max speed driveshaft can handle in 83 Monte

[othtim]

Hi. I have an '83 Monte LS. I'm swapping in a new motor this week, and I'm planning on getting the engine dyno'd. I'm curious what the max speed the driveshaft can handle is. It is a TH350 transmission, stock '83 Monte LS driveshaft.

 

[81Regal]

It's not the speed that will kill a driveshaft or rear axle, it's the torque or ability to get traction. I would upgrade the U joints if you are concerned.

 

[jrm81bu]

It's not the speed that will kill a driveshaft or rear axle, it's the torque or ability to get traction. I would upgrade the U joints if you are concerned.

There is still a problem with critical spped, you spin it fast enough and it will come apart.

Hi. I have an '83 Monte LS. I'm swapping in a new motor this week, and I'm planning on getting the engine dyno'd. I'm curious what the max speed the driveshaft can handle is. It is a TH350 transmission, stock '83 Monte LS driveshaft.

Fwiw, I had my Malibu on a chassis dyno, ran up too 6000rpm in third. I had a th350 in it then so the driveshaft was also spinning 6000( minus convertor slippage. With the 2.41 gears and whatever tires I had at the time it ran up to 170 on the dyno.

 

[stomis]

It's not the speed that will kill a driveshaft or rear axle, it's the torque or ability to get traction. I would upgrade the U joints if you are concerned.

There is still a problem with critical spped, you spin it fast enough and it will come apart.

Hi. I have an '83 Monte LS. I'm swapping in a new motor this week, and I'm planning on getting the engine dyno'd. I'm curious what the max speed the driveshaft can handle is. It is a TH350 transmission, stock '83 Monte LS driveshaft.

Fwiw, I had my Malibu on a chassis dyno, ran up too 6000rpm in third. I had a th350 in it then so the driveshaft was also spinning 6000( minus convertor slippage. With the 2.41 gears and whatever tires I had at the time it ran up to 170 on the dyno.

Ding. Critical speed will kill a driveshaft regardless of torque or horsepower. Your really dont need to worry about it unless your running big gears and small tires though. For instance when I had my 86 Supra it had 4.30s and like 215 or 225 tires. That driveshaft was near its limits.

 

[larryo454]

So whats is Critical speed????? For a stock shaft.I run a MT 33x 21.5 with 5.13gears and a th350 with a healthy 461bbc that i buzzzzz to 7000rpms on a stock shaft.The U joint is the scary part for me being so small.

 

[jrm81bu]

So whats is Critical speed????? For a stock shaft.I run a MT 33x 21.5 with 5.13gears and a th350 with a healthy 461bbc that i buzzzzz to 7000rpms on a stock shaft.The U joint is the scary part for me being so small.

It will vary, there is no set speed. It just comes down to how well it's balanced. Basically as rpm icreases the weight of the shaft itself starts to make the shaft bend, it can bend far enough to pop out of the transmission(in cases where there isn't enough of the yoke going into the tailshaft), or just put enough stress on the yokes and/or joints that they fail.
Yes the stock u-joints are a weak point if you have a lot of power, but critical speed doesn't need a lot of power, just rpm, think of a 3.8 with overdrive going for top end on a long highway, with a 2004r it only needs to turn 4760rpm(not saying it will do it, just an example) to match you driveshaft speed off 7000.

There was a problem with the newer Chevy trucks that weren't using a 2 peice shaft, people were turning off the speed limiter with tuners and the driveshaft would come out of them.

edit-And what rear end are you using that you have 5.13 gears and still have a stock driveshaft?

 

[FE3X CLONE]

So whats is Critical speed????? For a stock shaft.I run a MT 33x 21.5 with 5.13gears and a th350 with a healthy 461bbc that i buzzzzz to 7000rpms on a stock shaft.The U joint is the scary part for me being so small.

I'd be worried about a lot more than critical speed with that setup and a stock driveshaft.

As mentioned, the critical speed of any driveshaft is dependent on many factors.

RPM
Material
Wall thickness
Diameter
Overall length

The issue with critical speed is that the driveshaft starts bending at this point. Have you ever used a die grinder with a long shaft chucked in it? Works fine up to a certain rpm but once you cross the critical speed, the shaft starts buzzing and shaking really badly and effectively ends up bending the shaft.
What happened is that the die grinder spun faster than what the shaft could take.
Now just passing through the critical speed for a moment isn't necessarily bad, you just don't want to spend a lot of time at it's critical speed where it can do a lot of damage.

I also believe there is a half critical speed that you have to watch out for as well. There are quite a few different resonances that you pass through in the rpm range. The key is to not "cruise" at a speed that one of these happen.

 

[othtim]

81Regal: yeah I meant the critical speed. I'm not really concerned about breakage w/ a mild 350

So anyone know what the critical speed is? I'm going to be dyno'ing this motor in third gear. I've got 2.23's on the rear and a TH350. I don't want the driveshaft to fly out on the dyno!! 🙁

 

[larryo454]

So whats is Critical speed????? For a stock shaft.I run a MT 33x 21.5 with 5.13gears and a th350 with a healthy 461bbc that i buzzzzz to 7000rpms on a stock shaft.The U joint is the scary part for me being so small.

It will vary, there is no set speed. It just comes down to how well it's balanced. Basically as rpm icreases the weight of the shaft itself starts to make the shaft bend, it can bend far enough to pop out of the transmission(in cases where there isn't enough of the yoke going into the tailshaft), or just put enough stress on the yokes and/or joints that they fail.
Yes the stock u-joints are a weak point if you have a lot of power, but critical speed doesn't need a lot of power, just rpm, think of a 3.8 with overdrive going for top end on a long highway, with a 2004r it only needs to turn 4760rpm(not saying it will do it, just an example) to match you driveshaft speed off 7000.

There was a problem with the newer Chevy trucks that weren't using a 2 peice shaft, people were turning off the speed limiter with tuners and the driveshaft would come out of them.

edit-And what rear end are you using that you have 5.13 gears and still have a stock driveshaft?

Hi i have built a backhalf car with ladder bars and running mopar 8 3/4 with rich men pro gears and i know that the pro gears are not good for the street but thats it. O and the axle is back about an 1" from stock location and u can't tell the diff.

 

[jrm81bu]

Hi i have built a backhalf car with ladder bars and running mopar 8 3/4 with rich men pro gears and i know that the pro gears are not good for the street but thats it. O and the axle is back about an 1" from stock location and u can't tell the diff.

That's why I asked, those gears aren't available for a stock rear, and anythime you go to bigger rear you usually have to shorten the driveshaft. If your axle is set back farther than stock, i guess that's why you can still use a stock one.
It's odd that you would still have a stock shaft though, after doing all that work, and finding the yokes to make it work.