XT M8000 Brakes 'pumping up' on descents

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slimjim1

Fat boomers cloggin' ma leaderboard
Anyone else experienced these brakes, particularly the rear brake, 'pumping up' considerably on descents? I had a demo bike for a weekend and just bought a new rig, both with the new XT m8000 brakes. On both sets the lever regularly gets solid and the bite point moves out, leading to an inconsistent feel at the lever. My last two sets of the old m785 XT brakes were perfect and I'm starting to find it a bit confidence sapping on the descents.

Worth trying warranty (are they all like this?!) or should I just swap them over with the m785 on the old bike while I still can??
 
Boom King

Boom King

downloaded a pic of moorey's bruised arse
Sounds like air in the system. When it heats up it expands, causing the problems you are experiencing. Get them bled.
 
S

slimjim1

Fat boomers cloggin' ma leaderboard
Boom King said:
Sounds like air in the system. When it heats up it expands, causing the problems you are experiencing. Get them bled.
Click to expand...
I thought so too, but on two separate bikes? I've just been doing some googling and seems to be a not uncommon problem on the new XT's.
 
Flow-Rider

Flow-Rider

Burner
Boom King said:
Sounds like air in the system. When it heats up it expands, causing the problems you are experiencing. Get them bled.
Click to expand...
Fluid expands with heat, has no where to go and is uncompressible, if you had air in there it would compress. It happens on the early Avids all the time. If you run the pads to close to the rotor, when the system gets hot, the fluid expands and the callipers bite the rotor. It's more noticeable on hotter days. Something else is wrong.
 
Nautonier

Nautonier

Eats Squid
Sorry to derail the thread, but can anyone confirm that the bite point adjustment actually works on the new XT levers? Have heard that a lot of the EWS riders are using the new XT levers with Saint callipers, which is supposedly the ultimate combination.
 
link1896

link1896

Mr Greenfield
Flow-Rider said:
Fluid expands with heat, has no where to go and is uncompressible, if you had air in there it would compress. It happens on the early Avids all the time. If you run the pads to close to the rotor, when the system gets hot, the fluid expands and the callipers bite the rotor. It's more noticeable on hotter days. Something else is wrong.
Click to expand...

Same on all avids, happens on the elixir/world cups too.
 
Minlak

Minlak

custom titis
Nothing to add contractually obliged to mention....

Cough.......Hopes.....cough :spy::boink:
 
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northvanguy

Likes Dirt
I'm having the same issue....bleeding doesn't seem to alleviate.

I called Shimano in NSW and when i get around to it I'm sending them in.

Common problem apparently.
 
M

mcoccia

Likes Dirt
I'm also having the same issue with with my rear M9020 XTR. Worked great initially then felt like air in the system. I've bled it a couple of times and this hasn't helped though I think at the last attempt I may have stripped the thread on the bleed funnel resulting in air being drawn into the system. I'll give it one more try tomorrow using my reverb syringe in place of the bleed funnel.
 
moorey

moorey

call me Mia
Happy to report (ok, and brag a little) that in NZ, ridden hard 4-6h every day for 6 days straight, with some DH runs 10-20 min long, never had the issue....and I brake waaaay to much :behindsofa:
 
S

SummitFever

Eats Squid
I've got the M9000 race brakes and have not had a problem with them pumping up. Mine have the white pistons and there was some talk on MTBR that these are not susceptible to the pump-up issues.

Having said that, the "pump-up" sounds like an air in the system issue. I've found mineral oil to be very prone to having dissolved gas. You absolutely must degas the fluid fully before using it. The process is pretty simple:

- about 2/3 fill your syringe;
- block the syringe off;
- pull on the plunger to reduce the pressure in the syringe - you'll see a crazy number of little bubbles form in the syringe;
- release the plunger and the little bubbles will start to form up into bigger bubbles;
- keep doing this until you're not getting any more bubbles forming.

Note: if your syringe isn't of great quality or you pull on the plunger too hard, you can get bubbles leaking past the plunger. You'll be able to spot these, so just pay attention and back off on how hard you're pulling the plunger until air stops getting round.
 
S

slimjim1

Fat boomers cloggin' ma leaderboard
northvanguy said:
I'm having the same issue....bleeding doesn't seem to alleviate.

I called Shimano in NSW and when i get around to it I'm sending them in.

Common problem apparently.
Click to expand...
Cheers fellas, think I'll check with the shop I bought the bike from to see if its known and if there's an easy fix.

After the m785 I thought the brakes would be the last thing to give me troubles. Bit disappointing, thought I'd moved past that shit after putting up with hayes and avid for so many years.
 
scblack

scblack

Leucocholic
Flow-Rider said:
Fluid expands with heat, has no where to go and is uncompressible, if you had air in there it would compress. It happens on the early Avids all the time. If you run the pads to close to the rotor, when the system gets hot, the fluid expands and the callipers bite the rotor. It's more noticeable on hotter days. Something else is wrong.
Click to expand...
I find this too. I have Saints, and if they have sat unused for a couple of weeks the levers will pull to touch the grips. After a bit of use, the bite point moves out and they work perfectly fine.

Annoying but as long as I work them up a bit before a ride there is no issue.
 
S

schred

Likes Bikes and Dirt
I have the 820 saints and got this immediately, then did as per the vid, and used the bleed blocks. Symptoms are much reduced but still there as far as I can tell. PITA considering the old 785s from 5years ago were less trouble.
 
Duane

Duane

Likes Bikes and Dirt
schred said:
I have the 820 saints and got this immediately, then did as per the vid, and used the bleed blocks. Symptoms are much reduced but still there as far as I can tell. PITA considering the old 785s from 5years ago were less trouble.
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I have witnessed this when people bleed with pads(usually worn) fitted and wheel in. I suspect too much fluid and no room for expansion. I've bled brakes for people using the bleed blocks and not had complaints. Surprised you are still getting the same symptoms.
 
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