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Old 02-16-2018, 09:57 PM   #1
'68OrangeSunshine
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3.08 Ratios in a K/10 Sub

Would 3.08 ratios in a 12 bolt posi rear and D44 front work out in a '67 K/10 Suburban with a 292 L6 plant?
Currently Sub is set up w/ 3.73 12 bolt rear [which blew up] and a closed knuckle GM front diff w/ drum brakes. It has a 454 V8 [needs rebuild] and a TH350/NP 205 [also should be overhauled]. When gas was under $1.50/gal it was viable, but 6 City- 8 Hwy doesn't work for me. BBCs are fun but spendy.
I have a couple of 292 cores, and I know some tricks to wake an L6 up. I also have a SM465/T-221 core. Thinking also of a 700-R4. [Don't have it]. I have a core 3.08 12 bolt rear on a '72 K/S spare tub/frame.
Changing out the front diff to a D44 would give me power steering and power brake options. 1967 MY used ram-assisted power from the factory, and since Corvettes also used that system for P/S, parts are only touchable if you have a NASA-style budget.
Braking with the MY '67-'68-Only front brake drum was on the order of Fred Flintstone dragging his feet on the rubble. [Also it's a hard-to-get drum.] Sometimes when panic stopping, my best option was to select a softer target. Thus the desire for discs in front.
I can get a milsurp new-on-the-pallette D44 for '73-'87 CUCV Blazer, 6-bolt lugs, for $500 and $280 shipping. That's cheaper than rebuilding what I have. Only glitch is it's only available in 3.08. I hear the front D44 is the same as a '69-'72.
My '67 Suburban ''White Fang'' has been sitting since 1998. I'd like to get it going again. Still a pipe dream now.
Comments welcome.
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Old 02-16-2018, 10:27 PM   #2
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Re: 3.08 Ratios in a K/10 Sub

Only a couple comments. Someone in the truck section was looking for pictures of 67-68 power steering equipped K trucks. I assumed it wasn't available as I didn't see it listed in the option list. A lot of people agreed but someone posted this pic:



If the ram and control valve parts are the same as Corvette there are repair parts readily available and the seal kits are cheap. less than $20 for both kits. Rebuilt power cylinders and control valves probably only cost a couple hundred.

Manual trans and a 3.08 isn't a good combination. You'll be using a lot of clutch to get it moving.
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Old 02-17-2018, 12:14 AM   #3
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Re: 3.08 Ratios in a K/10 Sub

Why not run the BB with the 3.08's?

I picked up 1 mpg in town and almost 3 mpg on the highway when i swapped from 3.73's to 3.07's in my C10 'Burb.
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Old 02-17-2018, 12:55 AM   #4
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Re: 3.08 Ratios in a K/10 Sub

before you decide on a gear swap you need to do the math on rpm/gear ratio/trans gear/tire size....heres a calculator to help.....
http://www.csgnetwork.com/multirpmcalc.html
jumping to a od trans [700r4] from a non od trans [sm465,th350] makes a big difference in rpms
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Old 02-17-2018, 01:19 AM   #5
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Re: 3.08 Ratios in a K/10 Sub

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Why not run the BB with the 3.08's?

I picked up 1 mpg in town and almost 3 mpg on the highway when i swapped from 3.73's to 3.07's in my C10 'Burb.
Because I'd have to rebuild the 454 anyway, and I didn't like the mileage.
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Old 02-19-2018, 06:30 AM   #6
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Re: 3.08 Ratios in a K/10 Sub

Just so you know, that USGI surplus front axle is NOT a D44 but a GM 10 bolt.
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Old 02-19-2018, 08:27 PM   #7
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Re: 3.08 Ratios in a K/10 Sub

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Just so you know, that USGI surplus front axle is NOT a D44 but a GM 10 bolt.
Thanks. I didn't know that. How does it differ from the D44 used in '69-'72 trucks? The catalog said they were for '73-'87 GM trucks and Blazers and '73-'88 Suburbans. I thought they were still using the D44 for a front axle in '73.
https://colemans.com/shop/military-v...y-gmc-u-s-g-i/
Check it out.
I know the rears are 10-bolts w/GovLocs.
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Old 02-19-2018, 08:48 PM   #8
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Re: 3.08 Ratios in a K/10 Sub

I was going to get a set from Colemans for my dads IH Travelall but the gearing with T98 4 speed trans would not work so good together. Back then the pair was $400 delivered to CA.

GM 10 bolt was used from 79-91 in 1/2 ton and 3/4 ton trucks Some argue the strength vs the D44 but at this point I think its more about affordability and availability of parts. In some areas you cant give 10 bolts away, I recently got a free 3/4 ton 10 bolt thrown in when I bought a 14 bolt for $150.

They bolt in place of any 60-91 4x4 front and is OK for up to 35 inch tires. Not sure what people are doing these days to adapt to early steering box, I think most are upgrading to power steering so you just use the late parts.

If it was stored well its fine for a driver, hard core wheeling it needs some upgrades
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Old 02-20-2018, 12:10 AM   #9
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Re: 3.08 Ratios in a K/10 Sub

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Originally Posted by RedRoad View Post
I was going to get a set from Colemans for my dads IH Travelall but the gearing with T98 4 speed trans would not work so good together. Back then the pair was $400 delivered to CA.

GM 10 bolt was used from 79-91 in 1/2 ton and 3/4 ton trucks Some argue the strength vs the D44 but at this point I think its more about affordability and availability of parts. In some areas you cant give 10 bolts away, I recently got a free 3/4 ton 10 bolt thrown in when I bought a 14 bolt for $150.

They bolt in place of any 60-91 4x4 front and is OK for up to 35 inch tires. Not sure what people are doing these days to adapt to early steering box, I think most are upgrading to power steering so you just use the late parts.

If it was stored well its fine for a driver, hard core wheeling it needs some upgrades
Now the price is $395 plus $258 delivered to Tucson [if going to a shop that has a forklift].
Yes, my intention is to upgrade to Power Steering and Power Disc Brakes using more modern parts.
My '67 K/10 Sub was not originally configured for power assisted steering. An attempt to put a '69 P/S sector [off a C/10 Panel] was no success. I had unweildy steering geometry, and the gearbox kept sheering off 1/2'' bolts from the frame mount. When I tried to restore the manual gearbox -- with a JB Weld patch on a crack in the casing -- Good steering geometry never was restored. We had chopped the OEM draglink and the replacement wasn't a good feel.
The other major issue was braking. The '67-'68 OEM brake drum was specific to closed knuckle front ends. [Don't know it it's also a '60-'66 part?] But it was prettymuch ineffective.
For a powerplant I'm thinking of an L6 292, with a larger bore [depends on which block I use. One's still unbored and the other ran 250,000 at .030 over.] Add lump ports, HEI. Oversized valves, cam, 4 BBl (or FI), headers. etc. and it's a goer. Also 200 lbs lighter than a BBC. Turbo [mild] is possible but expensive.
Of course only a pipedream for the present.
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Old 02-21-2018, 01:43 PM   #10
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Re: 3.08 Ratios in a K/10 Sub

I chose to go with a 3.08 gear in the "GM" 12 bolt truck diff on my Eaton Posi. The 8.85" carrier has to be a type 3 for correct set up. There is a split in ratio's from type 3 to type 4 that many have with 4.11 gears. I was lucky as I have a diff spreader.
Here's my math with a 700r4 / 4L60 / 4L60e with an 0.70 over drive. With P235/75R16, that tire has a 29.88 diameter. At 60 MPH, in over drive, 3.08 final + tires=1454-1504 RPM with lockup. This should get the MPG up there in the mid teens or higher.
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Old 02-21-2018, 04:21 PM   #11
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Re: 3.08 Ratios in a K/10 Sub

Quote:
Originally Posted by LH Lead-Foot View Post
I chose to go with a 3.08 gear in the "GM" 12 bolt truck diff on my Eaton Posi. The 8.85" carrier has to be a type 3 for correct set up. There is a split in ratio's from type 3 to type 4 that many have with 4.11 gears. I was lucky as I have a diff spreader.
Here's my math with a 700r4 / 4L60 / 4L60e with an 0.70 over drive. With P235/75R16, that tire has a 29.88 diameter. At 60 MPH, in over drive, 3.08 final + tires=1454-1504 RPM with lockup. This should get the MPG up there in the mid teens or higher.

If you are going to try and use the 3.07 with a 4l60e you will have to run a trans fluid cooler. I tried it in my '69 Suburban and the trans overheated and blew out the front seal. I found that the 3.07 is too high for a 4l60e, it puts too much stress on the trans when in OD and locked up. I ended up putting a 3.73 rear in it and still get 20mpg.

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Old 02-21-2018, 09:52 PM   #12
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Re: 3.08 Ratios in a K/10 Sub

I'm just wondering if 3.08 ratios in a 1/2 ton 4wd are not a ''commie plot.'' I would be happier if the cheap surplus axles were available in 3.73 [which is what was in that Sub with a 283 and SM420 originally]. My '68 C/10 Stepside and '71 GMC Jimmy, are also 3.73s.
Having to change ring and pinions in the gears takes some of the cheapness out of the deal.
It may be cheaper to change out the axle sets for 3/4 ton units, if found in the desired ratio. There is a local surplus dealer who will trade used surplus axles -- front and back -- for $2000 plus exchange axles [cores]. But 3.73 may be rare in 14-bolt full-floaters. IDK.
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