slow tach

[Anonymous]

This summer when I started my 78 GS750, the tach moves slowly to about 2500 rpm then no further. When I shut down the bike its slow to return to zero. I took apart the cable and lubed it with no change. I took apart the gauges and found it sealed. I found the links here about taking apart the gauges and gluing it back together. My question to anyone in the know, is there any "user serviceable" parts inside? I tried leaving the gauge with the cable hole facing up and using a little liquid wrench around it. I was hoping it would work its way in and loosen up whatever is holding it up. No go with that either. Any suggestions?
Thanks,
Gary

[jonr]

Re: slow tach

Gary,

I've been inside both my gauges. There aren't any serviceable parts, but the parts in the magnet/spring/shaft mechanism should be oiled and move freely.

Taking the gauges apart is labor intensive and touchy. You may just want to try to score another tach on ebay. If you're up to it, then take it apart. DON'T pull the needle off once you have it open!

Good luck,
Jon

[Anonymous]

i found it pretty easy to remove the black metal ring clamp that fits the clear face to the orange cylinder body of the instrument. The ring has rolled edges on both sides that crimp the two plastic pieces together and with a small flat screwdriver it took me <5 minutes to pry up one side of the rolled edge so that the three pieces could come apart. Reassembly is as easy as re-crimping w/ a pair of pliers.

unfortunately, I couldn't figure out what was wrong after getting inside, and ended up finding a used one at a pick-n-pull place in town for $20.

[Anonymous]

Thanks guys!
I was afraid of that. I'm not afraid of labor but I hate laboring for nothing. I think I'll look into a new tach. Thanks for saving me a few of hours.
Gary

[Hotblack]

I hate to complicate things but your situation sounds exactly like what whas happening to my 550. I took the tach apart and the lube for the needle was quite gummy. Cleaning it and relubing it worked for me, three years of trouble free rev counting so far. Another thing you can try is drill a small hole in the side of the tach so that you can get a piece of wire in there and try to free the needle up manually. Just be carful not to scratch the face of the tach up. Either way I bet your tach is quite fixable.

[Anonymous]

Two points: 1) Try removing the tach, turning it over and putting a little light oil into the hole where the cable end goes. 2) Check to make sure the drive end (engine end) isn't spinning on the cable itself.

My tach was acting up like yours, and a loose end piece was the problem. I thoroughly cleaned and degreased the parts and stuck them back together with good ol' JB Weld. It's been holding for at least 3,000 miles so far and works fine.

The oil in the drive cable hole has helped to stabilize the needles in both my tach and speedometer. I'm sure you've already cleaned and lubed the cable.

[Anonymous]

Well, I guess I'll give it a shot. Most that can happen is that I'll have a broken tach. Not much different than what I already have. Thanks for the help.

[mark m]

The oil in the drive cable hole has helped to stabilize the needles in both my tach and speedometer.

I don't want to hijack this thread, but since we are talking tachs and it saves another tach question...

I have the opposite problem - I think my tach is reading high. It is definitely slow to come back down with the engine revs when I upshift or if I pull in the clutch and let the revs drop to idle. Also, I would swear my highway revs took a sudden leap up by about 400-500rpm a while ago, but it now seems stable, if not completely accurate.

Anybody have any experience with this sort of an issue? I will also be trying the oil in the drive cable hole when I get a chance to see if it improves the situation. Any thoughts on maybe putting some Varsol or kerosene (or WD-40) in first, to loosen everything up, then the oil?

What does the group like for lubing cables?


Mark

[chrissinc]

Mark is your tach an electronic one like on my GS750EF?If so I had a similar problem when I took the instruments apart to replace the cracked glass. Somehow when I put the thing together the rpms were about 1000 rpm too high, I had to re-open the tach and manually calibrate it by turning the needle slightly under the 0 rpm mark, not very sophisticated but the tach works like a charm now. No problems after 4 months so I'm pretty confident it's fixed. I also cleaned and lightly lubed the inards and the teeny bit of wobble in my speedometer at 45 KPH is gone now too, solid as a rock. Sometimes a clean and lube will do wonders. Can you take the guages apart and have just the tach sitting there plugged in whil the bike is running? I knew exactly where my idle was when the bike was warmed up so it was easy to calibrate. I may be 25-50 rpm too high at most, which is less than a millimeter on the tach.

[mark m]

Mark is your tach an electronic one like on my GS750EF?

Nope, it is a mechanical drive unit, cable driven off the exhaust cam.

I can see that I will have to get to pulling the gauges and trying the lube routine before anything else. It doesn't really screw me up, because the tach is working generally OK and the bike runs fine. I do have some other electrical issues to clean up (seems to be random grounding in the headlight bucket connection cluster) and I will clean and check all the wiring and gauge cluster all at the same time. That will be a good weekend project in a couple of weeks here...


Mark