Technical The elusive '39 Ford transmission

I have 24 total transmissions. Some side shift, some floor shift, 78 cases, 48 cases, one 18 case, etc. Plus misc internals and extra trans parts.
I understand the 25T/less torque idea, seems like it would be minute and still affected the same by shock. I'm not too concerned with gear ratio. I have 3:54 ring and pinion and a very healthy 8BA. I've had her to 85mph and can cruise at 75mph all day.
Shock is the transmission killer and what I'm trying to minimize. (I know, I know, easy left foot) Lots of good ideas here that I'll be implementing. The vast knowledge here is pretty impressive.

 

Well, I ordered and am waiting for “The Ins and Outs of Early Ford Transmissions Book” by Mac Van Pelt. It should be here in the next couple of days.
Meanwhile, I’m looking into Glyptal paint for coating the inside of the transmission case. What’s everyone’s thought on this? Any other treatments for the inside of the case?

 

A little tidbit is to make sure you use GL-4 and NOT GL-5; even if it says bright metal safe. Seems like local Napa can still get Sta-Lube GL-4 in at least two different weights.

 

Well, Build it tight. Remove tolerances up to specs. Take all the "slack" out before hammering it and you'll be just fine.

Understand what your dealing with, they are super hard but hate to be shocked (dropped Clutches are not our friend) if you want bulletproof it's not going to happen. They are for enjoyment, pure enjoyment.
- Tim

 

I used Glyptal on the inside of mine just to seal up any crap embedded in the cast iron. Just be aware that it needs to be baked before being placed in service...

 

I ordered it online shipped to the store for free. Since I hadn't ordered before they gave me a 20% discount. See if that is still available.

 

I admit to being a total novice, especially in this group. But I did rebuild the trans in my A coupe and it served me well and I'm about to rebuild one for my '39 Merc. I don't know how significant a difference can be had, but I have heard that the early truck cases with the full bottom rib are stronger. Maybe allow less flex?

 

In my opinion, the full length rib doesn’t give you any significant extra strength, particularly for the average build. We’ve seen plenty of full rib cores in our shop that were cracked or blown out. Back in the day guys built their hot rods to the most horsepower they could afford and then flogged them mercilessly on the streets and the track. It’s a different world nowadays. You should be comfortable with any Ford gearbox case that isn’t worn out.

 

I have built a bunch of these transmissions and there is lots of great info in this post, lots of great tricks that actually do increase the longevity of them under hard use. No one wants to hear it but…. By far, The best tip on getting a 39 box to survive is don’t launch hard with it! Get the car rolling a bit and then punch it. Speaking from experience, it does not matter what you do in building the transmission, if you can’t drive with some degree of restraint, you will break it! I have a strong 284” 8ba in my light roadster with skinny bias ply traction and it’s on its 4th transmission in 2 years. That is despite building each one with extreme care and the best parts and techniques, and knowing better many times over. In every case of breakage, my desire for excitement from a dead stop got the best of me and it peeled every tooth off first gear! This last time I installed one with a 25 tooth Lincoln gear set and so far the thought of blowing those gears through the bottom of the case has prevented me from letting things get out of hand. I think we tend to forget that the main reason so many cats used these gearboxes back in the glory days of hot rodding wasn’t because they were a great choice, it was because they were common and cheap. Cad or Packard boxes and most other stronger alternatives were comparatively expensive and harder to find. These days, I think if you have the option it makes more sense to build the car with a stronger box as the cost difference has somewhat equalized over the ages. Anyhow, do all the tricks, set it up snug, drive with care, but don’t expect miracles!

 

Nice car any other pics?

 

I'm not sure how you drive that car sedately at any time! It just screams loud & raucous
Is there a build thread??

 

They are notoriously fragile. Came around a corner and hit the gas; didn't NAIL it...just hit the gas in second gear. RR tire spun a bit on some sand and when it caught...BANG. Oh well...
Andy

 

I agree, it's awesome!

 

Just a couple, I don’t want to pollute the thread too much…

It’s difficult, the fucker really begs to be flogged! Ahhh no build threads these days, I guess I’m too lazy to do such things anymore. There are probably some pics in my shop thread I was posting on for awhile. I have not updated it in a VERY long time… this is actually the same car as my avatar, just totally redone as a street car.

 

So, has no one here annealed the gears, to remove some brittleness? Also, when re-bushing second gear, do you concern yourself with the little oil pockets in the bushing or run it smooth?
I'm running a pretty healthy 286ci in a '29 Briggs Fordor (my avatar) with 6.50 bias ply rear tires. I will have a talk with my feet, especially the left one, on how they are treaty the clutch and transmission.
What I'm hearing is set the gears up tight, tight, tight.

 

There is fine balance of exactly how tight to get it. Until you get in there and familiarize yourself with these clog boxes, there is a dance between tight tolerances and how it actually feels when you spin it by hand.

This will makes sense once you do it a few times. Buy the different shim packs from Mac Van Pelt and be prepared to to take it apart a few times before you get it where it needs to be.

 

Also, as the shim packs are only available in certain sizes - sometimes you can't get the correct end-play on the main-shaft stack without further tuning. I try to get down to about .003 or so. I have a surface grinder, so sometimes I can shave the shims (they are hard to hold on the magnetic holder), and sometimes I put in a thicker shim and just shave the back of 2nd gear. Lots of ways to skin the cat if you have the tools and know-how.

 

Bored&Stroked - Well, I do have a lot of equipment but, unfortunately not a surface grinder. I’ll just have to lap my shims. What grit should I use? I do have a mill and a lathe so, I can machine second gear or the case, if need be. Thanks for your input of knowledge.

 

I would not machine the case. I'm not doubting your ability, but you need to fool around with one and all of advice will make sense. They are fairly simple, but need to be set up correctly like anything else mechanical.

Also, if you don't have it yet, get Mac Van Pelt's book.

 

Just sayin'-----But started out with '39 box & '41 rear, after "Shearing the cob" & twisting axle keyways, I went to B/W 4 speed & 9" Ford rear. this has been a winning combo for 300,000 miles since 1978.
Have you considered a "La Salle' Trans???

 

Banjorear - I’m sorry I didn’t explain every bit of knowledge/experience that I possess. I have “fooled around with one”, actually a few of these transmissions. So, yes, most of this advice makes sense. If you read my very first post/question you will see I’m searching for more than how to rebuild a ‘39 trans. Yes, I have Van Pelts book and although I do think it is the most thorough on information as far as rebuilding, it still doesn’t provide any “above and beyond” tricks for improving parts strength.
Deuce Don - I have considered a LaSalle trans. But, I’ve only seen one LaSalle transmission in the wild and that was a side shift. Also, as I’ve stated, I am already well invested in ‘39 Ford transmissions.
My goal is to improve the strength of the parts of the ‘39 Ford style transmissions. That with good practice procedures in the rebuilding of said transmissions, should greatly improve its life expectancy.

 

30´s-40´s Ford transmission has good, enough big ball bearings. You dont need to increase any balls or any tricks....
Just use new good western bearings (NTN, FAG, SKF,...). Those transmissions are very strong. Problem , early days, was that oil they used was junk, old,.... 6306.2RS.NR and 6208.2RS.NR bearings are what I have used.
2RS = double rubber sealed. There is so much grease inside what bearing needs all its life. I havent use those splash washers when installed 2RS bearing. OK, You can remove inner rubber seal if You want that oil need to go inside bearing....

Vanbelt sales You can have all missing parts or new stuff replace worn ones.

Those bearings are 20euro (20usd) each here in Europe. Maybe same price there in US?

You dont need any tricks, just check that all parts (gears, teeth, syncros, needles bearings, rolls inside of mainshaft and those ball bearings are ok.
A

 

Ok, here’s a small tip for a performance build on the Ford 3 speed top loader……let’s call it a “39 style” transmission. First thing is that you want to stay with the newer type synchronized gearset that came out in 1939. This means using the 1939 shifter tower with the correct 91A-7230 fork. Then decide if you’re staying with the closed drive torque tube rear end, or changing to the open drive design like the pickup truck transmission had from 1942-52.

If going to open drive, use the 1951-52 pickup truck gearset. The 51-52 gears changed from the 42-50 versions in that the first gear teeth were redesigned to enhance their strength and resistance to breaking off under load. The other advantage is that the 51-52 cluster gears run on the loose needle bearings which (in my opinion) hold the cluster gear in place better than the caged roller bearings used prior to that. The 51-52 cluster gear and its mating low/reverse slider gear have what’s commonly called the “diamond” shaped teeth for first gear. They have a larger base or root to the tooth with a bit of a pointed tip to each tooth. They are much more resistant to snapping off under load. Since a hard takeoff in first gear is usually when disaster occurs, the redesigned gears hold up much better.

if you’re staying with the closed drive setup, your options are limited. The use of the 49-50 Ford passenger car 28 tooth cluster gear gives you the loose needle bearing design for inside the gear, so that’s good. Unfortunately it has the same first gear teeth shape of all the usual pre 51 gears. Your best hopes for the life of this gearset is to stay away from big fat tires on the rear end, and be careful about how you drive the car.

Then, there’s one more tidbit of little known fact……there’s a mainshaft that at least one gear mfr made that was created to use the 51-52 type gears in a closed drive application. We’ve had several of these come into our possession over the years. They had NO markings of any part number or manufacturer name. We always ID them by the exact resemblance to the 81A-7061 and the 51A-8061 closed drive mainshafts, except that the spiral spline section has the helix angle of the 51-52 low and reverse slider gear. With this odd mainshaft, we have built several closed drive 39 style transmissions that have the 51-52 pickup truck gears.

Lastly, building the transmission with good gears and shafts, along with keeping all the tolerances down to the minimum clearance levels, will help it live longer. These are not designed for 200+ horsepower and hard fast starts with big sticky tires. You can break much sturdier transmissions than the 39 style transmissions if you get too aggressive……

 

Mac - Thanks for the good information. Unfortunately, most all of my builds are closed drive. Is there a good way to identify the truck 51-52 and car 49-50 transmissions from the outside, without total tear down? That "odd" main shaft sounds like a part I need. Does anyone have an idea what company produced that shaft? Sounds like I need to disassemble every transmission I have and inventory all of my parts.

 

If you’re inspecting a typical Ford toploader 3 speed transmission, which happens to be the closed drive configuration for a torque tube driveshaft, you can open the top to inspect the gears. The easiest way to know if it has the 51-52 gearset is to carefully count the teeth of the low/reverse slider gear. The typical 36-50 gearset will have the usual 29 tooth gear. If you counted 28 teeth, it would confirm that you are looking at the 51-52 gearset…..but with the rare closed drive mainshaft. Since they are so scarce, you’ll probably fall asleep (like counting sheep) long before you ever found this unicorn. As always, my advice when speaking with customers regarding gears……count the teeth twice….. easy to miscount.