REVIEWS DEALS BIKESHOPS TRAILS

XT m8000 air intrusion

1260 Views 7 Replies 5 Participants Last post by Rod, Jan 12, 2022

Rod

Discussion Starter · Nov 1, 2021 (Edited)

Hey everyone,

I recently had a hole rubbed in my rear brake line so I picked up a replacement. It has been very hard to bleed, but more importantly the bleed gets worse in the following days. When I first bled the brakes I could slide the rear tire, but now that's almost impossible. I noticed a little fluid around the nipple so I'm going to start by replacing the bleed port o ring. Any guidance is appreciated.

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Cleaner

· #2 · Nov 1, 2021

Orient the master cylinder horizontally and at the highest point with the brake line and caliper hanging straight down beneath it. This is easy if the line is externally routed. If you have internally routed lines then you can hang the bike to get as close to this orientation as possible. Open the reach adjust and free stroke screws to allow air out more readily.

Use the funnel filled with fluid at the master cylinder and rapidly cycle the lever. You will see bubbles in the funnel if there is air in the system when you cycle the lever. You can tap the caliper and line along its length to help dislodge any air. Use a strap to hold the lever pulled and leave the bike in this orientation for a few hours or over night. This should get all of the air out up to the reservoir. If air is the problem this should address it. If you get a firm lever after this process then close everything up and go for a mild test ride to evaluate if the performance is safe. If air enters the system rapidly after doing this then there is a leak somewhere. Look for fluid coming out somewhere as a fist step.

If this does not result in a good lever then you can try pushing some fluid with a syringe from the caliper up to the funnel.

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Rod

Discussion Starter · #3 · Nov 2, 2021

Cleaner said:
Orient the master cylinder horizontally and at the highest point with the brake line and caliper hanging straight down beneath it. This is easy if the line is externally routed. If you have internally routed lines then you can hang the bike to get as close to this orientation as possible. Open the reach adjust and free stroke screws to allow air out more readily.

Use the funnel filled with fluid at the master cylinder and rapidly cycle the lever. You will see bubbles in the funnel if there is air in the system when you cycle the lever. You can tap the caliper and line along its length to help dislodge any air. Use a strap to hold the lever pulled and leave the bike in this orientation for a few hours or over night. This should get all of the air out up to the reservoir. If air is the problem this should address it. If you get a firm lever after this process then close everything up and go for a mild test ride to evaluate if the performance is safe. If air enters the system rapidly after doing this then there is a leak somewhere. Look for fluid coming out somewhere as a fist step.

If this does not result in a good lever then you can try pushing some fluid with a syringe from the caliper up to the funnel.

Thanks for responding Cleaner. I have already bled the brakes properly, but when I wake up the following day there's air in the system and it gets worse as days go by. It "should" be a closed system, which prevents this from happening, but that doesn't appear to be the case with my rear brake. I'm hoping I can look at it today. I have noticed a little fluid around the bleed nipple so I'm going to start there.

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fredcook

· #4 · Nov 2, 2021

Rod said:
Thanks for responding Cleaner. I have already bled the brakes properly, but when I wake up the following day there's air in the system and it gets worse as days go by. It "should" be a closed system, which prevents this from happening, but that doesn't appear to be the case with my rear brake. I'm hoping I can look at it today. I have noticed a little fluid around the bleed nipple so I'm going to start there.

For every bit of that fluid you see around the bleed nipple, that amount (or more as air compresses when you use the brake) of air volume is getting into the system. Fix your leak, fix your problem.

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Rod

Discussion Starter · #5 · Jan 5, 2022

Just wanted to report back that the air intrusion was happening at the lever. The cylinder that compresses activates the brake had a leak. All is good now.

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Taroroot

· #6 · Jan 5, 2022

Rod said:
Just wanted to report back that the air intrusion was happening at the lever. The cylinder that compresses activates the brake had a leak. All is good now.

Wow! Hey, thanks for posting follow up, i always appreciate that, sometimes people post for help and just disappear. It took a while, but now we know!

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EJ_92606

· #7 · Jan 11, 2022

So what was the fix? Replace the lever?

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Rod

Discussion Starter · #8 · Jan 12, 2022

EJ_92606 said:
So what was the fix? Replace the lever?

Exactly, when you pull the brake lever it actuates something inside the handle. Where this piece moved back and forth was the cause of the leak. Maybe I popped the bladder when the system was sealed and I tried to move the brake pistons outward. I don't recall doing that, but I may have done that. Anyways, replacing the lever solved my issue. I still need to rebleed the brakes, but they're almost perfect at this point.

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