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Going back to 3:23 from 3:91 Tech help and opinions needed

roadrunnerh

roadrunnerh

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Shortly after I bought my 68 Road Runner in 1993, I decided to swap out the 3:23 open 742 center for a 3.91 742 unit I bought from Herb McCandless with rebuilt clutch SG and new Strange 3.91 ring and pinion.
Now, I want to go back to 3.23's. I still have the 742 open 3.23, but I was thinking I would remove the SG from the 3.91 carrier and install in the 3.23 center section.
Doctor Diff told me it was an easy swap a couple years ago. Just change out the SG for open and since the gear depth was already set in the open 3.23, it was simple.
Any advice? I'm sure the Sure Grip unit is fine since I never raced and only have about 10K miles on the rebuilt unit.
What do you guys thing? I've swapped centers but never removed anything from the carriers other than replacing a yoke or pinion seal.
 
Take a pattern on the 3.23 set before you disassemble, swap out the sure grip, match that pattern ..... or check backlash, swap sure grip, set backlash just like it was .....
 
May want to change pinion seal on 3.23 open rear. Think guys here recommend dr diff for the seal. Think it's different than 741 or 489.
 
Backlash is back and forth play?
yes, I got a pinion seal and NOS Mopar 10 spline yoke.
 
No need to check pattern as they show poorly on used gears. Check backlash on both units (you may want to swap back in the future) Mark caps side to side. Remove caps and carrier assy's. remove both ring gears. Stone 3.23 ring gear and carrier to remove burrs. Install 3.23 ring on the sure grip and torque to spec. Loosely install the sure grip back in the 3.23 housing. Set backlash to .000". Now tighten opposite adjuster until you reach the original backlash number measured in the 3.23 unit. Not only does this set side bearing preload it puts the ring gear right where it was before you took it apart.
Doug
 
Since it's not original to the car, maybe you could work a trade for an equal unit, and swap them out ? I know I've been thinking of pulling my 3:23 SG, and going with a 3:55 - 3:91 SG, as it's time for me to start enjoying the car more than preserving it...
 
I’ve swapped out plenty of units and it’s not really hard. Like dvw said mark the caps to there side. Then I check backlash and pattern. You can use a piece of newspaper and spin it thru the ring and pinion and look at the marks it leaves. (I don’t remember where I read that trick but it works). Then I mark the adjuster on each side and count the turns it takes to unscrew each one. Install ring on the sure grip then reinstall the adjusters the same amount of turned for each side. Check pattern and backlash. You can fine tune by tightening one side and loseening the other if needed. There is probably something on Utube that will help you get the pattern close too. Good luck!
 
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I concentrate on the coast side for used gears. The above mentioned ways to set up, follow them and you’ll be just fine.
 
I'm swapping out my 3:23's for 3:91's and I'm going to run a taller tire in the rear which will give me a effective gear ratio of 3:73. Then if I decide to go to the strip and play around I will put shorter tires on to bring me back to 3:91.
 
The inside of the tooth is the coast side, it is towards the front of the car. The drive side is the back of the tooth, faces the rear of the car.
 
Here’s some pics. First is coast side. Second is drive side.

4B1B3A09-CF5B-42E7-ACC2-D2784BE2CF28.jpeg 183CB2C0-2879-41B9-80BF-643189BE10CE.jpeg
 
A few more of the coast side. The reason you want to concentrate on the coast side is because the drive side is “worn in” but the coast side really hadn’t been touched.....unless you drive around in reverse all the time. So, get your pattern set on the coast side and the drive will follow really close.

65EC7A95-44D6-46FD-A0F6-04004871A2F6.jpeg F3043877-3B22-48DB-B944-D34B78968288.jpeg
 
Hey guys, what are your thoughts on using a dust shield on the pinion yoke? My new factory one does not have that dust shield. Where can I find one? Mancini Racing used to sell just the shield, but no longer do.
 
When I changed out my gears the yoke that was in the car didn't have the dust shield, without the shield it leaves the pinion seal wide out for dirt, water and what ever to get into the seal. I bought a used yoke with the dust shield from a guy buy the name of Jack Forkey in northern NY. He had a bunch of them and he will mail it to you. His number is 315-783-0540, he is a great guy to deal with and he has a lot of hard to find Mopar parts
 
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