link1896
Mr Greenfield
Need finger dexterity of a 17 year old
SRAM Guide RS Brakes - Lever slow to return
- Thread starter Jesterarts
- Start date
LPG
likes thicc birds
Sorted out my Sram DB5 levers last night (same internals as the guide). I bought one internals kit off the taiwanese ebay seller who has he correct replacements. I spun an old piston a small pedestal drill and brought it roughly to the size of the new replacement using sand paper (240 grit to get the bulk of material off, 600 then 800 grit wet and dry to get the surface finish back where it should be). It was obvious how much thermal expansion there was as my first few rubs with 800 grit to see how much material I was taking off showed the same size until I dipped the piston in a bit of metho which cooled it down to ambient (which was about 30°C).
Interestingly enough I didn't have much scoring on the piston though I definately had issues when it is hot. I think the scoring comes from contaminationd (dirt and similar) getting in onto the pushrod end of the piston but not necessarily
On the old piston as removed the shoulders between the seals both measured 9.53mm. The straight diameter at the pushrod end measured 9.43mm. When I first sanded down the existing piston I only sanded the journal at the pushrod end as this looks to be the spot with the biggest change. Sanding this spot down did little to change things so I pulled it out and found that there shoulders between the seals were just over 9.5mm. I brought them down to what they were on the replacement piston and then they moved nice and freely. I would suggest that these shoulders cause the bulk of the trouble as they are the largest diameters despite the journal at the pushrod end often having the most visible damage due to contamination.
The levers seem to be moving nice and free but I need to bleed the brake line before I can test them properly. Once that is done I shouldn't have any excuses to sit home with a beer instead of riding when it's hot out.
Interestingly enough I didn't have much scoring on the piston though I definately had issues when it is hot. I think the scoring comes from contaminationd (dirt and similar) getting in onto the pushrod end of the piston but not necessarily
Did a few measurements using my Aldi verniers that I keep in the garage so not as accurate as a micrometer but the results were repeatable. My measurements for the new were all about 0.02 - 0.05 over Jesterarts measurements in the sketch above which is probably due to the high ambient temperatures and maybe inaccuracy from the cheap digital vernier.Got a caliper thing today and measured up the new piston roughly. Hope this helps. I didn't get the OD for where the seals sit as they where in there tight and I didn't want to fuck about with them. All figures are in mm obviously.
I will measure up the old one once I get a chance to take the brakes apart.
On the old piston as removed the shoulders between the seals both measured 9.53mm. The straight diameter at the pushrod end measured 9.43mm. When I first sanded down the existing piston I only sanded the journal at the pushrod end as this looks to be the spot with the biggest change. Sanding this spot down did little to change things so I pulled it out and found that there shoulders between the seals were just over 9.5mm. I brought them down to what they were on the replacement piston and then they moved nice and freely. I would suggest that these shoulders cause the bulk of the trouble as they are the largest diameters despite the journal at the pushrod end often having the most visible damage due to contamination.
The levers seem to be moving nice and free but I need to bleed the brake line before I can test them properly. Once that is done I shouldn't have any excuses to sit home with a beer instead of riding when it's hot out.
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Haakon
has an accommodating arse
Luckily I've been off the bike for a while, but I've been waiting for some weeks for my new levers - apparently SRAM ran out and have been waiting on a shipment.
I've posted my old ones back to the bike shop I got the bike from, and hoping for some shiny new ones in the mail next week.
I've posted my old ones back to the bike shop I got the bike from, and hoping for some shiny new ones in the mail next week.
CP
Likes Bikes and Dirt
I'm over my 1 month old Sram Guide RS brakes. Have bled them, the levers return quickly, but they're way too spongy still. I have the levers adjust to all the way out in terms of reach, and have manually adjusted the contact point. Even still, you can pull them in about 3mm off the grips. This isn't ideal on a DH run when you're often running at 95+% for extended periods of time.
Contemplating a switch to Saints...
Contemplating a switch to Saints...
stickso
Likes Dirt
Sounds like there's still air in there. I rebuilt my levers last week on my Guide R and followed Sram's bleed procedure and they're very firm without coming back to the bar.
First bleed I didn't follow the procedure to the letter and hadn't pushed the caliper pistons back in with a bleed block and the result on the rear was as you described. Must have been air hiding in the calipers because after pushing the pistons all the way in and bleeding properly they're better than ever.
cokeonspecialtwodollars
Fartes of Portingale
Have you got any details on this, my LBS keeps saying that they haven't had any advice from SRAM regarding recall or warranty.
CP
Likes Bikes and Dirt
I had a shop mechanic do the bleed (I don't have the tools). Felt great that day, but have gone off in a week. I was out of town, might try my local shop for another bleed and give them another chance. I really don't want to have to change brakes, but do miss the tight XTs on my old bike!
LPG
likes thicc birds
Went for a ride today and am happy to say that sanding the sticky piston worked out nicely even if it was too hot to really enjoy the ride. The new piston on my front brake lever and the sanded one in the rear lever both worked just as well as on a cool day.
The good brakes weren't the star of the recent work on the bike though. The new dropper post was partially down on a faster section letting me hop a little bit higher to clear a brownsnake that decided to unexpectedly cross the track right infront of me 3 minutes into the ride. Had to stop for a while and let my heartbeat slow down after that.
The good brakes weren't the star of the recent work on the bike though. The new dropper post was partially down on a faster section letting me hop a little bit higher to clear a brownsnake that decided to unexpectedly cross the track right infront of me 3 minutes into the ride. Had to stop for a while and let my heartbeat slow down after that.
Nambra
Definitely should have gone to specsavers
dk13 is right, had my levers replaced a week ago myself, they were 18 months old. Only the front was playing up but my LBS didn't take any chances and ordered a rear as well. When I picked up my bike I was pleasantly surprised to find I'd got a free upgrade from R to RSC too! The levers look like they might be refurbished but I'm cool with that.
It's surprising that your LBS is unaware of the issue, but then again I don't think SRAM is being very proactive either.
They are a bit of a pain to bleed but once done properly, they do feel solid, particularly with metal pads.
link1896
Mr Greenfield
Thanks for the kind words.
New Service kit contains pistons the correct diameter. No need to do anything but install
I was in the same boat. RSCs that we're 2.5 years old. I was in the LBS about something else and they brought up the issue and gave me two brand new levers.
I'd try your LBS or SRAM directly
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I know the problem well, my mate had his lever assemblies replaced a few weeks back and his brakes were out of warranty, the bike shop was all good. It is a known problem, mine were within warranty and also replaced. Both are as good as gold now, well, so far.