Vannin' Home Forums General Discussion Performance - non brand specific Dynotech Replacement Driveshaft (Upgrade)

shaft is all installed, you can see photos by looking at this public album http://www.facebook.com/media/set/?...000860743365&type=1&l=0b84ff8c46

Looks great!

Runs as good as it looks. No more driveline vibrations, I still get a sort of vibration but it's not from the driveshaft, I'm thinking something like suspension components and or a wheel needs some better balancing, I do need a front end alignment which is probably a BIG contributor to this slight vibration. But I am happy to say I can safely drive at highway speeds again, so YAY!!

Sweet

Does Dynotech have a particular part no. for that driveshaft?

I may look into it for my 94.

No they don't, every driveshaft they manufacture is custom made so you would need to provide them with measurements. If you go to there website www.dynotecheng.com and go to the order form tab, you can download the proper form for your application (Transmission to Center Line) and fill in the blanks.

Also your van just like mine came with 7290 U-Joints and dynotech cannot make a 4" diameter shaft with those specific U-Joints only because they cannot seem to get tube yokes for that u-joint. So you would probably have to get 1350's all the way around and change the pinion yoke like I did OR you can have dynotech make it with 1350 slip yoke and a 1350 to 7290 u-joint on the pinion side.

I contacted some other driveshaft people and dynotech is pretty much the least expensive when you compare quality, turn around time, so on. They also ship it for free which is a relief. But if you want my experience, it's worth every penny I am completely satisfied and it fits perfect.

I have a complete 8 3/4 axle (from a '73 Maxi) to replace the puny factory issued 8 3/8 (3300# rating) in my van. An equally puny 2.5" prop shaft (mopar-speak for drive shaft) with the tiny 7260 U-joints connects it to the 360/727. Since it was free for the taking, I grabbed a replacement from a C-class motorhome. Even though it had a 360/727 too, with a 7500# axle rating (Dana 70) I wasn't surprized by the size (4") of its' propshaft.



After sripping the rust and grime off it, I was surprized to find it also had 7260 joints on both ends.



In spite of the extra 0.66" length (axle CL to yoke CL) of the 8 3/4 (which has a 7260-sized yoke) , I've heard I can get away with using my old driveshaft, but I'd rather not.



Shortening/balancing is about $130, which I want to do, but I'm wondering if the extra
expense of also up-grading to larger 1330/1350, or even 7290 joints/yokes is worth it.
If JJ ever gets a 4" stroker crank (or 400 w/440 crank) , I want the driveline to be able
to handle the extra torque.

Upgrading the 1350's is a BIG improvement when it comes to durability. Also you can get 1350 u-joints just about anywhere that sells U-joints as it's very popular. The 1350 u-joints are used on vehicles that have well over 1000HP.

Reasons for having a 4" shaft other then torsional strength is to raise the critical speed a little, now of course the average critical speed for a 58" cl-cl 4" shaft is going to be about 6500-7000 RPM so the vehicle (depending on gear ratio and tire size) would have to travel like 150 MPH before you hit critical speed.

Anyways if you want my opinion from experience, just call up dynotech and order a shaft from them. It cost about 478 bucks for the shaft ready to install but it's worth it! I got the entire shaft made with 4" x .083" DOM 4140 Steel Tubing with spicer 1350 solid body u-joints, a spicer cast slip yoke good for 800HP (same slip yoke used on the dodge viper), and the whole shaft is balanced at a minimum of 5000RPM, the company dynotech actually made the machines to make the driveshafts. You get a lifetime warranty on the shaft and they are very nice people and have a hell of a reputation, been around since 1923!

Now in order for me to have put that 1350 driveshaft on the van I had to replace the pinion yoke because as you know chrysler uses 7260 or 7290, so I went on ebay and found that pinion yoke that is made for the chrysler 8 3/4 axle but it fits chrysler 9 1/4 axles as well. It's a forged pinion yoke made by victory performance who makes drivetrain parts for dragsters mainly. It was only about 100 bucks so the whole driveshaft change all in all cost me about 650 bucks which includes parts, shipping, so on...

It has been 5 days since I installed the shaft and I don't feel any vibration from the drivetrain at all, the shaft runs as good as it looks!

I did the math and calculated the critical speed and torsional strength of the driveshaft tube. For 4" x .083" x 58" 4140 DOM Steel tubing:
Tube Weight: 16.99 lbs
Critical Speed: 7705 RPM
Torsional Yield: 4570 ft-lbs
That's just for the tube, you are limited by the weakest link which is generally the u-joints.

I got this shaft with these specs because it is difficult to get a shaft made with 7290's and the 1350's are stronger so I said why not, if I ever need another shaft in the future I Know I can get one because the 1350's are so popular.

The shaft completed weighs 26 lbs.

But in terms of torque, the 1350's will certainly withstand the abuse, better then the 7290's. The 1350's almost are twice as strong as 7290's.

Personally If I was you I would just save up and get a dynotech shaft, this is the best investment I have ever made.

Wanted to update this tired old thread with photos, since I got rid of facebook long time ago.
https://drive.google.com/open?id=0B2IjmQ5Cc2XGeGRNRmwxa2gzTmM