Rebuilding the Mopar 3 speed: synchro choices Resolved!

[FarmerJon]

Guys, I need some knowledge:
I am building my first transmission, a Mopar 3 speed overdrive. I have built engines and a rear differential before and work in manufacturing, so I feel up for the task, but I have some options for Synchro type, and don't have the experience to know what will suit me best. Car has a lightly hopped up flathead, so not much power, but I do enjoy beating on it, and jamming the shifter like a maniac.

My options are:

Option 1 Pin type- what came in all R10g1 transmissions. The one I have is in good shape, but I will need to replace the aluminum blockers. However, a search here has numerous posts from guys who have had pins fall out/break off. Also some accounts of the Ramchargers mention problems they had with bending pins on hard shifts. This is what got me looking at what my options are.

 

Option 2 Strut type- what is supposed to be in my current '48 transmission, stock for '40-53. Basically a conventional synchro like in any of the popular 4 speeds of the 60s. My original plan was to swap this style in, despite needing to change out a number of other parts. 

 

However, when I bought a NOS assembly, I received Option 3-Constant Force type. This type doesn't use blocker rings, just copper cones/wipers integral rings in the clutch hub, and spring loaded ball bearings keeping it centered in the slider ring. It turns out this is from 35-39 Mopar 3 speeds, but at a glance and a couple measurements (although more needed) it looks like it would be compatible with the strut type input shaft, second gear and shifter fork. I cant find much info on this type, other than one mention that the ball detents can be easily overcome, allowing the gear teeth to grind.

It seems to me that it may be a good candidate to modify as a "slick shift" synchro, since it would keep it's original amount of syncronization.

With no blockers, I would think shifts would be shorter. However, I don't know how wise it for me to be WOT slick shifting a BW overdrive transmission.

So, what do you guys think?

Edited February 27 by FarmerJon

[Sniper]

All I can add is that in regards to the pin type synchros is that I broke a number of them power shifting the the A745 3 speed trans in my 64 300, warmed up 413.  I never had that problem with the strut types in my A833's.  No experience with the third type.  How any of this might apply to your setup, I dunno. 

[FarmerJon]

Well it is helpful to validify my distrust in the pin synchros. I am sure they are fine for Pastor Fred and Gramma Nan.

 

Here is the Tech article I found that discribes the different kinds of synchro

http://rspublication.com/ijst/aug 13/43.pdf

 

Edited January 21 by FarmerJon
Added PDF

[Sniper]

To small for this old man to read, lol.  Tried to open it in paint to zoom and it's too fuzzy zoomed out. 

[kencombs]

Been working on these cars way before they were 'old' cars.  And never had to repair a strut type, except for broken gears, not the fault of the synchronizer, rather the loose nut behind the wheel.   Me.  No experience with the third option but don't like it's looks.

[FarmerJon]

13 hours ago, kencombs said:

Been working on these cars way before they were 'old' cars.  And never had to repair a strut type, except for broken gears, not the fault of the synchronizer, rather the loose nut behind the wheel.   Me.  No experience with the third option but don't like it's looks.

Do the flathead 6s make enough power to put any particular gear in danger? 

[kencombs]

26 minutes ago, FarmerJon said:

Do the flathead 6s make enough power to put any particular gear in danger? 

Not normally, but circumstances can cause damage.   Damage the low/reverse slider from trying to spin the wheels, actually spinning on slick surfaces then hitting dry spot or 'speed-shifting' where common with all the low powered cars of the 50s.   The first was my mistake.   And a lot of other teenagers.  

Not so much the HP but the result of high (for a flathead) RPM and the inertia of that heavy crank/rod/pistons/flywheel when the clutch is engaged too quickly.   Mopars weren't as bad as Ford flatheads.   Dad made a lot of money supplying rebuilt 3spds to the local teen crowd back in the day.

 

[FarmerJon]

I got a Mopar NOS strut synchro 2nd gear today and was able to compare it to the Option 3 synchro. The cone is a match, but the dogs of the '35-39 synchro are about .020" too small to slide onto the dogs of the gear. I could open it up on the lathe, but unless I am gaining something, I won't bother and will just sell it and buy a Mopar NOS strut synchro.

 

Any of y'all have any experience or opinions on post-processing treatments, like Cryo or micro shot peening? Thinking of just having a few select things done, like first gear and the synchro parts.

[Ivan_B]

I've read about (and seen pictures) of those older type gears with the metal balls fallen out and getting stuck between the gears (not good). So, it might be safer to go with the shifting plate type, if you have to choose between the two.

[FarmerJon]

I could see that.

I didn't know this thing had spring loaded ball bearings inside it when i first cleaned it and popped it apart. You can imagine what sorts of words were uttered when i suddenly had small springs and balls all over the workbench. 

[Sniper]

8 minutes ago, FarmerJon said:

You can imagine what sorts of words were uttered

 

Surprise, surprise, surprise?

[SteveR]

In rebuilding my transmission I found it was a 39 case but had 41-41 brass stop rings as seen in your exploded drawing. Before I found this out I had ordered a 37 clutch gear. What I found is that the 37 clutch gear is not compatible with my 1st gear teeth It must have been changed at some point to the newer style

[FarmerJon]

17 hours ago, SteveR said:

In rebuilding my transmission I found it was a 39 case but had 41-41 brass stop rings as seen in your exploded drawing. Before I found this out I had ordered a 37 clutch gear. What I found is that the 37 clutch gear is not compatible with my 1st gear teeth It must have been changed at some point to the newer style

My '49 Mopar Parts interchange book shows '39 transmissions as being available with both styles, with the P7 having the early style synchro, and the P8 having the later strut type one.

[FarmerJon]

To give some closure to this, and consolidate what I have learned, here Is what I have come up with: 

I tracked everything down to convert to the '40s early '50s conventional blocker ring synchronizer assembly.
To do so I needed: main drive pinion(853864), clutch gear assembly(1115595) synchronizer stop rings (853867), second gear (852456), and the correct shift fork (1138246).
I also did the factory recommended upgrade and replaced my stamped synchro struts (detent plates) with the later solid ones. They most likely are directly interchange with early a-833 ones.
If you have a spare 833 one floating around your shop, I would love to confirm this. 

I also got a synchro spreader spring intended for Fluid Drive cars, it preloads the blocker ring to help the 2-3 shift be more efficient. It is part number 1115576

I found that the blocker rings (WT243-14F) are shared by many different makers, including ford (B5A-7107A, Studebaker (1555429) AMC  and Jeep(640397)

This lead me to see that Studebaker rings were made slightly different- they often have grooves that cut perpendicular to the inner threads, just like more modern rings. Apparently this is referred to as an 'oil bleed' and helps evacuate the oil that gets between the gear and the ring. Makes sense. Again, this helps the synchro be more efficient, which should give smoother, quicker shifts.

Of course, the rings I got did not have this feature, but were at least forged. I considered doing it right and making a drill fixture to add my own, but after talking to the engineer at my work (also a car guy) I ended up just cutting grooves carefully with a die grinder. 

After spending so much time reading about blocker rings, I really wanted to play with cutting teeth off the rings to further improve shifting, but I couldnt pin down what would give reasonable longevity, so I just mimicked the stock T5 rings, but cut 6 teeth less off.

I ended up having to have my heat pump repaired, so I am not able to send everything out for REM polishing, but I belive I have all my parts together. Hopefully I can get this thing back together and give yall a report on how it shifts in the next month or two.

Edited February 27 by FarmerJon

[9 foot box]

   It’s been 6-8 years ago, that I put an R10-G1 in my P15. It was missing some parts and needed a shorter input pinion shaft. I got what I needed from George Asche. He mentioned a fast second gear. So I found a 23T second gear, 853885 and 25T counter shaft, 692687. My spreader spring was bad, but a fellow member had mentioned one, so I contacted him for a replacement. I don’t know if it’s needed for non-fluid drive, I just wanted to replace it. My transmission was from a 53 Dodge, so it had a place for a detent switch for backup lights, that were on the car. Use the soft plug from the small parts kit on the left lower shaft, or a penny. There are old posts regarding slight leakage after install, even with the gasket. Thanks for sharing your progress.  Rick D.

[FarmerJon]

Thanks for putting those part numbers in! 

How do you like the "Fast Second"?

Do you use 2nd OD much? 

I chose to go with the standard 1.83 second, so that 2nd OD would be a better split between 2nd and 3rd.

 

Here is the difference in a 1940 "Fast" second transmission and a 1941-1956 "standard" second. The blue highlighted columns are BW overdrive gears, for standard 3 speed, ignore them.

Calculated with 3.91 rear and 28" tires.

 

 

As far as leakage,  I have seen many of the posts about it. I belive this is caused by a few factors.

1: many of the bolts, in bearing retainer and tailhousing, are open to the transmissions oil resevoir. My '55 OD has these holes counter sunk and filled with rubber so the bolt heads act as a seal. 

This will take some care to duplicate on rebuild, but thread sealant should also be used.

2: lack of vent/breather. There is no dedicated vent on these transmissions, just the opening for the input shaft. This has no seal, just a threaded portion in the bearing retainer to wipe off the oil that is trying to work its way out. So hot, expanding air is pushing out in the same place that oil is already barely contained. A filtered breather plug added to the top of the case might help, especially if a custom bearing retainer was made, that would fit a lip seal. The last versions of these transmissions had this treatment from the factory. 

 

[Young Ed]

Very interesting. Mine is a chronic leaker and seems to leak mostly after it's been run. 

[FarmerJon]

10 hours ago, Young Ed said:

Very interesting. Mine is a chronic leaker and seems to leak mostly after it's been run. 

There are a number of potential leak points, I am planning on taking some pictures that show them all, and note which can be fixed with transmission in the car, out of the car, and at rebuild time. I will make a dedicated post so it isn't buried in this one.

 

[Young Ed]

Thanks look forward to it. I had mine out of the car twice in 2022 trying to seal it up. I replaced the gasket for the input shaft and thoroughly cleaned and resealed the trans to bellhousing.