Specialized rear shock "Brain" rebuild with pictures & now forks too

[link1896]

I'd just machine a "dimple" on the inside of the air can at the point where you want equalisation to occur. Measure the dimple position off of one of your air cans that actually has the dimple. Use a dremel etc. with a small (2mm diameter) rotary burr. Give it a good polish afterwards to remove any sharp edges. You will not need much of a "dimple" because of the relatively high pressures involved. If you can, measure the wall thickness of the can so you know how much material you have to play with.

Effectivly this is now a solo air vs dual air debate.

Things that make you go hmmmmm.

As usual summit, thank you for the input.

 

[link1896]

Redbruces shock has been rebuilt and passed the car park test on the second vacuum bleed cycle. Equipped with yet another handy IFP fill port with a Schrader valve.

 

[link1896]

Yet to tackle the negative air chamber mods.

 

[link1896]

orings and quad rings for the 2012 USA (2011 Aus) Epic 29er with Fox Brain rear shock

position	cs	id
brain adjust knob	5	1.5
aircan to damper tube quad ring	20	3.5
IFP	17.15	3.52
nitrogen stopper	20	2
brain ass seal	10.7	1.5
hose end x 2 (polyurethane)	4.5	1.8
metering rod to inside of damper shaft	3	1.5
air can to head	34	2
damping body to bearing	19.5	2
bearing to damping rod (polyurethane)	12.37	2.62
IFP fill port	3	1.5
bearing to air can	24.99	3.53
travel indicator	20.29	1.6

 

[link1896]

Shaft clamp for the fork cartridge rebuild. 9.05mm for the upper shaft that's a sealing surface, yet to cut my piece in half but it's nice and smooth on the bore.

Next two clamps are not for sealing surfaces so finish isn't über critical

 

[link1896]

Introducing the new, highly refined fox black suspension oil.

 

[slowmick]

looks like you cleaned your chain with it...

 

[SummitFever]

Pffft. That's hardly in need of a service. I can't even see any metal shavings in that oil... :spy:

 

[link1896]

Specialized rear shock "Brain" rebuild with pictures

looks like you cleaned your chain with it...

this cartridge came out of a fork I picked up on Facebook for 120 bucks as the "fork won't hold air". I found the air side bone dry.

clearly it's gone 4000km too far between oil changes.

nitrogen pellet grub screw was loose, all nitrogen charge was gone so IFP was rocking about during movement so it's worn significantly against the chamber wall, hence the filthy oil.

 

[link1896]

Pffft. That's hardly in need of a service. I can't even see any metal shavings in that oil... :spy:

IFP has had better days, oil got cleaner as I drained it so hopefully there is not too much carnage.

 

[link1896]

Specialized rear shock "Brain" rebuild with pictures

Long term plan is to eliminate the grub screw/pellet arrangement for charging the IFP pressure with an exterior Schrader valve out through the lower mounting rod ala dual air.

The rod is already hollowed out to the max

 

[hifiandmtb]

Keep going :llama:

 

[link1896]

Keep going :llama:

Is this like a slow strip tease?

One experiment to try is dropping out the brass mass to eliminate the lockout and see if the shim stack is still suitable.

 

[redbruce]

all nitrogen charge was gone so IFP was rocking about during movement so it's worn significantly against the chamber wall, hence the filthy oil.

Interesting, same issue as my brain shock had.

I estimate mine had done 3 years and maybe 4000k with previous owner and another 1200km with me before shock started leaking (and went soft on firm brain setting).

5000k is obviously too long a service interval for the rear.

The front has done the same but has only had lower leg services (as brain appeared to be working fine).

Now you got me worried.

 

[link1896]

Interesting, same issue as my brain shock had.

I estimate mine had done 3 years and maybe 4000k with previous owner and another 1200km with me before shock stated leaking (and went soft on firm brain setting).

5000k is obviously to long a service interval for the rear.

The front has done the same but has only had lower leg services (as brain appeared to be working fine).

Now you got me worried.

I've seen varying service intervals, always expressed as hours. 50 or 150 hrs from memory

My long term average speed is ~18 km/h.

900 hrs or 2700km. I think I had a loss of some performance in the cartridge that's still in my fork at approx 3000km, so I'm inclined to think 150 hrs is a good interval to stick to.

 

[SummitFever]

With that sort of blackness in the oil, there must be some raw aluminium surfaces in the cartridge. I've never seen oil go black like that when the internals are fully anodized. Hopefully the blackness is just from some un-anodized surfaces and not surfaces that have worn through their anodizing.

 

[link1896]

With that sort of blackness in the oil, there must be some raw aluminium surfaces in the cartridge. I've never seen oil go black like that when the internals are fully anodized. Hopefully the blackness is just from some un-anodized surfaces and not surfaces that have worn through their anodizing.

IFP is raw aluminium. All brain assemblies I've had apart feature raw aluminium IFP.

 

[link1896]

Fully disassembled fork cartridge

 

[SummitFever]

IFP is raw aluminium. All brain assemblies I've had apart feature raw aluminium IFP.

Bummer. Haven't seen that sort of cheapness since the old Marzocchi days. The oil was dirty by the time you got the cartridge filled and bled.

Maybe its time to build that home anodizing setup?

 

[link1896]

With that sort of blackness in the oil, there must be some raw aluminium surfaces in the cartridge. I've never seen oil go black like that when the internals are fully anodized. Hopefully the blackness is just from some un-anodized surfaces and not surfaces that have worn through their anodizing.

Damage is only to the IFP.