Changing the gear ratio

[Graymist]

Is it possible to change the gear ratios on a truck, say for eg., from a 3.36 or 3.55 to a 3.90 or 4.10 ? How much would it approximately cost, and what other modifications would have to be made ? Thanks in advance.

[bikerboy]

you would have to change the gears in both rear axles, it can be done, but i have no idea on the cost.

[Pipeman]

Change the crown and pinions. Might as well drop in exchange diffs.

Call a gear shop for price.

[JM Transmissions]

Very possible. What axles you running? Cost wont be too cheap, you could just exchange them but thats the expensive route. Cheapest way is to get someone to just swap gears out, hoping you need no other parts or bearings. Likely you will need 2 bearing kits and a power divider kit for the front axle to do the job top notch though.

[Mr Bee]

What are you running for ratios now? and what do you hope to achieve? Sometimes suttle changes can be made by changing tire sizes. That would only work if you know someone willing to swap.

[hotshoe36]

I have asked Coast Powertrain in New Westminster about this, since I am no longer doing much train work with my old Volvo, and was quoted in the neighbourhood of $6K for both. I want to go from 100 km/hr @ 1550 rpm to 1300 rpm. I am already running 11R24.5 rubber, so an aspect (tread height) change wasn't in the cards.

Not sure how long it would take to get my money back, still thinking on it.

[Pipeman]

I have asked Coast Powertrain in New Westminster about this, since I am no longer doing much train work with my old Volvo, and was quoted in the neighbourhood of $6K for both. I want to go from 100 km/hr @ 1550 rpm to 1300 rpm. I am already running 11R24.5 rubber, so an aspect (tread height) change wasn't in the cards.

Not sure how long it would take to get my money back, still thinking on it.You need 3.70's.

100 KPH = 62.5 MPH X 3.70 Rear Axles X 474 Tire Rev per mile X .73 Top Gear Ratio / 60 = 1334 RPM's.

[hotshoe36]

Don't think so. I have an 18-speed and 4.30 now. I think I need 4.10 or 3.90 to get what I want.

[ralph]

Don't think so. I have an 18-speed and 4.30 now. I think I need 4.10 or 3.90 to get what I want.

Lucien is correct. You can do the figuring Lucien's way or just make your choices useing this site.

http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf

[Pipeman]

Don't think so. I have an 18-speed and 4.30 now. I think I need 4.10 or 3.90 to get what I want.

With 4.10 you'll be sitting at about 1,500 RPM's for 100 KPH.

Top Gear in a 13 or 18 speed is .73 ratio. You do the math.

11: x 24.5 will give you in the area of 475 revolutions per mile.

42.5 inches in diameter X 3.14 = Circumference which is 133.45 inches, 1 mile = 5,280 feet X 12 inches = 63,360 inches divided by 133.45 = 474.78 rev per mile.

Let's see what you come up with in your method of calculating.

[hotshoe36]

I don't have a method. I was going by my sticker, but I bought the tractor with 600,000 km on it, so I suppose they might already have been changed once. By your reckoning, I have the 4.10 and a little wear on the drive tires. Doesn't really matter to me what the nuimber is: What I want, is another gear at the top - for fuel economy - and I won't be using the bottom one(s) any more. I only used compound low once, even with the train, when a guy missed a shift in front of me on a steep grade, and I had to stop.

[Pipeman]

I don't have a method. I was going by my sticker, but I bought the tractor with 600,000 km on it, so I suppose they might already have been changed once. By your reckoning, I have the 4.10 and a little wear on the drive tires. Doesn't really matter to me what the nuimber is: What I want, is another gear at the top - for fuel economy - and I won't be using the bottom one(s) any more. I only used compound low once, even with the train, when a guy missed a shift in front of me on a steep grade, and I had to stop.

Well if you want 1300 RPM at 100 KPH it does matter what the number is.

I'm telling you that you need 3.70's to get as close as possible.

Or, 3.55 should give you 63.5 MPH which is slightly over 100 KPH.

3.58 will give you 62.7 MPH. which is just 2/10ths on a MPH higher speed than 100 KPH.


http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf

[bikerboy]

a guy from mackinnons has a blog, he posted he changed gears from 3.73 to 3.42 and it cost him about $2600, to get it done somewhere in southern ontario.

[hotshoe36]

I can see it being done at that price for lighter rears, but mine are 46's, and would get whatever else they needed (bearings, etc.) while they were out.

[Pipeman]

I can see it being done at that price for lighter rears, but mine are 46's, and would get whatever else they needed (bearings, etc.) while they were out.That's a good idea as the the majority of the labor is already paod for.

[hotshoe36]

Pipeman;

Thanks for those numbers, cousin. There's a cutoff with 3.55's available where I live. They're 40's from a 2005 Volvo, now I wanna know if the gears'll work in my '00 with 46's.

[hotshoe36]

They won't, apparently. And the cutoff is gone. But I still want 3.55's. Looking now for another cutoff. I'll use whatever I have to from it, even weld it on if I need to.

[Pipeman]

They won't, apparently. And the cutoff is gone. But I still want 3.55's. Looking now for another cutoff. I'll use whatever I have to from it, even weld it on if I need to.Super "40's will do the job for you also. They are used for pulling Super "B"s.

[hotshoe36]

Yeah, I know. But my train is parked, and it can just stay there till someone starts paying for its use. I like tri step-decks now.

[rbm]

i think it is going to take a long time and alota miles to pay back 6k, buy trying to cut engine rpms by 150-200, dosent seem to be worth it unless your keeping this truck for many more moons, or u need a new set of rearends

[hotshoe36]

Exactly. 1.1 million train miles in the rockies has taken this unit through most of its overhaul interval. The engine, transmission and most of the other components have been overhauled, leaving only the differentials to do. I could settle for addresing gear lash, but worn out is worn out.

BTW, we counted driveshaft/wheel revolutions and came up with 4.25. Good chance they'll turn out to be the original 4.3 ratio spec'ed for this truck, which means I probably have a tachometer error: The speedo and the GPS can't both be wrong. I'll be going to 3.7's. If they turn out to be too tall I'll change the tires.