Elijah808 Posted February 9, 2016 Posted February 9, 2016 Getting ready to throw a 8.25 Chrysler with a locker in the rear. It's coming off a Cherokee that was stock. Not sure what the best gear ratio to go with. I want to be able to run 35s with ease. Any advice would be great!
mnkyboy Posted February 9, 2016 Posted February 9, 2016 4.88 is as deep as an 8.25 can go so thats what you need. Still not deep enough though IMO.
Pete M Posted February 9, 2016 Posted February 9, 2016 and you'll likely want to add a 5spd to the equation if you want to run a freeway. :thumbsup:
Elijah808 Posted February 9, 2016 Author Posted February 9, 2016 and you'll likely want to add a 5spd to the equation if you want to run a freeway. :thumbsup: What trans would you recommend? Is it a direct swap?
Elijah808 Posted February 9, 2016 Author Posted February 9, 2016 4.88 is as deep as an 8.25 can go so thats what you need. Still not deep enough though IMO. Will a Dana 30 be deep enough for 4.88? Any suggestions for brands? Not sure what to buy
Pete M Posted February 9, 2016 Posted February 9, 2016 the AX-5 is the 5spd version of what you have now. :thumbsup: found behind 2.5 and 2.8Ls and goes right in. the AX-15 is the bigger brother (found behind 4.0s) and can be swapped in with a special bellhousing (2.5L dakota or I believe Novak or Advanced Adapter makes an aftermarket one).
mnkyboy Posted February 9, 2016 Posted February 9, 2016 I ran 4.88 with 33s and commuted on the freeway 90 miles a day,i could have sometimes maybe used a 5th gear but didn't really need it.
yxmj Posted February 9, 2016 Posted February 9, 2016 I have the exact same truck (but with the ax5) has 4.11's and with 31's she did not like 5th on the highway unless we had a tail wind....I would be looking at 4.56's . :MJ 1: .
Eagle Posted February 9, 2016 Posted February 9, 2016 Refer to my spreadsheet -- it goes up to 35-inch tires. For an AX-4, just ignore the OD column (that's fifth gear for the 5-speeds) and use the "1:1" column (that's 4th gear for the AX-4). https://docs.google.com/spreadsheets/d/1pHFuhGgj6dQDfzyfFJH5z7NCDLW2KX3ABQgAJr3lBvM/pub?hl=en&hl=en&output=html With 35s and 4.88 gears, 60 MPH is 2923 RPM. 70 MPH is 3410 RPM. Scroll up to one of the stock tire sizes (215/75-15) with 3.55 gears (which was the stock ratio behind the AX-4)and you get 2669 RPM at 60 MPH and 3114 RPM at 70 MPH. So with the 4.88s and 35" tires your RPMs will actually be slightly less than the stock setup -- which means the engine will work a little harder, but you don't have to worry about over-revving it.
Elijah808 Posted February 9, 2016 Author Posted February 9, 2016 Right on! Thanks guys gonna start hunting for an ax5! Now for gears where's the best place to order from? Any brands that are better then others?
Eagle Posted February 9, 2016 Posted February 9, 2016 IMHO a 5th gear will be wasted. You'll only be able to use it at freeway speeds, downhill with a tailwind. 60 MPH in 5th will be less than 2200 RPM. The [fuel injected] 2.5L made 117 horsepower at 5,000 RPM and 135 foot-pounds of torque at 3,500 RPM when it was introduced in the 1986 model year. This was raised to 121 horsepower at 5,250 RPM and 141 foot-pounds of torque at 3,250 RPM for model years 1987 through 1990. With 35-inch tires, even with 4.88 gears you would be running FAR below the torque and horsepower peaks in 5th gear, and I don't think the 2.5L engine will enjoy that. The graph below is for the later MPFI version. The throttle body numbers are worse, but the overall shape of the curves is similar. I'm still looking for a graph of the earlier version.
mnkyboy Posted February 9, 2016 Posted February 9, 2016 like i said,i didn't need a 5th with 4.88 and 33s. also keep in mind that a lot of AX5 failures have to do with 5th gear,i always figured i was better off with the AX4.
Elijah808 Posted February 9, 2016 Author Posted February 9, 2016 Don't plan on really using this truck on the freeway to commute
onlyinajeep726 Posted February 10, 2016 Posted February 10, 2016 Right on! Thanks guys gonna start hunting for an ax5! Now for gears where's the best place to order from? Any brands that are better then others? If I was going through the hassle of swapping tranny's, I'd find the aforementioned AX15 and get the Dakota bellhousing. If you are lucky enough to find an AX15 out of a '98-'99 (IIRC) Dakota with the 2.5L I4, then get that with every thing you can (bellhousing, shift fork, clutch and pressure disc, etc).
Elijah808 Posted February 10, 2016 Author Posted February 10, 2016 Can I continue to run my stock tire size at 4.88? Or will it be to hard on my motor?
Elijah808 Posted February 10, 2016 Author Posted February 10, 2016 USA Standard Gear? Good company shopping for gears now.
88whitemanche Posted February 10, 2016 Posted February 10, 2016 Yes there was a thread here about which brand to use..the info is more towards the end of the and the 3rd page... http://comancheclub.com/topic/45147-amc-20/page-2
Eagle Posted February 10, 2016 Posted February 10, 2016 Can I continue to run my stock tire size at 4.88? Or will it be to hard on my motor? What's your stock tire size? And how fast will you be driving? Just go to the spreadsheet I provided a link to above. Let's assume your stock tire size is 215/75-15. Go up to the top of the sheet, to the section for 215/75-15 tires. Go all the way to the right, to the two columns under the 4.88 axle ratio. You don't have a 5-speed, so ignore the "O.D." column. Your 4th gear is a 1:1 ratio, so just read down that column to find the RPM for various road speeds. If you do that, you'll see that 60 MPH is about 3600 RPM. That's about the same RPM as 80+ MPH with your stock gears. It won't kill you engine, but I wouldn't drive very far or very often much faster than that. Here's my frame of reference. Both the 2.5L and 4.0L MJ engines are descendants of the 232 c.i.d. (3.8L) engine that AMC introduced in 1964. We've had several of them in my family, all mated to three-speed manual transmissions. The 3-speed also had a 1:1 top gear, so the setup is directly comparble to your MJ. They were all geared so that they ran 24 MPH per 1,000 RPM. That meant that 60 MPH was exactly 2,500 RPM, and 3,000 RPM gave us a 72 MPH cruise. 2,500 was sort of the sweet spot for getting the best fuel economy, but they weren't bad right up to 3,000 RPM. Above 3,000 RPM the fuel mileage fell off quickly. At a 3,000 RPM cruise, the engines lasted forever. My brother and his wife had a Gremlin that they drove more than 200,000 miles, then they sold it to an auto parts store where it was used as a delivery vehicle for another 120,000 before we lost track of it. The torque peak is closer to 3,000 RPM than it is even to 3,600, but you're probably okay up to around 60 MPH.
onlyinajeep726 Posted February 11, 2016 Posted February 11, 2016 My brother and his wife had a Gremlin that they drove more than 200,000 miles, then they sold it to an auto parts store where it was used as a delivery vehicle for another 120,000 before we lost track of it. Not to side track, but I would love to have a Gremlin and swap a Jeep 4.0 and tranny in. That would be sweet.
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