Oops, sorry I didn't answer your post.

1 Used Viper Output Shaft - $200.00 from D&D
2 Reluctor Snap Rings for Viper Shaft - $15 D&D
1 Viper Output Seal -Viper - $10 D&D
1 Extension Bushing - Viper - $10 D&D
1 Chrysler Spicer 30 spline Trans yoke - $85 Dennys Driveshafts

Machine work on Extension Housing - 2 Hrs
Abrasive cut 3/4" off Viper Shaft - 2 Minutes
Bore old GM Reluctor for snug press fit over Viper splines - 10 Min

I've read that this upgrade weakens the tail housing but I honestly looked at the wall thicknesses before we started machining and we were left with plenty of casting wall. As a matter of fact there are other areas of the casting that are much thinner than anything we ended up with after machining.

I haven't driven the car yet. Still sorting out some false knock at idle and my rebuilt street twin has some issues with the clutch fork rubbing something at full travel. Mcloed said the rebuild would be plug & play but something's screwed someplace

That being said I came away feeling pretty darned confident in the T56 upgrade. I really didn't find any serious downside or compromises. And hey, just as luck would have it, My driveshaft length ended up perfect. I've got about 1" of travel "in" when the chassis is at a normal height. That should be plenty for those 5K clutch dumps!

 

For me, the machine work, disassembly and reassembly didn't cost a blasted thing. I did the disassembly and reassembly myself. A good friend did the machine work cause I had burnt him some Eproms for his BB Chevelle SS and I am currently tuning his blown 455 Olds. I've got way more hours in the tuning so he helped me out. Thats why I told you the approximate machine time with setup included. I would think that any small machine shop with a decent Bridgeport would be able to take care of you for under $75 per hour.

Sorry I can't give you firm numbers I'm a DIY'er.

Hope I've helped.

Steve

 

SABLT194,

Thanks much for your detailed info! I just called D&D and they have a few used Viper mainshafts on the shelf, so I've got one on the way (along with the bushing and seal).

I think I'm just going to bore out the F-body reluctor for a press fit over the shaft and use a couple of small setscrews to secure it. I see no reason why this would upset the VR sensor as the holes would effectively be out of the "reach" (the sensor effectively only reads the high portion of the teeth). Only one way to be sure, though

I need a larger driveshaft anyways (as the stocker is much too small to use with the 4.56s I want to install), so I'll just source the whole thing from Denny's and I should be good to go. Is the 30-spline yoke specific to the Viper, or is it a standard Chrysler part?

 

my understanding is that the Viper 30-spline design is a common Chrylser spec. It's based on a 31-spline design with one spline missing for air/oil flow. I belive the Ford Cobra-R and 2003 Cobra's 31-spline design is the same spec but without the missing spline.

But I'm not sure, ask D&D, they do all of them and should know.

 

Don't be surprised if you broke more than one thing. It happens all of the time, One thing breaks and causes another failure somewhere else. I took out my output shaft and a spider gear in the rear, all at one time.

Steve

 

Unfortunately it doesn't always work like that. Strange but true!

Steve

 

For those claiming that the '03 Cobra T56 has a 30- or 31-spline output - where are you getting your info? I got a chance to check out a Cobra T56 at work, and it had a 27-spline output (much to my dismay). However, I don't know if this is a production-level part, or something from a pre-production run (we've had it around for a while).

Just curious - not trying to say that anyone's wrong.

 

I don't know if I said it was in the Cobra or not but I believe I saw the ford T56 info on the Forte or D&D web page. Interesting that you found a 27 splin'er in that Cobra. Those guys will be snapping them too then.

For anyone that's interested,

I have run mine at the track and so far so good. 5K launch and nothing came loose. The only problem I'm having is that the Viper seal likes to squeal on the transmission yoke. When I first heard it I thought i thought were going very bad with my trany. But a lil investigation proved it was just the seal. It'l break in and quiet down after while.

Steve

 

They'll be snapping the inferior 10(?) spline inputs too; those grooves cut farther into the input, reducing the effective diameter, and that will be the weaker of 2 links. Expect a glut of 03 Cobra guys to be running a higher # of input splines.

 

Yikes! No ET Streets for them!

Anybody have any feedback on the 300M shafts yet?

Steve

 

Anyone happen to know the diameter of the Viper speedo gear? It looks like my current F-body speedo gear got dinged up pretty bad when the mainshaft broke (and then abused some more during disassembly), and I'd rather just install the Viper part and correct for the tooth count difference in LT1_edit - assuming that this part is the same diameter.

After finally getting the trans apart, I found that the mainshaft was broken along the groove for the front-most speed gear snapring. Further inspection showed what a co-worker refered to as a "discontinunity" in the cross-section of the shaft; to my eyes, it looked like a knothole in a piece of wood The splines were twisted along the entire length of this section of shaft, and many cracks were present along the very last snapring groove in the shaft (this one is unused in my application). Had the shaft not failed due to the irregularity, it probably would have broken a couple inches towards the back if given enough time. I'll get some pics to clarify this explanation sometime this week.

SABLT194, I just wanted to confirm that 3/4" is the right amount to trim off the Viper mainshaft. Looking at the Viper and F-body parts, it appears that there's about a 2" difference, but I could see where it wouldn't be necessary to trim off that much - but I don't have a 30-spline yoke in front of me yet.

 

Failure at the snap ring groove makes sense if the shaft is loaded well past it's design loads, as evidenced by twisted splines.

The "knothole" migh not be what it first appears. As the shaft cracks, or starts to fail near the outside diameter, the remaining amount of shaft is trying to resist the loads but over a smaller and smaller area. The final "bang" can twist and look like it pulled out a piece of the of the shaft. I'd really like to see pictures.

Were the twisted splines those which the driveshaft front yoke engages? Was the twist forward of where the yoke fits? Twisted splines indicate overload which is best cured with larger and/or finer splines: just increasing material untimate strength isn't as effective, especially if the shaft becomes stronger than the yoke.

IMO, manufacturers of transmissions tend to increase size rather than change materials when they need more strength. Material cost isn't really the reason, nor is machining cost; you just get more economical strength from size than from material.

Exceptions are when you can't increase size easily, like for instanace inside a planetary gearset. Here you could increase the number of planet gears, or as in the case of the THM 425 (60's front drive version of the THM 400) when used on the GMC motorhome, by changing material and using straight-cut teeth vs. helical.

 

I'll get pics of it, but it certainly doesn't appear to be what you describe. It looks very much like a material defect.

The rest of the shaft definitely shows signs of excessive loading

You just described it in a nutshell. The spline twist starts at the leading edge of the driveshaft yoke, and gets progressively worse as they progress towards the failure site.

After seeing the damage that wasn't directly related to the failure, I feel pretty good about going down the path of the 30-spline Viper part. Had the output shaft not failed due to what I believe was a material defect, it was on its way out anyways - and that was after only 300 miles of street use and 2 passes at the strip.

 

Eric,

I trimmed 3/4" off of mine but I think 1/2" is probably a better number to use to keep your driveshaft length the same.

also,

When you bore the tail housing out you may have to recut the oil return groove with a 1/2" endmill because the oversize bore for the bushing pretty much cuts away the original groove. You'll see what I mean when you get it apart.

also,

Pay attention to the orientation of oiling hole in the bushing during disassembly and installation of the new bushing.

Mine's still working good after about 30 passes so I'm still crossing my fingers.

Good luck

Steve

 

Thanks for the info, Steve. I saw that I'll have to open up the oil groove in the housing, but I didn't quite think about lining up the hole in the bushing with that groove - I owe you a beer for that piece of advice