trans gear ratio math, etc

[gringeltaube]

Not if you count the teeth, Lee. (and that's what counts...!)

The air shift T-136-27 high range gears are 33/22/33 which is exactly1.000000:1
Low range is 25/33 and 22/33, that makes 1.98:1.
With front axle engaged front and rear output turn at same speed!
Just checked that manual: seems they never looked inside a -27!

The sprag TC T-136-21 has the same high and low range gears and ratio, plus two additional gears for the slower front output: high is 33/22 and 21/34 (= 1:1.079), low 25/33 and 21/34 (= 2.137:1). See diagram.

 

[m-35tom]

yep, you must be specing the sprag unit, the air shift is on the same shaft for front and rear so has to turn the same rpm. i hope to have some gears this week.

 

[5tonpuller]

On the flat you will move. A slight hill and you be shifting.

 

[gringeltaube]

.... the air shift is on the same shaft for front and rear so has to turn the same rpm....

Same shaft??? Not exactly...!

 

[houdel]

yep, you must be specing the sprag unit, the air shift is on the same shaft for front and rear so has to turn the same rpm. i hope to have some gears this week.

Don't know, never taken one apart. I was just quoting TM 9-2320-361-20. The TM lists the transfer case as "Rockwell, model T-136-27, two speed synchromesh, air actuated, drive ratio (high range) 1.010:1.000 rear axle, 1.078:1.000 front axle.

I'd believe gringletaub over a TM any day of the week..... Methinks the TM was written by the same guys who bought the $500 hammers.

 

[gringeltaube]

Thanks for the confidence Lee, but careful, I could be wrong, too, any day...!!

In this particular case I'm sure since many years ago I worked a lot around these T-cases. I converted my first T-136-21 to air shift, same speed front and rear, before I even knew there was a newer model air shift T-136-27 that came std. behind the MF trucks.
Lately i've been studying the possibility to build a (cheap) overdrive TC prototype for the deuce. It should be possible without mods to the housing, using original parts and would end up .88:1 high range (14% OD) and 1.74 low. I think 1.74 is still low enough in most situations.

 

[m-35tom]

the bottom shaft drives the rear driveshaft and on the front of it is the lockup for the front driveshaft. they have to turn the same speed!!
another option is a gear set for 5th that would give .7088 od, that would give 60.4 mph at 2300 rpm with 42" tires. is that enough better to be worth while taking the trans apart to change gears??

 

[Stretch44875]

Would love to see a mod to the transfer or transmission for a tad more overdrive.

According to one tire manufacturer, 11-20 ndt's are 43 inches tall.

I would rather see a 5th gear mod. 4th to 5th seems really close on the deuce. But transfer would work also!

2400 rpm at 65mph would be perfect for me.

Dennis

 

[jwaller]

Would love to see a mod to the transfer or transmission for a tad more overdrive.

According to one tire manufacturer, 11-20 ndt's are 43 inches tall.

I would rather see a 5th gear mod. 4th to 5th seems really close on the deuce. But transfer would work also!

2400 rpm at 65mph would be perfect for me.

Dennis

ditto. this would be perfect. still enough rpm's to spool the turbo and pull freeway speeds without lugging and without shifting.

 

[m-35tom]

there are 2 different od gear sets that will fit the 3053 trans, one gives .71 and the other gives .66 trans od ratio. use this formula to figure your mph, mph = ( rpm * radius) / ( 168 * ratio) where your ratio is either 4.435 with the .66 od or 4.77 with the .71 od. you will get slightly different results depending on your tire size. these gears are no longer available and will have to be made, i would like to have 10 sets each made up and wonder how many people would spend the $$ to change the trans over. it is a simple enough job to do, it is harder to pull the trans than replace the gears. when i get a quote on gear prices i will post a survey to see what results i get.

 

[OPCOM]

I read the instructions in the manual. It's beyond my tools and skill level. Just for fun, what would a typical diesel shop or transmission shop charge for labor to put the gears in? (aside from R&R the tranny) I suppose they would need to do it as a rebuild, replacing what else was worn, in order to give any sort of warranty. I have used Inland Truck Parts in Irving, they charge $75/hr for example.

also, what is the lever for on the countershaft rear bearing cover? I saw this lever in TM 9-2520-34-1

 

[houdel]

An attractive proposition. A .66 OD ratio would allow those of us running stock 9:00-20 tires a cruise speed of 55-60 MPH in the fuel economy "sweet spot" of 2000-2200 engine RPM, and still be near the peak of the engine torque curve. Very interesting, keep us informed on your progress.

 

[Stretch44875]

I would pefer the .71 ratio...

 

[houdel]

I would pefer the .71 ratio...

You are probably correct, but I am greedy.....

 

[Recovry4x4]

I am wondering how well the 20,000# wrecker will carry the 55 MPH with the .71 OD or even the .66 OD? 4th and 5th are very close gears so a little bit of spread would be good. I hope these gears don't break the bank but being one off gearsets I see them being $$$$$.

 

[cranetruck]

Probably okay empty, but with any kind of load you'll be in 4th a lot not to mention the hills.
I have more of a problem with the 3rd to 4th jump....
Keep experimenting, that's what it's all about.

 

[Recovry4x4]

Since math is not my strong point, I'm wondering where 1100x20 tires would put me. Would stepping up to the 1100 tires be like keeping the 900 tires and te 0.71 OD? I've never stepped up to the 1100 tires on the tractor because of the possible loss of pulling power in 5th gear.

 

[cranetruck]

Kenny, figure about 7% equivalent change in the gear ratios when running on 1100's.
It's like going from .79 to .73 in 5th.

 

[Recovry4x4]

I think that might be the better answer for me. Thanks Bjorn.

 

[m-35tom]

gear speed chart for .79, .71, .66 od

this attachment is a chart of gear ratios / rpm / mph for 9:00-20 and 14.5r20 tires with stock trans and one with my proposed od gear set. it kind of puts it in better perspective and makes it easier to choose the best od ratio. i am leaning toward the .66 od for areas where most driving is on nearly level roads. your thoughts are welcome.........


well the attachment didn't work, i'll do it later, check back..............