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  #1  
Old 08-08-2003, 02:25 AM
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Default Rear end questions....

Does someone know the number of splines on a Mopar 7.25 VS 8.25. Looking at getting an 8.25 driveshaft, but I have to know the spline count!
Thanks,
Erik
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Old 08-08-2003, 03:48 PM
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I think you are confused here. If you are going to replace the 7 1/4 rear end with an 8 1/4 in your car the driveshaft length will be a bit shorter. The splines in the transmission tailshaft is what you are worried about not the rear axle. If you have a 727 or 4-speed the splines are the same, but different for the 904. Find out which tranny you have and look for the same set up in the boneyard e.g. - '73 dart/727 with 8 1/4 and you should be good to go. You may have to use the conversion U-joint to get it all hooked up so dont worry about the difference in size of the u-joints.
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Old 08-08-2003, 10:47 PM
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Default I probably am confused... :)

Well, I probably am confused but...
What I am looking for is a 84-89 Diplomat/Gran Fury drive shaft. Went from a 904/999 to 8 1/4. Earlier years had the 727. Not a lot of them in boneyards in the area. I have a guy who might be able to find me one, but he needs to know more exactly what it is. If I remember correctly, the shaft should be 1.6 inches shorter, but he needs more than that!
I guess I have to identify to him if it is a 727 or 904.
Erik
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Old 08-08-2003, 11:03 PM
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Like Dart said, the yoke width and the axle centerline to yoke centerline distance are all you need to be concerned about in the 3rd member. There are u-joints available for the width and the driveshaft can be shortened if necessary. The spline count you refer to is at the tranny, actually it's the dia. 727's are larger, and are not as common as the smaller 904 for SB's. If your present shaft is the correct length you can change the slip yoke to the smaller/larger size as long as you use the same u-joint.
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Old 08-08-2003, 11:29 PM
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Time out...What did you do to the car? Did you swap the rear end or the trans or both? What are you looking for exactly? Did you build this car up or what parts do you have (trans and rear end)? We will get it straightened out, but let me know what we are dealing with here.
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  #6  
Old 08-09-2003, 07:33 PM
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Default Ok, heres the scoop....

What I have is an 85 5th Ave. 318, 904, 7.25 rear. The car has had some performance improvements, including 4 barrel conversion, emissions gone, modified 904 with shift kit and all higher performance parts in, Performer intake, MSD 6A. Etc. Nothing radical, but definatly hotter than stock.
What I have always heard is that the 7.25 is weak. Besides which, I think the 2.24 gears are rediculous, and it is an open differential. I have found an 8.25 sure grip (either a 2.94 or a 3.21, not sure yet) that I want to bolt in before the 7.25 grenades itself. In this part of the world, (Erie PA) there is only one shop that does driveshaft work, and not only are they lousy, but they are expensive too. So, rather than paying a fortune to get my drive shaft shortened, balanaced, etc, I thought I would just get one from a mid to late 80's Diplomat/Gran Fury police car. I know from 84 on they ran the 999 tranny and the 8.25 rear, so it should be a direct bolt in. What I need to know exactly is what length, etc this drive shaft should be so that I can get the right one. Ideally, I could find a tired ex-cop car and yank it out myself, but it is never that easy, is it?
Thanks for listening!
Erik
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  #7  
Old 08-09-2003, 08:08 PM
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The only thing that will work will come from a car with a 904 or 999 with the 8 1/4 rear. I could measure one out of my cruiser if you like, but it might be a few days before I can get to it.
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Old 08-09-2003, 11:43 PM
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Default Great!

Hey DWC
That would be great. Any help at all would be appreciated!
Erik
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Old 08-10-2003, 10:08 AM
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Sonds like you got it figured out. That is what I would do also. Normally if you need to have a driveshaft shortened it only costs about $75, but you stated that the shop in your area wasn't very good. If DWC measures his driveshaft for you you could send your driveshaft to a competent shop to have it shortened. Normally you want to measure from the centers of the u-joint caps, so hopefully DWC uses this method.
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  #10  
Old 08-10-2003, 10:44 AM
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Default Thanks!

Thanks for the support, Dart.
One problem I have is that, since this is my daily driver, I need to minimize downtime. So sending my current shaft off to get it cut would not be a great idea. I have found that my cars don't run to well without them....

Now, does anyone have one of these driveshafts kicking around?
Erik
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  #11  
Old 08-10-2003, 03:58 PM
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Quote:
Originally posted by Dart
Normally you want to measure from the centers of the u-joint caps, so hopefully DWC uses this method.

That's the only correct way I know how to do it. We have actually cut our on shafts for our race cars in our own shop. Sometimes we get them so close they dont need weights, but we always take them out to have teh balance check for safety and reliability.
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Old 08-10-2003, 07:46 PM
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Default More questions...

Now, what else should I prepare for when doing the swap? Obviously rusty nuts and bolts, brake lines, etc. I understand I should have some shims ready to get everything angled properly. Any other obvious screw ups to look out for or tips that are recommended?
Thanks again!
Erik
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  #13  
Old 08-10-2003, 07:49 PM
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As long as everything is stock you wont need any shims. Heat the bolts on the axle u bolts cuase they stick and you can easly bend them trying to wrench off the nuts. Spray down the brake line fittings and bleeder screws too. Might even consider geting new wheel cylinders if it's been sitting up long.
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  #14  
Old 08-11-2003, 12:28 AM
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Default Except....

I think I am having some pinion angle problems with my car right now as it is, so I just wanna make sure it is right....
Probably gonna get new u-bolts anyhow. New flex hose. Wheel cylinders, etc. Has the bigger cop brakes in the back too. (11X2.5), so I wanna make sure they are right before I install them. I kinda like to have brakes....
BTW, do I have to change anything else, hydraulics wise, to accomodate the bigger drums?
Erik
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