Newbie needs your help

[Philipf9]

Ok guys, I'm a newbie and have gotten into the square body's to help my son with his first truck. So please be kind and help me out. I don't understand all the tech talk but I'll try. My son is looking to buy an 86 k10. It's had been altered and not stock. It has a 350 small block, 4 speed manual with granny gear. The axels have been changes from 1/2 to 1-ton with 4.10 gears, 35" tires and 4" lift. From my driving it, I seem to go through the gears pretty quick (2-4). The rpm gauge is after market so I don't know if I trust it, but at 45mph, it's seems to be running hard. At 60, it's screaming pretty loud. The aftermarket gauge says its at 3200. I guess my two questions are, is this normal sounding or does something odd about that setup jump out to you? Is this a decent setup for a 16 year old to cruise around town and on occasion cruise down highway?

Thank you in advance for all your help and advice!

 

[1987 GMC Jimmy]

Welcome! So first thing, that gear ratio is really short. Something for just cruising would be like a 3.08 for instance or taller. The RPMs are gonna be high with that ratio. Plus, that SM465 is not overdrive like a 700R4. That granny gear is just for crawling so it doesn't last long in the scheme of your power band, especially not with those gears. I'm all for people getting into square bodies, but that is a big truck and being a lifted K30, I don't know that a 350 is really doing it justice. A similar, however unmodified, setup from the factory would have more than likely come with a 454. Most square bodies in stock or even somewhat modified form with Small Block Chevys, 6.2s, or Six Bangers get respectable truck fuel economy. This one will not. I'm not trying to be negative, but those are some things that I see. It's a lot of truck, too. My little brother is sixteen, and he's building his own out of two trucks. It's gonna be an '82 K10 with a somewhat built 350, built 700R4, and moderate gearing. It'll be a fun truck, but I don't see that as too much truck for a first vehicle in terms of girth. My verdict is maybe look for something more modest that's cheaper and has a better power and drivetrain combination. But that's my opinion and only that. Good luck!

 

[rich weyand]

4.10 gears in final drive with 35" tires should only be 2360 rpm at 60. Something's goofy.

4.10 gears with 35" tires is same as 3.4 gears with 29" tires, so that's not out of line.

Either the speedo is off, the tach is off, the tire size is off (except you can just read that off the tire), or the gears you were quoted aren't what's in there.

The speedo could be way off if they changed the axles and tires but not the speedo gears. 3200 with 4.10 gears and 35" tires should be 80 mph.

First thing I would do is run it 10 mileposts on the interstate and see what the odometer difference is. Say it's 9.2 miles. Then displayed speed is 92% of actual speed.

 

[77 K20]

You will get a lot of opinions on this I'm thinking. For a first vehicle I think it would be a good one. Things to consider about it would be the lack of air bags (for safety) and the fact that it can be hard to see especially when backing up (little cars can dissappear under the tailgate). Sometimes those rounded stick on mirrors that you attach to the side mirrors can help see the sides of the truck for dogs/kids/small objects.

It should be a tough truck in case of a mishap though. Sliding into and over a curb, or something like that should result in basically no damage. Also they are fairly simple to work on so it can be a good vehicle to learn on. I learned on a '78 K5 Blazer.

Driving it around in town should be fine except for poor gas mileage. Teenagers typically have a heavy foot. Power should be ok- I doubt he'll be towing trailers right?

Are you sure it has 4.10 gears? Some of them had 4.56 gears in them instead. Or have you checked the speedometer with a GPS or an app on your phone? Either way being around 3,000 RPM on the highway is fairly normal for the older trucks that don't have overdrive. Mine with 4.10 gears, 33" tires and an automatic is at 3,100 RPM on the highway. I've finally put quieter mufflers on it to tone down the "screaming". But it will do it all day just fine.

And with a 35" tire the true measurement is probably closer to 34"

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[rich weyand]

Yeah, so with 4.11 and 34/35" tires, he's right at the yellow-green boundary, which is good.

I think the speedo is way off. Or the tach. Or both.