hodgeee

Farmtruck, Hey thanks for the info, I got one of the HD aluminums coming in the mail, all parts needed included to my door for $517. My good friend lent me the money with a casual payback time, so I ordered. I talked to JIM, and he convinced me that the Aluminum is the only way to go since my driveshaft is 61 & 1/2" long. The critical speed for our stock driveshafts is 5200rpms, that is way low, since I run up to 5800rpms at 3rd all the time. He told me the critical speed of this driveshaft is over 10000rpms easy. He also stated since my driveshaft is over 61", the heavy duty steel driveshafts they have would still blow from critical speed, but the design of the aluminum and the weight of it, and its level of flexability, make it great for high rpms, that ours need due to length!

Should have it by weeks end!

skid

If the critical driveshaft speed of 5200RPM is correct then by my math it should have held up to at least 113mph with 4.10 rearend gears.

Personally, since you vehicle is lowered, I would check you driveshaft angles to be sure that they are correct. You may need to adjust you pinion angle.

Skid

FarmTruc

iTrader: (5)

Congrats, Hodgeee, you'll like that driveshaft, it's a lot of money for something we don't usually think about but it's well worth it, it cured all of my problems (except for the small vibe between 75-80).

skid, i'm sure they just rounded the critical speed number, maybe it's lower or higher, also, there might have been a weak spot in the original shaft,

on your angle:

measure the tailhousing, then measure the rear yoke , they should be close to parallel and pointing in the opposite direction. the joints should have at least 1.5degs of angle on both sides of the shaft, when comparing it to the housing and yoke. that allows the needle bearings to work properly.

good luck and keep us updated,

allen

skid

I was just trying to state that I do not believe that the critical speed was the issue related to the failure. Even if they rounded the critical speed some it wouldn't make that much difference. At 80 mph the driveshaft would have only been going ~3800 rpm. By hodgeee's post I would believe that his driveshaft would have reached those speeds many times (probably even at full throttle) with the original gears.

Also, I’m not saying that I don't believe buying a better driveshaft would be wise choice but rather that I would hate to see it happen again to his $517 driveshaft if there were another problem.

Skid

MyLS1Hauls

iTrader: (2)

He may be on to something here. The pinion angle and the trans angle need to be the same. U joints are not like CV (constant velocity) joints in that a u-joint acutally speeds up and slows down as it rotates. If the two angles are different, they are not doing this at the same time and can at the least, cause driveline vibrations. Its easy to check and you can get the angle meter from Sears I believe.

Also, just to reiterate, the driveshaft speed is not dependent on what gear the transmission is in. The driveshaft will spin the same speed at a given MPH regardless of whether the trans is in 1,2,3, or 4. Now the axle ratio directly affects the DS speed though. In 3rd gear(1:1) with the torque converter locked up, the driveshaft is spinning the same rpm as the engine is, so its an easy way to determine what rpm your driveshaft is spinning at withouth having to do any calculations

FarmTruc

iTrader: (5)

I don't think there's any other way to explain the breakage right in the middle of the shaft. Denny says they come across this problem all the time, someone changes to 4.10's and has overdrive, then there shaft breaks in the middle.

it is hard to tell where it broke, the joint could have broken, then twisted up and broke the shaft or something like that, but having it happen to me 3 times, and now it doesn't, i'm a denny's driveshaft customer for life.

btw, there's a shop in SA, TX, called Driveshafts Unlimited, they built all three of mine and they all broke. I said "critical speed" and they were clueless, and built me a fatter shaft, "cause it's stronger" jeeez, what a nightmare.

hodgeee

Ok, Well I was really doing about 100 when this thing blew! at about 5400rpms in 3rd. I was just posting quickly out of anger and wasn't thinking right. I absolutely believe it was the critical speed, but I also beleive from all the bad wheel hop I have put the truck through, that the driveshaft was slightly damaged. I started noticing a vibration at the track when the truck would get up to 70 mph, until I pasted the finish line. That only started after getting bad wheel hop a few times! Dannys also stated that it could have been a defect in the original pipping, or maybe a thinner spot than usual. To me that is not hard to beleive at all. But I think I damaged it with my high speed driving, and my bad wheel hop at the track!

I also beleive that Jim might have been just spewing out a round number out of his head too for the critical speed. Cause I had done 120 to 140 before on the freeway with no problems doing 5800rpms, and even with 3.73 gears I know that the driveshaft was spinning at 5800rpms in 3rd cause the 1 to 1 ratio!

hodgeee

Oh last thing, cause of your posts, I used my lazer leveler to compart the angle of the driveline. It is right on from front to back with about .78degrees of angle between the Pinion yoke position and the front yoke position, but they are both perfectly horizontal with one another.

Hey FarmTruck: Did you get a performance gain with the lighter driveshaft. I was suprized that the stock driveshaft is very light anwyas. But was also dissappointed at how thin the wall thickness of our stock driveshaft was, the sheetmetal of our body panels is thicker than this thing!

Ryan23silverado

iTrader: (1)

hey hodgee, you should have a two degree angle between the rear end and the tranny output shaft. When you rev higher, the rear end noses up toward the bed. It is when you are at crtical speeds that you want it to be level.
Right now when you floor it, your rear end is pulling up higher than your tranny -that is not what you want.
Just my .02
By the way...looks like you did a number on that driveshaft man glad nothing too major happened. I have heard of cars without d/s loops being poll volted into the air when their driveshaft lets loose. That aluminum d/s should be pretty sweet.

FarmTruc

iTrader: (5)

For your angle: when you floor it in first and get traction, do you hear or feel grinding noises, if not you should be ok, i did and had to put 4 deg shims under the leafs, that solved my grinding noise.
cool on your angle being ok.

I think i did get a performance gain on the shaft, it was a very hot and muggy day and i dropped 1 tenth after the new shaft was in, and that was on a hot day.

If you think yours was thin, check out a broken f-body aluminum one, it's a POS, lol, well just not that strong, a buddy has broken two of them (from power, during launches) and that thing is very thin and has paper in the middle of it, hahahha, i'm sure it serves some purpose, but that thing is very light.

keep us updated on the shaft, i'd definitely like to know.

allen