rear and trany question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

69pickupnyc · 01-03-2010, 11:23 PM

has any one put a 308 rear with a 700r trany and did it have a negative effect on gas milage? I put a 700r trany in my 1969 short bed and did not have to cut the drive shaft.

**americanmusc1e** · 01-04-2010, 12:11 AM

I have a 700r4 and 3.08 gears........ and, yes, my mileage is worse than the old 3.08 and TH350 combo................i'm switching to 3.73's soon

69GMCLonghorn · 01-04-2010, 11:24 AM

It depends on what size tires you're running, engine set up, etc... If you have zero power under 2000, you'll probably get worse mileage. My thing is, if you don't have the high gear, you can't use it, even on downhill. So you might run 3rd gear now and then. The torque converter should still lock up, then when you're on the level or downhill, upshift it and get the better mileage. Just speaking from experience with too much gear and not enough engine.

powell72 · 01-04-2010, 05:24 PM

It sounds like you could use some more gear or stay in third a little more. I've always heard don't run a 700 in overdrive under 1800-2000 RPM. That overdrive drum is small and doesn't handle the heat well.

69GMCLonghorn · 01-04-2010, 06:48 PM

Quote:

Originally Posted by powell72

It sounds like you could use some more gear or stay in third a little more. I've always heard don't run a 700 in overdrive under 1800-2000 RPM. That overdrive drum is small and doesn't handle the heat well.

I have heard that, too... 4L60's are the same way. My '95 actually had a decal in the door jamb that said something to the effect of "don't lug it"... My thought is, design the dang thing so it pulls back into 3rd when it should and we wouldn't be having this discussion! I manually shifted the '95 until the bushing in the steering column was shot...

01-03-2010, 11:23 PM	#1
69pickupnyc Registered User Join Date: Dec 2009 Location: new york city new york Posts: 32	rear and trany question has any one put a 308 rear with a 700r trany and did it have a negative effect on gas milage? I put a 700r trany in my 1969 short bed and did not have to cut the drive shaft.

01-04-2010, 12:11 AM	#2
americanmusc1e Senior Member Join Date: Jan 2009 Location: Austin, TX Posts: 1,079	Re: rear and trany question I have a 700r4 and 3.08 gears........ and, yes, my mileage is worse than the old 3.08 and TH350 combo................i'm switching to 3.73's soon __________________ -- Josh Instagram: @americanmusc1e OLD SKOOL-- 1970 C10. 454/Th400/3.07 posi Build Thread FARM TRUCK----1949 Chevrolet 3800 Power Wagon Hauler Build Thread 1999 4wd OBS Tahoe - daily. DM me if you can't see photos i posted

01-04-2010, 11:24 AM	#3
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: rear and trany question It depends on what size tires you're running, engine set up, etc... If you have zero power under 2000, you'll probably get worse mileage. My thing is, if you don't have the high gear, you can't use it, even on downhill. So you might run 3rd gear now and then. The torque converter should still lock up, then when you're on the level or downhill, upshift it and get the better mileage. Just speaking from experience with too much gear and not enough engine.

01-04-2010, 05:24 PM	#4
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Re: rear and trany question It sounds like you could use some more gear or stay in third a little more. I've always heard don't run a 700 in overdrive under 1800-2000 RPM. That overdrive drum is small and doesn't handle the heat well. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html



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