Vehicle speed sensor bypass?

[yellowmedicine]

I have an 89 blazer with a 700r4 and want to swap in a sm465/np205. I have access right now to a pre-tbi sm465 and am wondering if there is any way vehicle speed sensor can be by-passed? Also does anybody know about a switch that was used on 87 and newer tbi sm465 equiped trucks? Something to help with fuel mileage at cruise speed or have I heard wrong. If so is there any way that can be wired to a toggle switch if I were to go with the older sm465? What year did they switch to a hydraulic clutch?

Thanks

 

[lectric80]

I don't know about any switch used with the sm465 that helps with fuel mileage.

As for the speed sensor, in that year they don't really have anything to do with the TBI computer so you should be able to swap out the speedo head and install the correct cable for one of the older Blazers with 465/205 combo.

I am not certain what year they went to hydraulic clutch.

 

[bronc3buster842001]

I just read about that switch. Here is where I read it. Its right above the pic of the shafts.


http://www.novak-adapt.com/knowledge/sm465.htm

 

[AJMBLAZER]

Vehicle speed sensor...you mean the VSSB for a speedo?

The '89 doesn't have that. Started in '90.

 

[yellowmedicine]

Good call AJMBLAZER! I learned a bunch from this web site, www jagsthatrun com. I thought they all mounted on the tail of the tranny. Guess '87 through '89 run off the speedometer. Thanks for the help.

 

[AJMBLAZER]

The speedo gear is in the tailshaft, same as all of these trucks pre 1990.

 

[cabledawg]

85 or 86 was the first year of the hydro clutch. As for the VSSB thing, my 90 Burb had an electric speedo output, but my 465/205 had a mech. So my speedometer doesnt work, thus the VSSB doesnt work. Aside from the occasional trouble code (usually on longer cruising runs or engine braking), nothing else seems to be affected.

 

[yellowmedicine]

Ok. You should look into getting that hooked up. Your ecm uses vehicle speed to set fuel/air mixtures, idle speed, and a bunch of other stuff. They make aftermarket ones you can run off your speedo cable.

 

[cabledawg]

Aftermarket one I bought didnt work. Not the right signal output, even though it says it works with most stock setups. And really, it doesnt seem to affect the engine performance at all. But then again, I've got ~250k miles and havent changed the oil in 3 years, the plugs or air filter in 5, and the only reason it has new coolant in it was due to a hose blowing out last year. Even with all that, she averaged 20mpg while going from Kansas to North Dakota earlier this year.

See this is why I love this generation TBI and the 350SBC. Half the s*** could be broken and it'll still run