Torque Converters and Rear Main Bearings

[James_Douglas]

I am starting a new thread so people can have the information I have dug up. 

 

In researching the Powerflite Transmission and it use in flathead sixes I found out the following:

 

1. Chrysler in a Service Bulletin tells us to use a later and different rear main bearing if we are using a torque converter.

 

The engineer in charge of the Powerflite program in a January 1954 presentation to the SAE stated the following:

 

2. "We have two converters of different diameters: 12½ in. for all De Soto and Chrysler 6- and 8-cyl models, and 11¾ in. for all Dodge models. The smaller converter is also used on Plymouth Hy-Drive."

3. "In these converters, the impeller is attached rigidly to the crankshaft...Early in the torque converter program, it was found that a flexible drive caused excessive engine main bearing rap. The explanation for this lies in the added inertia of the system, which resists crankshaft deflection." [Italics and Underline mine]

 

What item three tells me is that is the reason for the revised rear main bearing. Even with the unit bolted hard to the crankshaft there was a lot of stress on the rear main. Later in the article he goes on to talk about thrust loads on the crankshaft from the converter.  What this tells me is that anyone using any kind of torque converter should use the redesigned rear main bearing.

 

He also talked out the stall speeds:

 

4. Engine stall speed: The engine stall speed was made less than the engine speed for maximum torque, even though the performance is better when the stall speed is higher. The higher stall speed results in increased gasoline consumption, greater coaling needs, and, of course, much more engine noise. Two limits were arbitrarily set up for maximum stall speed: 1400 rpm in 6-cyl models and 1500 rpm in 8-cyl models.

 

He then goes on to talk about the "fluid converter range" [Torque Multiplication] and the "fluid coupling range" [when the unit is coupling and not adding any extra torque]:

 

5.  The use of a torque converter of generous diameter was the most important factor in securing the efficiency in the fluid coupling range. It is also our experience that 3-element converters are the most efficient because there are fewer gaps to bridge in the oil path. As a matter of fact, we are now planning [as of January 1954 article date] to make the change to a single-stator unit in the very near future.

 

This information tells me, I had to pay the SAE $30 for the article, is that there were two sets of torque converters. One for the six and another for the V8. That a torque converter puts a strain on the rear main bearings and the six required a different one to deal with it.  It also tells me that the two stator converters (introduction until late 1954) although they have a slightly "longer" RPM range for torque multiplication, that at the "fluid coupling stage" they slip a little more and thus use more gas and loose a little power for high load mountain driving.

 

I will be looking for a late 1954 Powerflite torque converter. If anyone runs across one...drop me a note.

 

To those looking to putting a modern automatic on a flathead, you may wish to go pay for and download the SAE article. In it it shows the converter torque curves which would help you have a modern converter made to match what the engines were doing.  Also, the later rear main bearing would not be a bad idea.

 

Best, James

[Andydodge]

This might be useless information but here in Oz where we sometimes in a single year had both the short 23" Dodge/Plymouth engine and the long, 25" DeSoto /Chrysler version....the difference apparently depended on which transmission was specified.....ie, if a standard 3 speed was wanted then you got the 23" engine.......if a 3 speed with overdrive attached was wanted then you got the 218 version of the 25" DeSoto/Chrysler engine and if the Powerflite was wanted then you got the 228 cube version of the 25" engine......for whatever reason it appears that the Powerflite auto was never attached to the 23" engine here in Australia and in the final use of the sidevalve engine in the Australia only 1957-1962 Chrysler Royal in seems that the 23" engine may not have been available as it seems that only the 250 cube 25 DeSoto/Chrysler engine was the only six specified and the 303/313 Poly the only V8......the six could be had with either the standard 3 speed or with the 3 speed & Overdrive, the V8 only with the Powerflite then Torqueflite.........I have various Oz Chrysler workshop manuals and none indicate nor specify a different rear main bearing depending on what gearbox was attached which is interesting............regards, andyd     

[Loren]

It's curious idea that a rear main bearing would be different between transmissions.

The only thing I can think of is the Thrust but that would be more important on a manual transmission with the clutch pressure than an automatic.

I'd like to know what the difference is. I could see HyDrive being different but not an Automatic.

I just got a 25 inch engine apart and the Thrust flange had ripped off the bearing. The engine came out of a forklift so it had plenty of clutch actuations in it's life time.

 

[Dodgeb4ya]

All the old Federal Mogul Spec and Application books make note of this special TQ rear main bearing.

This has been brought up here a couple years ago.

[kencombs]

There was a set of .010 mains for a 230/Powerflite on Ebay a year or so ago.  I saw them, bookmarked it and went back the next day to buy and they were gone. NOS Mopar too.

[James_Douglas]

I have in my files, and talked about it in another thread, that there is a Chrysler Service Technical Bulletin that states that ,"it is essential..." that a car with a torque converter use the revised bearing. When you couple that with the technical discussion at the SAE conference of the problems with main bearings and torque converters...

 

I posted the above so people could make their own decisions based on the best evidence I could find.

 

I have a "stock" early rear bearing in my parts and the "later" bearing in my parts. The big difference is the later bearing has only a single oil groove down the middle. I suspect, but I do not know, that the "stock" earlier version that has the three oil grooves may crack at that rear groove do to the thrust loads the author alluded to.

 

Since I will be using a PowerFlite with a six, I will use the bearing with one oil groove.  Now, if someone can help me find a late 1954 torque converter that is a 12-1/2 incher...that has one stator...I will be good to go!

 

James.

 

[greg g]

Wonder if this guy might be of any assistance.  Looks like his parts source is in California.

 

https://www.charlietranny.com/PowerFlite Band.htm

[wayfarer]

9 hours ago, James_Douglas said:

 

Since I will be using a PowerFlite with a six, I will use the bearing with one oil groove.  Now, if someone can help me find a late 1954 torque converter that is a 12-1/2 incher...that has one stator...I will be good to go!

 

James.

 

 

I'd suggest that you get busy on the www and call every Mopar related business you can find that deals with pre-60 stuff. There are still a bunch of boneyards that are Mopar only or that have high percentages of old Mopes.

Edited December 21, 2019 by wayfarer

[James_Douglas]

Ii have feelers out to the usual suspects. The big issue is that often the engines come out and the converters with the bell housing with them. Once it is separated from the transmission and the date code...there is no way to tell the 2 stator or the 1 stator ones apart.

 

I am looking for a custom converter maker that will work with me on this. It is more likely that I can modify one to single stator than I will fin done...

 

I have the luxury of time on this as it will be March before I can do much in the garage, even though I feel good enough to get back to it now.

 

James.