Rock Shox Monarch Plus RC3 IFP pressure issues

There appears to be something wrong with multiple Monarch Plus rear shocks. I had one that developed very stiff platform on 20-30% travel and besides the increase in damping force, also made a *klunk* sound. It appeared to be happening only when compression was set to open, trail and climb modes were unaffected.

I first thought that I had bad luck with the damper, but I now know at least 4 instances of this issue in my friends.

Story

When I investigated the issue and opened the IFP cap to check IFP pressure, some pressure was relieved even when I had not touched the valve core. The valve was few revolutions loose and had been resting on the IFP valve cap (see image below)

IFP cap with marks from valve core shoulders

The valve was several revolutions loose and I then tightened it. Next I tried to re-pressurize the IFP and when I was removing the adapter+pump, the o-ring from the adapter blew off. Somehow the valve core was still open when the the adapter un-threaded. Finally I ended up cutting the wider part of the valve needle to make sure this is not possible, after this no o-rings have been blown.

Note: if you cut the valve needle, it is not as easy to check the pressure of the IFP, but the valve still works and you can just pump the desired pressure or to make extra sure, first release some pressure and then pump it back up. This way you know that the pressure is  what your pump says.

cutting the needle from valve core

This made the *klunk* a little softer but  did not fix it. I then rebuilt the whole shock and used the same seals/valves at it had been ridden like 2 months. After rebuild (including new oil, grease and bleed of the damper) it has worked flawlessly for months.

Now I check the IFP pressure always when ever I get a new Monarch Plus shock and do it before compressing it even once in the frame. I just got a new frame & shock and when checking, the pressure was released and the valve core was 1½ revolutions loose..

I now hope that it is enough to pressurize the IFP before riding the bike to prevent the *klunk* from happening.  My fear is that the IFP could be faulty installed or some other failure..

To check and correct the IFP pressure

  1. set rebound and compression to open
  2. open IFP valve cap and hope that no pressure is released (see the video below and sorry about the Finnish, see description for English)
  3. check if the IFP valve core is loose
  4. <optional> remove the valve core and cut the valve core needle to make sure it stays closed when needed <optional>
  5. use valve core tool to tighten the IFP valve (I have come across that they are loose from 1.5 to 4 revolutions!)
  6. thread Rock Shox Monarch Air Valve Tool (00.4315.027.010  or https://www.sram.com/rockshox/products/air-valve-adapter-tool ) to your shock pump
  7. pressurize the IFP as Rock Shox service manual instructs (250psi for Monarch Plus)
  8. thread the IFP valve cap back on

FAQ

Q: I did what you told and everything went to shit.
A: I take no responsibility on what you do based on this guide, you do it on your own responsibility (as every DIY project, duh). This post is mostly about sharing knowledge of a possible issue in your rear shock.

Q: How does the lowered IFP pressure / *klunk* affect my riding?
A: The damping performance is ruined and the platform or “notch” that is created effectively ruins small bumb compliance as the travel stops at the *klunk*

Q: What causes the platform or *klunk*?
A: It is very probable that the lowered IFP pressure induces cavitation in the damper oil, producing gas or foam to hinder the damper smoothness

Q: I already have the *klunk*, what should I do?
A: Contact RockShox, this should be a warranty issue, at least with quite recent shocks.
A2: You can check the IFP pressure as described above, but it will probably not help a lot. Next step is to do rebuild or at least re-bleed the damper. (I will try this the next time I have this issue)

Q: Shouldn’t the IFP be pressurized with Nitrogen?
A: Nitrogen is best but air is good enough and even supported by Rock Shox in the service manual. (air is around 78% Nitrogen and 21% of Oxygen)

Q: The service says that this is normal and related to air pressure equalization between the positive and the negative chamber.
A: Could be, but that is a very small step and shouldn’t happen on every compression. Otherwise the pressure would be constantly leaking from either chamber. The *klunk* described is a very clear platform (you need more force to compress the shock over it) and you’ll definitely know that something is not right

What’s wrong with my Reverb?

I recently got a broken reverb from my friend.
He said that it had had some sag and finally it totally collapsed.
I of course was interested if it could be fixed.

The post could be compressed by hand and did not hold the position.

First I noticed that it was lacking almost all of the pressure.

Continue reading “What’s wrong with my Reverb?”

Checking the bearings on Specialized Hi-Lo hubs

I have reused the original hubs from my 2011 Specialized Enduro Comp as rebuilt wheels with SixPack Racing spokes (double butted, 2-1.8-2mm) and Stans Flow Mk3 rims.

I thought that the bearings could be smoother and decided to take apart the hubs and check what kind of bearings they have.

1st step was naturally to take off the brake disc to prevent any contamination. Continue reading “Checking the bearings on Specialized Hi-Lo hubs”

Reducing sag on Reverb Stealth

Has your Reverb Stealth developed sag?
You don’t dare to use your Reverb in the winter in fear of the sag and expensive rebuild?

About 20mm of sag after riding an hour in -17C

Fear not, the sag does necessarily mean full rebuild, as it can easily be reduced with fork oil level tool (and few open end wrenches).

Continue reading “Reducing sag on Reverb Stealth”

Recon Silver bushing replacement part 1: removal

My trusty RockShox Recon Silver had one broken bushing as shown in my previous post. I believed that the bushings could not be changed as 2011 Recon (Silver) manual says so, but then I heard that they could be replaced and looked into 2013 manual which did not contain the info, that lower legs should be replaced after bushing wear.

I then tried to reason between running it with the broken bushing until it breaks, taking it to local shop for bushing replacement or buying new bushing and trying to fix it by myself.

The little engineer/mechanic in me took over and soon I was googling how the bushing could be replaced. I finally found a post on mtbr.com forums that had some good stuff written by username bad mechanic . So I ordered new 32mm bushings and started gathering materials for the tools.

M12 washer seemed to be properly oversized to make the extractor tool.

32mm_bushing_and_washer_for_removal_tool
32mm bushing and M12 washer. NOTE: the old and compressed bushings were only 34.5mm, so proper tool diameter would probably be 34mm.

Continue reading “Recon Silver bushing replacement part 1: removal”

GoPro mount adapter for bicycle lamp

It is best to have as much light as possible when mountain biking in the dark. Mostly this means to have at least two reasonably powerful lamps, one in the handlebar and another in your helmet. The one in the handlebar should point pretty close to give you peripheral visibility in front of you while spotting the route ahead.

I wanted to have some easy mounting solution for my helmets and GoPro mount was an easy choice as I already had some mounts on my helmets. I started working with an J-buckle as it already has holes in it for easy screw attachments.

J-buckle in parts
J-buckle in parts

I then took a small piece of 20mm electrical tubing and attached it to the mount. First try revealed that there was a small clearance issue between the rubber band on the lamp and GoPro mount.

Tube, clearance issue and fix
Tube, clearance issue and fix

Continue reading “GoPro mount adapter for bicycle lamp”

Fixing reverb remote with bent piston & broken bushing

Last summer I managed to ride into a pretty severe OTB (over the bar), which resulted in a few weeks break from driving, buying knee and elbow protectors and the most severe of them all, a broken Reverb remote.

From outside I could tell that the remote had a bent piston and broken bushing. After the breakage, I could still use it a little on the rest of the ride, until it leaked too much and stopped working. The leakage resulted probably because the piston head was not perpendicular to the cylinder. Normally the bushing keeps the button level and guides the (straight) piston rod and centers it in the cylinder.

Bent piston and broken bushing
Bent piston and broken bushing

When I took the remote apart I also found that there were some scratches inside the cylinder, probably due to still using the remote after the initial breakage.

reverb_remote_parts

scratches inside the cylinder
scratches inside the cylinder

Continue reading “Fixing reverb remote with bent piston & broken bushing”

How much temperature effects the pressure?

I heard/read multiple instances of people pondering if they should or shouldn’t change their tire and/or shock  pressure for winter. This got me thinking how much of a change there is and should I take it into account?

Science to the rescue!

Ideal gas law
Ideal gas law

In this scenario the amount of gas ( nR ) does not change and also the change in volume is not significant. We can then derive the following equation to calculate the necessary fill pressure to achieve a desired riding pressure, based on the temperatures of filling and riding.

ideal_to_fill_pressure
equation to calculate the filling pressure

Continue reading “How much temperature effects the pressure?”

RockShox Reverb rebuild (without Reverb bleed tools)

I have a 125mm RockShox Reverb (A1) in my Enduro bike. The bike was bought second hand and the Reverb had some sag and extended easily if bike was lifted from the saddle. So it was clearly in need for full rebuild but I was lazy and kept riding as it still mostly worked.

Then came winter weather with -10 degrees C, which was enough for the Reverb in its current condition and it didn’t stay up anymore. At home I took it from the bike and it had leaked oil (or something similar but more gooey) under it, no use trying to fix it by pumping more air.

Oil / slime on the bottom of the post
Oil / slime on the bottom of the post
the foam washer had also given up
the foam washer had also given up
Leaked internal seal head and slimy IFP
Leaked internal seal head and slimy IFP

Continue reading “RockShox Reverb rebuild (without Reverb bleed tools)”

Doval 30T MTB3032 14% oval

After monitoring my current 2×10 (32-24 : 11-34) gear usage and comparing different oval chainrings I came to a conclusion, that Doval 30T 3032OCP would be good for my usage, but also ordered 32T 104bcd version.

  • only oval that is available for 104bcd in 30T size with the 3032 mounting system and 99.5bcd

    Doval 99.5mm bcd (image from DOVAL )
    Doval 99.5mm bcd (image from DOVAL )
  • “double oval” i.e. rapid transition to minor axis after power stroke on major axis (see mtbr forum for more pictures and details)
  • cheap and easily available from ebay

Continue reading “Doval 30T MTB3032 14% oval”