I have an 89 international single axle,2spd rear end with 5.57 ratio(tag), 5yrd gallion bed. a 7.3 diesel, 5 spd trans, and when I am taching 2500 rpm I am only running 50mph. I need to get about 65mph at 2200, save my engine. I have to make 50 mile round trips and the guys are gonna run me over since I cant run any faster when I need. can anybody point me to correct direction? I found a source for complete used rear pumpkins($500), but I need to know the correct gear ratio. any help would be appreciated.
Formula I use ..... Mile per hour X axil ratio X 336 then divide by tire diameter ( inch ) equals the engine RPM's . This gets it pretty close assuming 5'th gear is direct . Example ... Lets say some knucklehead want's to know how many RPM's the 396 will be cranking in the 1967 Chevelle at a given speed with 4.11 rear ratio . Speed ? lets say 110 MPH Ratio 4.11 Tire diameter 26 inch . 110 X 4.11 X 336 = 151905.6 Then divide by 26 = 5842.52 RPM at 110 MPH And that's about as far as I would push the 396 . LOL !
Thanks, I will give that a try
I think you will be looking for something around 3.90. I used to run a Freightliner that was set up to run no more than 65, it had a Cummins set for 2100, direct 10 speed trans and 22.5 rubber, and that is all it would do. I looked in an old spec book from the late 80's and found a number of 2 speed rears with 5.57 gears, but they all had 7.17 low gears. so I don't think going to a 3.90 will hurt startability. It may make a difference in shifting going down the road if you use the 2 speed to split all of your shifts. George
ok, in a steep learning curve, I understand gear ratios, but I gotta say, the split confuses me a bit, somehow it changes at the spiders? and I do not know what my low range would currently be, I can tell you that there is not much difference in the high and low, I can tell which is which but not much difference. I can start in 2nd high when empty, like real easy, most likely could idle off stop in 3rd high. I do have a pic of the rear end tag, I'll try to post it
OK, now I am totally confused. It definitely says Spicer, but my spec book dated Oct 1988 doesn't list any Spicer rear ends with a 5.57 ratio. The ones that I found were Eatons, but your tag definitely says Spicer, and If the long number that ends in 3X is the model number, it doesn't match anything that my book shows. Sorry if I have caused any confusion. George
I think your spot on suggesting the 3.90 ratio trucker1 . 3.90 on the high side would put it rite in the 2100 to 2200 RPM range at 65 mph . Seems like the ideal setup would be a two speed rear with 3.90 high side & maybe 5.57 on low side for most diesel applications on an off road . The 5.57 / 7.17 two speed rear ratio is about perfect for a single axil dump truck with a small block chevy power plant . We have a 1966 Chevy C-60 set up like that . The 350 makes good power around 3,000 to 3'500 RPM's . Damn old truck amazes me , pound for pound it will pull with anything given it's size & load hauled . Just an example of matching the engine & gears I reckon
Have you considered putting a direct/overdrive "brownie" box in the driveshaft between the transmission and rear end. They were real common on the older farm trucks in the 2 ton range. They have been fairly easy to find for a couple hundred dollars at the truck wrecking yards. Might be a reasonable option if you have room. Many are a 16% overdrive. Shortening a driveshaft into two shorter ones is not a huge cost item. Just when mounting be sure to maintain equal driveline angles but that is normally easily doable.
me too also............ it is in an International/Navistar 1654 1989 version, bought by the Army. has a 7.3 diesel, 5spd tranny
can you tell me what my low side is supposed to be? 5.57 and my guess 7.xx
Sorry, can't help with that, as I said, my book doesn't list any axles withy a high of 5.57 from spicer, but the vast majority of the axles listed did have a 7.17 low. George
A 2 speed axle works by a single shift fork switching it between single reduction, that of the ring and pinion alone, and double reduction where there is a planetary gear set inside the ring gear that gets added in. As far as I have ever seen, the planetary reduction is always the same radio from the old grain trucks all the way up to the 52k heavy haulers. 1.36 times the faster ratio, more or less. I would not go 65 mph at 2200. Maybe shoot for 2600. That 7.3 does not like to run that low of RPM and 65 MPH will be taking all it's got and it may not even be able to pull the truck at 2200 RPM at that high of a speed.
two speed rear ends use a planetary to reduce the input gear from the main HIGH ring gear reduction through planetary reduction and out the axle shafts. All two speed rear ends are a fixed split ratio that is the same across the the full line of ratios, in my boom truck its 4.88 on the high and 6.something. I will say I'm throughly not impressed with the strength of the 2spd rockwells, my 23,000Lb rated single drive is on its 3rd gear set in 66,000miles. granted this truck lightweights out at 29,000lbs. with a 175hp diesel in pretty hilly terrain.
I have a 1980 C60 with an 8.2L Detroit, 5 sp and 2 speed split. You cant beat it past 52 mph. What I found was someone before me swapped the rear end from a gas truck in it. The gasser rearends were much lower geared than the diesels rearends but otherwise were a direct swap. Mine is 5.57/7.17. I'd love to go to a 4.50-4.88 high gear. John
that is exactly the problem I have, the 7.3 does not like High RPM, it is not a 2 cycle. 7.3 is a grunt motor, the injector pump is shut down around 2500, rev limiter of sorts. this formula seems to bare out what you think JD, it was posted earlier in the thread. mid 4.xx is what I am going to look for. so to sum this up, on the split, the reducer gear will basically feed off what ever ring/pinion combo is used and be 1.36 varation of the the main gears installed, .....correct? Formula I use ..... Mile per hour X axil ratio X 336 then divide by tire diameter ( inch ) equals the engine RPM's . This gets it pretty close assuming 5'th gear is direct . Example ... Lets say some knucklehead want's to know how many RPM's the 396 will be cranking in the 1967 Chevelle at a given speed with 4.11 rear ratio . Speed ? lets say 110 MPH Ratio 4.11 Tire diameter 26 inch . 110 X 4.11 X 336 = 151905.6 Then divide by 26 = 5842.52 RPM at 110 MPH
I agree the gassers have the RPM's to pull that gear set
o.k., well, I just snapped the driver side axle, on flat hard ground, had about 4 yds of gravel, air brake did not release, was slipping the clutch and had another set of eyes watching the brakes to see which one was locked up and POW, snapped the sob at the splines, unbelievable. do I have to pull the pumpkin to remove the spline chunk or can I Punch it all the way out from passenger side? I wonder if it has like a spool center.
I have in the past gotten lucky with a round magnet attached to a piece of pipe, YMMV. You have to pull the other axle shaft to pull the pot anyway, might as well see what you can see. I don't remember if those are normally open through.
The easy way might just be to up size the tires to 24.5 rubber, it will gain you 8mph or so.