R75/5 LWB Fork Fluid Situation

[olironrider]

… a couple items to consider: both the top spring retainer and bottom cap require a 36mm wrench; your tool roll came with one.



It is inadequate for the job. I use a 1 7/16” x 3/4” drive socket, shown above the OEM tool. The face of the socket you see, has been machined flat and smooth; to get a maximum grip on the bottom cap minimal wrenching faces; also minimizes scarring of the triple-tree top plate when removing the spring retainer, which is shallow also.

Equally important is that, both those items are torqued to 70 FTLB ! I have an inline adapter for my 1/2” drive torque wrench to the 3/4” drive of the socket. Care must be taken to counter-hold the fork/triple-tree assembly while applying that 70 FTLB… you can cause misalignment of the front suspension, otherwise.

Both the top spring retainer and bottom cap will “sweat” the thin fork oil through their threads. I apply a skim coat of LOCTITE 565 Sealant to their threads at assembly; this application also backs-up the large crush washer at the bottom cap. Doing the same to the top cap will help the crush washer involved, too.

Considering the torque involved, removing the bottom cap to access the bumper for replacement, requires the same care.

Attempts to “flush” old fork oil and debris out of the assembly by pouring liquid in from the top, has marginal effect. There are several parts in the damper rod head, more in the bottom of the stanchion itself that do not fully flush. These control compression and rebound of the forks; involve very fine “piston rings”; hair-fine springs with check balls.

Study this link to understand…

MAX BMW Motorcycles - BMW Parts & Technical Diagrams - R75/5 (2476)

BMW Parts for your R75/5 (2476) Production: 08/69-07/80 ECE

shop.maxbmw.com

It might help by removing the suspension springs; refastening the bottom cap to the damper rod and, using the now floating slider as a “toilet bowl un-clogger” to surge repeated volumes of cleaning liquids throughout the fork ?

When ready for fork oil, it is not just, “fill with new fluid”; measured 280ml per fork is the specification for a fully disassembled fork. Considering you intend to do less, I might suggest 265ml ?

How often have I seen, “Not Enough Time to Do it Right the First Time However, Plenty of Time to Do it Right the Second Time” ?

 

[80092]

So the top spring retainer was inadequatly torqued from the start. If properly torqued the cover with the pins would loosen without issue.
Place the top spring retainer in a vise with sandpaper to keep the retainer from spinning. Mount the pin tool and loosen. The sandpaper is applied to the aluminum sleeve.

 

[olironrider]

… another picture for the album: the Damper Rod !



From left to right: damper rod head with three(3) “piston rings”, upper valve puck and spring, “hour glass” shaped rod, three(3) piece lower valve puck, c-ring, bottom ball/spring check valve. The damper rod is about 12” long overall.

 

[schwarze]

Well, well, well...last week my brother and I took on the maintenance challenges of this old "survivor". After replacing the oil seal in the pinion gear side of the Final Drive Unit, our attention was upon the forks--removing the decorative caps (focusing on the one that is fused to the fork top spring retainer), draining/replacing the fluid in both tubes, and inspecting and cleaning/replacing the front drum brakes.

Removing the "fused" decorative cap was not a problem; we loosened the handlebars and hung them by rope above the bike without need to disconnect any cables/controls. Using constant downward pressure while unscrewing, we were able to control the "pop" when the fork spring pushed it free of the tube. We took the fused parts to a machinist who used a lathe the size of a Subaru to free the parts. Done and reinstalled with new washers from my Motorrad.

Thanks to all for your insights. The ability to exchange ideas is critical to prepare.

 

[schwarze]

Well, the job is done. The fused decorative cap and top nut were separated by a local machinist whose lathe, the size of a small car, did the heavy work as guided by his skill and experience. The fork fluid was changed, brakes inspected and cleaned, and the front wheel reinstalled. Thanks to all. These bikes are awesome.

 

[schwarze]

Update: Job done with the help of my brother and a friendly neighborhood machinist who separated the decorative cap from the top cap (spring retainer). These bikes were built for owner-involved repair. Great stuff.

Schwarze