overdrive gears available soon

hi all, ernie (sqsanta) had wanted to know if this project had died, but it is just delayed a little. i have a major gear manufacturer lined up to make 25 sets of .69 od gears. i have to have a gear cutter custom made for the mainshaft gear and that may take up to 8 weeks. here are pictures of the modified mainshaft. i am purchasing 25 new main shafts and making this change to them for the first batch. the area where 2nd gear runs is resized for needle roller bearings and them rehardened. bearings are custom made. 4 holes in 2nd gear to make it like the newer production gears for better oiling. what do you think gerhard??

A) Main-shaft and 3rd gear mods: Does it look good? YES
Will it last longer than stock? HOPEFULLY YES!
Would this be worthwhile as an upgrade even for stock .79 o.d. (3053A) trannies? TIME WILL TELL.

B) .69 o.d.: does it make sense? OWNERS WILL SOON FIND OUT ...

G.

OOOOPS! I meant 2nd gear mods!

That's beautiful work, Tom. Are the needle bearings captive in the cages? I see 4 big holes in the gear disk and one in the hub. Do you also drill 4 in the hub?

awesome. you have made something that will last a lot longer than the truck ever will. top notch my friend. I am wanting this even more now.

So will the .69 make the jump from 4th to 5th seem similar to the jump from 3rd to 4th?

SasquatchSanta said:

Does anyone know the speed ratings for Goodyear 395/85R20s? I’ve Googled around and can’t find anything?

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I searched and found this at www.goodyear.com

I had to search their site, using MV/T as a search word, then went into engineering data.

MV/T™ TUBELESS TIRES ON 5° TAPERED OR TYPE III TUBELESS RIMS
395/85R20
Load range G
Single tire load 9,370lbs @ 95psi
Weight 210lbs
Rim width 10.00
Tire width 15.4
Tire height 46.6
Static radius 21.5
SPEED RATING 68MPH

Thanks for the Goodyear speed rating data.

Considering the goal (my goal) is to keep engine RPMs over 2,000 and under 2,400, a speed rating of 68MPH is perfect.

With 46.6 Dia Rubber, .69 gears will yield the following speeds:

2,000 RPM = 57.4 MPH Minus 2 MPH For Tread Wear = 55.4 MPH
2,100 RPM = 60.3 RPM Minus 2 MPH For Tread Wear = 58.3 MPH
2,200 RPM = 63.0 RPM Minus 2 MPH For Tread Wear = 61.0 MPH
2,300 RPM = 66.0 MPH Minus 2 MPH For Tread Wear = 65.0 MPH
2,400 RPM = 69.0 MPH Minus 2 MPH For Tread Wear = 67.0 MPH

The attached Torque, Horsepower, Smoke and Fuel Consumption chart indicates 2,000 RPM to be ideal. Over 2,400 and fuel economy goes south.

yes kenny, the jump to 5th is very similar to the 3 - 4 shift. the change to 2nd gear is the 4 holes to let oil into the front side of the gear from the rear. yes the needles are captive in the cage, this allows much higher rpm than if the needles are touching each other.

Tom, with this mod would it be wise to consider 50 wt synthetic for lube or just use ole GL1?

i am running 40 wt in mine now with the .71 gear set

Keep in mind the loaded radius X 2 is what the actual number for calculating tire size should be, when figuring speed at a given RPM.

goodyear says 21.5in multipy by 2 for a number of 43, I would use a number like 44, to calulate...(due to the lighter load on the tire, also lower pressures will change the loaded radius as well.

The change from 46.6 to 44 in the calculations changes the speed at 60 by about 3mph at the same rpm. So only 1 mph different than your final figure.

my $.02


I know my 42's measure in about 40, and only have a radius of about 19....so i calculate them at 38"

chevycrew sez:

Keep in mind the loaded radius X 2 is what the actual number for calculating tire size should be, when figuring speed at a given RPM.

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Thanks for the insight --- I learned something today --- Thanks

not sure i agree or disagree about using radius for the calculation. with steel belted radials doesn't it make sense that the circumference is the all important measurement since one rotation will equal that distance?? i just throw this out for input, i use the published radius from michelin for my math, but you can use a gps and knowing the speed and rpm solve for the radius. compare it with what you think it is.............

Yeah...you are probably more right. I should have known that too...

So all in all the diameter, is more important than the radius, but circumference is the most important.


Sorry I dont know what I was thinking

well, i'm not saying circumference is the right way. most of the formulas i see use the radius or loaded radius which is less.

kenny, if you shift at 2300 2-3 drops 960 rpm, 3-4 drops 880 rpm, and stock trans 4-5 drops 484 rpm. with .69 od 4-5 drops 714 rpm. now that does not really sound like a lot, but the difference is that stock you drop to 1816 rpm and with .69 you drop to 1586 rpm.these figures are only valid if you shift at 2300. the real plus is when you run 5th back up to 2300 which is a very conservative rpm and you find that your speed is about 62 mph. at 2300 rpm!! now the multi fuel engine is very reliable up to but not past 2600 rpm so 300 more rpm in 5th will be as fast or faster than you really want to go. by the way i have paid for the gear cutter so this really is going to happen probably by the end of feburary.

Since my gear calculations suck and the like, about what speed would this be with 1100 NDTs or even 900 NDTs. I'd like to switch everythitng here over to 1100 tires but I fear the wrecker won't pull the 1100 even with the stock OD. It does weigh in excess of 20,000#. The new cargo truck should have no issue pulling 1100 even with the .69 gear should I be able to afford it.

2300 rpm with 9:00-20 would be about 57 mph, with 11:00 it would be about 62mph

have settled on .69 as the only ratio for the first run of 25 sets. .71 was just real close and that small amount more will have more plusses than minuses........... with stock 9:00-20 tires 2300 rpm will yeild 57 mph , with 14.5r20 or 11:00-20 tires 2300 will give 62 mph

what about 2800 RPM? thats what I run mine at. O boy!

Recovry4x4 said:

Since my gear calculations suck and the like, about what speed would this be with 1100 NDTs or even 900 NDTs. I'd like to switch everythitng here over to 1100 tires but I fear the wrecker won't pull the 1100 even with the stock OD. It does weigh in excess of 20,000#. The new cargo truck should have no issue pulling 1100 even with the .69 gear should I be able to afford it.

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Kenny, I never had any problems with speed in 5th gear with my 1100's, my empty weight is 17,000 lb. Top speed just over 60 mph for hours on end.
Wouldn't even want to drive that fast with the loads I was hauling last year cross country, 55 was plenty good.
My problem, if any, with the gear box is the relatively big jump between 3rd an 4th (without shifting between HI and LO)...

If you don't have to be concerned about installing snow chains, OPCOM's (Patrick's) set-up with dual 1100's in the rear looks and seems to work well. Looks better if you don't have the narrower bed.

Tom, to get a more meaningful statistical result, you may want to add one more choice in the poll above for those of us who would never consider the modification.