Rear Shock Pressure Loss after Riding - 2018 Trek Slash Re:Aktiv

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Rear Shock Pressure Loss after Riding - 2018 Trek Slash Re:Aktiv
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O+
Posted: Apr 30, 2020 at 10:06 Quote
Hi Folks,

Really would appreciate some help on this one:

I recently picked up a used 2018 Trek Slash 9.8. It came with the stock "RockShox Deluxe RT3, RE:aktiv" rear shock.

After riding it for the first time, I noticed the shock felt way too soft and sag was around 40-50% and PSI was reading around 120. I assumed it was my error and I had not set it up properly before the ride...even though I had checked and set it to around 28% Sag @ 210 PSI. Oh well.

Next day I pump up the shock again and set to 28%, same thing happens. Halfway into the ride I feel it going soft and by the end of the ride it's sag point is sitting around 50%. I dunk the shock and replace the valve core, no visible leaks.

I then take it to the local Trek shop, they do the standard air can service and say it's good to go. I take it out for a ride and same thing happens. I take it back to them and they insist nothing is wrong, because it's not losing pressure when they do a dunk test nor when it's sitting there static. They say they rode it around the lot and there's no issues. Now their tech is insisting I just need volume spacers installed and nothing is wrong with the shock. This just doesn't feel right.

Shock holds air when static, but loses pressure after riding. It's not a "pump loss" issue because the sag point is changing after riding.

Has any had experience with a similar issue or any guidance? Should I push for a rebuild or just pick up a different shock?

Thanks for your help!

Posted: Apr 30, 2020 at 10:59 Quote
When you put air in the shock, what method are you using? When filling a shock you should add air in around 30psi increments, actuating the shock after each 30 psi. Is that the method you used?

O+
Posted: Apr 30, 2020 at 11:19 Quote
Davec85 wrote:
When you put air in the shock, what method are you using? When filling a shock you should add air in around 30psi increments, actuating the shock after each 30 psi. Is that the method you used?

Yep, that's what I'm doing. With a standard shock pump I use on other bikes that has no issues.

Posted: Apr 30, 2020 at 14:29 Quote
New seals first. Should solve your issue.

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Posted: Apr 30, 2020 at 15:01 Quote
eshew wrote:
New seals first. Should solve your issue.

'
Tried that and new valve core. Seals were replaced by the shop and issue persists still.

Posted: Apr 30, 2020 at 15:11 Quote
Well I guess I could have read that above couldn't I....

The air is obviously leaking somewhere, either seals or air valve. Any small knicks in the piston? or could you over pressurize it initially to see if it'll settle where you want it?

I guess it could be leaking somewhere else, maybe rebound dial?

Next time you go ride bring a water bottle filled with soapy water & give it a good squirt prior to hitting the harder trails, see if that gives you any bubbles to ID the leak.

Or baring that new shock, although it would be nice to fix that one as it's essentially worthless in it's current state

O+
Posted: Apr 30, 2020 at 15:18 Quote
eshew wrote:
Well I guess I could have read that above couldn't I....

The air is obviously leaking somewhere, either seals or air valve. Any small knicks in the piston? or could you over pressurize it initially to see if it'll settle where you want it?

I guess it could be leaking somewhere else, maybe rebound dial?

Next time you go ride bring a water bottle filled with soapy water & give it a good squirt prior to hitting the harder trails, see if that gives you any bubbles to ID the leak.

Or baring that new shock, although it would be nice to fix that one as it's essentially worthless in it's current state

No visible knicks. I've tried slightly over pressurizing, but I'll give that another shot today and bring some soapy water on the ride to check for leaks...and then report back. Thanks for your help!

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