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7.25 Differential setup
https://slantsix.org/forum/viewtopic.php?t=35721		 Page 1 of 1
Author:  dakight [ Sat Jun 06, 2009 10:34 am ]
Post subject:  7.25 Differential setup
Where can I find good detailed setup instructions for a late (crush sleeve pinion) 7.25 differential. I have a gear set and installation kit on the way and it should be here sometime next week.

I went with the 3.55 ratio on a sure grip and plan to just use a little bit taller tire to help offset the ratio difference. Since I don't plan frequent highway trips with the car I think it will work out fine. I did the calculations and found that 70 mph with a 3.23 and a 24.7" tire is about 3000 rpm. The 3.55 would come in at about 3300 with the same tire. Go to a 26" tire and it drops to around 3150-3200 rpm. I think I can live with that.
Author:  dakight [ Sun Jun 07, 2009 5:57 pm ]
Post subject: 
Maybe someone could scan the relevant pages from the appropriate FSM, or point me to a place on the web to obtain the neceassary information? I've searched and I can find generic differential setup instruction but none specific to Mopar or the 7.25.
Author:  AnotherSix [ Mon Jun 08, 2009 3:15 pm ]
Post subject: 
The FSM would be the place to start.

the main difference between the older 7.25s and the later is the late rears have adjusters for the carrier, like a 8.25 does.

You do not use shims on the carrier to set the back lash and bearing preload. You do need a hex tool to adjust and tighten them, a shaft with a hex on the end and some way to turn it on the other end, I forget the size.
Author:  dakight [ Mon Jun 08, 2009 5:40 pm ]
Post subject: 
I've got the correct tool on the way and I believe I can handle the backlash/carrier bearing preload adjustments. My concern is the correct technique for setting the pinion depth. I don't have the FSM for that year; I was hoping that some one would be able to scan that section for me. I don't need the entire FSM myself because my car is an earlier year and I have the FSM for it.
Author:  dakight [ Wed Jun 10, 2009 6:16 am ]
Post subject: 
Let me ask this a different way, and maybe, just maybe, someone will have a response. What is the best way to accurately set the pinion depth on this differential. Surely someone out there has a simple and reliable method to do this without special tools.
Author:  Charrlie_S [ Wed Jun 10, 2009 7:17 am ]
Post subject: 
There are only two ways to set the pinion depth.
A) pinion depth setting tool.
B) trial and error using a tooth pattern check, and comparing the pattern to the charts, in the FSM.

Even using the tool, you should still do a final tooth pattrn check.
Author:  dakight [ Wed Jun 10, 2009 1:39 pm ]
Post subject: 
So, I will use an old bearing if I can get it off intact, or get an extra new bearing for this purpose and grind out the center to make a "setup bearing." I will start with the washers from the old setup, adjusting for pinion markings, check the mesh pattern and adjust from there. Does that sound about right?
Author:  Doc [ Wed Jun 10, 2009 2:42 pm ]
Post subject: 
Yes, that is how you do it with-out the special tools.
Note, the bearing ID is hardened steel and will not "open-up" easily.
A stone hone is about the only way to do it.
DD
Author:  dakight [ Wed Jun 10, 2009 4:07 pm ]
Post subject: 
Do you mean a brake cylinder hone? Any tips for getting the old bearing off without destroying it?
Author:  emsvitil [ Wed Jun 10, 2009 4:13 pm ]
Post subject: 
You can make a hone with 400-600 grit wet/dry paper, steel rod, foam and duct tape, and wd40....

Tape stripe of sandpaper to rod.

Roll the paper around the rod with foam underneath.

You want the OD to be slightly bigger than the ID of the hole you're enlarging.

Spray sandpaper with wd40, insert into hole and drill away.........
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