Technical Hot Rod Manual transmission build: what type synchro? Now with solution!

Resolved!

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 most R10g1 transmissions. The one I have is in good shape, but I will need to replace the aluminum blockers. However, the p15 website 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?

 

No experience with Mopar 3-speeds, but the T86 Borg-Warner used on many Studebakers did not like to be WOT speed-whooped. It would hang up between first and second. Redline MTL and a Hurst floor shift conversion are your best friends here. You'll have to make the mounting brackets and rods, but that ain't rocket science.

BTW, the overdrive isn't usually hurt by WOT shifting. If it's in good condition and full of Redline MTL, it will usually be good to go.

jack vines, whose first B-W overdrive was more than sixty years ago

 

Don’t WOT shift with a synchro box.

That aside in 30 years of building transmissions for historic race cars the big issue constantly is with new synchro parts, if you’ve got NOS stuff or really good used bits that’s what I’d go for unless there’s a big advantage/disadvantage in doing so.

 

@Hillbilly Werewolf not advice but would you be interested in selling that parts catalog or making some photocopies for a price?

 

The inside of this Mopar box isn't significantly different from the Borg Warner boxes of the same era, as far as the concept goes.
It does seem to be difficult to get consistent, quick shifts when I really want them. I will likely use the Redline oil, but I am pretty fond of my column shifter. I already went though the selector mechanism and took some slop out of it, polished everything that touches, found shorter levers for it, and am going to do the same with the linkage. Hopefully that helps, even if it isnt perfect.
I am also thinking of sending all the trans guts to New England Gear Polishing for REM polishing. That should make sure everything slides smooth.

Well "luckily" there is only NOS and NORS available for this thing, so I dont have to worry about West Taiwan parts biting me.
Got any tips for making old transmissions stand up to abuse? Thinking of sending 1st gear and maybe a few other parts to get cryo treatment or micro shot peened, since the cost seems fairly low.

I got my 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.
The P15 forum had two guys able to contribute first hand experience with killing pin synchros, so at least I know I am on the right path switching to the strut type.

 

I wouldn’t bother with treatments or coatings on a road car unless you’re modifying stuff.
The big thing to ensuring your gearbox lasts is building it properly to the correct tolerances, might sound daft but people build gearboxes in a way they’d never dream of doing with say an engine. It then fails and they say it couldn’t take the power. where as actually it was just badly built.

 

Any thoughts of fast column shifts is bad juju. The OEM mechanism, no matter how much one polishes it, just has too much monkey motion. Enjoy it as a cruiser.

jack vines, who for the past sixty years has installed a Hurst in every manual transmission he's owned.

 

To give some closure to this, and consolidate what I have learned, here Is what I have co e 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, 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. 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 was reasonable, 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.

 

Where did you track down the spreader spring? I'd like to find a couple for a 1938 Chrysler C-18 OD, they're a bit different from the one you have but have not been able to find a part number in my parts books.
Can anyone advise if it's OK to run without them? It's been suggested to me that you can.

 

I lucked into the spreader spring on Ebay. I have not seen another for sale. I may look at duplicating mine.
I would think that it would work without the spring, but might take a split second longer to synch. Maybe if you found stop rings that have Oil grooves it would make up the difference.

My Mopar Streamliner catalog gives these part numbers:
Synchronizer spreader spring 686584 1938-1939
Clutch gear 679214 1938
Stop ring 692689 38-39 (C18 w/ Overdrive)
Hopefully this helps.

 

Thank you kindly for the reply, it does help, especially the part number for the spreader spring, I have all the other parts. The one you show in your pics is what my shop manual shows as the one I need for a '38 C-18, pic attached, so I think that would be the 686584 part number, but you say it's 1115576 for Fluid Drive, so should I assume that's a change up number for the same spring? Thanks again!

 

Really admire the research you put in to work out all of the parts and modifications. After doing all of that doing all of that I am not sure how much you will actually gain sticking with the column shift beyond some smoothness. But that could be a blessing based on the transmission strength. Still a nice project and I am sure the info will be helpful to others. Good luck.

 

The Mopar parts interchange book I have lists them as different numbers, not as a replacement number, so I would belive that they are slightly different, even if they look the same. Do you have the original out of your transmission? Even if damaged, you may be able to use it as a template to make a new one, or compare to available ones.

Thank you. Hopefully it will be helpful to others in the future.
I accept that the column shift may negate much of my improvements, but can always add a floor shift later. They are difficult to find for these transmissions (especially with OD) so I would likely need to modify one from a ford or Chev. I have a number of more important things this car needs, like a new dash wiring harness and rebuilding the rear end, so for now the column shift will stay.