Please help: lots of strange 'pedal bob' with rear shock in lock-out

[Jerry]

Hello all,

Let me introduce myself first. I am Jerry and new to the Chiner community after many of you DIY bikers inspired me to build my own mountain bike. Thanks for that!

My chiner is built around a 29er carbon Pro-Mance M7007 Super Light frame, size XL because I am tall guy. It is ready to race and the first riding impressions are very positive. But it need still some finetuning.

However, one very annoying thing is that when I select the rear shock, a RS Monarch RL 168x38, in full lock mode (lever fully to the familiar turtle), there is a lot of bouncing in the back end of the bike. It is as if my rear wheel has become the shape of an egg. In 'open mode' of the rear shock the bouncing has almost completely disappeared. Very strange, but in 'lock mode' is therefore hardly decent to cycle.
 
Are you, especially Pro-Mance M7007 but also Hongfu FM158 owners, familiar with this problem? If so, how did you solve this annoying and inefficient 'pedal bob' problem? Or is there probably something wrong with the shock, even though that brand is new as mine?
 
Thanks in advance for your help.
 
Greetings.

[dan_cx]

Disregarding the frame for the moment... Was the shock purchased new or used? I only ask this because a purchasing new shock rules out the possibility of a previous owner/shop making internal adjustments, etc.  In either case, depressurize the shock & remove the valve core. You are removing the valve core to ensure there is absolutely no air in the shock assembly. Reinstall the valve core, place the lockout in the open position and pressurize the shock to 100psi. Cycle the shock through its travel 5 times. You may hear or feel the air swapping from positive to negative chambers each time. Pressurize the shock to the equivalent of your body weight + riding gear, in psi. (Example: Rider 170lbs + helmet, shoes, hydration pack 15lbs = 185lbs. Pressurize to 185psi) This is always a good thing to do to establish a proper baseline for suspension tuning.

You may also want to look into the Debonaire upgrade option as well. It will increase the volume of air in the shock, which will aid in a firmer lockout, and give a greater range of adjustability to the rear shock.
https://www.sram.com/rockshox/products/debonair-upgrade-kit

[sclyde2]

This sounds just like the same issue that someone else had on here, except they were using the hydraulic lockout version (xx) of your shock.

Short answer: Are you using a chain ring around 30t or smaller?  If so, this is what is causing your issue.  If it bothers you, get a bigger chainring or don't use the lockout.

Long answer - check some of my earlier posts