stirk
Burner
The R/RS has a much smaller end, why is that? Trying to fix the problem?
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SRAM Guide RS Brakes - Lever slow to return
- Thread starter Jesterarts
- Start date
link1896
Mr Greenfield
Issues are around the diameter not length, I'm thinking this sample has been damaged. Keen to see it in a better shot and if the other lever's piston is the same.
But really, NFI.
Nambra
Definitely should have gone to specsavers
Saab says he bought and fixed - perhaps an old version of the part. Although the narrowing between the two seals suggests it might be a new piston?
hifiandmtb
Sphincter beanie
link1896
Mr Greenfield
Nope, just stupid. I sided with everyone on MTBR who gave him a hard time. O-Ring material compatibility charts have existed for a long time.
EPDM ( the synthetic rubber used on all DOT fluid systems ) has a very big "no" next to mineral oil.
hifiandmtb
Sphincter beanie
Yeah, didn't say it wasn't stupid, just an interesting fact.
link1896
Mr Greenfield
Sorry dude wasn't directing my anger at you, but rather at PVD. He should know better, the whole exercise reeked of clickbait.
link1896
Mr Greenfield
Did the other levers piston look the same at the tip?
bowtajzane
Likes Dirt
link,how's the new and improved guides going ?
danthebloke
Likes Dirt
Soon
I will let you know next week when i get mine fitted.Ive had my bike about a year and a half and they only started playing up a couple of months ago or so .Took it in to the bike shop and they said no probs,the only hassle is the week and ahalf wait .But cant really complain.
I will let you know next week when i get mine fitted.Ive had my bike about a year and a half and they only started playing up a couple of months ago or so .Took it in to the bike shop and they said no probs,the only hassle is the week and ahalf wait .But cant really complain.
link1896
Mr Greenfield
Sorry, been a busy few weeks.
My mate who's a machinist came over and we went over my technique on the manual lathe, sadly there are no efficiencies to be found, my technique is fine. Going to add digital readouts to the lathe and see if I can speed things up. Currently takes me 60 mins per piston.
Can't find anyone to run a batch of parts for a sane price yet on a cnc lathe.
My mates workshop is running 24/7 on all machines and can't find spare time ATM.
My mate who's a machinist came over and we went over my technique on the manual lathe, sadly there are no efficiencies to be found, my technique is fine. Going to add digital readouts to the lathe and see if I can speed things up. Currently takes me 60 mins per piston.
Can't find anyone to run a batch of parts for a sane price yet on a cnc lathe.
My mates workshop is running 24/7 on all machines and can't find spare time ATM.
bowtajzane
Likes Dirt
Boom Kings new and old pistons.
Old on left, 9.48mm at its widest.
New on right. 9.35mm at its widest.
Other critical dimensions match so my theory of swelling is bogus.
Both are turned in lathes.
[/QUOTE]
do you mean "not" bogus as the new one is smaller?
Old on left, 9.48mm at its widest.
New on right. 9.35mm at its widest.
Other critical dimensions match so my theory of swelling is bogus.
Both are turned in lathes.
do you mean "not" bogus as the new one is smaller?
hakka
Likes Dirt
I have 4 bikes with Guides, 3 of those are currently out of action with this problem, all in the space of a few weeks.
Talking to the mechanic at the LBS, sram are saying there was an error in tolerances in the earlier brakes. All my brakes that are having issues were fine right through last summer, and as soon as it started to warm up in the last few weeks the issues began. There must be some swelling going on to trigger it. The brakes are all between 14 and 22 months old.
Sram australia have sent replacement levers for one set, the others were from CRC which I haven't posted yet.
My 2017 stumpy has guides, no problems yet but ordered a set of hope e4s so I don't have to wait for the guides to fuck up. I'll have to persevere with the guides on the other bikes, 4 sets of hope e4s is an expensive exercise.
Talking to the mechanic at the LBS, sram are saying there was an error in tolerances in the earlier brakes. All my brakes that are having issues were fine right through last summer, and as soon as it started to warm up in the last few weeks the issues began. There must be some swelling going on to trigger it. The brakes are all between 14 and 22 months old.
Sram australia have sent replacement levers for one set, the others were from CRC which I haven't posted yet.
My 2017 stumpy has guides, no problems yet but ordered a set of hope e4s so I don't have to wait for the guides to fuck up. I'll have to persevere with the guides on the other bikes, 4 sets of hope e4s is an expensive exercise.
link1896
Mr Greenfield
do you mean "not" bogus as the new one is smaller?[/QUOTE]Boom Kings new and old pistons.
Old on left, 9.48mm at its widest.
New on right. 9.35mm at its widest.
Other critical dimensions match so my theory of swelling is bogus.
Both are turned in lathes.
If the plastic wasn't DOT fluid compatible it would cause the pistons to swell in all directions, not just the critical larger diameter faces. (Assuming new samples have only had the OD of the large diameter faces reduced)
But the only true way to test this is a long term exposure with a control sample.
My current theory is the original pistons were turned up too close to the bores diameter, and with use and contamination from the lack of seals, the surfaces have been ruffed up and caused an increase in the diameter. Plus any lube applied at the factory has migrated.
Due to the risk of contamination, I've gone cold on the idea of aluminium pistons. We'll see if the aluminium pistons in my levers last a year.
link1896
Mr Greenfield
You are screwed.
You could put the offending pistons in a drill and gently wipe a bit off their diameter
bowtajzane
Likes Dirt
link,what type of contamination do you think will occur
with the Ali piston......
with the Ali piston......
