Rear gears - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chvtrkman · 03-15-2011, 04:53 PM

Factorystock,Sorry I lost track of this thread...my kids were on the computer and I forgot to go back to it. The tranny I swapped for the 3 spd is a New Process GM MY6...They were used in Chevy trucks from early to mid 80s I believe.My goal was to improve my gas mileage a bit w/o having to change rear end gears.while it did get the revs down some, I still only get 10-11 mpg.

piecesparts · 02-27-2011, 07:54 PM

If the tires are truly a 30.6" tire and you have a TH350 tranny, then according to my calculations, you are running a set of 5.79 gears in the rear end as stated above. I would also question the RPMs from the tach to make sure.

**special-K** · 02-28-2011, 10:11 PM

Because it's cool to have a factory dash tach in a truck. Who really needs a tach anyway? The highest performance vehicle I have is my Harley and that has no tach. I listen to the motor. Most trucks have automatics that shift themselves.I've always put tachs in what I drive because it says performance,like cool wheels and tires or dual exhaust. Extra gauges in cars from the '60s and early '70s set them off. Same with trucks.

chvtrkman · 03-05-2011, 10:15 PM

I've got the same HO52 diff in my '69 C-20..I always thought the ratio was a 4:56, but I suppose if it's actually a 4:57 I wasn't far off..Anyway, my engine spun @ 3000 rpm when doing 55 mph, but since yanking the 3 spd saginaw out and replacing with a 4 spd OD, the rpm is down to 2200 @ 55 mph...Don't know if this helps you at all, but I much prefer being able to hear myself talk when trying to have a conversation with a passenger.

factorystock · 03-05-2011, 11:31 PM

Quote:

Originally Posted by chvtrkman

replacing with a 4 spd OD, the rpm is down to 2200 @ 55 mph..

Always nice when not having to change out the rear end. Any specifics on the year and model of this 4 spd OD, and modifications necessary?

03-15-2011, 04:53 PM	#1
chvtrkman Registered User Join Date: Sep 2007 Location: PA. Posts: 178	Re: Rear gears Factorystock,Sorry I lost track of this thread...my kids were on the computer and I forgot to go back to it. The tranny I swapped for the 3 spd is a New Process GM MY6...They were used in Chevy trucks from early to mid 80s I believe.My goal was to improve my gas mileage a bit w/o having to change rear end gears.while it did get the revs down some, I still only get 10-11 mpg. __________________ _____________________________________________ 69 C-20 292, 4 spd O/D, 4:56 rears. No a/c p/s p/b p/w......restoration project,"Operation:Stovebolt" 78 C-10 305 TH350 new (old) daily driver 02 Suburban Z71 a.k.a. the family truckster 99 Silverado 1500 Z71

02-27-2011, 07:54 PM	#2
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Rear gears If the tires are truly a 30.6" tire and you have a TH350 tranny, then according to my calculations, you are running a set of 5.79 gears in the rear end as stated above. I would also question the RPMs from the tach to make sure. __________________ Frank

02-28-2011, 10:11 PM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,858	Re: Rear gears Because it's cool to have a factory dash tach in a truck. Who really needs a tach anyway? The highest performance vehicle I have is my Harley and that has no tach. I listen to the motor. Most trucks have automatics that shift themselves.I've always put tachs in what I drive because it says performance,like cool wheels and tires or dual exhaust. Extra gauges in cars from the '60s and early '70s set them off. Same with trucks. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

03-05-2011, 10:15 PM	#4
chvtrkman Registered User Join Date: Sep 2007 Location: PA. Posts: 178	Re: Rear gears I've got the same HO52 diff in my '69 C-20..I always thought the ratio was a 4:56, but I suppose if it's actually a 4:57 I wasn't far off..Anyway, my engine spun @ 3000 rpm when doing 55 mph, but since yanking the 3 spd saginaw out and replacing with a 4 spd OD, the rpm is down to 2200 @ 55 mph...Don't know if this helps you at all, but I much prefer being able to hear myself talk when trying to have a conversation with a passenger. __________________ _____________________________________________ 69 C-20 292, 4 spd O/D, 4:56 rears. No a/c p/s p/b p/w......restoration project,"Operation:Stovebolt" 78 C-10 305 TH350 new (old) daily driver 02 Suburban Z71 a.k.a. the family truckster 99 Silverado 1500 Z71



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