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8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
https://www.slantsix.org/forum/viewtopic.php?f=20&t=66869		 Page 1 of 1
Author:  Chuckster [ Tue Nov 01, 2022 4:53 pm ]
Post subject:  8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
My 15 year-old grandson and I are working on his '72 Dart Swinger with a Slant 6 - 3 on-the-tree. The saga so far: viewtopic.php?f=12&t=66237
It appears that a P.O. changed the front end to '73 up disc brakes and swapped in a later model 8.25 rearend to have the 4.5" wheel bolt circle. This axle has the 2.45:1 gears, which makes acceleration from a dead stop very slow. I'm sure quarter mile times would be measured with a calendar, not a stopwatch! Anyway, a friend of ours gave us 2 gearsets for an 8.25 rear, 3.21 and 3.91.
I'm not sure how to identify what year the rearend assembly was made and if the 3.21 gears will fit the center section. We pressure washed the rearend today and found the following casting numbers:

2408906 F0 16 or T6

It would be appreciated if anyone could identify the year of the rearend, and if the 3.21 gears will fit.

Thanks,
Chuckster & Logan
Author:  volaredon [ Wed Nov 02, 2022 5:22 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
I've heard 2 different schools of thought on the 8-1/4, not sure which one is right.answer. I've heard that it is just the carrier that is different and either carrier will fit any 8-1/4 housing/
And I've also heard that the actual housing is different above and below 2.45.
I do know that the spline count where the axles engage the carrier changed at the end of 1996/beginning of1997 model year 8-1/4s from All the messing around I've done on Dakota's and square body Cherokees. I did have an open carrier here that had come out of my 96 Dakota which has 3.91sin it, I swapped it's original ring gear onto a spicer trak- lok limited slip back when I got the truck. Not sure if I still have the original carrier here anymore or not.
All 8-1/4s up to 1996 no matter what body style they were built for had 27 spline axles. Starting in 97 they went to 29 spline.
Author:  Greg Ondayko [ Fri Nov 04, 2022 5:04 am ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
I wish I could offer some more insight.

I do know that I was Setting up and 8.25 For Brian one time and No matter what we did we could not get the last / play correct due to this issue.

I want to say we kept the case and swapped the Diff Carrier but I am not sure.. that was well over 10 years ago!
Author:  hank2 [ Fri Nov 04, 2022 1:35 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
From what I could find on the web, which wasn't much. The carrier must be changed to go to the bigger rings. Some mentioned a need to use some different bearings as well. I saw a couple of mentions that the ring is offset a good bit on the very tall geared 8.25 from where the 2.7 and up would mount. So, I guess that the carrier change is a must. One old post from somewhere, mentioned that he did the carrier change and was able to get a kit from Dr. Diff, off menu, for whatever bearing changes and ? that were needed.
Author:  Rodrju [ Fri Nov 04, 2022 1:58 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
A few years ago I sourced a stock 8.25 from a 1975 Valiant that had 2.45 gears. I had a carrier and 3.21 gears from a 1974 Duster 8.25 installed with zero issues.

I do not know the casting number of the case I have but I can say it’s been good overall.
Author:  Killer6 [ Sat Nov 05, 2022 6:47 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
It is the carrier that changes. The Dakotas are everywhere with 3.55's, but have the tone wheel for RWAL, not sure whether that can be tossed & a ring gear for w/o a tone wheel can be just installed. Bearings in the Dak housings are larger iirc.
Author:  Chuckster [ Tue Nov 08, 2022 7:47 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
So, if we can score a Sure-Grip unit and use it when we install the gears there shouldn't be an issue. Am I understanding this correctly?
Thanks!
Author:  volaredon [ Wed Nov 09, 2022 10:10 am ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
I don't think the abs tone wheel will interfere if you did get a newer version out of a Dakota or Cherokee, and transplant into your housing


In fact i have wanted to get measurements next time I'm in a boneyard as I think the overall width and spring perch distance on a 2wd Dakota or a Cherokee would be dang near a bolt in. If you get one from a Dakota it would have to come from a 2wd as a 4wd has the perches on top of the axle tubes, a Cherokee or a 2wd Dakota has them in bottom like cars do. And the XJ Cherokee (all years) as well as Dakota's up til and including 1990 have what's known in the A body world as "big bolt pattern"
Author:  Killer6 [ Wed Nov 09, 2022 4:55 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
volaredon wrote:
I don't think the abs tone wheel will interfere if you did get a newer version out of a Dakota or Cherokee, and transplant into your housing


In fact i have wanted to get measurements next time I'm in a boneyard as I think the overall width and spring perch distance on a 2wd Dakota or a Cherokee would be dang near a bolt in. If you get one from a Dakota it would have to come from a 2wd as a 4wd has the perches on top of the axle tubes, a Cherokee or a 2wd Dakota has them in bottom like cars do. And the XJ Cherokee (all years) as well as Dakota's up til and including 1990 have what's known in the A body world as "big bolt pattern"

Not even close. Spring perches are close, only ~.2" wider than rbe A-body, that's doable w/o any real mods.
Housings are wider by 5.84" flange to flange over an 8.25" A-body, & LBP 7.25" A-body with 10"× 2.5"wide brakes.
It is 4.04" wider flange to flange over a std. SBP 7.25" w/9" brakes.
Overall track (wheel mount surface to surface) is 63", only .400" narrower than C-body & '71&^ B-body/wgn.
That's 7.44" wider than std. A-body track.
Of course, You csn always run for a set of high backspace FWD style rims & make it work.
Author:  volaredon [ Thu Nov 10, 2022 3:39 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
Ok then..... I never had a chance to measure them out, I was just wondering. Are those measurements from a Dakota or fron a Cherokee?
And among the different rear ends for a given body style (this site caters mostly to A bodies so I'll stay with them for the question that I have. You specify dimensions for a 7-1/4 rear end. As long as they came out of an a body (originally) wouldn't an 8-1/4 or 8-3/4 rear measure out the same, both overall width and spring perch width?

Then plan B would be to get a Dakota or Cherokee 8-1/4 and rob it's guts to put in your a body housing
Author:  Killer6 [ Thu Nov 10, 2022 4:00 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
That was a 2wd Dakota, 7.25" rear, '87 8ft. bed, 2bbl carb V-6. I have (2) '90 versions of the same, 8.25" rears & A-500's, haven't put the ruler to them yet, but don't anticipate much difference drum-to-drum.
Author:  volaredon [ Fri Nov 11, 2022 5:22 am ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
I've worked on a few 87s, they don't have OD and both I worked on were 2.94 rears.
Anyone have measurements on a Cherokee rear to compare? Many had 8&1/4s others had a Dana 30.
Author:  Killer6 [ Fri Nov 11, 2022 3:19 pm ]
Post subject:  Re: 8.25 REAREND CASTING NUMBER I.D. - WILL 3.21 GEARS FIT?
volaredon wrote:
I've worked on a few 87s, they don't have OD and both I worked on were 2.94 rears.
Anyone have measurements on a Cherokee rear to compare? Many had 8&1/4s others had a Dana 30.

Yeah, the '87 has cruiser gears, & an A-998 or A-999 L/U trans. It also came with 14" rims, I swapped brackets for the larger rotors, had 15's on it. The '90's A-500's & 3.55's, one has a button in dash to kill the OD. I may have measured a Jeep rear at work, but where I put the specs are a mystery I don't have time to solve right now!! Lol!!
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