Airhead Tech Pages


Slash 5 fork rebuild

John Briggs and Kim Dromlewicz


Fellow Bimmerphiles:

I thought I would share my adventures rebuilding the front forks on my 71 R60/5 with you. This all started with a strange clunking noise whenever I hit a substantial bump. I pondered the various causes and sent a missive to the list and the consensus was that my fork bumpers were likely to blame. I proceeded to tear down the front forks and will include this in my discussion since there are a couple of ways to approach this.

First I removed the front wheel, fender, handlebar brackets. and loosened the fork boots. I then removed the fork top pin caps and large nuts securing the fork to the top steering bracket. The fork clamping bolts on the lower steering bracket were then loosened and the forks eased out of the two brackets. I have found that my headlight brackets etc stay in place no problem when I do this.

I now have the entire front fork assembly off the bike. I then removed the lower nut and washer at the fork bottom and removed each fork tube from the lower aluminum fork assembly.

I could have used another approach to this point. Rather than remove the tubes from the steering bracket I could have removed the nuts at the fork bottom and slid the lower fork assembly off. Even though this may have been quicker I would still do it my way since this avoided working upside down on the lower fork tubes while removing and refitting the shock absorber assemblies.

The shock absorber assembly is held in place in the fork tubes by a circlip and a screwed pin fitting. These are very easy to remove and should not be a problem. I then removed the shock absorber from the fork assembly. This slides out and essentially provides a piston type fit to the fork tube with three wiper rings on the top barrel of the shock assembly.

The prognosis was right on the money. I no longer had any bumpers!!! Not only had they deteriorated but they had disintegrated leaving a few lumps in the bottom of the fork legs and a lot of sticky rubber crud over everything. I disassembled the shock absorber assembly and cleaned all the parts taking care to clean the lower ball and spring, and the upper valve which seats against the upper shock barrel and is held in place by a spring also. I was impressed with the simplicity and robustness of the design. Nothing too tricky or fancy here!! I had to fiddle a bit with one of my valves since it was seized on the shock rod.

When I ordered the replacement bumpers etc I could not get a set of wiper rings for the upper fork barrel. Lee at BMW Motorrad could not help so I was most careful in cleaning these rather fragile little things. I didn't try any other place (perhaps someone can offer some advice here). I also forgot to order the gasket that goes at the bottom of the shock absorber assembly where it bolts through the lower aluminum shock leg, so I ended up making one.

The reassembly was very straightforward except for the part where I had to recompress the wiper rings on the upper shock barrel to reinstall in the fork tubes. I ended up using a piece of aluminum from a soda can to fashion a ring compresser. This is the part I would not want to do upside down with the fork tubes still in the bike!!!

I also had a little sag in my front fork springs so rather than fork out (sic) more money I made up two one inch spacers which I dropped in the top of the fork tubes on reassembly. This seems to work, however I will likely replace these springs this winter.

My front forks work beautifully!! 5 weight oil of course , and even that is a little heavy for cold mornings.

I would highly recommend that anyone with a slash 5 who has any fork problems check this out. It is not difficult and with any luck can be done in 4 hours.

Cheers
John Briggs
john.briggs@fwc.com

To Jim Buchanan

Please go right ahead and use this write-up. In my opinion once you hit that send key anything you write belongs to the universe. I would suggest that you also tag on Kim D's reply (below)

John Briggs

Kim Dromlewicz:

          
     ] One thing is that the 3 metal compression rings on the top of each 
     ]shock piston rarely, if ever, need replacing.  This is according to 
     ]several BMW mechanics that I asked.  They said that the only time 
     ]they need replacing is when someone has damaged them.  So don't 
     ]concern yourself unnecessarily with the fact that they weren't 
     ]replaced


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Last Update: 11 September 2010