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Road Hydro rear brake pull much longer than front brake

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Road Hydro rear brake pull much longer than front brake

Old 06-05-21, 06:33 PM
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DarKris
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Road Hydro rear brake pull much longer than front brake

I've had this issue for a while and could never get it sorted. On my Giant Toughroad GX size L I have Shimano RS405 Hydro levers and the front brake has such a short pull before the brakes engage, but the rear has a much longer pull before they engage. I replaced the pads for both wheels at the same time and based on the limited riding I've done with this bike since changing pads (I've done at MOST 100 miles mostly flat riding on those pads) I think I can rule out pad wear. Also swapped rotors out and no change.

Not sure if this is normal for the rear brake, but I just can't figure this out.
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Old 06-05-21, 08:03 PM
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Sounds like you didn't push the pistons back on the front brake. Very short lever travel is not normal w/ Shimano. When you install new pads you MUST reset the pistons.
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Old 06-06-21, 06:51 AM
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Originally Posted by cxwrench View Post
Sounds like you didn't push the pistons back on the front brake. Very short lever travel is not normal w/ Shimano. When you install new pads you MUST reset the pistons.
I did try pushing them back in but the results were the same. I’ll try again and see if that changes anything

UPDATE: That did it. The issue was before I tried pushing the pistons in with the pads still in. Took the pads out and got the pistons re-adjusted on the front.

Oops

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Old 06-08-21, 11:47 AM
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The pull will always be shorter on the front brake because the brake line is shorter, there's less fluid to move the pistons, ergo, less elasticity. But you may have air in the rear brake line. To test quickly, lift the bike by the handlebar and bounce it a few times on the rear wheel. If there's a bubble it will float to the reservoir and the lever will get really soft and spongy after a couple pulls. That being the case, take it to the shop for a brake burp.
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Old 06-08-21, 03:34 PM
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Originally Posted by oldbobcat View Post
The pull will always be shorter on the front brake because the brake line is shorter, there's less fluid to move the pistons, ergo, less elasticity. But you may have air in the rear brake line. To test quickly, lift the bike by the handlebar and bounce it a few times on the rear wheel. If there's a bubble it will float to the reservoir and the lever will get really soft and spongy after a couple pulls. That being the case, take it to the shop for a brake burp.
Sorry, this is just plain wrong. I have no problems getting front and rear brakes to feel exactly the same. If you always have mushy rear brakes compared to fronts you're doing it wrong.
Your other advice about getting the air to move is spot on.
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Old 06-08-21, 08:31 PM
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Originally Posted by cxwrench View Post
Sorry, this is just plain wrong. I have no problems getting front and rear brakes to feel exactly the same. If you always have mushy rear brakes compared to fronts you're doing it wrong.
If brake hose were perfectly rigid and brake fluid (DOT or mineral oil) were perfectly not compressible, certainly. But there is no perfectly non-compressible fluid or flexibly rigid hose. Indeed, Shimano makes two grades of hose, BH90, most rigid for high performance applications, and BH59, less rigid for tooling along the bike path. I imagine brass tubing would be close to perfectly rigid on a bicycle, but that would cause steering and suspension problems.

I have never ridden a disc brake bike whose front and rear brakes behaved perfectly alike. Most were bikes tuned by mechanics who had a lot more experience than myself. On the other hand, in my research for this I came across a conversation about "wandering Shimano bite point." Evidently, most bleed techniques leave a tiny bubble at the bleed nipple, usually in the rear brake because of the orientation of the caliper. I've removed the caliper, tapped it, tapped the hose, tipped it every which way, but this video advises to remove the nipple entirely and let the oil flow over.
.
I'll try this on my next Shimano bleed and share the outcome.
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Old 06-08-21, 09:11 PM
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As I said when I do them they feel the same. Sometimes it's hard to get it right, most times it's not a big deal. If a caliper and it's pistons are really dirty it's more work because you have to clean and lube but it's not a problem. I measure the reach and make sure that's the same and then check it again w/ light pressure on the levers to confirm that's the same too. If they're not the same it's because the mechanic is doing some part of the procedure incorrectly.
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Old 06-08-21, 10:05 PM
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Originally Posted by cxwrench View Post
As I said when I do them they feel the same. Sometimes it's hard to get it right, most times it's not a big deal. If a caliper and it's pistons are really dirty it's more work because you have to clean and lube but it's not a problem. I measure the reach and make sure that's the same and then check it again w/ light pressure on the levers to confirm that's the same too. If they're not the same it's because the mechanic is doing some part of the procedure incorrectly.
Cleaning, lubing, and measuring go without saying. I'm betting on incipient bubbles in the caliper. And I might have been selling myself short by being satisfied with bleeds "as good as the best guy's."
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