Driveshaft Upgrade - What do I need

Driveshaft Upgrade - What do I need - 09/08/14 02:47 AM

I have a 1970 Duster with a 340 4-speed and an 8 3/4. Engine made 470hp and 455 lb-ft. I currently have a stock driveshaft that's about 2 1/2" diameter with the 7260 U-joints. This factory driveshaft seems to have some jump-rope effect going on, and also makes me a bit nervous with this amount of power.

I see that there are a lot of options out there. At what power level would you need chromemoly tubing, forged weld yokes, etc. Please make a recommendation. I would like to go for 1350 U-joints.

Also, it seems that I always have to measure the driveshafts- you'd think the measurements for this application would already be available...

Posted By: fourgearsavoy

Re: Driveshaft Upgrade - What do I need - 09/08/14 02:59 AM

If I were having a new shaft made I wouldn't do anything less than 1350 joints

Plenty of room to grow in the future and you have more joint than you need for now.
Gus

Attached picture 8264029-rearviewsavoy.jpg

Posted By: 71yelladustr

Re: Driveshaft Upgrade - What do I need - 09/08/14 03:24 AM

on the 1350 joints especially with a stick. Then you can put a set of slicks on and test out your 8 3/4.

Posted By: goldduster318

Re: Driveshaft Upgrade - What do I need - 09/08/14 03:36 AM

Yep - 1350's it is.

What about the material for the tube and weld yokes?

Posted By: 71yelladustr

Re: Driveshaft Upgrade - What do I need - 09/08/14 03:47 AM

Forged yokes with u bolts instead of straps. Chrome moly shaft a little overkill for your application IMHO. Id say we are close in power output and beat on mine pretty hard.I don't have a chrome moly tube in mine and is holding up just fine.

Posted By: jbc426

Re: Driveshaft Upgrade - What do I need - 09/08/14 05:58 AM

Strange Engineering has a heck of a deal on custom drive shafts with forged ends and the rest of the parts.

I'm calling Dr Diff and he'll have the stuff drop shipped from them. I like hearing his advice and rely on his wisdom regarding drivelines, plus he's great to deal with.

Posted By: DoctorDiff

Re: Driveshaft Upgrade - What do I need - 09/08/14 06:32 AM

I recommend DoctorDiff/Strange 1350 driveshaft assy:

Strange Engineering street/strip driveshaft with Spicer slip yoke, Spicer U-joints, Spicer Weld yokes and 3" cr-mo tube

DoctorDiff forged steel 1350 pinion yoke includes U-bolts

http://www.doctordiff.com/strange-engineering-driveshaft.html

Posted By: goldduster318

Re: Driveshaft Upgrade - What do I need - 09/09/14 01:21 AM

Seems reasonable.

Now with the measuring part. I'd have to measure for the driveshaft with a 7260 yoke installed when I'd really be using a 1350 yoke. Will this throw it off? It's not easy to get under the car at ride height. Guess I'll throw some jackstands under the rear axle.

I just can't believe that there isn't a known measurement for a 108" WB A-body with an A-833 (or 904 for that matter).

Posted By: jcc

Re: Driveshaft Upgrade - What do I need - 09/09/14 01:26 AM

A 340 at 470 hp and an 8.75 and considering 1350's IMO is a good candidate for an ALUM DS.

Posted By: moparfan53

Re: Driveshaft Upgrade - What do I need - 09/09/14 02:40 AM

Quote:

Seems reasonable.

Now with the measuring part. I'd have to measure for the driveshaft with a 7260 yoke installed when I'd really be using a 1350 yoke. Will this throw it off? It's not easy to get under the car at ride height. Guess I'll throw some jackstands under the rear axle.

I just can't believe that there isn't a known measurement for a 108" WB A-body with an A-833 (or 904 for that matter).

There is a known measurement (assuming you mean the original/factory length), the Chrysler parts book as well as the FSM has that info. When I get home I will post the length if nobody else has by then.

There used to be a chart in the tech archives here on Moparts. I took a quick look but did not see it.

Posted By: RapidRobert

Re: Driveshaft Upgrade - What do I need - 09/09/14 03:37 AM

I'd find out if the 1350 and the 7260 front yokes are the same (for distance) & if not then I'd get it in hand (or borrow one) & install it with the front and rear (axle) up on stands (vehicle fairly level) & butt the yoke all the way in the trans & get an exact C to C distance then subtract 3/4-7/8" from that dimention but go with what Doc says, he's the man but (just me) I would not go with a "known A body shaft measurement"

Posted By: draginmopars

Re: Driveshaft Upgrade - What do I need - 09/09/14 05:05 AM

Quote:

Seems reasonable.

Now with the measuring part. I'd have to measure for the driveshaft with a 7260 yoke installed when I'd really be using a 1350 yoke. Will this throw it off? It's not easy to get under the car at ride height. Guess I'll throw some jackstands under the rear axle.

I just can't believe that there isn't a known measurement for a 108" WB A-body with an A-833 (or 904 for that matter).

We searched for the tech specs, in order to have a shaft built,but couldn't find the exact measurement differences of the 7260 vs 1350

So, we ended up just getting the yokes and joints for the Dart and Satellite (Thanks Dr.Diff)
and having our local drive shaft man, tube them for us.

Here are some pics of the shaft yokes
the (727)trans yoke is .650" longer with the joint cups centered as best I could eye ball it

the shaft yoke appears .500" longer

Posted By: DoctorDiff

Re: Driveshaft Upgrade - What do I need - 09/09/14 06:42 AM

You can measure off the 7290 pinion yoke, but the 1350 slip yoke dimension is totally different.

Posted By: 383man

Re: Driveshaft Upgrade - What do I need - 09/09/14 07:00 AM

If I did not have the right yoke I usually borrowed one as I always measured any cars driveshaft I was having made even if I had what the readings were supposed to be. Always do a center to center reading and have the shaft made the right size the first time.

Ron

Posted By: goldduster318

Re: Driveshaft Upgrade - What do I need - 09/09/14 11:27 PM

Quote:

You can measure off the 7290 pinion yoke, but the 1350 slip yoke dimension is totally different.

I have the 7260 yoke on the diff still (will replace it with the 1350 of course). Is that still okay to measure with?

Also, when I look at the photo

It shows dimension "A" to be basically from the edge of the yoke at the diff when the directions say the center line of the U-joint. I can pretty easily get the A and B dimensions I think.

Thanks again.

Posted By: DoctorDiff

Re: Driveshaft Upgrade - What do I need - 09/10/14 05:21 AM

Yes, the measurement will be the same.