Tachometer cutting in/out?

[jboogie13]

1991 ecodiesel, 1.6TD tach, Bosch alternator(original?) 173k.

So as the title states, my tachometer is cutting in and out. The belt will squeal sometimes but not all times when the tach cuts out. I have loosened the belt and all pulleys seem to spin freely with no wobble or play. Car has A/C and P/S. When the tachometer "cuts out" the needle will stay in the location shown in the picture regardless of speed or rpm. Sometimes i can goose the throttle and it will come back and sometimes no luck. Could my alternator be on its way out? loose W terminal? something in the tachometer itself? Im going to throw an alternator belt at it some time next week but i dont think that is the sole culprit. any help is appreciated!

[8v-of-fury]

Need a new belt, and it needs to be tighter.

The alt takes its signal from the W on the back of the alt.. but the alt has to be spinning in order for it to tell the tach what is up.

I had this exact problem when I got my 88 this past summer. If the alt slips at all, the tach will not read accurately.

[jboogie13]

it does seem like the alternator is spinning even with a squealing belt, but i guess the interruption in signal voltage is enough to throw it off. I should also add that 90% of this phenom occurs in wet weather, very rarely in dry weather.

[8v-of-fury]

You have an old belt that is loose. If it happens worse when wet, its loose. If it can slip that easily... its loose.

Yes, the alt still may be spinning but it is not putting out any amperage or a tach signal.

[jboogie13]

dammit, i hate when things get extra loose when wet . thanks for the help, i will throw one of them fancy gates lawnmower belts you Canadians swear by to fix the slipping. 

[air-cooled or diesel]

you can find gates at napa, and a good price too. dont over tighten belt, but you need a new belt.

[bbob203]

I have the absolute shortest possible belts to use for both the ac and alternator, I have manual steering. For the ac belt I'm using a gates xl green stripe part number is 9370 dimensions are 12mm width x 949mm outer circumference and for the alternator belt I'm using a gates xl part number 7265 dimensions 9.5mm/10mm x 690mm out circumference. in addition to the doing the belts I also cleaned and lubed the tensioner pulley bearing by pulling the shield off giving it a good bath and filling it with VW cv axle lube (this is key to keeping the noise down and this thing to not freeze up and kill your belt) and used a thin fender washer to correctly align the pulley. I was running this same ac belt for awhile and It has no wear and hasn't stretched past it's initiAl retension several thousand miles ago. I was running a conti belt after I took the failure of my previous solution i posted that ended with belt failure after 1000 miles. The conti belt probably had at least 5-8k (hard to believe)on it but it was still useable surprisingly I've never had a conti v belt shred on me cuz I always keep a close eye on it. I knew it needed replacing before to long so I went to my friendly oreillys and had them give me one size lower than the computer advised. this is where it gets a bit tricky maybe to tricky for some. In order to get both belts on you have to have to pull the airbox(turbo diesel only) and the harmonic balancer pulley. I spent about 1.5-2 hours screwing with it but it paid off. ac belt has >4-5mm of deflection not running and 0 running the alt belt has >4-5mm not running and immeasurable but slight and significantly less deflection while running than any other belt I've ever used previously with equal non running deflection. These gates belt are very well made and come with 3 year warranty.

[bbob203]

Both those belt cost me a total 25 dollars and some change. they work awesome drive around a bunch in some nasty Ivey rainy snowy crap the other day and had no problems where before I would've been squeeling it up all day. Cool thing about gates is they they can be slightly tighter than the conti belts and not stretch and wear. They only require 1 retension and they are good for quite awhile even in inclementweather. Hope this helps.

[92EcoDiesel Jetta]

I have practically the same car 92 eco w ac and pw str. I've spent countless hours and a fortune in belts fighting that stupid alt belt tensioner. One of the things tried was a 1/2 " lawnmower belt and I can tell you from experience it's only a temporary measure.

[jboogie13]

I have practically the same car 92 eco w ac and pw str. I've spent countless hours and a fortune in belts fighting that stupid alt belt tensioner. One of the things tried was a 1/2 " lawnmower belt and I can tell you from experience it's only a temporary measure.

I wonder if scuffing the pulleys to remove the glaze before installing a new belt would help increase the amount of time before the belt began to slip and squeal again. Or maybe coat the pulleys with something?

[Smokey Eddy]

i noticed often that the wire coming from the alternator would regularily break down and eventually disconnect and be held together by insulation only.

[jboogie13]

i noticed often that the wire coming from the alternator would regularily break down and eventually disconnect and be held together by insulation only.

which wire are you talkingabout, the w terminal?

[bbob203]

i noticed often that the wire coming from the alternator would regularily break down and eventually disconnect and be held together by insulation only.

which wire are you talkingabout, the w terminal?

w terminal wire that runs tach