6066 (1960-1966) GMC Truck Club Bitcoin now accepted here! 
Pay Dues
Pay Dues or become a Site Supporter
 



Go Back   6066 (1960-1966) GMC Truck Club > 6066 GMC Truck Club Forum > Transmissions and Rear Ends


Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

Reply
 
Thread Tools
  #1  
Old February 17th, 2013, 03:48 PM
tinman64 tinman64 is offline
Junior Member
 
Join Date: Feb 2013
Location: canada
Truck: 1964 1000
Age: 62
Posts: 19
Rep Power: 73
tinman64 is on a distinguished road
Default tranny swap

I recently purchaced a 64 1000 with a 305,3speed,3.07 gears,I had never even seen a big block v6 before and am interested in keeping the 6 in it.I have heard all the negative reviews about the poor fuel milage these engines get,and was thinking about changing the tranny to a modern day O/D trans.The current set-up would put the engine@ about 2200rpm@ 60mph with a 28' tire,which isn't too bad.By changing trans to an O/D ( final drive about 2.15) the rpm @ 60mph would be about 1550rpm,this is right where the engine makes its most torque.Of course this is on paper.Has anyone changed their transmission to an O/D,and what were the results?Any help would be appreiciated as I would like to keep the original engine but not if it is,too expensive to drive.
Reply With Quote
  #2  
Old February 18th, 2013, 03:20 AM
Corts60's Avatar
Corts60 Corts60 is offline
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Portland
Truck: 1960 GMC Suburban
Posts: 62
Rep Power: 84
Corts60 is on a distinguished road
Default Re: tranny swap

When I put Stromberg 97's on my old '60 with 3.90 gears and a 3 speed, I was about 2900 RPM at 60. I never drove over 60 and I was still able to pull 11 MPG. That really is about what you'll get out of a big block Chevy as well.

One thing I am going to try and do on my next build is run a TBI set-up and some kind of overdrive tranny. I am hopeful that I could get about 15 MPG with that set-up and that would be just fine for as often as I drive my Suburban.
__________________
1960 GMC Suburban -305A (Soon to be 351E) & SM-420
(2nd Owner)
1978 Chevy Silverado - 350 DIESEL & T400 w/ overdrive (2nd Owner)

Suburban build thread on 67-72chevytrucks site:

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #3  
Old February 18th, 2013, 03:27 AM
Funky61's Avatar
Funky61 Funky61 is offline
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Corona, CA
Truck: 1961 Suburban 1962 GMC Utility
Posts: 1,129
Rep Power: 408
Funky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really nice
Default Re: tranny swap

Here are some sites for reference that I used for this swap.

http://www.classicjunkyard.com/new_process_a833.htm

http://www.customclassictrucks.com/t...n/viewall.html
__________________
1961 GMC Suburban 305A Overdrive
1962 GMC Utility 305D
Reply With Quote
  #4  
Old February 18th, 2013, 04:02 AM
raycow raycow is offline
Senior Member
 
Join Date: Jan 2013
Location: San Francisco, CA
Truck: 1960 C-10 Short Fleet
Posts: 129
Rep Power: 101
raycow is on a distinguished road
Default Re: tranny swap

My truck originally came with a SM420 and I replaced that with a T-5 from a S-10. This was a fairly easy swap, but it wasn't a bolt-in. Here are the issues I needed to deal with:

1. I had to replace the clutch disc with a 14 spline disc from an Astrovan.

2. Transmission mounting holes had to be enlarged slightly to clear the stock 1/2" bolts. The lower two mounting holes on the T-5 had no threads, so I had to use longer bolts with nuts in those holes.

3. Input shaft and bearing retainer were too long. A commercial spacer plate is offered to solve this problem.
http://hamiltonintakes.com/products/...5-swap-adapter
My time is a lot cheaper than my money, so I shortened the T-5 shaft and retainer myself. Other people who have done the T-5 swap reported that they did not need to shorten anything, so you may not run into this problem. If your T-5 shaft is too long you will know immediately when you compare it with the one on your 3 speed.

4. I had to get a different driveshaft. Any driveshaft shop can make up the shaft you need, but I was able to find one in a salvage yard that worked fine after I changed the yoke. Here again, my time was cheaper than my money.

I swapped the T-5 only because my truck already had a floor shift. If it had been a 3 speed with a column shift, I would have used a factory SM318 3 speed with overdrive instead. This is very similar to the transmission you have in your truck now, except that the overdrive unit replaces the tail housing. The SM318 overdrive transmissions were offered on Chevy passenger cars and trucks from 55 to 65 and are not difficult to find.

The overdrive 3 speed is an easier swap than the T-5. You won't need to do anything with the clutch disc or input shaft. Depending on the transmission year, you may need to swap the driveshaft or driveshaft yoke, and that is all. If you get a car transmission you will need to use bolts with nuts in the lower mounting holes as with the T-5.

If you need more info, please feel free to ask.

Ray

Last edited by raycow; February 18th, 2013 at 04:19 AM.
Reply With Quote
  #5  
Old February 18th, 2013, 10:43 PM
tinman64 tinman64 is offline
Junior Member
 
Join Date: Feb 2013
Location: canada
Truck: 1964 1000
Age: 62
Posts: 19
Rep Power: 73
tinman64 is on a distinguished road
Default Re: tranny swap

Thanks for the input,I was thinking more like an automatic trans,does'nt sound like anyone out there has experimented with an automatic,I think it might be worth a try.Would there be any balancing issues when switching from a flywheel to a converter and flex plate.Any experts out there?
Reply With Quote
  #6  
Old February 19th, 2013, 01:47 AM
Funky61's Avatar
Funky61 Funky61 is offline
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Corona, CA
Truck: 1961 Suburban 1962 GMC Utility
Posts: 1,129
Rep Power: 408
Funky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really niceFunky61 is just really nice
Default Re: tranny swap

Here's the info for starters...


http://www.6066gmcguy.org/SM420.htm
__________________
1961 GMC Suburban 305A Overdrive
1962 GMC Utility 305D
Reply With Quote
  #7  
Old March 27th, 2013, 02:11 AM
melmashman melmashman is offline
Junior Member
 
Join Date: Feb 2013
Location: Tucson & San Francisco
Truck: 1965 GMC Pickup 305e V6
Age: 78
Posts: 26
Rep Power: 76
melmashman is on a distinguished road
Question Re: tranny swap

My 1965 GMC Truck/Camper which I just inherited from Dottie, my step-mom, has a 305eV6. She recently passed away, but was able to obtain new motor mounts for it which it badly needs. I am planning to have them installed in May near Prescott, Arizona.
I got to thinking that the clutch must be pretty old by now with over 100K miles and I thought it might be a good time to put a new one in.
Then I got to do more thinking and the one thing I disliked about the vehicle was its lack of an overdrive. I took it to Alaska and maxed out at 50mph without severely overworking the wonderful engine. So now I am thinking I might switch out the 3 on the column to a used factory SM318 3 speed with overdrive Ray mentioned. I suspect the rear-end is geared too low, but did not want to mess with it now.
I don't know if I can get all the ducks in a row to get it done at one time (it would be done by a truck garage - not me), but I wondered if anyone could help me with sourcing the parts.
Also, do you think my thinking is correct or nuts?
Reply With Quote
  #8  
Old March 27th, 2013, 03:34 AM
BillT BillT is offline
Senior Member
 
Join Date: Jan 2013
Location: Moneta, VA
Truck: Drove and Owned Many
Posts: 301
Rep Power: 150
BillT is on a distinguished road
Default Re: tranny swap

I super-tuned my '66 GMC 1000 with a 305 V-6 just before a long trip years ago and I was getting a consistent 15 1/2 MPG out of it, highway.

I would have loved to have a Factory OD with my 3-Speed back then as I would love to have one today for my '72 C-10, but I always found them very hard to find.

I checked into aftermarkets and found them to be pretty expensive.

I went the inexpensive route with my '72 and put tall tires on the rear. I've got 265/75R/15's on the rear and a matching set of 235's on the front.

It did make a notice-able difference.

Bill
__________________
Drove and owned many, but some of the more interesting ones were:

-'60 GMC 2500 Dump, 305 V-6
-'62 GMC 4000 Flatbed, 305 V-6
-'62 GMC 6500 Flatbed Dump, 478 V-6
-'67 GMC 7500 Box, 6V-53 Detroit
-'71 GMC 9500 Flatbed Dump, 637 V-8
Reply With Quote
  #9  
Old March 27th, 2013, 07:07 PM
raycow raycow is offline
Senior Member
 
Join Date: Jan 2013
Location: San Francisco, CA
Truck: 1960 C-10 Short Fleet
Posts: 129
Rep Power: 101
raycow is on a distinguished road
Default Re: tranny swap

Melmashman, you might want to look into this one before it gets away. I didn't realize they were getting hard to find.
http://www.stovebolt.com/ubbthreads/...&Number=925247

Ray
Reply With Quote
  #10  
Old July 17th, 2013, 05:41 PM
huntaaar huntaaar is offline
Temporarily Suspended
 
Join Date: Jul 2013
Location: grand rapids
Truck: 1967 c2500
Age: 35
Posts: 13
Rep Power: 0
huntaaar is on a distinguished road
Default Re: tranny swap

Quote:
Originally Posted by BillT View Post
I super-tuned my '66 GMC 1000 with a 305 V-6 just before a long trip years ago and I was getting a consistent 15 1/2 MPG out of it, highway.

I would have loved to have a Factory OD with my 3-Speed back then as I would love to have one today for my '72 C-10, but I always found them very hard to find.

I checked into aftermarkets and found them to be pretty expensive.

I went the inexpensive route with my '72 and put tall tires on the rear. I've got 265/75R/15's on the rear and a matching set of 235's on the front.

It did make a notice-able difference.

Bill

What do you mean by "super tuned" 15mpg is my goal (im at ten now up from 7). tell me more about the set up you had. thanks.
Reply With Quote
Reply

Bookmarks

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tranny swap Archiver Previous Forum Posts 4 October 5th, 2012 01:38 AM
Tranny swap Archiver Previous Forum Posts 0 July 17th, 2006 02:10 AM
Tranny swap Archiver Previous Forum Posts 0 March 9th, 2006 01:09 PM
Re: Tranny swap Archiver Previous Forum Posts 0 March 9th, 2006 12:49 AM
tranny swap Archiver Previous Forum Posts 0 December 19th, 2001 03:18 AM


All times are GMT +1. The time now is 12:38 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2013, Jelsoft Enterprises Ltd 711710599629|1709638725|0