Sticky downshifts

ScottMDMC · Jul 8, 2013

Hey Guys,
I finally took my project MK3 for it's first road ride. Stuck the new tires on it Sat. afternoon and went for a spin. She felt great, nice and smooth and strait, I was excited. The only thing that concerns me is the downshifting. She up shifts nice and easy but the downshifting is not so. She does but, you have to blip the throttle and do a little more coaxing. After warming her up on that ride I changed the gear box oil again but have not had the opportunity to try another ride. She is not quite legal yet. Any thoughts?
Thanks, Scott

ML · Jul 8, 2013

if the clutch is dragging at all, I find the downshift suffers more than the upshift. Try re-adjusting the pushrod screw to a half turn out from contact and adjust the handlebar lever ferrule to allow 3mm of play at the pivot.

ScottMDMC · Jul 8, 2013

Thanks, I will check that tonight.

MarkR · Feb 2, 2015

sorry, "noob" here, I'm having exactly the same problem / issue. UpShifts fine, but I have to rev the motor to get the clutch to dis-engage (or is it engage?, I can never remember the correct term). When I've pulled in the clutch I can't downshift (4 down to 3, or 3 down to 2) unless I rev the motor, and it takes a second as I can feel a little torgue when I rev it before the clutch begins working. Anyway, when I inspect the clutch cable all the way to the gearbox and I'm not seeing a "pushrod". Is it in the gear box?

fyi, It's a fairly "new to me" 1974 850 Commando.

Thanks. Awesome Site. Great resource.

Snorton74 · Feb 2, 2015

The pushrod is #31. Its accessed through the primary behind the slotted clutch adjustment screw/bolt #47 in center of clutch.

Hobot · Feb 2, 2015

Could be a number of things besides above items. 1st thing to check next is primary chain tension is loose enough before tinkering deeper into drive train but AMC should be just as sweet up as dn.

MFB · Feb 7, 2015

Back in March 2012 I found a solution to my gearshift problem. After a full rebuild of the bike I could not get it to change gears. To cut a long story short, I eventually discovered that the face of the pawl ( a brand new one) was dragging against the edge of the ratchet plate. This meant that, after pushing the plate into position so as to select a gear, the pawl then dragged the plate back a little as it moved back to the central position. This movement wasn't enough to pull it out of gear, but enough to ensure that when the gearlever was pushed again, the pawl didn't engage with the next tooth on the ratchet plate but the same one as before, thereby just pushing it into the same gear it was already in.
After grinding some 20 to 30 thou off the face of the pawl, it now changes perfectly.
For photos and replies, search "Gearchange Problem Solved". Pawls are inexpensive and plentiful so it doesn't require too much bravery.

daveparry · Feb 7, 2015

It's always been necessary to "blip" the throttle when changing down on British bikes. I'm not sure if Japs are the same or not but certainly all the British bikes (and BMW's) that I've had have been this way. Unlike car gearboxes bikes don't have synchromesh so it's necessary to increase the revs. to get gear speeds to match each other.

pete.v · Feb 7, 2015

I think that having the rear wheel turning is more effective than blipping the throttle. There are points of acceleration at which you upshift and the same for what you down shift. I just cannot come to a stop sign and expect to click click click and be in first. I just doesn't work like that.

Even sitting static in the garage on the center stand, you need to spin the rear wheel to select different gears. Things need to be indexed into place.

It's a "rear wheel moving(turning)" thing rather than a "rpm" thing.

FYI. Please excuse me if I seem to be dumbing this down put some, I am just covering the basics here. Some obvious things get missed in translation of issue discriptions. I think some assume these (gearboxes) must fuction like a 4 speed in a car.

Beach · Feb 7, 2015

It might be the spring(#4 in pic) misadjusted...I had trouble shifting to lower gear, it acted like the ratchet wasn't working...After moving shifter a bit the bike would shift down...Don't know if this is the same problem or not by the description, but I guess it might be...

Hobot · Feb 7, 2015

aH SO the infamous pawl spring got me 3 times out of 2 AMC trannies. Main trick I learned was ignore the manual clearance between spring leg and pawl as long as ya get the 2 legs parallel in area the pawl swings by. One of my springs failed d/t rust but was not broken just lost enough springy ness I quess as couldn't get it to hold so fiddled a new spring to work and has for years since. Crooked spring leg goes to the bottom.

DogT · Feb 8, 2015

I'm with hobot, loosen the primary chain a bit and see how it goes. Not sure about the MK4 but the early ones were a bit strange to adjust, like mine. Better loose than tight, it seems to solve a lot of problems, even sticky clutch.

MarkR · Feb 14, 2015

Took awhile to find my way back to the garage . . .

So to be clear, I was talking about down shifting when in motion - at basically the same point/speed at each gear when I had up shifted (probably slower, but in the general range)( know I can't come up to a stop, and go from 4th to 1st). Anyway, the little torque I felt was when I had pulled the clutch in and "blip" whilst trying to downshift. I'd feel the bike surge for a second before the clutch would disengage. Is that normal?

So I followed the manual, and this website's instructions on adjusting the clutch . . . now I have a new problem which may or may not be related. When I kick the bike, the kick start doesn't "grab". It sounds like a ratchet clicking (it worked fine for about 3 kicks and then it stopped grabbing). Every once in awhile it grabs but mostly not. And when it does, it then "un-grabs" right when I put my weight into and then - pain.

Anyway, I've been reading / searching . . .

I've tried re-adjusting the clutch - even completely loosening the clutch cable and the set screw, and it's still "ratcheting" when I try to kick it.

Advice would be appreciated.
Thanks, MarkR

Beach · Feb 14, 2015

Grease on the clutch plates???

DogT · Feb 14, 2015

If it's not catching when trying to start, it's most likely the pawl is worn. There are soft ones (old) and hard new andover ones.

MarkR · Feb 14, 2015

so even though the "Haynes" manual says to replace the "Ratchet Assembly", you think it's the Pawl?
And it's something that can be fine right up until it's not?
Sorry for the Noob Questions.
Mark

Hobot · Feb 14, 2015

say WHat Mark? I looked in expecting to see the fault and solution joy but instead see a bad sign learning what a pain these things can be to toughen ya up so rest of life makes simple sense. Almost no one ever really knows what wrong till its finally fixed but one thing a lot of us learn is can be more than one thing at once. Once ya get the sludge trap cleaned out and finish waxing the new paint you won't need any the manuals.

MarkR · Feb 14, 2015

Sounds like it's not clutch related - correct?

Should I try both the Pawl and the Ratschit Assembly - shown as #3 and #20 on the Parts Diagrams in snorton74's post (parts 04-0111 and 06-2015)?

Are there other things I should do while in the "neighborhood"?

(is this going to be a can-o-worms?)

I got up this morning, wanted to do a little minor "tinkering" on the bike and then go for a ride, as it was a beautiful day. I replaced the Exhaust Rings and Squash Washers, replaced the 4 Rubber Muffler Mounting Bolts, Adjusted the Clutch, Cleaned / Polished the Header Pipes and Mufflers . . . Started right up, warmed it up, re-tightened the Exhaust Rings. Shut it off and went in to wash my hands, grab my helmet and gloves and . . . Murphy showed up.

Egholt · Feb 14, 2015

Have you replaced the kick start pawl (no.20 in the drawing) with a new one ?

I have replaced mine , the new one will not fit , until grinded down on the back .
It will engage both ways .

If you have replace it with a new one , check the curve on the back , with the old one .

Michael

Hobot · Feb 14, 2015

Again the trick with pawl spring is getting the leg sections the pawl swings by essentially parallel more than trying to match factory clearance. Pure old school trial and error tweaking checking then assembled tested. Crook goes down. Might be shocked at how much rust above oil level and pretty hard not to want to clear up the items and grease or paint to stop the decay but thats more wrenching and then thought might occur it'll neve be this easy again to check or refresh the wear prone bushes which can also snag sweet shitfs so put any thought of Commando short cuts out of mind or just use it till something obvious fails. Oh yeah I found a way to get my outter cover off pretty easy now, claw hammer claws in the fill hole to kind of bump the bottom half open first then ease it slightly bottom out cockeye'd on off and similar back on as mine seem to fight me it approaching squarely as common sense would guide w/o enough trial and error learn curve pains done. In for a penny down for pounds and pounds.

Sticky downshifts

Similar threads