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Old 03-14-2017, 07:29 PM   #1
bobbylong
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Granny geared 71' K10, I need to go faster...

Fellow Chevy truck lovers

I have a ’71 K10 that I will be using as a daily driver (in the DC area) for about 18 months. It’s a 4 speed with a 350, nothing special, just a good old truck. I’ve had it stored in Oregon for the past couple years and have only driven it a handful of times, but enough to know that it simply wasn’t made for today’s highway driving. I will be driving it form Oregon to DC early this summer and as I said before it will be my daily driver for about 18 months until I transfer overseas.

I’m considering a transmission swap, gear change or something to help it get down the road at a quicker pace without putting so much stress and high RPMs on the engine. I’ve built several cars in the past and one 2WD truck, but I’m ignorant as hell about 4WDs. I’m looking to you (the experts) for ideas. Please don’t say, “just drive it the way it is” or “if you want comfort, get a new truck.” I would like some real advice. After all, working on this truck is almost as cool as driving it.

One thing I’m thinking about is pulling the front drive shaft and changing the gears in the rear, or maybe pulling the transmission and transfer case and putting in a cheap 5 speed or something. Whatever I do, is only going to be temporary until I return from my next deployment (of 2 freaken years!) when I plan to do a frame off rebuild.

Any good ideas?
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Old 03-14-2017, 08:07 PM   #2
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Re: Granny geared 71' K10, I need to go faster...

Pricey but, put a gear vendor overdrive in it. You can still use it in the truck after you get back from deployment. Try to find a clean used one!
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Old 03-14-2017, 10:30 PM   #3
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Re: Granny geared 71' K10, I need to go faster...

Here's how I see it:
change ring & pinion ( on the cheap, just do the rear like you said)

gear vendors - but you can only run this in 2wd, must shorten rear driveshaft

ranger overdrive by advance adapters - (they call it a gear splitter because you can shift into OD in any gear) cheaper than gear vendor, fits between trans & bell housing, can use in 4wd, must shorten rear, lengthen front drive shaft

NV4500 trans - gives you a 5th gear overdrive, cheaper than gear vendor. Depending on how you do it, close to or a little more than the Ranger

the quickest, cheapest, easiest option is to change the rear gears only
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Old 03-14-2017, 10:31 PM   #4
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Re: Granny geared 71' K10, I need to go faster...

Easiest thing to do would be put the tallest tires possible on it. If it is stock height a three or four inch lift would give you more room and not be hugely expensive. There are lots of tire speed calculators on the interweb you can use to research how much change you will see. Plus they would be easy to resell later. You didn't mention if it is a manual or auto tranny. Or what transfer case you have. If you have an automatic a later model 700r4 swap may be the way to go and it may work in your long term plans. These guys are Jeep guys but the site is full of information.
http://www.novak-adapt.com/knowledge/
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Old 03-15-2017, 10:35 AM   #5
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Re: Granny geared 71' K10, I need to go faster...

HO455

Currently it has a four speed manual in it, but ultimately I'm thinking about converting that to an automatic. I've heard automatics aren't as reliable or as resilient, but I don't plan to use it as much of a work truck or attempt any significant off road driving. I do however plan to pull my 68' Camaro on a trailer to local car shows at some point, but only a few times a year at best.

I'd like to make that conversion now, but I'm thinking it may be a little more complicated than I'm able to take on now. I'm guessing I'd need tranny, shifter, linkage, cross member, transfer case, drive shafts and whatever else...

I have no idea what type of transfer case I have, nor do I know how to tell. I'm guessing there'd be a tag or stamp on it that may say what it is?

Bobby
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Old 03-15-2017, 10:57 AM   #6
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Re: Granny geared 71' K10, I need to go faster...

Leave it the way it is, that's cheapest. You can change out the engine faster and cheaper than just about anything else. Except taller tires of course. What gears and tire size do you have now. Unhooking the front shaft and only doing the rear gears is lame... in my opinion.
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Old 03-15-2017, 11:50 AM   #7
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Re: Granny geared 71' K10, I need to go faster...

work truck use and stick shift = nv4500 and a round pattern 205 or 241 or my last choice 208 behind it all t-cases need to be of the 32 spline input gear .

work truck and auto with overdrive should be = 4l80-e and simple way to run tranny electrics is www.usshift.com been around for years . the new unit design does 4 different shift programs . ( if you have the older one its a simple upgrade fee for anyone interested )

same t-case options as the nv4500.

your k20 if my my dads old one was sm465 4 speed with np 205 t-case and 4.56 gears .

stock 4.56 & 235/85/16 ( 31.7") = 3320 rpm @ 70mph

nv4500 swap = 2535 rpm @ 70mph

stock again with tall 285/75/16 ( 32.8") = only drops from 3320 rpm to 3267 rpm

nv4500 with 285/75/16 ( 32.8") = 2450 rpm @ 70mph

these rpm's will be the same with the 4l80-e also in overdrive as the 4500 share .75 5th ratio

even if you went to a 34.5ish tire aka 35" its 2341 rpm @ 70mph .

hope this helps .

play here for the info I gave http://www.grimmjeeper.com/gears.html
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Old 03-15-2017, 12:14 PM   #8
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Re: Granny geared 71' K10, I need to go faster...

Well, since he has a K10 likely not 4.56, so he's probably on the cheaper side of the carrier break for taller gears. But then again, who knows what he has.

And, by the way, drive it the way it is, is real advise! Just saying that because OP posted that might not be good advise. Else get a GV (gear Vendors), that's what I would do.

I ran the 4.10s with 33s and loved it. I got 4.56s with my axle swaps and it's too low for highway and I'm probably going to stick with 33s. I am considering a GV. I have my ear to the ground to try and get one on the cheap!

But playing with taller tires is a great way to figure out what gears you want before you make the dive. In that instance it would be feasible to borrow some taller tires from someone and try them on the rear(just don't engage 4wd) then you can see if the effective ratio gets you where you wan to be, before you spend on gears and labor.

But you can plug in your gear ratio to get a rough on paper rpm like sweet did below.

Pictures of the truck and axles would be great. We are very nosy here... we like pictures!
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Old 03-15-2017, 01:17 PM   #9
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Re: Granny geared 71' K10, I need to go faster...

4.10's and 33" tires = about 3200 RPM at 70 MPH.

I drove my 69 that way for YEARS as a DD.

Have the engine ported, polished, and balanced while you're away, come back, drop it in, and enjoy!
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Old 03-15-2017, 01:26 PM   #10
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Re: Granny geared 71' K10, I need to go faster...

is me . . . I mixed info I guess.

he needs to pull a cover and find out what he has and we can help 10x better there.

just for kicks tho .

3.08
31" tire @ 70
no o/d = 2337 rpm
o/d swap = 1753 rpm
33" no o/d = 2195 rpm
33" o/d = 1646 rpm

3.42
31" tire @ 70
no o/d = 2595 rpm
o/d swap = 1946 rpm
33" no o/d = 2438 rpm
33" o/d = 1828

3.73
31" tire @ 70
no o/d = 2830 rpm
o/d swap = 2122 rpm
33" no o/d = 2658 rpm
33" o/d = 1994 rpm


keep in mind were is your power curve on your engine . to low a rpm can hurt as the motor dosnt work as easy as in the sweet spot.

and if you don't have a tach get one . you will be surprised what rpm you are turning to what you think you are . . . sounds are miss leading in this department and worse with non stock style muffler.
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Old 03-15-2017, 03:27 PM   #11
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Re: Granny geared 71' K10, I need to go faster...

I've driven my '83 K-10 across the country twice, once from Washington to Georgia as a 6.2 diesel SM465, and once as a 350 SM465 towing a trailer from Washington to Mississippi. I have a 33" tires and either 3.42 or 3.73 gears (can't remember, not near truck right now) and it did just fine going 70 the entire time except up mountain passes. Stock ratio should be 3.73 and I would leave it that way if you plan any towing.

Just my .02 cents
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Old 03-16-2017, 01:12 AM   #12
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Re: Granny geared 71' K10, I need to go faster...

Just throwing this out there, it sounds like your 2 cheapest options are new taller tires or two ratio swaps (change it to drive it and change it back or change the front to match).

Is the rest of the drivetrain in good shape? If so, will gas savings recover the money you spent on mods?

You might be money and time ahead just driving it. These were designed to drive, even on highways.
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Old 03-16-2017, 01:36 AM   #13
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Re: Granny geared 71' K10, I need to go faster...

Quote:
Originally Posted by BILT4ME View Post
4.10's and 33" tires = about 3200 RPM at 70 MPH.

I drove my 69 that way for YEARS as a DD.

Have the engine ported, polished, and balanced while you're away, come back, drop it in, and enjoy!
I like this combo,but you might be better going to 3:73 gears...better on the highway, lower rpm's with the 33's...I love the 4 spds in my trucks, I have changed out automatics to 4 spds...they are tough and rarely need any attention...I have had the same clutch in one of my trucks with a 454 and tow some very ridiculously heavy loads.....you have the sm465 trans with the 205 transfer case, you cant get a better combo....if you want to spend alot of money, one of the posters mentioned the NV4500 5 spd with the round pattern 205,hard to find t-case...and the NV 4500 is expensive....Like I said you may be better off with 3:73 gears front and rear...I had a truck once with those gears and loved it
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Old 03-16-2017, 05:45 AM   #14
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Re: Granny geared 71' K10, I need to go faster...

I would NEVER EVER run different ratios in front and rear of a 4wd. I'd sooner sell it and buy a 2wd and let someone who needs 4wd have it. I mean, what in the world is the point of having a 4wd that isn't a 4wd, that now has gears that lower it's pulling power? Just get the truck you need... or spend the money to do what is (perceived as) needed correctly.

Maybe you don't want to hear this, but it sounds like you need to. When these trucks were new the national speed limit was 70mph. These trucks sold as hot cakes and more than today were used to travel all over the country hauling campers and families. The only difference was, back then virtually nothing had overdrive. Cars were running the way tall gears you want now. But...people weren't the thoughtless zombies who drive by nerves, not their brains. I take pride in driving relaxed in the right lane while all the nervous fools chase each other down the road because that's how fast everyone else is going, in my '72 or my '95 with 4L80E. Screw the fools, I have no problems getting where I'm going on time and have plenty of time to do what I need to do. O/D was not created to make cars go faster. The point is to lower RPMs at same speed to save fuel and make engines last longer. But give a fool a way to get to point-B faster and they are zapping down the road w/o a thought.

The fact is, these trucks have been running for about 50 years (that's half a century) just fine with what gears they were built with. People are just used to hearing the drone level of O/D instead of an engine making power. On a 4wd I would put taller tires on for a win/win situation... better 4wd performance while getting down the hiway better. If you want automatic and you want O/D, why not a 700r4? Zillions of GM 4wds ran them. They are the trans that put O/D GM trucks on the road. You'll spend less gas money swapping to one and they do just great.
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Old 03-16-2017, 07:06 PM   #15
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Re: Granny geared 71' K10, I need to go faster...

Jeffahart

these are the only picture I have until I get to Oregon and she the truck again.
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Old 03-16-2017, 08:06 PM   #16
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Re: Granny geared 71' K10, I need to go faster...

The transfer case is a NP205.

The front axle is not original and is out of a later truck.

You really need to pull the covers and find out what gear ratio you have.

When I bought my Suburban the rear axle had been replaced with a 14 bolt (3.73:1) but retained the original Dana 44 front axle with a 4.10:1. Yep, no way to use the 4WD but it drove down the road fine.
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Old 03-16-2017, 09:52 PM   #17
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Re: Granny geared 71' K10, I need to go faster...

that's a pair of gm 10 bolt axles . note: the little ear's on the bottom of each diff. there from a 80's truck/blazer/burban

anywere from 2.73-3.73 ratio can be had . . lots were 2.73 or 3.08 tho .
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Old 03-16-2017, 11:10 PM   #18
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Re: Granny geared 71' K10, I need to go faster...

Sweet looking truck. As SweetK30 said put a tach in it and see what it the RPMs are. If you have a way to verify your speed ( the only use for a Prius is that huge digital speedo they have. You can see it from two lanes over) then you can figure out your gear ratio from your RPM in high gear. If your not happy put a set of 2" lift springs on it and fit some taller wheels and that combo will be hard to beat. Where in Oregon is the truck?
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Last edited by HO455; 03-16-2017 at 11:19 PM.
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Old 03-16-2017, 11:48 PM   #19
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Re: Granny geared 71' K10, I need to go faster...

just sell me the truck and get a two wheel drive...
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Old 03-17-2017, 12:13 AM   #20
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Re: Granny geared 71' K10, I need to go faster...

Nice truck, looks like a keeper. You know, you got me thinking. I'm not sure gears are your issue. You may just have noise that you think are high Rs. Mount a cheap tach onto your steering column. Like said already above.

Plus... do you by chance have a flex fan? They are noisy junk that sound like high Rs. If that's the case, you may just need to get a proper clutch fan and do some re-insulating. These two things could make you a happy camper.
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Old 03-17-2017, 07:53 AM   #21
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Re: Granny geared 71' K10, I need to go faster...

How fast do you want to go? With those 10-bolts you will have much taller gears than I thought at first. The lowest gearing you could have are 3.73s. I imagine the whole reason for the axle swap being done was to get taller gears. I had a '90 Blazer 4spd with 3.08s and that think flew down the hiway. I ran 33/12.50s on that. I was glad to have the granny first because the gears were so tall. In my trucks with 4.10s I almost never use 1st. Gotta figure 3.08s spin right about one revolution less than 4.10s to go the same speed. About the same gain as adding O/D. If I owned that truck and wanted higher hiway speeds I would put a 700r4 in, but not if it has 3.08s unless I planned to go with lower gearing to gain grunt
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Old 03-18-2017, 04:50 PM   #22
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Re: Granny geared 71' K10, I need to go faster...

No need to pull the diff covers to get the ratio. Put a mark on the drive shaft and a mark on the wheel. Chock the front wheels, put trans in neutral, jack up one rear wheel and rotate one revolution. Count the times the driveshaft turns. Just over 3=3.08, just under 4=3.73, just over 4=4.10, you get the idea. If there is a locker in the diff both rear wheels will need to be off the ground.
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Old 03-18-2017, 10:03 PM   #23
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Re: Granny geared 71' K10, I need to go faster...

Look around for a GM 4x4 NV4500. You'd need to get a short 32 spline input and have the input of the TC machine to accept the larger input bearing. A late round pattern 205 will already have a 32 spline input and bolt to the trans. Then there's the clutch and bellhousing. You can drop a bunch of money and get a mechanical clutch BH from AA, or go hydraulic.
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Old 03-20-2017, 12:23 PM   #24
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Re: Granny geared 71' K10, I need to go faster...

Quote:
Originally Posted by Richard View Post
No need to pull the diff covers to get the ratio. Put a mark on the drive shaft and a mark on the wheel. Chock the front wheels, put trans in neutral, jack up one rear wheel and rotate one revolution. Count the times the driveshaft turns. Just over 3=3.08, just under 4=3.73, just over 4=4.10, you get the idea. If there is a locker in the diff both rear wheels will need to be off the ground.
Only turning one rear wheel will give an erroneous reading. The spider gear to side gear ratio will do that.
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Old 03-20-2017, 02:10 PM   #25
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Re: Granny geared 71' K10, I need to go faster...

I wouldn't drive that truck ANYWHERE with the cross member under the transfer case nearly ripped off like it is.

There is a LOT of stuff under there that is not original and MAY be cobbled together. Be VERY wary of doing anything that may be unsafe in that.
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