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View Full Version : LS swap Dakota timeslip February 25 2016



casias
02-27-2016, 11:51 AM
In my previous post, I had predicted this truck would run "12.5 at 110 or so". I received a lot of flack for this prediction, so I went to the track to back up my claim. As predicted, this truck has an abysmal 60 foot time on street tires, and with the nose about 1" higher because the LS engine is lighter, it starts to buffet really bad at about 90 mph.

Coming straight in off of the highway, to the staging lanes, I didn't even shut off the truck. Ran 13.35/108.6 (2.27 60 ft) and 12.963/110.09 (2.26 60 ft), then 12.76/109.99 (2.10 60 ft) with each run driving right back to the lanes. With caltracs and slicks, this would probably be closer to 12.30, which would be better than I predicted. With gearing, it might even see 12.20 or less.

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1237_zpstluwlplz.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1237_zpstluwlplz.jpg.html)


The track prep is excellent, and it was about 60 degrees, but wheel-spin was killing me early on.

Fourth run, I aired down the tires to 20 psi, and had roughly the same 60 ft at 2.15. Right at the lights, there was a brief vibration, BAM, and the sound of my driveshaft following me down the track.

Looks like I am going to need a different driveshaft design.

Broken front flange, damaged exhaust.

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1247_zpsfu4qngm5.png (http://s1261.photobucket.com/user/casias2/media/IMG_1247_zpsfu4qngm5.png.html)

What was left of the driveshaft.

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1250_zps51clgwd0.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1250_zps51clgwd0.jpg.html)

Going home on a trailer.

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1249_zpsqz8tfhgu.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1249_zpsqz8tfhgu.jpg.html)


Mods.

6.0 LY6 with 200k miles.
LS9 cam.
Toilet flange and pvc intake
Cast exhaust manifolds, 2 1/2 inch crush-bend dual exhaust
Tuning by HP Tuners.

SB440R/T
02-27-2016, 02:29 PM
Nice runs, sorry for the bad luck. Throw some slicks on that thing and let it go. I can see a low 12 in that.

Adobedude
02-27-2016, 02:35 PM
I concur, nice runs, on street tires no less. Sorry about the broken parts.

casias
02-27-2016, 03:41 PM
As long as that driveshaft is (107"? thereabouts), I have always been told it was on the fringe of coming apart, even with 5 inch diameter. So I have always planned on a two-piece.

But I want to finish the Durango, so I am just going to have another made, then plan the two-piece later.

Edit: 77" not 107". Memory is not great after 3 years, but I just measured it.

SB440R/T
02-27-2016, 03:53 PM
As long as that driveshaft is (107"? thereabouts), I have always been told it was on the fringe of coming apart, even with 5 inch diameter. So I have always planned on a two-piece.

But I want to finish the Durango, so I am just going to have another made, then plan the two-piece later.

Was it a stock piece from something else or custom made for that application? My understanding is that any slight imbalance on those things will make them into straws and bend in pieces.

casias
02-27-2016, 04:15 PM
Was it a stock piece from something else or custom made for that application? My understanding is that any slight imbalance on those things will make them into straws and bend in pieces.

Custom. It is about 7 inches longer than the club cab R/T driveshaft, which is already 4.5 inches in diameter and wrapped in fiber to cut down resonance. I had a couple of companies offer various solutions, but the price was really up there. Something like $1000 to $1100. I had this one made locally for $450. It held up for 3 years of hard street driving, but never saw over 100 mph (automatic jail in Florida for 100+ MPH on a public road). I guess 110 was that much too much.

blackknight
02-27-2016, 04:23 PM
Nice runs ! I don't think I've ever heard of anyone ever tearing a driveline apart on one of these things , but now that you say it was a custom piece and longer , that might be the culprit !

Adobedude
02-27-2016, 04:41 PM
:biggthumpup:

Sick 660r
02-27-2016, 04:45 PM
You're lucky you had the exhaust under there! Are you sure it wasn't the yoke that failed first? Can you give specs? Driveshaft OD/ID, wall thickness, length between welds, length between u joint centers and the u joint size?

Are you sure your pinion angles were correct? Any wheel hop?

casias
02-27-2016, 05:06 PM
You're lucky you had the exhaust under there! Are you sure it wasn't the yoke that failed first? Can you give specs? Driveshaft OD/ID, wall thickness, length between welds, length between u joint centers and the u joint size?

Are you sure your pinion angles were correct? Any wheel hop?

Pinion angles are within 3 degrees. Rough length is 77" +- 1/2 inch center u-joint to center u-joint (Earlier statement that it was 107" was poor memory). Once I get it up on the lift, I can get that actual measurements.

The tube was 5" with ends turned down to 4 inches, aluminum ends, and 0.083 wall thickness. Dakota size U-joints.

Because it happened at high speed, I think the driveshaft reached the critical speed. So my options are, have another one made and keep it below 90 for now, have a carbon fiber-wrapped aluminum driveshaft made.

Sick 660r
02-27-2016, 05:18 PM
The weld yoke seems short. A longer one would have helped a little. The thickness is kinda thin which would help with critical speed but hurt torsional strength.

If that's a cheap cast yoke then a little vibration may have caused it to fail before the ds faile. Either way, it's still a long DS.

http://pstds.com/product-category/all-carbon-fiber/

Sick 660r
02-27-2016, 05:20 PM
A DS loop would be high on my to do list.

Sick 660r
02-27-2016, 05:44 PM
What's your gear ratios and max rpm? The 0.083" wall is helping a lot.

casias
02-27-2016, 09:38 PM
What's your gear ratios and max rpm? The 0.083" wall is helping a lot.

Dunno. Never bothered to look into it. Maybe now I will.

Patrick
02-27-2016, 11:31 PM
The weld yoke seems short. A longer one would have helped a little. The thickness is kinda thin which would help with critical speed but hurt torsional strength.

If that's a cheap cast yoke then a little vibration may have caused it to fail before the ds faile. Either way, it's still a long DS.

That tube yoke is pretty conventional. The one you're running is not too common.

The thin wall thickness doesn't help enough with critical speed to even matter over the gain in strength with a thicker wall tube.

Looks like a critical speed failure to me looking at the pictures, as that is not a typical fracture of the slip yoke. Looks like the top half of the slip yoke lug ear got taken out when the tube unraveled. The balance weights being that close to the circle welds don't help either.

If it were my truck I'd go two piece at that length. And you can get parts to make a steel shaft / aluminum shaft to shed a little weight.

Sick 660r
02-28-2016, 12:42 AM
That tube yoke is pretty conventional. The one you're running is not too common.

The thin wall thickness doesn't help enough with critical speed to even matter over the gain in strength with a thicker wall tube.

Looks like a critical speed failure to me looking at the pictures, as that is not a typical fracture of the slip yoke. Looks like the top half of the slip yoke lug ear got taken out when the tube unraveled. The balance weights being that close to the circle welds don't help either.

If it were my truck I'd go two piece at that length. And you can get parts to make a steel shaft / aluminum shaft to shed a little weight.

I was just about to tell him to send you a pm lol

Sick 660r
02-28-2016, 12:51 AM
Patrick, how is critical speed affected by the smaller diameter ends? Also, why do the weights being close to the welds matter? Is it a welding/heat issue?

casias
02-28-2016, 11:42 AM
As long as that driveshaft is, I have always been told it was on the fringe of coming apart, even with 5 inch diameter. So I have always planned on a two-piece.




It held up for 3 years of hard street driving, but never saw over 100 mph (automatic jail in Florida for 100+ MPH on a public road). I guess 110 was that much too much.





Because it happened at high speed, I think the driveshaft reached the critical speed. So my options are, have another one made and keep it below 90 for now, have a carbon fiber-wrapped aluminum driveshaft made.

Thanks Patrick. I don't know you, but you pretty much confirmed what I have known all this time. Suppose you could loan me a few bucks for the work I need done. I am PM my paypal to you. :).

Patrick
02-28-2016, 10:34 PM
I sense sarcasm.

casias
02-28-2016, 10:58 PM
I sense sarcasm.

Sorry. Not meaning that at all. I tend to come off that way online.

casias
04-12-2016, 11:51 AM
Update on the driveshaft.

After contacting a local company, paying for a new 2-piece driveshaft which was supposed to have "All new, with forged Spicer U-joints", I went to find a reworked Cherokee shaft that was total garbage.The price had gone up from "about $850" to $950, and the tube diameter went from 3.5 inch which was agreed upon to 3 inch. Here are some pictures. I left without it. Which put me about 2 weeks behind.

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1312_zps19wh5dh7.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1312_zps19wh5dh7.jpg.html)


http://i1261.photobucket.com/albums/ii596/casias2/IMG_1313_zpsq1fn489b.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1313_zpsq1fn489b.jpg.html)


http://i1261.photobucket.com/albums/ii596/casias2/IMG_1311_zpsb4j1qfnt.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1311_zpsb4j1qfnt.jpg.html)




So I called a shop that was recommended to me by a few people. Driveshaft Specialists in San Antonio. 1-866-455-6622.

After a discussion with Brent, sent some measurements, and had them build the shaft. They supplied a 1410 yoke for my 6l90 transmission, 1350 u-joints (Spicer forged), and a 1350 pinion yoke for the 9.25 axle. Cost.....$850 shipped. They did really nice work and built a shaft that would last a lifetime.




http://i1261.photobucket.com/albums/ii596/casias2/IMG_1422_zpstzoe6qja.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1422_zpstzoe6qja.jpg.html)

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1423_zps0g5north.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1423_zps0g5north.jpg.html)

http://i1261.photobucket.com/albums/ii596/casias2/IMG_1424_zpsdznoszsr.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1424_zpsdznoszsr.jpg.html)




I reinforced the original crossmember with 1 inch 0.120 DOM, and put in some wood blocks for alignment. Using the Tremec driveline calculator, angles came in perfect. So I put in a few drywall screws and called it done (that's a joke).




http://i1261.photobucket.com/albums/ii596/casias2/IMG_1432_zpszd9qib2x.jpg (http://s1261.photobucket.com/user/casias2/media/IMG_1432_zpszd9qib2x.jpg.html)





Actually, I ran out of time, and didn't take any good pictures before I took it off of the lift. But I did take video. Also, check out the video that shows what happens to a long driveshaft at critical speed. It shows it better than I could explain.



Results: Much less "uneasiness" in the drivetrain now. I wouldn't consider a long driveshaft like that again. I will take the weight penalty of the 2-piece steel for driveability.




https://www.youtube.com/watch?v=WJMLzAe2K0s&feature=youtu.be




Driveshaft surpassing critical speed




https://www.youtube.com/watch?v=3gRY-kdpmeA





and driveshaft with severe angle misalignment




https://www.youtube.com/watch?v=gmV4qwLfOMY