Welcome and gear change - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DangerRanger · 11-11-2016, 01:28 AM

Just found this forum...and certainly glad I did. I have a 59 longbed fleetside. Somewhere in its life someone swapped out the original V8 for a 327 and a turbo 350 trans. My hope is that someone out there has some experience with this set-up. My question is, it feels as though the RPM's are running high at highway speeds (sorry no tach installed yet). I believe that the stock rear end is in it. Should I consider changing out the rear end gears or ??? I would appreciate any thoughts.

55dude · 11-11-2016, 02:53 AM

WELCOME! keep the gears and change transmission to a 700R4, the overdrive will help since the stock rear gears are probably 4:11 and you won't lose your current off the line torque.

1project2many · 11-11-2016, 08:24 AM

Howdy

If your only concern is lowering RPM on the highway then I believe the 700R4 swap suggestion is the easiest. The original gears were likely 3.90:1 although any number of axles could have been installed over the years. With a .70 overdrive ratio and a 3.90 rear gear, effective final drive ratio would be 2.73:1. If you were seeing 3000 rpm on the highway, swapping that trans in would bring rpm down to 2100. 700R4 transmissions easily replace the turbo 350 and are still fairly easy to locate.

Some folks want to change the rear axle to get posi-traction, to use rear disc brakes, to have a stronger axle, or just because they want something newer in case they need replacement parts. If you want more than just lower engine rpm there are a number of axles that will work and I suggest searching for some of the threads here where this is discussed.

DangerRanger · 11-11-2016, 10:00 PM

Thank you all! My goal with this is a daily driver. With that said I think I will step up my search for a 700R4 tranny.

dsraven · 11-12-2016, 04:10 PM

you may wanna check on the site for requirements needed for electrical shifting on the 700r4 o/d.

1project2many · 11-13-2016, 08:37 PM

Yes, when the time comes you will probably want a diagram to help make sure the torque converter clutch is wired correctly.

Try to get a later version of the transmission. Over the years there were many changes to help them live.

Make sure not to get the electronic 4L60E version of this transmission. Electronic version has a large electrical connector on the passenger side rear.

DangerRanger · 11-15-2016, 01:12 AM

Thanks all, I have started the shopping process for a replacement trans. Wish me luck.

11-11-2016, 01:28 AM	#1
DangerRanger Registered User Join Date: May 2015 Location: Belfair, Washington Posts: 3	Welcome and gear change Just found this forum...and certainly glad I did. I have a 59 longbed fleetside. Somewhere in its life someone swapped out the original V8 for a 327 and a turbo 350 trans. My hope is that someone out there has some experience with this set-up. My question is, it feels as though the RPM's are running high at highway speeds (sorry no tach installed yet). I believe that the stock rear end is in it. Should I consider changing out the rear end gears or ??? I would appreciate any thoughts.

11-11-2016, 02:53 AM	#2
55dude Registered User Join Date: Jan 2007 Location: tacoma wa. Posts: 1,037	Re: Welcome and gear change WELCOME! keep the gears and change transmission to a 700R4, the overdrive will help since the stock rear gears are probably 4:11 and you won't lose your current off the line torque.

11-11-2016, 08:24 AM	#3
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,158	Re: Welcome and gear change Howdy If your only concern is lowering RPM on the highway then I believe the 700R4 swap suggestion is the easiest. The original gears were likely 3.90:1 although any number of axles could have been installed over the years. With a .70 overdrive ratio and a 3.90 rear gear, effective final drive ratio would be 2.73:1. If you were seeing 3000 rpm on the highway, swapping that trans in would bring rpm down to 2100. 700R4 transmissions easily replace the turbo 350 and are still fairly easy to locate. Some folks want to change the rear axle to get posi-traction, to use rear disc brakes, to have a stronger axle, or just because they want something newer in case they need replacement parts. If you want more than just lower engine rpm there are a number of axles that will work and I suggest searching for some of the threads here where this is discussed.

11-11-2016, 10:00 PM	#4
DangerRanger Registered User Join Date: May 2015 Location: Belfair, Washington Posts: 3	Re: Welcome and gear change Thank you all! My goal with this is a daily driver. With that said I think I will step up my search for a 700R4 tranny.

11-12-2016, 04:10 PM	#5
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 7,874	Re: Welcome and gear change you may wanna check on the site for requirements needed for electrical shifting on the 700r4 o/d.

11-13-2016, 08:37 PM	#6
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,158	Re: Welcome and gear change Yes, when the time comes you will probably want a diagram to help make sure the torque converter clutch is wired correctly. Try to get a later version of the transmission. Over the years there were many changes to help them live. Make sure not to get the electronic 4L60E version of this transmission. Electronic version has a large electrical connector on the passenger side rear.

11-15-2016, 01:12 AM	#7
DangerRanger Registered User Join Date: May 2015 Location: Belfair, Washington Posts: 3	Re: Welcome and gear change Thanks all, I have started the shopping process for a replacement trans. Wish me luck.



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