3 on the tree

[raycow]

Hi Steve -

Thank you for the update.

I am glad to hear that you haven't given up on this project and are still looking for a workable solution. Mel is very fortunate to have found you.

Ray

[melmashman]

Ray and Others,
I received the note below from Steve who I have complete confidence, but wanted to get a 2nd opinion. The NV4500 solution just is not going to work due to adapter issues.
Steve is recommending an SM365 4 speed with a change to the rear end to provide lower RPM's at highway speeds for about $3k. The splitter option he mentioned is too expensive. Based on your expertise would you recommend this SM365 approach? Hey - thanks for your help!!
Thansk - here is Steve's message:
Mel,
The easiest and most cost effective solution is to just put in a new clutch and reinstall the 3 speed but its not going to help with the highway driving, I think a good option is to put in the SM465 and change the rear end gear to something more suited for highway speeds. The overdrive unit I was looking at is the best option but also the most expensive (around $3300 just for the unit plus the SM465), its a completely different unit from a regular overdrive built into a transmission its an add on that would go on the back of the SM465 and it allows you to "split" each gear if you wanted in other words you have a overdrive in each gear except 1st so technically you would have a 7 speed transmission this is all controlled by a button on the shifter you have the option of turning it on or off in each gear. I'm not sure you really need something like this or want to spend that type of money. I'm guessing we can put together the SM465/gear change and all necessary components for around $25-$2800??. We have a 1968 GMC (shop truck project) with a 305 V6 and the SM465 trans/ bell housing as long as the transmission doesn't need major hard parts like an input shaft or gear set we can rebuild it and put it in your truck if the trans is not re-buildable we would need to buy one from Novak or another source this would bump the cost up depending on the price of the trans. I'm waiting for our transmission builder to come back from vacation to discuss this option. Let me know if you think this is something your interested in.
Thanks

[Rick]

Mel,

I converted my 62 sm318 to a "old style" 3 speed + overdrive (from a chevy).
I paid $400 for the unit, and another $350 to have it checked out, repaired and resealed.
This was 7 years ago, the unit has worked flawlessly since. (once I got the bugs worked out)
It is almost a drop in swap, only the rear yoke, needs to be changed.
I have it in a 62 1000 series. With the original 305 & 3.07 rear gears, I get as high as 18 mpg on the freeway (65 mph engine runs 1750 rpm)
Today I have it behind a 401 in the same truck and get the same mileage.

I feel this is the most practical swap you can do. Yes, other transmissions are better, faster shifting, stronger & smoother. But cost wise you cant beat this swap.
Note here: this transmission has handled the torque of my 401 for more than 5 years. However I do not abuse it.

My 2 cents,
Rick Rusconi

[raycow]

Mel -

IMO, Steve's solution is workable, but it all depends on a major unknown: Finding a suitable rear end.

First, you need to determine your present ratio, so you know what you are starting with. This is easy enough to do by counting driveshaft revolutions. There is no need to take the cover off and count the teeth unless you want to. Next, you need to decide how much rpm reduction you want, as a %. Most overdrive transmissions run in the 25-30% range (0.70-0.75 O/D ratio), just to give you an idea of what is out there.

You probably have a H052 or H072 rear (3/4 and 1 ton, respectively). These two are very similar, with the main difference being wheel bearings. The tallest gear ever offered for these was 4.11, so I don't think you will be happy with another of the same type. GMC also used a Dana 60 rear for some 3/4 ton applications, and taller gears are available for this one at least down to 3.54.

In 1973, GM replaced the H052/72 with 2 versions of the 14 bolt rear, which may still be in use. I don't know the specific ratio applications, but they are definitely available in the 3.xx range. This is something you will have to research. The main problem with the 14 bolt is that all the ones I have measured are wider than the rear you have now. Assuming you want to keep the wheels in the same place, you will either have to get wheels with a different offset, or else narrow the axle housing (expen$ive).

Fortunately, other truck makes used the same 8 bolt wheel pattern that you have, so you can extend your search to include Ford and Dodge in the hope of finding one of suitable width.

Regardless of what rear you end up with (including later GM), it isn't likely to be a bolt-in, mainly because of spring pad spacing, so you will probably have to relocate the spring pads. You will also have to cobble the parking brake cable hookup unless you get a transmission with the parking brake on its output shaft. Fortunately, those are fairly common.

As for the SM465 transmission, it will almost bolt up, but not quite. You will have bore out the center hole in the bellhousing to accept the SM465 bearing retainer. The "correct" 4 speed for your truck would be a SM420, which will fit your bellhousing without needing any modification. The SM465 wasn't offered until 1968. Both transmissions are of similar strength, but the SM465 has better parts availability, particularly the 2nd gear synchronizer, which is getting hard to find for the SM420.

Rick's post got me thinking again about the SM318 and its GVW rating. It didn't seem reasonable that GM would sell a truck with a transmission which wasn't adequate for the maximum GVW of the truck it was installed in. I wasn't able to find the applicable GMC literature online, but I did look at some Chevy specs. The C-20, which is their 3/4 ton, is rated up to 7500 GVW, and it came with a SM318. Their next heavier series, the C-30, is rated up to 10,000 GVW and you couldn't get a SM318 in that one. If you wanted a 3 speed, you got a T-89, which is stronger.

So where I am going with this is that I was wrong about the 6000 GVW rating for the SM318. If you are at 7500 or less, GM claims it is strong enough for the job. This means that the SM318 with the B-W O/D should again be given consideration. It will definitely be an easier and less expensive installation than the SM465 plus a rear end swap. Btw, the B-W O/D can also be used as a gear splitter if you wire it for manual control, which is what I did in all the cars I installed one in. As I said in a previous post, I would have one in my truck now if it had come with a column shift.

Ray

[steve c]

Thanks for the info on the rear end Ray I have not looked into which axle Mel has or looked for a ring and pinion. The trans swap will be easy since we have the correct bell housing no machining will be needed , the shop truck we have has all the correct parts. The SM318 sounds like a good option but I have yet to find one. The Gear Venders OD with the SM465 would be very nice but just very expensive.
Steve

[raycow]

These things do turn up on ebay, but they go pretty fast. You just gotta grab them before they get away.

http://www.ebay.com/itm/Manual-3-spe...34daec&vxp=mtr

http://www.ebay.com/itm/1958-1959-19...6752a3&vxp=mtr

Ray

[David R Leifheit]

And sometimes these transmissions "fall" into your lap.

Okay, it *looks* similar but it is out of a Ford (was bolted to an inline 6 I scrapped out of a mid 60s truck).

Somewhere I even have the "overdrive" cable to control it.

*If* I ever get to work on my '62 1000 this will probably be the transmission, or I'll see if the overdrive will bolt onto a GM transmission. I think the difference is the mounting from the case to the bell, and probably the splines.

http://www.oeltd.net/doc/parts/IMG_0780.JPG
http://www.oeltd.net/doc/parts/IMG_0781.JPG
http://www.oeltd.net/doc/parts/IMG_0782.JPG
*note* big pictures...

[raycow]

Originally Posted by David R Leifheit

*If* I ever get to work on my '62 1000 this will probably be the transmission, or I'll see if the overdrive will bolt onto a GM transmission. I think the difference is the mounting from the case to the bell, and probably the splines.

That's a pretty good transmission you have there. It's a T-85 or T-89. You can tell which one if you take off the side cover. T-89 has straight cut L&R gears. T-85 is helical.

BOP bellhousings were made with the Ford bolt pattern in the 60s, but never Chevy or GMC. You MIGHT be able to bolt that trans to a GMC bellhousing with an adaptor plate, but I'm not sure if the input shaft is long enough to allow for the plate thickness. Longer input shafts were made for AMC, Stude and Willys/Jeep applications, and those will usually swap. but they won't be easy to find. GM input shafts are about the same length as Ford.

The O/D unit and midplate might bolt onto a GM case if you drill a hole for the reverse lockout rod. GM pattern T-85/T-89 cases are pretty scarce though.

If it were mine, I would get it apart now just to just to halt any further rust progression. That thing is too valuable to lose.

Ray

[tatastruck]

Sorry to hijack. I have a 64 long bed with three on the tree and they have already relocated it to the floor however I really don't like this transmission so I'm looking to change it to the 4 speed. How hard is that will it bolt up to my existing bell housing?

[raycow]

Originally Posted by tatastruck

I'm looking to change it to the 4 speed. How hard is that will it bolt up to my existing bell housing?

If you get an SM420 transmission (used 67 and earlier) it will bolt to your present bellhousing with no modifications needed. You will need to replace the driveshaft, and, of course, cut a hole for the shift tower.

If you get an SM465 (used 68-up), you will also need to have the bellhousing center hole bored out to approximately 5.125" to accept the front bearing retainer. This is a job any machine shop should be able to do.

Ray