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Discussion Starter · #1 ·
Hi guys
I recently bought a 2003 4.8l and didn't get a chance to view it cold. I have noticed when cold the brake pedal goes to the floor before any noticeable stopping, once it warms up it gets alot better. Have done a search and am not convinced it would be vacuum as it gets better when up to running temperature, I did readyou can check vacuum lines with a compressor and spray and wipe is this recommended? going to try changing brake fluid, do you think this will help? Or if anyone has a better idea please let me know.
 

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I won’t be vacuum related, the lack of vacuum would make the pedal harder, not softer. It will be air in the brake lines, assuming you are not losing fluid. Or a seal somewhere if you are also losing fluid. But it sounds like you just need to bleed it.


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Discussion Starter · #3 ·
Thanks Andrew1964 I'll do some more searching for leaks and have to change the fluid as well hopefully I'll be able to sort it.
 

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Thanks Andrew1964 I'll do some more searching for leaks and have to change the fluid as well hopefully I'll be able to sort it.
Have you checked it by having someone place foot on brake and you watch for bubbles in reservoir?

Foo

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Discussion Starter · #5 ·
Will check for that Foo, thanks mate
 

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Discussion Starter · #6 ·
Hi guys trying to bleed these brakes couldn't get any fluid out at the caliper then realised it's supposed to be at the load sensing valve. Got a spurt out of that and the pedal finally went to the floor. Now we can't pump the brake pedal back up. HEELP
 

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The load sensing valve is just one component in a line that needs to be bled. I don’t know what technique you are using to bleed the brakes, but if you allow the pedal to rise before you close off the bleed nipple you will just suck air back in.
Pumping the fluid through using the brakes is only one method. You can also gravity drain it by cracking the bleed nipple until the fluid starts flowing, and keep topping up the reservoir. Leave the brake pedal out of it. Potentially more wastage, but once you have fresh new fluid coming through with no air bubbles, you can close it off and move on to the wheel cylinders. It’s slower, but it works, and you don’t need a helper.


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Further to my previous post, if you couldn’t pump any fluid out of the (rear?) wheel cylinder, then the whole system must be chock full of air! Does any fluid ooze out by itself, or does it seem dry? Maybe the load sensing valve is seized and not letting any fluid past the piston (unlikely, but you never know).
Have a go at the gravity method I explained above, and see if it will drain through the wheel cylinder. If it’s not getting through then you could have a problem with the LSV.


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Discussion Starter · #9 · (Edited)
Never heard of the gravity method I'm guessing you disconnect at the master cylinder and fit an open reservoir to the brake line? Definitely had pressure on the pedal until the bleed valve was retightened even took the entire valve out of the brake caliper did get tiny amounts first time I bled each spot but definitely no flow like you'd expect. I even loosened the fittings on the master thinking of bleeding one section at a time but no leakage at all after mucking around there's definitely airr in the lines now no brakes and still no closer🤔😫
 

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No, you just let it run from the master cylinder through to the wheel cylinder. If you loosen the bleed nipple the fluid should start to drain down and the fluid level in the master cylinder will drop. Keep pouring fresh fluid into the master cylinder to keep it above the minimum level. If you let it empty, air will enter and you’ll be back where you started.


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The 4.8 I am sure will have ABS as well, I find these things are diabolical to bleed properly. Compared to my good old non ABS GU anyway. Best thing is download and read the bleeding and troubleshooting section in the Electronic Service Manual. You can search for it on this forum.
 

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Discussion Starter · #12 ·
No, you just let it run from the master cylinder through to the wheel cylinder. If you loosen the bleed nipple the fluid should start to drain down and the fluid level in the master cylinder will drop. Keep pouring fresh fluid into the master cylinder to keep it above the minimum level. If you let it empty, air will enter and you’ll be back where you started.
Thanks mate will give this a go tomorrow morning if I get a chance.
 

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The 4.8 I am sure will have ABS as well, I find these things are diabolical to bleed properly. Compared to my good old non ABS GU anyway. Best thing is download and read the bleeding and troubleshooting section in the Electronic Service Manual. You can search for it on this forum.
Thanks mate will give this a go tomorrow morning if I get a chance.
The link is in my signature
 
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