8 1/4" axle gear interchange

[Kern Dog]

Hello...
I have a non original 8 1/4" axle in a 69 Dart of mine....

It is a 2.71 geared CONE Sure Grip....

I want something better. This car may be getting an A-500 with overdrive so I'd like a 3.55 or a 3.91. That likely means a truck or van.
I'm curious about what donor vehicles I can look for that have a gear set that will fit and work. I read that the 1997 and later models had a different spline count for the axle shafts but I don't know how that would affect the ring and pinion or if it even does.
Who knows what is the cutoff year for the gear set? I'm looking to pull the gears from a donor and install them into this axle using the Sure Grip it already has. The best I can tell is that this is a 1973-76 A body axle. The perches are 43" apart, it does have 11" drums though. No A body that I have ever seen had 11" rear drum brakes so either these have been swapped in or this is some rare and weird setup.

 

[RustyRatRod]

I cannot answer your specific question, but the 8.25 has a carrier split regarding the gear sets. I do not remember where it is. In other words, you need one carrier for gear sets numerically lower than 2.xx and another for gear sets numerically higher than 2.xx. Does that make sense? I'm sure one of these other guys can get more specific than that. I'm sorry I don't know more. Worst case is you will need another carrier to upgrade the gears, but again, I'm unsure where the split is, so you may not. If you do a search, we have a thread all about the 8.25 axle. I'm sure it's in there somewhere.

 

[Kern Dog]

I know mid 2000's jeep liberty's had 8.25 rear ends and i believe most were geared in the 3.2x-3.7x range and many had limited slips. Maybe you can grab an entire carrier and pinion out of one of those and drop it in?
I love the 4 door cruiser and you have an amazing start to that project already

I recall hearing that the 2.45 and 2.21 ratios shared a carrier design but that the 2.71 and higher numbered ratios used a different one. If this is true, my diff carrier would work with a better gear.
I have a 3.21 gear set here but want a deeper gear. The 3.21 matched with a .69 overdrive would be a really tall 2.21 final drive.
I also have an 8 3/4 housing I could use in this car but it would be overkill. I'd like to keep this 8 1/4" unit in place....The 11" brakes will go though.

 

[junkyardhero]

you are correct, the 2.45 is the split on the carrier.

you could keep your 2.71 and run a later transmission with the deeper primary gear set and a lock up converter.

punch out of the hole and around town, reasonable RPM while cruising highway speed and the lock up will shed some more RPM as well.

 

[Kern Dog]

The engine that is going into the 4 door is a mild 360 with a 340 cam. The 360 is now in a 67 Dart with 4.10 gears and it really rips for being such a basic engine. I'd hate to step backwards that much by sticking with such a mild axle gear. The A-500 transmission has a something like a 2.75 first gear, right? That is .30 more than the 2.45 a 904 uses so if I add the .30 to a 3.55, I'm at least at a 3.85 ratio equivalent, sort of close to the 4.10 I'm used to.
I wonder if the 1987 model would have a 3.55 or better?

That is a 1987 V6 4WD so I'd bet the axle ratio would be right what I need.

 

[Dartnut]

When I talked to Cass last time (Dr. Diff), He told me that the cut off for lower gears in an 8 1/4'' rear was 2:45 and with 2:71 and higher ratios would accept 3:55s and higher gears, so you're good to go.
I'm not sure about using newer gears like a Dakota has, but I would seriously look at buying new gears and installing them.
They're really not that expensive and if set up right, they shouldn't howl like used gears might.
I would buy them from Dr. Diff with no hesitation, he has always been good to me with prices and fast shipping...

 

[remytherat]

Almost all of the early dakotas and early jeep XJs have 3.55s that you can use. 3.91s seem to be rarer

 

[RustyRatRod]

you are correct, the 2.45 is the split on the carrier.

you could keep your 2.71 and run a later transmission with the deeper primary gear set and a lock up converter.

punch out of the hole and around town, reasonable RPM while cruising highway speed and the lock up will shed some more RPM as well.

Good then that means all he needs is a gear change.

 

[4mulas]

Well I’m sure learning about this 8 1/4 stuff had no idea. Not sure if this helps or if the info is relevant but it might be easier for you that the bone yard- I had a Quick Look at rock auto under a 1987 Dakota with 6 banger and they list 8 1/4 gears with the ratio you desire for pretty cheap

Like:
More Information for DORMAN 697356

Or this Richmond one where they mention the carrier break of 2.71:
More Information for RICHMOND CR825

Both seem pretty reasonable price wise? Or is this ona super tight budget?

 

[Kern Dog]

Holy crap....I had no idea that they were that cheap!
Thank you for looking those up. I'm disappointed in myself that I didn't do that myself....I had it in my head that all new parts are more than I wanted to spend. I figured that new gears were always $250 or more for a set.

 

[RustyRatRod]

Holy crap....I had no idea that they were that cheap!
Thank you for looking those up. I'm disappointed in myself that I didn't do that myself....I had it in my head that all new parts are more than I wanted to spend. I figured that new gears were always $250 or more for a set.

I got a set of 4.11s for my Ford 9" on sale at Summit for like 129 bucks. lol

 

[mopowers]

I've heard that the cheap offshore gears are more likely to make noise, so I'd stick with a good quality gear. I remember Cass telling me that when I built my Dana 60. Not sure if things have changed as that was many years ago now.

Also, if you end up getting a used OE ring and pinion from Pick n Pull, you should measure the backlash in them prior to removing. You'll want to replicate that backlash when reinstalling or very close to it.

 

[4mulas]

I've heard that the cheap offshore gears are more likely to make noise, so I'd stick with a good quality gear. I remember Cass telling me that when I built my Dana 60. Not sure if things have changed as that was many years ago now.

Also, if you end up getting a used OE ring and pinion from Pick n Pull, you should measure the backlash in them prior to removing. You'll want to replicate that backlash when reinstalling or very close to it.

you’re probably right. A guy here pretty much says he only uses motive gears as the others can be harder to set up. For what it’s worth though my new motive gear set is set up very well but they are slightly noisy anyway….

Re-installing used gears in a different carrier may be very difficult to do with success. Agree, measure the backlash first and pattern the gears to, take pictures of the pattern and compare your before and after as well.

 

[Kern Dog]

I have an axle guy that has set up all my gears for 20+ years. He said that for many Mopar axles, the factory gears have a much higher reliability factor. The last job he did for me was 3.92 gears in my 2007 Dodger truck.
I was hoping to try this myself but I'm not 100% sure on that yet.

 

[RustyRatRod]

I've heard that the cheap offshore gears are more likely to make noise, so I'd stick with a good quality gear. I remember Cass telling me that when I built my Dana 60. Not sure if things have changed as that was many years ago now.

Also, if you end up getting a used OE ring and pinion from Pick n Pull, you should measure the backlash in them prior to removing. You'll want to replicate that backlash when reinstalling or very close to it.

I got the Summit brand. Summit is known for using good products.

 

[mopowers]

I got the Summit brand. Summit is known for using good products.

Any idea who makes them? I know quite a few of their branded parts are made by some pretty solid manufacturers. They're basically just re-branded parts at a cheaper price.

I have an axle guy that has set up all my gears for 20+ years. He said that for many Mopar axles, the factory gears have a much higher reliability factor. The last job he did for me was 3.92 gears in my 2007 Dodger truck.
I was hoping to try this myself but I'm not 100% sure on that yet.

I've never built a 8-1/4", but I've set-up a number of 8-3/4's and a couple Dana 60s. If you get some gears, we should give it a shot.

It looks like the 8-1/4" has threaded carrier adjusters, which should make it a lot easier than a Dana 60. The only issue if you can even call it that is nailing the pinion depth, which could take some trial and error without the proper pinion depth tool. That could be a pain without a setup bearing (pinion bearing that's been honed out for a slip fit). I have them for a 8-3/4 and Dana 60, but not for a 8-1/4. Without a clam-shell bearing puller, you risk damaging the pinion bearing if you attempt to pull it to try a different pinion shim.

It also looks like the 8-1/4 uses a collapsible spacer like a 489 case. I wonder if they make a solid spacer so shims can be used to set pinion bearing preload instead of the collapsible spacer?

 

[RustyRatRod]

Any idea who makes them? I know quite a few of their branded parts are made by some pretty solid manufacturers. They're basically just re-branded parts at a cheaper price.


I've never built a 8-1/4", but I've set-up a number of 8-3/4's and a couple Dana 60s. If you get some gears, we should give it a shot.

It looks like the 8-1/4" has threaded carrier adjusters, which should make it a lot easier than a Dana 60. The only issue if you can even call it that is nailing the pinion depth, which could take some trial and error without the proper pinion depth tool. That could be a pain without a setup bearing (pinion bearing that's been honed out for a slip fit). I have them for a 8-3/4 and Dana 60, but not for a 8-1/4. Without a clam-shell bearing puller, you risk damaging the pinion bearing if you attempt to pull it to try a different pinion shim.

It also looks like the 8-1/4 uses a collapsible spacer like a 489 case. I wonder if they make a solid spacer so shims can be used to set pinion bearing preload instead of the collapsible spacer?


View attachment 1716417850

I have no clue. US Gear maybe? I can tell you this. They set up super quick and easy and the gear patter is perfect. I got it on here somewhere.

 

[mopowers]

I have no clue. US Gear maybe? I can tell you this. They set up super quick and easy and the gear patter is perfect. I got it on here somewhere.

That's great. When I talked to Dr. Diff a long time ago about it, he mentioned that some offshore brands may give a different pattern at different spots on the ring gear.

 

[496 polara]

My Newport had 2.71 gears. It now runs 3.55 with a suregrip with no issues.
I was looking for a 3.21 and bought a used ring and pinion and then found the suregrip with gears so in she went.

 

[Sterling]

I did a 8 1/4 for my buddy's son, has a 74 Dart. Got a set of 3.55 gears from the U-Pull It out of a older Dakota that the bed was removed. He got a sure grip and new bearings. A I made a solid spacer out of chrome moly tubing, and shimmed the bearing preload to specs.

 

[Kern Dog]

I was at the Rocklin location looking at parts for my truck and I did see this truck...

I slipped under it to look at the tag on the differential. Some of these trucks had 2 tags, one was some part number, the other was the gear ratio. This one only had one tag, the one with some 4 digit number. I didn't have a 1/2" socket with me to pull the cover.
It got me thinking....
Years ago I pulled an 8 1/4" axle from a Dakota and used it in a Dart Sport. I had to cut off the shock mounts and spring pads then weld compatible spring pads on it. I was crunching the numbers and wondered if it makes more sense to try that with this car if the truck axle has good gears and its own Sure Grip in it. Leaving the internals intact would save time and money.
The axle fit the wider Dart Sport body but I'm wondering if it will fit the tighter wheelhouses of the standard sedan Dart.
Even if I only wanted the ring and pinion, I'd have to buy the whole axle to bring it home where I could disassemble it.

 

[JDMopar]

If you could get the width measurement of the outside of drum to the outside of the other drum, then compare that to the same measurement of the 8 1/4 in your Dart, you could determine which way to go. Swapping the whole thing would be my preference if it were me doing it. If it's pretty close and you aren't planning on great big rear tires, it just might work.