1982 FXB Transmission 4th gear shift issue

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bob1123
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1982 FXB Transmission 4th gear shift issue

#1

Post by bob1123 »

I'm working on a 1982 FXB. My brother bought it recently with a lot of issues. I've gotten all the issues sorted out except for a difficult shift from third to fourth gear. Other gear shifts are smooth/normal. When I go from 3rd to 4th it feels somewhat "crunchy" and won't go into gear unless I push it firmly into fourth. Once it's in fourth it rides good and downshifts smoothly. I tried to adjust the shift linkage and no change. I tore into the bike to check out an internal transmission problem. My thoughts are 1- the plate might be worn and isn't pushing the fork enough to go into gear, 2- the fork isn't shimmed right and isn't pushing the clutch dog over enough, 3- the dog/gear is worn out/broken. I took the top of the trans to look at the shifter plate. It wobbles back and forth a little, but not a whole lot. The plate doesn't seem worn very worn, the rollers and my shift fork adjustment tool fit pretty snugly. When I shift just the top it shifts very smoothly and rotates the plate well. I looked at the alignment of the forks. The forks seem pretty centered, no huge gaps on either side. I'm not super experienced at checking this though and the service manual isn't very helpful. The dog clutch and gear look ok from what I can see. No missing chunks or anything. Thoughts on what to check or focus on? Is the small amount of wobble left to right in the plate acceptable?
Mongrel505558
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Re: 1982 FXB Transmission 4th gear shift issue

#2

Post by Mongrel505558 »

I don't have a lot of experience with the cowpie shifter lids, but the rest of the transmission is pretty much identical to the ratchet top transmissions. You can shift it cleanly by moving the forks with the lid off, but not with the lid. The third/fourth fork may need to be shimmed toward fourth gear. I agree that it's difficult to tell when the fork is centered between gears. Hard to measure without moving the fork and the gaps are too wide for any kind of meaningful measurement with feeler gauges. There's a tool for the ratchet top trannys that transfers the position of the drum slots to the forks, so I assume they make one for the rotary top boxes, too. I find that if you're careful you don't really need the tool.

But if you have slop in the plate you're losing motion that would otherwise be pushing the fork toward fourth gear. Perhaps the combined slop in the linkage and plate just doesn't leave you with enough travel to get the job done.

Has the gearbox been apart before? The reason I ask is the 3/4 shift clutch can be installed both ways, but only works one way. The dogs are different on the fourth gear side, and they are marked. That clutch has to go in with the marked side facing the main drive gear or you won't get fourth very effectively.
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Re: 1982 FXB Transmission 4th gear shift issue

#3

Post by RUBONE »

Make sure the shift fork rollers are the correct type, the short -52 like Sportsters use, not the taller 4 speed pre cowpie type. The long ones can drag and cause lots of shifting issues.
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Re: 1982 FXB Transmission 4th gear shift issue

#4

Post by bob1123 »

Will report back with pictures and a video of the plate wobble tomorrow.
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Re: 1982 FXB Transmission 4th gear shift issue

#5

Post by nifty »

My 2c

Re poor shifting 3-4 with L79-84 trans lid

Additional to OE SM & Mongrel & Rubone replies

Particularly for FXB:
Slacken off both belts, check for run-out/wobble at trans pulley, grab or lever against pulley, check for MDG slop and end float.

I have found one late 4 speed where faces of mounting ears for inner primary were .020" out of square to trans shafts (low at front), Puts huge over-loads on mainshaft, MDG bearing and bush, and primary bearing, not to mention misalignment of 3-4 shift clutch and impossible to align chains or belts. I found by measuring freshly rebuilt trans. Maybe a one-off, or there could be more like this. Would certainly explain problems and poor life of parts. I have always checked sprocket run-out, now I also check for equal height of mounting ears for inner primary.

-79 external shift linkage invariably completely worn out, AM complete kits avail for FL & FX

Shifter cover/lid, castle top, cow pie, -79, no H-D spec, lid clearance to shaft portion of carrier, detent plunger pushes cam-plate in one direction, which loads cover bore in one place, cover bore poorly lubed (not at all if trans run low on oil) bore of lid wears, limited scope for installing thin-wall bushing, aim for 0.003” lid clearance to shaft portion of carrier, assemble with Moly grease.

Shifter camplate -79 Deburr, smooth/polish cam tracks, particularly sharp edges which can snag rollers.

Shifter pawl carrier: -79, centraliser pin .250”, chamfer edges; deburr (for ease of installing springs).

Pawl clearance to carrier pin -79, no H-D spec, aim for max .010”.

Shifter pawl carrier end float, plate shift, -79, no H-D spec, aim for .005” (after shimmed)

Shifter linkage shaft end float, plate shift, -79, no H-D spec, aim for .005” (after shimmed)

Shifter linkage shaft, lube with Moly grease.

Pawl carrier springs, -79, ends deburred & polished.

Cam follower/detent housing: -79, lap plunger to bore.

Cam follower/detent spring, -79 ends deburr &, polish.

Cam follower/detent plunger -79, polish.

I also lap shift clutches to shaft splines (all transmissions)

Nifty
bob1123
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Re: 1982 FXB Transmission 4th gear shift issue

#6

Post by bob1123 »

Thanks for all the help! This is my first time tearing this deep into a 4 speed. I know parts of this bike have been apart before. I wouldn't be surprised if the trans has been apart too.

Didn't think to check the main drive pulley, will check when I can get back in the shop.

I made two videos and uploaded to youtube:

First showing the small amount of wobble in the shift plate:
https://www.youtube.com/shorts/fKPgKBsqvv0

The second showing the forks. Angle for the camera isn't perfect, but seems pretty centered in person. The cowpie specific tool was a pain to source.
https://www.youtube.com/watch?v=WsLXIQNnEPM

I did find some small chunks of metal in the kicker cover. Looks like small pieces of an old gasket or locking tab? The larger pieces are thin and can be bent by hand. Now thinking I might need to tear it down completely and clean everything.
20230604_224140(1).jpg
20230604_224148(2).jpg
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Re: 1982 FXB Transmission 4th gear shift issue

#7

Post by RooDog »

Are you going to keep the belt drives?
Front, and Rear?
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Re: 1982 FXB Transmission 4th gear shift issue

#8

Post by Mongrel505558 »

From the looks of the throwout bearing oil slinger, water has gotten into that transmission. I would definitely tear it down just for that. While you're at it replace the mainshaft ball bearing. There are some really cheap ones out there. Try to find a decent one. Look for rust and pitting on gears and everything else.
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Re: 1982 FXB Transmission 4th gear shift issue

#9

Post by RooDog »

If it were not for the rear belt drive I would recommend getting rid of the cow pie tranny, and going with a 5 into 4 conversion using Harley guts They are of much better design than the antiquated 4 speed, and give better gear ratios.
As for the rear belt, I do not have personal experience fitting a 5:4 tranny with a belt pulley, so I'll leave that up to the experts....
....RooDog....
bob1123
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Re: 1982 FXB Transmission 4th gear shift issue

#10

Post by bob1123 »

My brother wants to keep this bike as original as possible. Keeping the rotary and belts is a priority. Any thoughts on the wobble in the cover? Is the amount of play in the video acceptable?
bob1123
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Re: 1982 FXB Transmission 4th gear shift issue

#11

Post by bob1123 »

Dog clutch between 3rd and 4th was installed backwards in the trans at some point. I think that was the shifting problem. Small chunks pictured were from the mainshaft bearing on the kicker side, the little metal cover on the side of the bearing had gone to pieces. No junk in the main part of the trans, just the kicker cover. There was some play in the drive sprocket with the belt off. Going to run everything through the parts washer, replace mainshaft bearings/seals and re-assemble. Everything else looks good.
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Re: 1982 FXB Transmission 4th gear shift issue

#12

Post by RooDog »

Funny. The 1-2 clutch is non directional, but the Hi, 3-4, clutch is marked which way it needs to be installed. An easy mistake to make, but inexcusable....
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Re: 1982 FXB Transmission 4th gear shift issue

#13

Post by Mongrel505558 »

"An easy mistake to make, but inexcusable...."

And won't shift. If you look at the shape of the 4th gear side of the 3/4 shift clutch and the mating surface shape of the main drive gear, the direction of rotation of the components, and where the forces are being applied you should be able to picture why. The ramps are there to assist and maintain engagement.
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Re: 1982 FXB Transmission 4th gear shift issue

#14

Post by Mongrel505558 »

bob1123 wrote: Sat Jun 10, 2023 10:03 pm Dog clutch between 3rd and 4th was installed backwards in the trans at some point. I think that was the shifting problem. Small chunks pictured were from the mainshaft bearing on the kicker side, the little metal cover on the side of the bearing had gone to pieces. No junk in the main part of the trans, just the kicker cover. There was some play in the drive sprocket with the belt off. Going to run everything through the parts washer, replace mainshaft bearings/seals and re-assemble. Everything else looks good.
The reason I pointed out that it looks like you had water in your gearbox at some point is because of the rust and pitting on your throwout bearing. I had a mainshaft bearing eat itself because of water damage. Anyway, good luck with it.
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