ran my Vin# through a decoder to see if it would give me specs on my truck specifically the diff ratio but it only gave me the basics with not a lot of info.. My COE is currently doing 3000rpm at 63mph and I would like to get those revs down to below 2000. I have been given a diff out of the same model Dually but a diesel version and have counted the crown wheel 41 teeth and the pinion 10 teeth so 4.1 ratio but have no idea what ratio my current diff is. Has any one found a site where I can find this out ? Cheers Willy
Not sure if this will help, it was posted on the HAMB site some tim ago, as I was also looking to find out the ratio of an axle on a car.: skipperman Senior Member Join Date: Dec 2002 Location: Atco,N.J.(Camden county) Posts: 1,336 Re: how to check rear end ratio?????? This ain't gonna make sense with the numbers you gave--BUT--- the way to check a rear ratio is .... If it's an open rear (NON posi)---Mark the driveshaft with chalk.... HOLD one wheel still...turn other wheel TWO REVOLUTIONS and count how many turns the chalk made ... If it's a posi ....(don't hold either wheel) turm wheel ONE revolution and count how many turns the chalk made ....... That's it bro ...... jersey Skip skippermanView Public ProfileSend a private message to skippermanFind More Posts by skippermanAdd skipperman to Your Contacts 03-04-2004, 11:00 PM #9 draggin'GTO Senior Member Join Date: Jul 2003 Location: Canyon Country, CA Posts: 1,357 Re: how to check rear end ratio?????? For an open (non-posi) rear leave one tire on the ground and turn the driveshaft (mark it) until the other tire (mark it too) that is off the ground rotates exactly TWO times. The reason for the two tire rotations is because the spider gears are a 2:1 ratio. The number of turns of the driveshaft will be your gear ratio. For a posi rear (working properly) get both tires off the ground and turn the driveshaft until the tire(s) rotate exactly ONE turn. This method works every time.
If you are using a GM ch***is with the 14 bolt rear, the axle code is stamped on the top of the right hand axle tube(US p***enger side). Google that code or have a GM parts person look it up.
OK thanks guys. I considered buying a gearvendors overdrive but $4k is a bit much. The diff out of the diesel truck was free! RMR&C thanks for that info I will have a look at those numbers and Google it 65 Standard my engine and trans are the standard combo that came with the donor truck
General specifications These are the specs for a 14 bolt: 10.5” diameter ring gear Axles are 30 spline axles 1.590” diameter shank on the pinion Gear ratios: 3.21, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13, and 5.38 Carrier break: 3.21:1 - 4.11:1 and 4:56 - 5.38 1.50” axle spline diameter 1.34” axle shaft diameter Axles are different lengths from side to side Removable pinion support Weight: 550 pounds (250 kg) GAWR: 8,600 pounds (3,900 kg) Max. Pinion supported with bearings on both sides of the teeth which minimizes pinion deflection ***uming you have either the 3.73 or the 4.10 you will need either a 2.48 or a 2.73. The problem here is they aren't available, and if they were, I think it would turn your truck into a big pooch. If you really are serious about the 2000 rpm at 63 mph consider a higher overdrive (Allison 1000 6 spd is the highest at .61) and a higher rear axle ratio. These suggestions aren't cheap, but you're asking for something unusual from a truck differential. I am going to run an Allison 2400 (very similar to the 1000) and a 3.54 rear axle, this will put me in the 2000 rpm (sweetspot) at 65mph ball park. My red line is 2800
OK my existing rear axle number stamped on the rhd tube is KMD G0220 and the spare axle is GBX G2321 I'm thinking IF my existing is 5.38? and the new one I have I already know is 4.1 then that might just drop the revs enough. Doesn't have to be below 2000 but anything lower than 3000 would be better
I googled the numbers but couldn't find any info. May be I will just need to jack the truck up and turn the driveshaft
It is frustrating trying to help you with almost no useful information. We need to know transmission final ratio, (in od if you have one) or trans name so it can be googled, differential ratio, (go count it out, don't go by the stamped numbers if you don't know the history, gears can be changed) tire height, measure with the truck sitting on pavement, (measure from the pavement to the top of the tire) (this is not the tire diameter which is measured from one side of the tire to the other and doesn't take into consideration tire squash) If I have this info, I can make recommendations to help you out
Was the truck you used the running gear from a usa truck imported, also was it a clean unmolested, If it was, and I had the vin #, I could find out what it was born with, not a for sure on the ratio, but a good idea what it might be. As others have said pull the cover and you will know
This is his donor,88 dually 24k miles on the clock from Forestview fire dept in California 90% chance it is 4.10 ratio, 10% it is 3.73 or 4.56. I don't know what auto trans Chevy was using in pick-ups then. Turbo 400, 700-R4?
turbo 400 I think definitely not a 700R. Looks like the most accurate way to figure it out is to pull the cover and count the teeth. If it turns out it is a 5.3 then the 4.1 will go some way to dropping the revs at the speed limit here in NZ 100kph or aprox 63mph
If he doesn't have an OD transmission, mph per 1000 rpms puts the differential at 4.10 He really needs a 6 speed Allison which comes with either a Chevy bell housing pattern or a sae 3. The chevy version will bolt up, probably have to change ****** mount. You aren't going to find gears for that differential that will give 30 mph per 1000 rpms. If you choose to go with the 3.21 gears your lower gears will be big jumps and it will be a pooch in town.
Mike, the 3/4 ton 14-bolt is a 9.5" ring gear while the 1 ton 14-bolt is a 10.5" ring gear. Here is a 3/4 ton 14-bolt And here is the 1-ton 14-bolt
Good to know. Mine is a 4:10 rear and I may swap it to 3:73 someday. First I will do a real tune up on my truck and get a baseline. I checked the plugs when I arrived and they were semi-blackish with carbon. On my trip from St Louis to KC, I averaged about 12.5 mpg. Nowhere near what I want. No tachometer, so I don't know what my rpm was and the new speedo seemed to be on the fritz too. (last minute wiring job). I want to lean out the carb and I am still thinking about installing a throttle body fuel injection system. I'd like to get closer to 18-20 mpg, if that is possible.
I lucked out and got a Dana 80 with 3.55s and along with the Allison that has a .61 OD I will have very long legs. I have never sat down and figured out the top speed, but I'm betting over a hundred mph if that Detroit will pull it. I'm hoping for 12-15 pulling a large heavy travel trailer.
I cleaned the axle tube better and found this stamped on top. KMC G 084 1 This is an 1982 4.10 geared 14-bolt.
my Vin # 1GBHC33W5DS119141 is from the donor fire truck. If my existing rear gear ratio is 5.3 and I fit a 4.1 it shouldn't cause it to "pooch" as you say Steve should it? I was still getting 16.7 mpg at 3000rpm so with a 4.1 rear it should get closer to 20 mpg? maybe
Willy, I am quite sure you have a 4.10! I have driven pick-ups with 4.10 gears and in direct they run about 20 mph per 1000 rpms. A 5.38 geared differential is almost unheard of in that size truck here in the US, 4.56 is even unusual. Edit: After rereading your last post, I think 16.7 mpg is pretty good for your truck. Getting 20mpg would be almost magical.
I was just thinking that because it was a fire truck with a utility body they may have ordered it with a 5.3 Oh well the best way to tell is to take the rear cover off and count some teeth I suppose
I tried to decode the vin with a dealer here but that was built before computer history. , microfiche only and in this country, a usa made truck doesn't show up , the best way is pull the cover, or if you have the glove box door, there will be all the option codes, they are easy to decode
While we have been doing all this speculating, any one of us could have counted it out a thousand times. LOL
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