How does a 4-sp transmission fail?

[dwyer12180]

Hi all ---

I have a 1973 R75/5 with 51,000 miles. Everything seems to be fine so far but I think the transmission is beginning to make howling noises (and I've got a weird vibration at certain speeds, like 50 mph. ??) The howl is barely audible in the wind and with earplugs, but I didn't notice it a month ago.

Anyway, I've heard that most 4-speed transmissions need work between 50,000 and 75,000 miles. My bike shifts fine (as far as I know) but does make all sorts of gear clatter in neutral. Seems to run OK.

When a 4-sp transmission needs repair, what will it do? What will happen to tell me that I'm on a short leash? I ride a lot and ride far, and I'm experiencing a little anxiety wondering if I'm beginning to have a problem. Lots of summer touring planned.

Anyone near the Albany, NY area who does transmission work? Or could take a look at this for me? Any other suggestions appreciated.

Thanks alot !

--Scott

[20774]

Certainly, the noises present a problem. I would think another telling thing would be more than spooge (a technical term!) showing up on the magnetic drain plug. If you start seeing slivers over metal, metallic or not, then most likely a bearing is going.

I think that if a tranny lets go, it's much more costly than fixing it proactively. Tom Cutter at http://rubberchickenracinggarage.com works on Airheads. He's in Yardley, PA, just over the board from Trenton, NJ.

[donbmw]

Sounds to me like you have a bearing going out. I had this on happen on my R90 last year. Something did not fill right and started smell gear oil getting to hot. Before it went over the last year or so I was getting a vibration on and off speed.

Don

[GregFeeler]

It does sound like you need to pull your gearbox and have it checked. The 4-speed /5 tranny is a different beast then the 5-speeds and there are (in my opinion) only a handful of people in the U.S. and Canada qualified to work on them. Another option would be to find a good 5-speed as a replacement. I have an R75/5 I've put 78,000 miles on and firmly believe there is a gear missing between 3rd and 4th on the 4 speeds. It's on my list to put in a 5-speed at some point.

[stevel]

Hi all ---

I have a 1973 R75/5 with 51,000 miles. Everything seems to be fine so far but I think the transmission is beginning to make howling noises (and I've got a weird vibration at certain speeds, like 50 mph. ??) The howl is barely audible in the wind and with earplugs, but I didn't notice it a month ago.

Anyway, I've heard that most 4-speed transmissions need work between 50,000 and 75,000 miles. My bike shifts fine (as far as I know) but does make all sorts of gear clatter in neutral. Seems to run OK.

When a 4-sp transmission needs repair, what will it do? What will happen to tell me that I'm on a short leash? I ride a lot and ride far, and I'm experiencing a little anxiety wondering if I'm beginning to have a problem. Lots of summer touring planned.

Anyone near the Albany, NY area who does transmission work? Or could take a look at this for me? Any other suggestions appreciated.

Thanks alot !

--Scott

Scott:

I had a similar problem with my 4 speed. It would vibrate at about 50 mph in 4th gear. I tore mine apart and by the time I priced all of the replacement parts needed, the expense was great enough to almost pay for a good used one. I purchased a /6 five speed for my bike, which made a great upgrade. It is a bolt on swap. The only unusual thing is that the clutch actuation rod for the /5 is too long, so you either have to cut down the /5 rod or get a /6 rod.

You will need to get rid of the 37/11 rear drive at some point and get a higher ratio /6 rear drive. The swap will make a huge difference, if you ride the bike a lot.

Sincerely, Steve in Smithville Flats, NY