1986 k10 305 Questions

[Tracy06]

Hey guys, First post and first time square body owner. I bought an 86 k10 swb with a 305 in it, 4x4. I had to do some brake and starter work to it but yesterday was really the first time that i got it out on the road. Im not sure what tranny it has in it, but it shifted 2 times (auto) and the cruising rpm at 55mph was around 3200. I feel that that is alittle much but I dont really have much to go on? The truck has 33s on it which probably make a difference. Can anyone tell me how to the find out what tranny I got and if 3200 is normal? All the tags on the door and stuff have been mismatched and what not due to it being a basket case of body parts. Thanks.

 

[Charlie]

 

[75gmck25]

Unless your speedometer or tach are off, you have some really low gears. If you take a look at the chart on this site, it provides the rpm for different tire sizes at 65 mph. https://tiresize.com/gear-ratio-calculator/
Based on this chart, you have lower than 4.56 gears, which are the lowest stock GM gear option I am aware of for a square body. Also try using the GPS on your phone (in Waze or some other app) to verify that your speedometer is correct.

There are several sites with pictures of the transmission pan shape for a TH350 3 speed auto, and a TH700R4 overdrive transmission. Just compare pictures to figure out what you have.

Bruce

 

[Tracy06]

Unless your speedometer or tach are off, you have some really low gears. If you take a look at the chart on this site, it provides the rpm for different tire sizes at 65 mph. https://tiresize.com/gear-ratio-calculator/
Based on this chart, you have lower than 4.56 gears, which are the lowest stock GM gear option I am aware of for a square body. Also try using the GPS on your phone (in Waze or some other app) to verify that your speedometer is correct.

There are several sites with pictures of the transmission pan shape for a TH350 3 speed auto, and a TH700R4 overdrive transmission. Just compare pictures to figure out what you have.

Bruce

Thank you for the info. It definitely feels like and sounds like its turning that many rpm when cruising. I might have a transmission problem, not sure maybe its not shifting all the way.

 

[Tracy06]

It looks like the truck has the th350 transmission in it by the looks of the pan. So that should only have 3 years and two shifts correct?

 

[HotRodPC]

The truck should have a Th350. That gear raitio is likely a 4.10. Those the gear calculator is accurate, he may not be configuring for Non Lock Up converter. That'll set you back 200-400 rpm so it's proabably 4:10.

 

[Tracy06]

Is there a way to tell gears? Turn of the rear tire vs turn of the drive shaft?

 

[HotRodPC]

Yep !!!

http://www.gmsquarebody.com/threads/how-to-calculate-gear-ratio-wo-removing-covers.3860/