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#40639 08/10/2004 2:53 PM | Joined: Jan 2000 Posts: 51 Member | | Member Joined: Jan 2000 Posts: 51 | I've been thinking [which is not always a good thing to do] and have the chance to buy a new in crate chevy rear end for a 70's 4x4 pickup or blazer. The rear end is a 308 . I have a 59 apache with a 235 and a sm420 4 speed. Is this a good set up or would I be better off with a 343 rear end. I would like more speed on the highway and I know I would update the brakes at the same time. Any thoughts? | | |
#40640 08/10/2004 3:40 PM | Joined: Jun 2000 Posts: 2,773 'Bolter | | 'Bolter Joined: Jun 2000 Posts: 2,773 | 3.08 is pretty tall for a 235. I have them in my 69 with 350/th400 tranny, and am not happy with the ratio. Looking at swapping for 3.42s and going with a 700R4 (overdrive) tranny. It takes a real torque monster to get going with the 3.08 gears, but once you get up to 70 it does cruise pretty nice.
Fred
52 3600
69 C-10
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#40641 08/10/2004 4:51 PM | Joined: Jan 2000 Posts: 51 Member | | Member Joined: Jan 2000 Posts: 51 | Thanks Fred, that was my fear and I think that I'll wait for a 3.42 to come around! | | |
#40642 08/10/2004 5:25 PM | Joined: Apr 2000 Posts: 499 'Bolter | | 'Bolter Joined: Apr 2000 Posts: 499 | 1st gear in a TH400 is 2.48 and with 3.08 is 7.63 overall ratio. That would be like starting in 3rd gear all the time with what you have now, if you have 4.56 or in 4th if you have 5.13 rear gears. But you have a sm420 with a 7.02 1st and a 3.57 2nd gear. 1st gear with a 3.08 would be 21.62 and second gear would be 10.99. With the 3.42 gears you get 24.00 in 1st and 12.20 in 2nd.
Your sm420 has 7.02, 3.57, 1.70, and 1:1 in 4th. Multiply each of those gear ratios by the rear gears that you're considering and compare it to what you have now and how you use those gears.
'67 GMC 3/4 292 4spd
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#40643 08/10/2004 5:35 PM | Joined: Apr 2000 Posts: 499 'Bolter | | 'Bolter Joined: Apr 2000 Posts: 499 | Fred T
The 700R4 has a 1st gear of 3.06 and with 3.08 rear gears would give a 9.42 1st gear instead of the 7.63 you have now. You would have a better 1st and OD
'67 GMC 3/4 292 4spd
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#40644 08/10/2004 6:16 PM | Joined: Dec 2000 Posts: 506 Shop Shark | | Shop Shark Joined: Dec 2000 Posts: 506 | Gary,
For around here the 3:08 would be perfect. I run a 2:73 with the 4 speen and its fine. The only reason I don't have a 3:08 was the 2:73 was free. If the price is right go for it.
52pu
"Drugs are money, money is power, power is security." - Kent Heiner
Nedrow population 2212
Carbon footprint family of 2/11 tonnes of CO2/yr
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#40645 08/10/2004 8:57 PM | Joined: Oct 2003 Posts: 5,152 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Oct 2003 Posts: 5,152 | I have 3.08 gears in the rear of my '55 1st Suburban. Running a GMC 270 and a sm420.
It doesn't like to pull a loaded trailer uphill, but running around without a load the limitations are front suspension, not gearing.
I've been very happy with it.
In the 70's I had a Blazer with 3.08 gears, a 350 and a 4-speed. It did fine (of course it also had a low range).
1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble... | | |
#40646 08/11/2004 6:03 AM | Joined: Feb 2000 Posts: 5,194 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,194 | I run a 3.08 with a 250 and turbo 350 trans in my '37. It runs great and I am real happy with it. I just took out a 3.42. Joe | | |
#40647 08/11/2004 2:34 PM | Joined: Jan 2000 Posts: 51 Member | | Member Joined: Jan 2000 Posts: 51 | Thanks for all the input guys. I do run empty 99 percent of the time and would like to run up the interstate to get to my camp in the Adirondacks [2 hour drive]. What little I get on the interstate now scares the heck out of me! This NOS rearend looks like an easy swap, comes complete with e-brake cables and all... I have some time to ponder this as it would be a winter project... | | |
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