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#1 |
Registered User
Join Date: Apr 2006
Location: Hockinson, Washington
Posts: 115
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Low gears, high RPM's, and the gas station. Near Portland, Oregon
1968 C-10
250-6 SM465 Been awhile since I have posted here, about a year to be exact. I would like to drive my truck a lot more since I got it running again, but all I can seem to get out of it is about 53 mph. I probably could get more speed out of her, but my desire to go faster is quickly trumped by my desire not to blow up the motor. In a perfect world I would go with a Gear Vendors overdrive and not look back. Here in the real world, I am thinking more along the lines of changing out the gear ratio to something a bit taller, like 3.08's. I did get a quote for this work with a drive in drive out option from Body Armor in Vancouver, WA, which came in around $1700. yeah, not so much... I was told that I could only go posi with this ratio in a 12 bolt, is this correct?? This is going to be a driver, not a street warrior I would rather not if I didn't really have to. I need some tips and insight, my grandfather used to be the go to guy for that sort of thing so I never really thought twice about rear ends and trannys. He has since passed, and I parked this thing the day after his funeral. That was 6 years ago. I would like to really enjoy it once again, but I don't have the time to do this particular work, and I would rather not be parted from too much of my cash. Need some advice. JM
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1968 Chevrolet C-10, 2WD, Longbox, Vortec 350, 700R4, 3.73 gears Good judgment comes from experience, and experience, well......that comes from bad judgment. 1968 Chevy C-10 "Longshot": Bought used from my Uncle George in 1994 and proceeding to beat the hell out of it for 4 years. Sold it. Bought it back, dumped an ungodly amount of money into it since then. |
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#2 |
72 Chevelle Club
Join Date: Jun 2007
Location: Newton , Iowa
Posts: 2,052
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
Wrong you can put 308's in it . You may have to change the carrier but alot of these trucks came with 308 open diff. Mine had an open 308 in it .
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I Have The Right To Remain Silent,But Lack The Ability 1972 Chevelle ... Mine 2006 Trailblazer... Hers 2002 Buick century ... Kids 2002 K1500 Z-71 EXT CAB ... Daily Driver 2005 Rockwood Roo ... For Camping 1974 Harley-Davidson XLH Sportster 84'' stroker |
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#3 |
"Junkyard Dog"
![]() Join Date: Jan 2008
Location: Springfield Oregon
Posts: 2,527
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
Putting 3.08 is no problem. You WILL have to change the carrier unless you have 3.40 gears which it does sound like. 2.76,3.08-3.07,3.40-3.42 all use a common carrier. The 3.73,4.11, and 4.56 use the same carrier. They may be telling you that do to the availability of the open carrier new. They are plentifull used. This assuming you have the 12 bolt differential. PM me, I know someone in Portland that can help ya.
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#4 |
I have a radical idea!
Join Date: Jan 2005
Location: Sweet Home Alabama!
Posts: 6,513
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
$1700 is crazy expensive for a gear change. If it were me, I'd change the whole rearend out from a truck that already had 3.08's. Of course parts and parts trucks are a easy to find here. They may not be where you live. Either way, new 3.08 gears and all bearings and seals for your rearend + labor shouldn't much over $500.
BTW, Bob is right, the vast majority of 3.08 geared trucks didn't have posi from the factory.
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'67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! |
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#5 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
swap the whole axle... junk yard cost shouldn't even be close to 150 bucks IMO.
Or, you could donate $25 tot he board, so you can post a WTB thread in the parts board, and do a WTB 3.07 rear axle. |
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#6 |
Out of the carpool lane.
Join Date: Jan 2000
Location: Clark Co, WA
Posts: 5,673
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
You didn't say what rearend you currently have. I'm guessing it's probably a 3.73 or maybe a 4.10. You should be able to get up to around 70 with no problems with either gear. You really didn't describe your concern or issue other than you want to swap out rear gears. Based on my own experience several years ago with 3.08's, I really don't recommend them, especially if you've got intentions of using your truck as a truck regularly. You'll have to use more clutch with the 3.08 gear and unless you regularly use your truck at highway speeds, it's just not worth it. Also, I second what everyone else mentioned- it should cost you no more than about 500-600 in Portland. The place that gave you that price should be strung up by their testicals!
Now, another option to consider strongly is to install a V8 Camaro T-5 in your truck. I've got one in mine and they're very easy to install. I'll have to look for the link another time, but I've written about it on the board a few times. I'd be happy to help if that's the route you end up taking. The total cost is about $700 and you end up with an overdrive gear and a great useable 1st as well!
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1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 01-31-2008 at 06:05 PM. |
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#7 |
Registered User
Join Date: Mar 2005
Location: Just outside Durham, NC
Posts: 894
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
I would tend to agree with Brad, I wouldn't want 3.08's behind my 6cyl. I have pushed my truck down the highway at well of 75~80mph with no issues.....keep in mind, you have 7 mains on 6 cylinders.....the bottom end is rock solid on these motors, and the 'relatively' short stroke of the 250 means it can take higher RPM's with lower piston speed when compared to a 292.
If fuel economy is your main concern, I would say buy a motocraft 500 cfm 2bbl, an adaptor plate to bolt it to your current intake, swap an HEI in, give it a decent tune up (plugs, wires, timing, etc), toss some seafoam in there to flush everything out (I actually do seafoam BEFORE the tuneup), and for a quick and cheap gearing change, if the tires are old, upgrade to slightly taller tires. I have driven my truck 400 miles straight with a 3/4t 4x4 on a flatbed behind me moving at ~60mph the whole way (trailer inertia brake constraints, not engine) with no issues (Think I made 15mpg). Even with gears changes, short of fuel injection, an RV cam, and a couple of tricks to make the drag on these trucks a little lower I think 16~17mpg is about the best you will get on the cheap....I hope to one day push 20mpg....but that will likely involve the above listed mods.....along with a GV overdrive.
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1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's ![]() 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM! Last edited by shelby987; 01-31-2008 at 10:03 PM. |
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#8 |
Registered User
Join Date: Feb 2000
Location: Center City, MN, USA
Posts: 3,254
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
Figure out what your rear end gears are. There is a code stamped on the rhs, front of the axel tube. If you pull the cover you can count teeth and divide. There is an RPO code on the build sheet.
Beg, borrow, or steal a tach. When you are going 53 mph, record what the tach is saying for rpms. So lets say you figured you have 4.11 rear end gears and are in your top gear. You should be turning 2600 rpms at 52.69 mph. If you had that same tranny and 3.08 gears you could go 70.31 mph at 2600 rpms. Factory rear end gears GENERALLY are 10% different between gear sets. 3.73 is 10% higher than 4.11. (4.11 - .411 = 3.699). 3.07 is ABOUT 20% higher than 3.73. And on and on. Newer trucks have a gear in between 3.73s and 3.07s, something like a 3.42. If you swapped your SM465 for a modern, overdrive tranny, you GENERALLY get 30% lower r's at the same speed. As Longhorn Man pointed out, your cheapest bet is to swap in a whole axel that already has 3.08 gears in it. Be careful. This is where we get in trouble. If you have that new (used) axel sitting there, you may as well freshen up the brakes. As long as the brakes are new you may as well paint it up nice. As long as it is painted up nice you don't want to stick a nice shiny rear end into a rusty frame. You can't paint the frame right without removing the box. As long as the box is off you may as well paint it...
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'70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN |
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#9 |
Registered User
Join Date: Mar 2005
Location: Just outside Durham, NC
Posts: 894
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
I always just jack up the rear of the truck (if it is an open rear, only one wheel needs to be off the ground). Rotate the lifted wheel off the ground, and count how many times the pinion yoke rotates (just over 4=4.10's, just under 3.73, three and a half times 3.42, four and a half times = 4.56). It has worked for me many times without fail.
Make sure you get a tach that is 6cyl. friendly, some are 8cyl. specific, others have a dial switch inside the housing that needs to be changed depending on the engine. Again, I think with regular maintenance, these engines are more than happy at 3,000+rpm on the highway.... my 03 saturn turns 3,200~3,300rpm on the highway at 75~80mph.....I regularly drive 12 hours straight stopping only for gas.....and I would say my 250 is probably more stout than the 2.2 in my car.
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1969 SS 350 Camaro Sold 2008 1970 3/4T K20, stock height with 33's, 250 I6, 3 on the tree, and locked front and rear 4.10's ![]() 1980 Chevy Malibu 2 dr Sold 2007 1993 Olds. Cutlass Ciera Wagon Traded 2006 2003 Saturn L200 w/5pd. D/D My list spans 5 decades with One common thread.....GM! |
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#10 |
Senior Member
Join Date: Aug 2005
Location: OKC, OK
Posts: 2,365
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
they are nuts if they think they can charge $1700. I can buy a new Moser rear end for that if I don;t get to fancy. Should cost anywhere from $250-$500 depending on parts and labor.
Mike
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Mike Redpath Last edited by Musclerodz; 02-01-2008 at 03:05 AM. |
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#11 |
Registered User
Join Date: Jan 2006
Location: Kaufman, Tx
Posts: 827
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Re: Low gears, high RPM's, and the gas station. Near Portland, Oregon
Yeah, for $1700 you could freight the rear end down here to Tx, I'll take your gears and carrier out (to use in my truck), and set you up with my open carrier and new gears, bearings, and all. Then freight it back up to ya.
I'd bet we could get all that done for $1700, or maybe a little less. Find someone who hasn't lost their freakin' mind. Jay
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You only need two tools in life - WD-40 and Duct Tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape. If a hammer doesn't fix it, you have an electrical problem! Slot Cars, 1:24 Scale, 100MPH@100,000RPM, fastest things on wheels! ![]() Last edited by Psycho71; 02-01-2008 at 04:32 AM. |
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