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General Category >> Rubber Side Down! >> occasional grind when downshifting to first
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Message started by Robertomoe on 09/26/07 at 16:53:42

Title: occasional grind when downshifting to first
Post by Robertomoe on 09/26/07 at 16:53:42

Im pretty sure there's an easy answer to this, but I dont know it yet

Sometimes when I am downshifting into first the pedal will vibrate and give out a grind noise, something Ive heard on cars before but never on bikes. What is it?

and yes, clutch is in

Title: Re: occasional grind when downshifting to first
Post by Brewbrother on 09/26/07 at 17:16:04

JMHO, but I think you are going to fast to shift into first gear. Apply the brakes for a moment, then downshift.

Title: Re: occasional grind when downshifting to first
Post by forrest on 09/26/07 at 17:18:19

Yep, if you are still going too fast your bike may protest a bit going into first.

Title: Re: occasional grind when downshifting to first
Post by rokrover on 09/26/07 at 17:45:29

Usual...... first gear takes a while to spin down to stationary (because of the arge ratio difference) so the dogs can mesh quietly when clutch is pulled. I have two approaches -
1) pull clutch and wait several seconds (3 or more) before shifting down from neutral - OR -
2) get the bike rolling by pedaling with your feet (or downhill roll) so mesh speeds on mainshaft / layshaft match up before engaging first.

Bike transmissions don't have the benefit of synchromesh cones that match the locking dog speeds on input / output shafts to ease gearshifts in autos.

Title: Re: occasional grind when downshifting to first
Post by Robertomoe on 09/26/07 at 20:17:16

so even if Im coasting to a stop and I want to downshift it early and hold the clutch the whole way, I should wait until its in the right range?

Title: Re: occasional grind when downshifting to first
Post by grandpa on 09/26/07 at 20:49:46

YES!!

Title: Re: occasional grind when downshifting to first
Post by justin_o_guy2 on 09/26/07 at 21:00:16

If you are in a hurry to downshift it to 1st, let the clutch out in neutral & give it a throttle blip, that will spin the tranny guts up to match the belt spinning the output shaft. Pull the clutch & downshift. IF you are wanting to let the clutch out, hold the engine rpm up high enough to not drag the rear wheel. Then roll throttle off.

Title: Re: occasional grind when downshifting to first
Post by Rockin_John on 09/28/07 at 00:37:01

Assuming you have a 5-speed; its second gear is only slightly higher than first on the older 4-speed. If you aren't a heavy weight, or starting uphill, you have the option of pulling away from a stop in second gear. It doesn't require much clutch slip, and probably little or no damage done to the clutch. Clutches are easier to replace than gears. Try it and see if it is has potential for you.

I can do it smoothly, without chattering the clutch, and a minimum of slippage, and I weigh in at 250+! Like I said, it's not much different from taking off in first on my 4-speed 87. In fact, if the pavement is smooth, after slipping the clutch for 5-6 feet on the 87, I can dump the clutch; grab a big handful of throttle, and spin/smoke the tire across an asphalt intersection! What fun!!!

Title: Re: occasional grind when downshifting to first
Post by justin_o_guy2 on 09/28/07 at 10:42:00

If I want to, I can run the bike down from 5th to first & never use the clutch & not lurch the bike around, but the wrist & toe timing between second & first is a trick, BUT, there's NO way I can spin the rear tire. All I can get is a wheelie.

What am I doing wrong John?