Need help with tach signal.

[JTroiano]

I need help with my tach signal hook up. I have a 96 Suburban that had a 350. I heard that you can solder a wire to a diode in the alternator and use that as a tach signal. The chevy was getting the signal for the coil. Any help or direction would be greatly appreciated.



Jon T

 

[JLEONARD]

On a first gen alt you don't need to solder a wire. You remove the rear sheet metal cover and connect to one of the rectifier leads under the screw head using a ring or U terminal.

I used one side of a speaker wire for my lead going to the tach.

Don't know if that's the same for a second gen or not.

You will then have to calibrate the tach using a handheld tachometer.

Jay

 

[JTroiano]

Thanks Jay, I'm trying to use the factory tach so I don't think I can calibrate it. I heard that it is pretty close. Maybe I should just start it and touch it to one of the diodes and see if it works?



Jon T

 

[JLEONARD]

No Jon not the diode... . one of the rectifier leads. That will effectively create an "R" terminal like the marine alternators have.

Unless the method is different to feed a tach designed for a gasser.

I've always used tachs designed to get fed from an alternator pulse.

The GM tach may be different.



Jay

 

[JTroiano]

I got it. It takes me a while. Thanks Jay. I'm going to try it and see what happens. If it fries it then I'll have to buy a nice new one. I was looking at where you were from. I used to work in Bristol at Stevens World of Wheels about 25 years ago.

 

[PToombs]

Try this, it may help; https://www.turbodieselregister.com/forums/showthread.php?t=132600&highlight=tach+wiring

 

[RyanB]

I am really interested in hearing if this works with the gasser tach and the signal off the ALT. On my conversion I had a Diesel tach and it worked great just wiring up the tach wire to the 2nd Gen Alt like mentioned above.



I would love to hear other details about the conversion... pics look great. Anymore? What intercooler are you using and do you have any close ups of the twin setup. ?



RyanB

 

[JTroiano]

Ryan, I had to cut the heck out of the core support to get it to all fit. The intercooler is out of a 97 vintage truck I think. I have a friend that gets me parts to free, because I work on his race car and I just give him a year range and he gets me the stuff. I had to cut all the ears off the intercooler and radiator. The turbo set up is the standard set up. I can get you some better pics if you want. I fab it in the truck to make sure everything fits. The intakes for the small turbo was tuff because I put the AC on top. I used a 94 Dodge pu frame. It was 1" longer that the chevy so I left it and used the extra length for clearance for the over sized front tires. I think I would have been better off using the chevy frame and adding the axles. It was a long process getting all the mounts and cross member made. Let me know what info you want. I wont be trying the tach signal for maybe a week. I am making the harness longer and still have some more wiring to do before I get to the tach signal.



Jon T

 

[JTroiano]

Sorry, I don't know how to put more that one pic per post. I just got high speed. Before I never bothered.

 

[JTroiano]

One more and I have to clean the kitchen before the wife comes home.

 

[JLEONARD]

I was looking at where you were from. I used to work in Bristol at Stevens World of Wheels about 25 years ago

Cool!

They are really big now. Fords, Chevys, some others. I haven't been past there in a while as I don't normally travel thru Bristol.

Jay

 

[RyanB]

Nice pics! yeah my rad support was cut up pretty good too but I have it back looking like it came out of the factory (metal work and braces) I am running a duramax IC though. I am about to put my twins on in the next few weeks only my configuration is going to be different. My large turbo will be sitting up on the fender with the 5" pipe comming right out of the hood. Its a trailer queen/pull truck now so its all good!

 

[JTroiano]

Jay, I started as a lube tech a long time ago. The guy next to me, tought me the basics of electrical diagnosis.



Ryan, I wanted it to come through the hood. But it isn't to practical for what I need the truck for. I wanted a chrome 5" stack with one of those flipper things on the top. The looks I would have gotten on the street. I tride to get the exhaust lined up on the two turbos, so there wouldn't be any wasted energy but there wasn't enough room to do it.



Jon T

 

[JTroiano]

OK. I have the alternator hooked up and it charges at 15 volts. I let it idle for a little and it stays between 14. 8 and 15 volts. Shouldn't it go down after the battey is charged? I also have the factory tach hooked to the rectifier. At idle it reads 3,000 rpm and a little off idle it reads 6,000 rpm. So how do you make it read accurate? Does some one know how to make a signal gererator thats adjustable?



Jon T

 

[autoworld]

the problem is you have a gas model tach, go to the salvage yard and get a diesel cluster, in the gm models, the tach gets its signal from the gm alternator but the pulley is too small to make it accurate. we did some r&d and had machined a replacement pulley for the alternator that brings it verrry

close, after we got that accomplished (for the 95 suburban that had a 350, now commonrail) we had them make us 8 for future use.

good luck

dawna

 

[RyanB]

I think its all with the tach and has nothing to do with the pulley! I used a Stock Dodge Cummins ALT with my GM diesel tach and it is 100% accurate and has the stock pulley on it. Other than having a $35 external reagulator in the setup which you can't even see back by the firewall everything is like stock with out having to have any funky brackets or pulleys. (I have heard of people haveing belt tracking issues with the brackets and pulleys that arn't stock)



Pretty sure if you put the Diesel tach in the truck like stated above it will work just perfect but that doesn't answer why the volts are so high... hmmmm



Keep us updated... Ryan

 

[JTroiano]

I called and alternator shop and they said 15 was OK. I'll keep an eye on the battery. If it starts cooking I'll do something. I didn't even think about a diesel tach. That would be to cool. I'll have to see if I can find one.



Another cool thing I found out is the 243 transfer case in the suburban and the 241 from the dodge have the same out put shafts and rear cones or what ever you want to call them. So the speed sensor and ring fit perfect in the 241. The output shaft even has the groves cut in it for the snap rings.



Two thing I've noticed when driving it is the steering sucks. Its tight but wont turn back to center on its own. I tried to adjust the caster but need to take the bolts out and loosen it up. I may have the preload in the steering box to tight. Has anybody else had this problem?



The other thing is when doggin it in forth it sound like the trans is rattling? Normal?



Thanks for all the help so far.



Jon T

 

[JLEONARD]

FWIW I recently replaced my alternator and regulator and am also seeing 14. 9/15 V.

 

[autoworld]

I think its all with the tach and has nothing to do with the pulley! I used a Stock Dodge Cummins ALT with my GM diesel tach and it is 100% accurate and has the stock pulley on it. Other than having a $35 external reagulator in the setup which you can't even see back by the firewall everything is like stock with out having to have any funky brackets or pulleys. (I have heard of people haveing belt tracking issues with the brackets and pulleys that arn't stock)



Pretty sure if you put the Diesel tach in the truck like stated above it will work just perfect but that doesn't answer why the volts are so high... hmmmm



Keep us updated... Ryan

right, the stock cummins has a bigger pulley, that's why we engineered one for the GM alternator, and as long as you are regulating the dodge one, its all good.

 

[JTroiano]

Anybody know where I can get a diesel tach cheap? The big wrecking yard here doesn't have one.



Jon T