Final drive ratios and overdrive

[quikshft]

Guys,

I was just thinking that I hardly ever use first gear in my truck, and that part of the reason I'd ever go to a 6speed is to actually use 5 gears. I suspect that the NV5600 has a low first that also would see really limited use. Then I kept thinking and it seems that if I had a lower (numericaly) final drive ratio, I might actually use first gear to get rolling. When I'm empty and light I could still use overdrive to cruise, but when towing perhaps top out in fourth gear. Does this make sense? I might end up with about the same set up (with regard to ratio) as I would if I did actually swap a 6speed into my truck and didn't use first gear in that set up. What is the overdrive ration of these two transmission?

These might be previously discussed questions, but right now the way I use it, I've got a 4speed in my truck, and I believe that if I had an NV5600, I'd then graduate to a 5speed, which I already have... . are you with me?

 

[wtrenholm]

The ratios are as follows:



NV4500 NV5600

1st-5. 61 1st-5. 63

2nd-3. 04 2nd-3. 38

3rd-1. 67 3rd-2. 04

4th-1. 00 4th-1. 39

5th- . 75 5th-1. 00

... ... ... ... 6th- . 73

Rev-5. 04 Rev-5. 63



Overall the same first and OD, just much better splits on the six speed for towing. I certainly like mine.



Wayne

 

[phillips5]

I thought going to a 307 0r 8 what ever it is so when I pull hard direct will be a 70 mph gear. There have been times when I have pulled weights that we shouldn't pull with our trucks. I needed first gear and 3. 54 rear I have pulled a number of front loader mixers and tractor trailers back to the shop. With a 308 gear I would really have to slip the clutch. I would hqve to hook the chain to my fith wheel hith and to tha front axle of the other truck so it would pull down on mine so my tires wouldn't spin

 

[dpuckett]

I looked into getting a 3. 07 to go with my 5 speed, and it just isnt worth it, even for a 2wd. Have to change out hub to hub; everything is different. I think I'd be ahead of the game getting a USGear o/d unit, and having a "choice" of 4. 10s or ~3. 25. Have a decent cruise RPM, yet have luggin ability for pulling. Be really cool with 3. 54s and a OD Oo.



Daniel

 

[1stgen4evr]

Ratio questions

Of course the ratios are finite but the application is different for every owner. And sometimes different every time the owner goes out with the truck. As you can see, the question brings more to the table than can be filter to a single finite answer if you consider application as part of the decision.



I too have pulled loaded dump trucks across town. My solution to that was to burn the rubber rather than the clutch. I hate pulling the transmission.



My present application would be very nicely server with a 3:07. I almost never use the lowest gear. That would give me the option of running loaded in direct and returning empty in OD without the harsh load on the Getrag OD.



The 3:07 is rare at best and almost like the unicorn for the dually. I want one and will eventualy find one. I just have to wait till someone kills their truck and not the rear end. Considering the life of the Cummins, I may be in for a long wait.



Others would have no need whatsoever for the 3:07. Quite a few folks use the 4:11 and are completely satisfied with that. I think I will drive a new truck just to see for myself what the six speed does.



Considering the money, I will have to stay with what I have. I am just to tight to do otherwise.



1stgen4evr

James

 

[phillips5]

I talked to toledo driveline and gear 5 years ago and they said thay could sell me a ring and pinion 3. 07 for $300 . It was suposed to work maby they were wrong. Thay call themselfs Fleet Pride now.

 

[Philip]

The 3:07 gears has its own axle housing and carrier assy. If you try to install them into an axle that was not machined as a 3:07 axle. Then they will not work.



The junkyards know this is a oddball axle ratio. They charge high prices when they do get one in. I found out the hard way.

 

[phillips5]

Oh. well shoot I new it was to good to be true. My brother recked a CDT that had a 307 he bought new. They totaled it and wanted $ 7000 to by it back they said the yards pay that because the engine. This was in 91. and it was a 89

 

[RSchwarzli]

Hold on a moment. Tell me if I am misunderstanding, but are you saying that you can run a 5 speed Gutbag with 3. 07's? Would 5th gear not be to low a RPM for the engine to run smooth? What speed would you be at running 2000 RPM? 400 MPH? All said and done is that not a lower final drive ratio than even the NV 5600? Sorry for asking, but i'm just not following.



Robert

 

[1stgen4evr]

Getrag and 3:07

Well, note that I said the application for each owner will determine what would work for that owner. I pull a trailered load that is about 12 to 15k pounds. I am taking or bringing (rental) and one or the other is dead head empty. I would be using 4th when loaded with a 3:07 and 5th only when empty. With the 3:54 I almost never use 1st.



As it is, I run in OD whether loaded or empty. The Cummins will putt along the interstate with no load and wouldn't even care about the rpms. The main thing I would gain is that the Getrag would not be working loaded hard in OD. Since I only have 403k miles on my original Getrag I feel that it might not hold up as long as the Cummins the way I am using it.



Like others have said, I also would benefit when in the mountains if I had some closer ratios. May spring for a US Gear or Gear Vendors OD some time in the future. I would also use 215s rather than the 235s to reduce the overall load on the drive train.



I'll let someone else do the math on just how fast the thing would run but I am sure it would run 70 to 75 with a comfortable engine speed.



So like I said, individual application.



1stgen4evr

James

 

[Philip]

it would run 70 to 75 with a comfortable engine speed.

Doing a little math. Mine runs around 1730 RPM at 70 MPH with the 3:07's.

 

[1stgen4evr]

Doing a little math. Mine runs around 1730 RPM at 70 MPH with the 3:07's.

I like those numbers. Philip did yours come with the 3:07 or did you retro that. I haven't seen a 93 that was factory with 3:07. Is the OD ratio on the 518 the same as the Getrag? Although I have one of each, I can't tell because of the slip with the automatic. I don't think I have seen the OD ratios compared anywhere.



I again mention application. Some owners because of how they use their truck would not be happy with that combination. It would work beautifully for me.



1stgen4evr

James

 

[JVanvuren]

Here's a great link for those of you who want to calculate rpms with certain gear ratios, tire sizes, etc. I used it all the time when considering different ideas for my offroader 4x4:



http://www.4lo.com



Enjoy!



John

 

[EZGZ]

How about a Gear Vendor overdrive?

http://gearvendors.com/

For a long time nobody had an adapter that would work for my 4X4 but when I checked on it a while back they said you can get it now. They have it for the Getrag also.

I have a 4:10 axle ratio. With the OD unit I could end up with an extra gear between 2nd and 3rd and 5th that would = 3:21 axle ratio.



I know it sounds confusing but it really isn't. Some folks refer to it as a transmission splitter because with our wide spaced transmission ratio it gives you something in between.



Example: Your pulling a load. You come to a light at the bottom of a short steep hill. You start out OK but your cement mixer truck takes so long to shift from 2nd to 3rd you loose your ground speed and have to putt up the hill like a snail in second.



If you had the Overdrive unit you would have a gear change in between

2 and 3 it don't work in 4th because the tall side would = the old 5th but when you get to 5th your home free and cruising down the highway at 75 MPH in 5th overdrive at 1800RPM which is your best torque. But it is also where my harmonics is worst and hard on my transmission. I also have a standard cab truck without a carrier bearing and did not want to overwork my U joints and change the axle angle.

Conclusion: Save the money and leave a little earlier, Enjoy the scenery. On an older truck the payback isn't there. Plus I couldn't use it if in 4 wheel drive in the winter. One mistake in 4 wheel drive and I would have the 3:21 rear with a 4:10 front=desaster

 

[quikshft]

As just a youngin' one of my first 'cars' was a Toyota LandCruiser with a Hone overdrive... . it don't work too good with the 4x4 engaged. Don't ask how I know.



Based on this chart first posted by wtrenholm, I see the overdrive ratio is pretty close between the two trannies is question here.



NV4500 NV5600

1st-5. 61 1st-5. 63

2nd-3. 04 2nd-3. 38

3rd-1. 67 3rd-2. 04

4th-1. 00 4th-1. 39

5th- . 75 5th-1. 00

... ... ... ... 6th- . 73

Rev-5. 04 Rev-5. 63



And as I suspected first gear would be no more useful (at least when empty) with the 5600, but overall you will gain a gear so I guess my thinking was sort of on track. However it sounds like swapping to 3. 07's might be as big a struggle as installing the NV5600, not nearly as sexy though. I should probably start a fund and save toward this but I've already got a couple special funds with no money in them. Guess I don't need another of those! Beside 1stgen4evr's got 400 thou on his Getrag, I'll probably spend a couple years getting to that mileage at least.

 

[Philip]

Philip did yours come with the 3:07 or did you retro that

They were under it when I got it. I know the rear axle had been changed out before I got it. The front axle does not appear to have ever been removed. It has been repaired one time That I know of. There is a lot scrapenal damage in the inside of the front axle cover.



The 518 has a . 68 OD ratio. If my memory is working right.

 

[dpuckett]

Originally posted by BSchwarzli

... ... Would 5th gear not be to low a RPM for the engine to run smooth? ... ...

Actually, I think Philip is right- about 1730 in 5th. Basically, add another gear on top of my 4. 10s (or put in a 25% OD). Not at all too bad, esp on I-25 or I-70 in CO, WY, et al, where speed limit is 75; actual is 80+. Ideal BSFC efficeincy comes at about 1750RPM, so that is the ideal for MPGs, not necessarily towing heavy. And if you dont have the power, BOMB it till it does. If I get 22 mpg @67mph, 6500ft with 4. 10s, I could in theory, get 27 or so with 3. 07s. I have yet to drive a full tank @50-55 in mine, so I cant say for sure. And then you have to figure in the aerodynamics (or lack of) of our bricks on wheels cutting some MPGs. I think a 3. 25 would be ideal for me.



Daniel

 

[JLEONARD]

I would like to comment on the rpm/fuel economy issue... ...

And my knowledge is based on marine applications but the theory should apply. .

Diesels use fuel based upon horsepower used... . not RPM.

So to pull a load or the truck alone at 70 mph takes a certain amount of horsepower.....

whether you have 3:07 or 3:54 thus a different engine rpm should not be the major factor.

OK. Got my combat hemut one... fire away.

Jay

 

[dpuckett]

That's true, to a point, Jay

BUT, if you will go back a few issues, they had an article about BSFC (brake specific fuel consumption) curves, volumetric efficiency, etc. Basically, it takes fuel to make power, and it takes fuel to make RPMs. WIth my 4. 10s, I'm taking a double hit to go 70- about 2450 RPM. i. e. , it takes more fuel to make x hp at 2500 RPM than it does to make the same power at, say, 1800 RPM. So in the effort to increase MPGs, one needs to find the best BSFC point and try to run at the point. Put another way, try to set up your gearing to make your road speed and engine speed coincide to the best BSFC possible. True, it may only take 100 hp to run 70, but it will use less fuel to use that 100 hp at 1800RPM than it does at 2500RPm.



Daniel

 

[BCook1]

Ok, how about this.

I would not swear to it, but I think some of the UPS trucks have low numeric dana rear diffs. They might be a source of parts. Switching to a lower diff ratio or adding larger tires has the same end effects. One of these is that the number of miles per hour you pass through between each gear increases. For example, if you go from 25 to 45 now in third gear, a lower diff ratio means you will have to travel from about 30 to 55. this does not seem like much but it means you will spend more time between shifts and you will increase the stress on drivetrain components. The time between shifts will actually slow your truck down acceleration wise. As for stressing components, look at why really large equipment uses planetaries. Huge torque, small driveshafts, all the torque multiplication occurs near the tire. Maybe I hit my head on something but I don't think you would like the results of the lower numeric gears. 4. 10s and a six speed should serve you better. I already hit over 70 in 4th with my getrag. I think you would find 5th useless unless you wanted to drive 100 all the time. As mentioned earlier, I think you would find the truck falling on its' face when shifting up to the next gear. Someone tell me if I sniffed too much #2.