The Stovebolt Site Forums The Shop Area Driveline How Do I Separate OD from Trans? SUCCESS!

'61 Apache with 235 3-speed Saginaw with overdrive:

While greasing my U-joints recently, I noticed an excessive amount of play in the output shaft of the overdrive unit. That likely explains the odd vibrations and noise I sometimes get at interstate speeds.

I have a spare transmission with overdrive, and would like to swap the overdrive unit in the truck with my spare. Is it as simple as unbolting the unit from the rear of the trans, or is there any trickery involved?

Thanks!

-Kevin

There is a lot involved but it is possible. But from the sound of things the bearings are likely bad and it needs to be
disassembled anyway. If you want to send me a PM, I can give you some guidance.
If it is the original transmission with the 4 bolt side cover, it is a Muncie SM319, not a Saganaw.
Fred

What's the condition of the spare assembly? It would be a lot simpler to just swap the whole transmission than trying to do a partial repair with the trans still in the vehicle.
Jerry

The last time I lay on my back in my driveway (with the truck up on jackstands) and bench-pressed a transmission into position...was the last time I'm doing that. I had hoped it would be more manageable to just swap the overdrive units.

The condition of the spare transmission is wholly unknown. I bought it a few years ago from a fellow stovebolter, and it's sat in my garage ever since.

-Kevin

Thanks for the info; I'll send you a PM. To my knowledge, it's the original transmission, although the engine is a Jasper Engines rebuild. I had been led to believe that the stock transmissions were Sags. I'm always learning something new! The shop manual is not very informative in this regard.

-Kevin

I use a 4X4 timber through both windows of the cab, remove the floorboard, and hang the transmission from a cable come-along. My days of fighting transmissions from the bottom side are long gone, as well.
Jerry

A quick update:

I got the overdrive unit removed from the main transmission housing. There is no internal trickery...it was just that the gasket really had the housings stuck together. I can see that a challenge is going to be keeping the roller bearings in place when removing and installing the overdrive unit in my truck. They are not captive in a race or anything. Consequently, I'm making some locating pins from 6" bolts, so that I can slide the overdrives straight off and back on. Hopefully the gear oil will provide enough stiction to retain the bearings in place. I'll try and post photos of everything tomorrow.

I took note of the casting numbers on the housings of the transmissions and overdrive units. I can find no comprehensive online listing of transmission casting numbers. By perusing different tri-five, chevy, and camaro forums, I was able to discern that both transmissions are Saginaws truck transmissions, with build dates sometime between 1958-1965. I cannot yet resolve it better than that. It is quite possible that the trans currently in the truck is original.

-Kevin

The quick way to identify a Saginaw is by the number of bolts holding the side cover on. There will be seven of them. The earlier SM-319 Muncie has a 4 bolt side cover. OD-equipped Saginaw transmissions are extremely scarce, so definitely do not discard or misplace any parts. Pack the bearing rollers with heavy wheel bearing grease during reassembly. The grease will dissolve and disperse into the lube oil with no ill effects whatsoever within a few miles of operation.
Jerry

Saganaw overdrives were not available until 1966 and continued through 69. Completely different unit, full synchro,
special solenoid and governor, fine spline output shaft. Also different shift lever spacing on the side cover due to the
larger 7 bolt side cover.
Fred

Kevin, I did a little peeking through the web and found a post on another forum that says the Saginaw 3 speed OD transmission repair and overhaul instructions can be found in the 1961 Chevrolet Passenger Car manual. I don't have one of those books to check, but feel confident that the info is accurate.

There are a bunch of those available on evilbay like this one that wasn't the cheapest, but the best condition for the least money. Hope the info is helpful.

That is great help! I dug out the manual for my '60 Impala (1958, plus '59/'60 addendum), and there are some additional diagrams that seem helpful. Info on the overdrive unit is more plentiful than the transmission itself...probably because the overdrives were more widely used.

I'll probably end up dropping the whole transmission anyway, but I may give the OD swap a try. We'll see if the roller bearings stay in place.

Using the casting numbers and online info, I got a Fel-pro gasket kit today. The fit is fine, but I am unimpressed with how thin the gaskets are...1/128"...the thickness of two sheets of copy paper.

I have an ulterior motive here. I want to learn as much as possible about the internals of the transmission/overdrive mating. I want to eventually do the 4-speed on-the-tree overdrive mod that's popular with the tri-five guys. I've talked to guys who claimed to have done it, and there's one already modified for sale on marketplace.

Thanks!

Kevin, Glad the other info was helpful. Does the OD transmission you have look like the one in this publication??? If so, read through the publication as there are some warnings about splitting the OD from the transmission and NOT disturbing the overdrive adapter plate. You don't want to create a bunch of extra work by having to completely tear down the main case assembly too.

According to HRL, a Saginaw tranny has a 7 bolt side cover. Dan's picture above does not.

Success! The overdrive transmission is back on the road, and working fine....but there's a bit of a story:

Using the Borg-Warner overdrive manual, some good advice from rfs56trk, and considerable online info (including the link from Gdads51), I started to disassemble one of my spare OD units to see how the one that's in the truck would come apart. Looking at the B-W manual, I was expecting to gain access to the two sets of bearings/races in the tail of the OD, as indicated in figure 3. As I was disassembling the OD, I noticed there was only a bronze bushing at the output shaft, not bearings. I ran an endoscope down the tail to make certain. I couldn't find a date of publication of the B-W manual, but I guess there were production changes throughout the years.

I then scoped out the OD unit in my truck, and discovered that the bushing was completely missing! I ran the scope through the oil drain hole and both fill holes, checking for debris. It seems that whoever last worked on this OD failed to install the bushing. The collar where the bushing goes had been gradually wearing away the yoke, and had worn it down by 1/64". I got a bushing and rear seal set from NAPA for about $32. I drove in the bronze bushing, replaced the seal, and refilled the transmission with oil. When I replaced the yoke, I went ahead and replaced both U-joints. (If the bushing were damaged rather than completely missing, it can be pulled from the rear with the correct puller)


Basically, I was able to make the repair without having to disassemble or remove the OD from the truck. The test drive was smooth! This trans has had a bit of vibration for as long as I owned it...I attributed it to being old and worn. The vibration was generally only noticeable when driving down the interstate at 75-80mph. It had gotten worse lately, which is what led me to start checking into it.

Thanks to everyone who contributed information!


The other issue I encountered is regarding transmission identification. The internet is replete with opinions and assertions about what is a Saginaw or Muncie transmission. The tri-five forums are a dumpster fire of conflicting opinion and partial information. There isn't even universal agreement on the years of production, while some conflate the characteristics of the 3-speeds with 4-speeds. It's a hot mess.

From what I can tell: A Chevy transmission made at the factory in Saginaw Michigan in 1960 is not a 'Saginaw', while a Chevy transmission made at the Saginaw factory in 1966 is? I'm painting with a broad brush here, but the early 'Saginaw' transmissions were just known as 'Chevy', as there was no need to differentiate. Later transmissions (3 & 4 speeds) made in Saginaw were known as 'Saginaws' to differentiate them from the 3 & 4 speed transmissions made in Muncie, Indiana. The term 'Saginaw' was retroactively applied to the earlier Chevy Saginaw-built transmissions as casual reference. (Borg-Warner transmissions have a uniquely-identifiable case, and transmissions made in Dearborn seem to be BOP applications)

Ultimately, casting numbers will tell you what era and model of transmission you have. Use primary references, not just what someone posts. Some people will argue with you, to satisfy their need to be 'right'. Just get the parts you need that fit your transmission, fix it, and drive it! If someone feels compelled to argue, they can find all the verbal judo they want at the tri-five forums. They have people there who seem to enjoy tearing each other down, rather than buoy each other up.

I hope this story and info helps!

-Kevin

Just to add a little more smoke to the dumpster fire, from someone who was paying the rent and feeding his family by working on these things when they were nearly new- - - - -the heavy duty 3 speed Borg-Warner T-85 that was mostly used in Pontiacs was modified by B-W to make the original automotive 4 speed used in late 1950's muscle cars, the T-10 by moving the reverse components to the tailshaft housing, and adding an extra forward gear to the main case.
Jerry

For those who are dealing with OD’s, make sure the electrical generator is secure to the case. I had one in a Jeep, the electrical generator popped out while on the road which did not work well!

Ed
,

Which one is the "electrical generator"- - - - -the solenoid, or the governor?
Jerry

Related to Ed's electrical comment above, I've encountered an issue on two different trucks: If the battery is in a low state of charge (you just now had to jump-start it to get it running), the alternator or generator may not have enough capacity to recharge the battery, AND kick in the OD solenoid at the same time. The first time this happened, I thought I had a weak solenoid...the second time, I finally had an 'ah-ha!' moment. I haven't measured the amount of current the solenoid draws when activated, but it must be considerable. The current required to hold the solenoid is much less.

-Kevin

Jerry,

Didn’t know at the time, wires on it which kept it from escaping.

Ed