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Old 03-21-2021, 07:53 AM   #1
2935ford
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Default 3 Speed Trans Open Drive to Close Drive?

I have a '48-50's pickup "78" case open drive trans I would like to convert to closed drive (torque tube).

Issues?
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Old 03-21-2021, 08:38 AM   #2
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Default Re: 3 Speed Trans Open Drive to Close Drive?

You will need the main shaft as well as the rear bearing retainer & clam shells from any of the different 3-speed Ford transmissions depending on what rear engine mount you choose to utilize. Stuff like this can still be found on flea-pay or from used parts sources. The 39 thru 48 car transmissions all use the same or similar gears & shafts depending on the drive gear ratio preferred,
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Old 03-21-2021, 08:43 AM   #3
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Default Re: 3 Speed Trans Open Drive to Close Drive?

As long as your trans isn't the late (51/52???) f1 type with the pointy gears it is a straightforward conversion as long as you have the correct output shaft and associated parts at the output end.
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Old 03-21-2021, 09:04 AM   #4
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Default Re: 3 Speed Trans Open Drive to Close Drive?

Thanks rotorwrench and Mart. Mart not F1 51/52.

I understand the car gears is a better choice than the truck gears.
I'm using the stock A rear and I have the 3:78 gears in it.
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Old 03-21-2021, 09:53 AM   #5
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Default Re: 3 Speed Trans Open Drive to Close Drive?

What you want is a 16T input and a 28T cluster. You might have those even if a truck trans. Whip the lid off and count up.
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Old 03-21-2021, 10:04 AM   #6
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Default Re: 3 Speed Trans Open Drive to Close Drive?

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Thanks Mart, I'll have a gander!
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Old 03-24-2021, 06:17 PM   #7
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Default Re: 3 Speed Trans Open Drive to Close Drive?

My jalopy has a 39 ish rear with 3.78’s, about the same year truck trans. I also had leftover 46 parts and put the later gears in the early case, good shape. Wish I didn’t, 1st seems tall and with aluminum flywheel prone to stall. I guess a 29 tooth cluster is the way to go
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Old 03-24-2021, 08:58 PM   #8
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Default Re: 3 Speed Trans Open Drive to Close Drive?

Funny- Seems that most people are looking to convert a closed driveline to an open one. (IMHO)
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Old 03-26-2021, 12:23 PM   #9
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Default Re: 3 Speed Trans Open Drive to Close Drive?

^^^^^
I have more parts to go closed on hand than to convert to open drive.
I like to use what I have.
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Old 03-26-2021, 12:35 PM   #10
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Default Re: 3 Speed Trans Open Drive to Close Drive?

The cluster gear is 28-24-18-14. Haven't seen the part number yet.
The 18 gear is a bit chewed up (of course.....being the expensive set).
As is the low/reverse sliding gear.
Will also need synchros and roller bearings etc for a nice rebuild.

I will clean up the case and check for cracks.
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Old 03-26-2021, 12:46 PM   #11
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Default Re: 3 Speed Trans Open Drive to Close Drive?

Quote:
Originally Posted by 2935ford View Post
The cluster gear is 28-24-18-14. Haven't seen the part number yet.
The 18 gear is a bit chewed up (of course.....being the expensive set).
As is the low/reverse sliding gear.
Will also need synchros and roller bearings etc for a nice rebuild.

I will clean up the case and check for cracks.

That should be the most common gear set with a 2.82 1st gear. That give you a 10.65 OVERALL 1st gear ratio which is just fine for a street-driven car. DD
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Old 03-27-2021, 08:08 AM   #12
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Default Re: 3 Speed Trans Open Drive to Close Drive?

Thanks V8COOPMAN
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Old 03-27-2021, 11:35 AM   #13
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Default Re: 3 Speed Trans Open Drive to Close Drive?

Just a thought here, but might consider trading it for a closed transmission. I would think the open would have more value than a closed unit.
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Old 03-27-2021, 03:42 PM   #14
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Default Re: 3 Speed Trans Open Drive to Close Drive?

The conversion is easy, but the harder part is finding a really nice main shaft. I've found a few NOS ones in recent years - but they are hard to find as of late. Make sure you mic the nose of the input shaft - it should not have any rust pits and should not be worn in the least. Do not buy the repop caged roller bearings for the cluster and main shaft - every one that I've seen has the wrong material and heat treatment of the cages on the ends - causing rapid wear and potential failure of the bearings. Try to find NOS originals or used ones in really good shape.

Do not buy the repop cluster gear shafts (the .750 ones that go from end-to-end in the case) - they are of the wrong material, wrong hardening and are .001 undersize. This causes lots of issues over time - starting with a nasty tendency to leak gear lube on your garage floor, rapid wear, etc. I make my own shafts from linear shafting materials. You can surely use original shafts - just try to find one that is not worn (and many are).

The fitment of the main shaft to the input shaft is critical - so using the best parts possible is key. The goal is to reduce the amount of play/deflection in the fitment - which takes really good bearings and unworn main shafts. Make sure you pay close attention to the amount of end-play on the main shaft (with the gears stacked on). I try to achieve the low-end of the scale (which is .004) - in some cases going to .003 if I can.

Also, I have Charlie NY re-bush the 2nd gear for a tight fitment on the actual main shaft I'm using. He recently did 4 of them for me - he does really nice work! Having tight tolerances seems to help prevent the all to common "popping out of 2nd" problem that many of these transmissions experience.

Lastly, Mac VanPelt's rebuilding book is a good resource for all the specifics and various parts combinations (as there are multiple synchro hub/mainshaft combinations - just one example). He is a good source for rebuild parts as is ThirdGen Auto and others . . .
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Old 03-28-2021, 12:42 PM   #15
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Default Re: 3 Speed Trans Open Drive to Close Drive?

JSeery....thanks.....I have 2 open drive trans to work from and a Merc side shift case.

Bored&Stroked.....thanks....good info to pay attention to.
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