Another Tach and Charging issue. J100STLESB

[M Strawn]

I have a J100STLESB, (1990 100GT). I noticed my Tach began intermittently dropping out, usually at lower RPMs. Next thing I noticed was low voltage on the meter in the dash. Some research here led me to believe that the rectifier has gone bad. When I start the engine I do not measure any increase in voltage across the battery terminals at any RPM. I do see a hairline crack in the potting compound on the top. I followed the procedure posted by Joe Reeves to check the 35 amp water cooled unit. I got no difference in Tach operation when I moved the gray tach wire to either of the two yellow wires in the rectifier bundle. Should I suppose that the tach has also gone south?

 

[Barnacle_Bill]

Most likely just a bad rectifier.

 

[emdsapmgr]

Your model does not use a rectifier. It came from the factory with a combination rectifier/regulator. It's water cooled and sits under the flywheel at the top of the block. Part number: 583529, which supercedes to: 585195 Likely that's the part that needs replacing.

 

[M Strawn]

Thanks for the input, I have one on the way. Looking at the bolts it would appear that the flywheel has to come off, no problem with that but, how does one prevent the flywheel from turning while re torquing? Special tool required?

 

[emdsapmgr]

Yes, it's tricky. You can purchase an automotive flywheel holder inexpensively at an auto parts store. It's torqued to 100-105 ft lbs, so it's got to be held securely in order to remove the nut. I would not wedge a screwdriver between the flywheel teeth and the block, as something may break in the process.

 

[M Strawn]

Thank you for the input. It's running nicely and charging nicely now.