How bad is slipping tranny affecting mpg? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BB72CHEVKT · 09-04-2007, 12:03 PM

My third gear in my 69 turbo 400 is slipping. I am only getting 8-9 mph with rebuilt carb and stock 350. I do not know rear gears and am running 31" tires.

ChevLoRay · 09-04-2007, 12:07 PM

I guess mine is slipping, too. These don't get great gas mileage but a slipping tranny will probably have other symptoms than poor mileage.

Mine AIN'T slippiing and my mileage isn't much better. I put $10 in it every month, whether or not I drive it. It always needs it and it hasn't moved. Got a locking gas cap, too.

Anyway, I changed out the flex hoses from the pump to the carb and the gas smell/leak went away. Should be better, now.

BB72CHEVKT · 09-04-2007, 12:34 PM

Quote:

Originally Posted by ChevLoRay

I guess mine is slipping, too. These don't get great gas mileage but a slipping tranny will probably have other symptoms than poor mileage.

Mine AIN'T slippiing and my mileage isn't much better. I put $10 in it every month, whether or not I drive it. It always needs it and it hasn't moved. Got a locking gas cap, too.

Anyway, I changed out the flex hoses from the pump to the carb and the gas smell/leak went away. Should be better, now.

A lot of folks on here are claiming 15 mpg some higher some lower and
I thought with a quadrajet and keeping my foot out of it 12-15 was realistic.
I hope it will be with a new tranny if not I may have to keep my new truck and sell the 69 to pay for the 72.

**Palf70Step** · 09-04-2007, 01:13 PM

Chances are with 31" tires your speedo/odoemeter is offg also, so you are probably getting better mileage than you think. Gearing & the type tranny (slipping or otherwise) play a factor also. Obviously with a non-overdrive tranny you'll get worse. A turbo 400 does worse than a T350 because it tanks more to run the tranny...Again it may be small, but it does add to the overall mileage.

Longhorn Man · 09-04-2007, 04:19 PM

42% of the ppl responding to my poll http://67-72chevytrucks.com/vboard/s...d.php?t=172346 claimed 10 - 12 MPG.
If your tranny is slipping, there's no way of tellin how much extra fuelit's burning.
Why do you think it's slipping?

BB72CHEVKT · 09-04-2007, 04:54 PM

Quote:

Originally Posted by Longhorn Man

42% of the ppl responding to my poll http://67-72chevytrucks.com/vboard/s...d.php?t=172346 claimed 10 - 12 MPG.
If your tranny is slipping, there's no way of tellin how much extra fuelit's burning.
Why do you think it's slipping?

It does not shift properly in drive. It shifts ok manually. It is the original tranny w/140k mi and the truck sat for 14 years. I also had one go out before and it would act similar.

BB72CHEVKT · 09-04-2007, 05:10 PM

Thanks Lonhorn Man just looked at you poll that make me feel like I can improve a few mpg.

09-04-2007, 12:03 PM	#1
BB72CHEVKT Junior Member Join Date: Mar 2007 Location: Hideaway, TX Posts: 4,948	How bad is slipping tranny affecting mpg? My third gear in my 69 turbo 400 is slipping. I am only getting 8-9 mph with rebuilt carb and stock 350. I do not know rear gears and am running 31" tires. __________________ 71 Suburban 350/700R4 Project Trixie 72 CHEVY,Highlander,SWB,396,T400

09-04-2007, 12:07 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: How bad is slipping tranny affecting mpg? I guess mine is slipping, too. These don't get great gas mileage but a slipping tranny will probably have other symptoms than poor mileage. Mine AIN'T slippiing and my mileage isn't much better. I put $10 in it every month, whether or not I drive it. It always needs it and it hasn't moved. Got a locking gas cap, too. Anyway, I changed out the flex hoses from the pump to the carb and the gas smell/leak went away. Should be better, now. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

09-04-2007, 01:13 PM	#4
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,725	Re: How bad is slipping tranny affecting mpg? Chances are with 31" tires your speedo/odoemeter is offg also, so you are probably getting better mileage than you think. Gearing & the type tranny (slipping or otherwise) play a factor also. Obviously with a non-overdrive tranny you'll get worse. A turbo 400 does worse than a T350 because it tanks more to run the tranny...Again it may be small, but it does add to the overall mileage. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

09-04-2007, 04:19 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: How bad is slipping tranny affecting mpg? 42% of the ppl responding to my poll http://67-72chevytrucks.com/vboard/s...d.php?t=172346 claimed 10 - 12 MPG. If your tranny is slipping, there's no way of tellin how much extra fuelit's burning. Why do you think it's slipping?

09-04-2007, 05:10 PM	#7
BB72CHEVKT Junior Member Join Date: Mar 2007 Location: Hideaway, TX Posts: 4,948	Re: How bad is slipping tranny affecting mpg? Thanks Lonhorn Man just looked at you poll that make me feel like I can improve a few mpg. __________________ 71 Suburban 350/700R4 Project Trixie 72 CHEVY,Highlander,SWB,396,T400



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