Author Topic: Gear swap  (Read 1852 times)

Offline Powderhound

  • New Users
  • Posts: 1
  • Newbie
Gear swap
« on: April 11, 2016, 09:51:16 PM »
My truck has 315 70r 17 4.56 gears and a turbo 400, right now my tranny barely heats up but I have to turn 2900 rpms to do 60 and like 3400 to do 70 I have a bbc 502 and it makes me nervous runnning that high all the time. I was thinking about going to 3.73s that would put me at 2700 rpms at 70. My question is it's a heavy truck and I regularly put 1300 pounds on the bed would that high of a gear heat up my tranny when towing stuff?

Offline raf2330

  • Newbie
  • Posts: 25
  • 78BigBlock
Re: Gear swap
« Reply #1 on: April 17, 2016, 01:53:51 PM »
I would consider adding an external trans cooler, I have done that with the TH400's/454 I've had and never had an issue. While I can't say what the 17's do to your ratio, I ran 3.73 for several years with camper on and towing on the 16.5 wheels, it was OK, switched to 4:10 and loved it. Never any tranny issues.
78 Crew cab dually, mine since 97.
Working, & working, & working on dad's 73 w/big block.

Offline Da67goatman

  • Site Supporters
  • Junior Member
  • ******
  • Posts: 749
  • Burban
Re: Gear swap
« Reply #2 on: April 17, 2016, 05:35:29 PM »
I would suggest an overdrive trans before regearing. A 700r4 just makes more sense, lower first to get moving and benefit of overdrive for the highway.
<Pitcrew>
1989 R2500 Suburban mild 350 TBI 700r4 10.5" 14bolt 4.10 w/ 33s
1992 fullsize Blazer 4x4  35s no lift, 4.10s, Hella driving lights, TJ Flares, Huge bumpers, Snorkel, custom interior

Offline jg1977c20

  • Registered Users
  • *
  • Posts: 104
  • Newbie
Re: Gear swap
« Reply #3 on: April 19, 2016, 02:37:31 AM »
3:73 is fine most guys who dont like the 4:10's swap to this and say they like it - regarding the tranny swap to an od 700r4 - i'd want that 700r4 freshly built for heavy duty use - they are not as strong as the th400 or th350 especially the sun shell and you never use OD for towing or hauling under any circumstance .
1977 c20 cheyenne camper special 8200gvw

Offline Da67goatman

  • Site Supporters
  • Junior Member
  • ******
  • Posts: 749
  • Burban
Re: Gear swap
« Reply #4 on: April 19, 2016, 03:46:24 AM »
if you use the right parts and be smart about it there's no reason you can't use overdrive when towing.  Upgrade the sunshell with the 6 pinion planetary with corvette servo and oversize .500 tv valve with good quality clutches.  I know a guy running a 468BBC with 44s and 4.56 and he has hauled his boat and his quads without any problems. 
<Pitcrew>
1989 R2500 Suburban mild 350 TBI 700r4 10.5" 14bolt 4.10 w/ 33s
1992 fullsize Blazer 4x4  35s no lift, 4.10s, Hella driving lights, TJ Flares, Huge bumpers, Snorkel, custom interior