74 Charger Rear End Swap Question

[Savage6]

Hey everyone,  I am swapping the 8 1/4 out of my 74 Charger for an 8 3/4.  Do I need to keep the rubber isolator and stock shock mount, or do i need to find a set of different shock mounting plates from say a 64-72 b body? 

[Ghoste]

Personally I would lose the rubber isolator for the older style stuff for the sake of performance.  I know there are quite a few parts that would need to be changed but if you've come this far.

[Savage6]

I think you are right.  The rear end is already under the car and ready to go.  Would you happen to know if the shock mount itself is different than the 72 model?  i have everything together with the old isolators between the shock mount and the spring perch and it is making the 489 case point towards the floor a heck of a lot.   I would love to be able to just remove the isolators and go from there, but nothing is ever that easy, especially when it is your first time doing something. 

[Ghoste]

Nacho or one of the other 3rd gen gurus will be able to tell you exactly.  I think I know the answer to your question but they will know for sure so rather than me screw it up in some way...
Nacho?

[Savage6]

I have a feeling i'm going to need the 72 shock mounts, and have to cut the round part of the rubber spacers off to fill the space in the bigger holes on the perches.  I will keep my fingers crossed though!   

[FLG]

From nacho




"first... iso stud guide is 3/8" againts the 5/15" non iso stud. I don't think thats a problem. If some problem, just make a small drill job on plate and axle perche IF NEEDED ( I think holes have enough play to fit those ).

second and main... bushing needs to be removed to fit shock plate and axle perches FLAT over springs

third... Lower plate, althought not really mandatory, I would change to make the complete change up job. The U bolts fits closer between then on non iso assemblies"

[Savage6]

Thanks FLG,  I will see if I can get the right parts and make this thing work.  I'm anxious to feel the difference between an 8 1/4 with open 2.71 gears  and the 3.55 suregrip that is in the 8 3/4!!!!!

[flyinlow]

I put a 71 RR 8 3/4 in my 73 charger. Used new Mopar HD springs. The rubber isolated spring holders from my 8 1/4 did not fit. Got new shock plates from Mancini. I did not get the old shock plates from the junk yard axle unfortunately.
When Dodge went to the new torsion quiet ride on 73 and up B bodys they added all those isolators. I think PST makes poly replacement ones if you want to go that route. Most people pitch them and go with the more ridged 72 and earlier mounting.

[Savage6]

Well, I think I am going to pitch them and go 72 style.  I feel like I almost have to because I believe they are making my pinion angle way off.  The added lift is causing the pumpkin pinion to point too far down because its holding the housing up too high and binding at the driveshaft.   I am going to have to pick up an angle finder eventually....

[flyinlow]

Well, I think I am going to pitch them and go 72 style.  I feel like I almost have to because I believe they are making my pinion angle way off.  The added lift is causing the pumpkin pinion to point too far down because its holding the housing up too high and binding at the driveshaft.   I am going to have to pick up an angle finder eventually....

The early axle perch does not fit the isolated mount spring holder without mods. Not sure why it would change you pinion angle if you did the mods or went to the early style shock braket. Your back end will ride a litle higher with the sollid mount shock plates.

Going from a 2.73 to 3.55 will be quite a difference!

If you are going from a 318 to a BB the bigger engines had extra leaves and extra half leaves on the front half to help keep the pinion angle within limits with the higher torque engines.

[Savage6]

I wish I had a 383 or 440..  but my 318 runs pretty good,  someday!    I am hoping you are right about the car riding a little higher.  I think If the mod makes the car ride higher, then that would mean that the rear end  housing would be in a different location (lower) than before and hopefully will make the binding disappear by changing pinion angle.  Or I could be way off and never have the car on the road again!  But at least I will have tried!   

[flyinlow]

The ride height change is small, just the thickness of the isolator that you take out. 1/2-3/4" when compressed.

The pinion angle is set by the way the axle perches are welded on the housing. Changing from one stock Mopar axle to a different one should not change the angle much. You can get wedges that fit between the perch and the springs and change the angle slightly 2-4*. Changing front hangers or rear shakles or a different arched spring can change it as well.

Normal is about 2-7* nose down compaired to the driveshaft if I remember  correctly. That way as you accelerate hard and the pinion rotates nose up it becomes close to a straight line with the driveshaft .

You can have a lot of fun with 318. I did the axle change on mine before I installed the 440. My old stock radiator was not up to the challenge of the higher freeway rpm's with the 3.55

[Nacho-RT74]

From nacho




"first... iso stud guide is 3/8" againts the 5/15" non iso stud. I don't think thats a problem. If some problem, just make a small drill job on plate and axle perche IF NEEDED ( I think holes have enough play to fit those ).

second and main... bushing needs to be removed to fit shock plate and axle perches FLAT over springs

third... Lower plate, althought not really mandatory, I would change to make the complete change up job. The U bolts fits closer between then on non iso assemblies"

[Nacho-RT74]

I think PST makes poly replacement ones if you want to go that route.

yes, and I would use that route, to keep the best of both worlds

[Savage6]

What is the best thing to do about the large hole in the spring perch?  Its way too big for the small peg on the leaf springs???  Does anyone make a filler or spacer for that conversion, or is that something that I am going to have to come up with myself. 

[Nacho-RT74]

some ppl has used large and thick washers