going to be my next idea to throw at it. Now if it would simply return to winter weather so I had the right conditions.

 

I think the older Jags (sure my XJ40 for example) needed the brake pedal pressed halfway down with the ignition on to bleed the rear brakes. I'd be surprised if the system had changed much in x308s. I base that assumption on needing to do the same thing on a Ford Sierra I had needing the same & both XJ40s & x308s used a fair bit of Ford parts.

 

Hooli, the XJ40’s had the cannon ball brake system like the XJS’s. An electric pump is what forced the brake fluid out the rear calipers.

 

Fair enough, was just an idea.

 

That was the ticket! I must have missed that part of the procedure. Engine running, a few presses of the pedal, and it bled out. Thank you, sir. I've not encountered needing the engine running before.

Brakes finally feel solid.

 

On a conventional vacuum brake system, I haven’t either. There must’ve been some serious goop in that hydraulic system. Glad you got it situated now.

 

Excellent result. I wonder if vacuum boost helped kick the fluid movement off quicker & that pushed the air out? Or it was trapped in the ABS block & something else freed it cause the engine was running? Either way it worked.

I didn't mean engine running in my post & been told these cars have a different brake system to XJ40s since I said that. But glad it worked for you.