3.0 or 3.5 Driveshaft?

I am ordering an aluminum DS and have a choice between 3.0 or 3.5". The toatl length will be about 49".
Should I go with the 3.5"?
1330 ujoints btw

I would probably go with the 3.5 if you have room and you're not going to spin it too fast, such as with an OD tranny and a high (numerically) rear end ratio.

I am running a 3.7 rearand a c4. is that to fast? I thought increased diameter helped
[addsig]

Nah, you'd be fine. If you have a 4:11 or higher and an OD you can really spin the shaft fast at highway speeds, which can cause vibration issues in some instances.

*I am running a 3.7 rearand a c4. is that to fast? I thought increased diameter helped*

This all depends on tire size

[addsig]

My tire size is 26"
If I did want to go with 4.11 & an AOD, the 3" is better?

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2007-03-23 14:02, jetnoise wrote:
My tire size is 26"
If I did want to go with 4.11 & an AOD, the 3" is better?
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

The bigger shaft will only cause a problem if you run at sustained high speeds with the setup you mentioned above. If you're just street driving or drag racing, I would go for it.

The 3.5" tube will be stronger, should be lighter and will spin faster without vibration.
Go for the 3.5inch shaft

<font size=-1>[ This Message was edited by: ALAN6773 on 3/24/07 6:55am ]</font>

A larger diameter shaft has a higher critical speed than a smaller diameter shaft.
[addsig]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2007-03-23 17:51, gork1rogues wrote:
A larger diameter shaft has a higher critical speed than a smaller diameter shaft.

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Critical speed is determined by the length. At 49"x3.5" you'll be fine. I have a 2003 Marauder that has a 3.5" 57-58" long driveshaft. We (Marauder owners, went through this issue extensively due to the long length of the shaft.) Good up to 120 MPH with 4:10 gears in .70 OD.

I am eventually going to put 4.56 gears in, so I bought a 2000-2001 police MMX driveshaft. Same 3.5" but made from metal matrix composite, a fancy word for better alloy.

To back all this up I chatted back and forth with a guy who used to make driveshats for "Dana". He sent me some proprietary info with charts, numbers, and a spreadsheet to calculate critical speed. You can probably find one on the net somewhere.

Good luck
[addsig]