You are here

Slipping Boom

I have a faint recollection of a post about boom slippage, but may be confused - if this is a repeat question, I apologise.

My P38 boom has started slipping; counterintuitively, towards me. This has the annoying effect of converting the front chain retainer into a milling tool for the boom tightening screws. That, and the small retaining (spirol?) pin has dropped off: sheared or loosened, I can't say.

Am I using the cams incorrectly? Any top tips?

I had a challenging time getting a frozen crankset boom unstuck on an antique P-38, but never had your slipping problem, so I can't offer any good advice beyond the obvious: adding another coat of paint to the part of the boom that gets inserted into the main frame, maybe roughening it up with sandpaper and the like.

Call up Lightning and talk to Tim Brummer. If anybody knows how to deal with this, it would be him.

Safe riding,

On the slipping boom, just be careful tightening down the two boom pinch bolts. I had one of mine crack (LCD did a great repair of the frame) but now religiously tighten them with a "clicking" high-quality torque wrench set to 40 inch-pounds (I go to the bike shop and have them do it).

My P38 has a cam system, which a threaded frame boss makes difficult to adjust. I have improvised with a handmade plastic washer.

I had that same problem, if I am understanding your post correctly.
What confuses me is you say the boom slips towards you and I don't see how that is possible as one's feet would be pushing the boom away.
I'm not sure what you mean by front chain retainer either. Do you mean the front derailleur?
Ditto for the retaining pin. At least my 5 year old P-38 does not have one.

My boom would rotate to the left or right sometimes when I was applying really strong force to the pedals, usually when starting up on a rise from a stoplight.
I fixed it by lubricating the 2 pinch bolts that hold the boom in place with a light grease. DO NOT lubricate the boom itself.
I then tightened down the bolts but be careful of applying too much pressure and stripping them as another poster mentioned.

The Voyager has a plate on the front derailleur onto which the separated chain can be spooled for transportation.

Actually, you are only pushing the boom away at the bottom of the stroke by which time you should be reversing the pressure to pull (if clipped in). The chain, however, is pulling the boom back hard at mid stroke while the crank hub (BB) is free-floating and does not bear pressure rearward or foreword on the boom. Two or three things are key: Don't lubricate the boom in its sleeve. Tighten the pinch bolts to spec., as suggested, and apply Loctite. Stop parking the bike against the back wall of your garage at 10 MPH. chuckle chuckle......

I've been in touch with The Man (after getting 'stranded' at minimal torque, mid-ride). For anyone that faces the same problem, just spin the levers around until you get the correct tension: they won't necessarily be aligned neatly to the boom. The nuts only have a locking function.

I still really enjoy the bike, but in darker moments find myself wondering if mine was built on bring-your-pets-to-work day.


User login

Powered by Drupal