Denied 1 Piece Driveshaft

[69 MOD]

Went to my driveshaft guy that I've used for years and he told me that I don't want a 1 piece shaft over 65" in length or it will not last under continuous driving at highway speeds.

My measurement came out to 71" total...
He said at that length I will end up with a vibration from the tube flex.

Kind of crushed my dreams of no carrier bearing.

I know many here have had 1 piece shafts for years, who's had trouble?

MOD

[nastety92]

I'm interested to see what others have to say. I'm in the same boat now with my Suburban.

Nick

[GR8-68]

Also interested in hearing input on this as I was planning to do a 1 piece also

[kwmech]

Doing a 1 piece in that length runs into several issues and variables. One being tube flex as you know. Another...... yeah it's possible if you increase tube diameter to at least 3.5''----4'' would be preferred. Issue being with a 4'' tube is clearance for one, and another the amount of weight hanging on the tail shaft bushing in the trans if it is a slip yoke. A turbo 350 or 700 the bushing wouldn't last long. A turbo 400 would last longer but eventually prematurely wear out, thus creating a leak. Fixed yoke on a 400 or manual. Manual may be ok since the majority of them have a bearing (still have to deal with the diameter). 400 fixed yoke, pretty much the same thing with even more weight due to the slip yoke assy in the driveline


What application? rear diff, trans, engine and HP

[wbc409]

I had a 68" driveshaft in a 71 for years without a problem. It was a 3" tube I believe. I think it was a take off from a Ford van. The truck had a 700r4 in it. The driveshaft shop also said they wouldn't do anything over 70-71 inches. To many problems.

[69 MOD]

'72 w/127" wheelbase
400 sbc 400hp/500tq
700r4 trans from a Vette with the Vette tailshaft housing (which increases the DS length to 71)
Stock 12 bolt w/3.73 in rear

[Andy4639]

I had the 1 piece installed when they did my 6.0 LS motor and 4L80E transmission. Almost 3 years ago and it's fine. My truck isn't on bags though. I drive it a lot 2 Hot Rod Power Tours and a lot of highway driving. I can't remember if it's 3.5" are 4".
No problems that I know of.

[darrellyates]

Originally Posted by 69 MOD

Went to my driveshaft guy that I've used for years and he told me that I don't want a 1 piece shaft over 65" in length or it will not last under continuous driving at highway speeds.

My measurement came out to 71" total...
He said at that length I will end up with a vibration from the tube flex.

Kind of crushed my dreams of no carrier bearing.

I know many here have had 1 piece shafts for years, who's had trouble?

MOD

Well, one piece driveshafts on new GM trucks are longer than required from 67-72. On the 5.3 I pulled from a short, 2004 Tahoe, the driveshaft was the correct length to use, however, it was larger in diameter than the original. I talked to my driveshaft guy, who used a formula to figure out what would and wouldn't work. It combined shaft speed, torque load, and diameter plus thickness of the driveshaft and gave a "terminal" speed where failure could occur. That is, a top recommended driveshaft rotation speed. The larger the diameter of the tube, the higher speed it could handle. We used a 3.5 on my new shorted truck. I would have to measure, as I don't remember the length. A good driveshaft guy can calculate this out for you. You may have to modify where the shaft goes thru the crossmember, but you can work this out if you want.

[Shinysideup]

Originally Posted by 69 MOD

'72 w/127" wheelbase
400 sbc 400hp/500tq
700r4 trans from a Vette with the Vette tailshaft housing (which increases the DS length to 71)
Stock 12 bolt w/3.73 in rear

The vette tailshaft splines are shorter engagement area because it doesnt need to move at all in vette setup. I have the same trans but swapped tailshafts and housing.

[harpo231]

My shaft guy came up with 4" singlewall alum for mine ,but it's a SWB
He said most important is pinion angle to avoid shaft bowing/vib/etc

[biketopia]

Originally Posted by 69 MOD

'72 w/127" wheelbase
400 sbc 400hp/500tq
700r4 trans from a Vette with the Vette tailshaft housing (which increases the DS length to 71)
Stock 12 bolt w/3.73 in rear

Originally Posted by Shinysideup

The vette tailshaft splines are shorter engagement area because it doesnt need to move at all in vette setup. I have the same trans but swapped tailshafts and housing.

There is a different yoke available for those trans. My brother has TH400 from a vette in his big block wagon and had to get the correct yoke so it would slide and work with the different spline set up in the vette as stated since it doesn't need to slide in the original application. .

[Andy4639]

I forgot to say my truck is a LWB.

[cknfrmr]

Originally Posted by GR8-68

Also interested in hearing input on this as I was planning to do a 1 piece also

I was gonna text u on this post Larry.

[jocko]

This is a good question, glad you posted. Personally, if my trusted driveline guy told me not to do it, I'd either go along, or get a 2nd opinion from another trusted driveline guy. (But, I REALLY trusted my driveline guy in SoCal when I last asked him about something). If #2 said no, then I'd probably really start to listen. While I've had 1 support bearing go out before, I've had no other issues with the spilt shafts. Is elimination of the support bearing the only reason for the desire to switch to a single shaft? If so, not sure it's worth it.

[KQQL IT]

Inland driveshaft balked at my 55'' 3.5 .083 wall dom tubing. Wanted a 4''.
Driveline service built it with out any problems yet.
Does a 1.67 60ft on a regular basis

[69 MOD]

Thanks for the input guys, I'm not new to driveline work and hearing other people confirm what I was told (and kind of knew) is good.

Originally Posted by jocko

This is a good question, glad you posted. Personally, if my trusted driveline guy told me not to do it, I'd either go along, or get a 2nd opinion from another trusted driveline guy. (But, I REALLY trusted my driveline guy in SoCal when I last asked him about something). If #2 said no, then I'd probably really start to listen. While I've had 1 support bearing go out before, I've had no other issues with the spilt shafts. Is elimination of the support bearing the only reason for the desire to switch to a single shaft? If so, not sure it's worth it.

I trust my guy completely, he's built me driveshafts for jeeps, cars, trucks etc. over the last 20 years and I have no reason at all to doubt his word.

That was one reason because of bearing failure, but he showed me a different style carrier that I think will be the trick.
The bearing is pressed into a sleeve instead of the rubber, he said it's the best thing out there right now.

[Coley]

He is correct regarding the 'whip' associated with driveshaft length.
In 'engineering circles', this is regarded as 'critical speeds' relative to rotation and is dealt with by changing the diameter or stiffness of the shaft.
Noting that the smaller the diameter the more likely the unit is to 'whip' at high speed....so as you increase the diameter you lessen or remove the 'whip' in the driveshaft.
Your shop should be able to use past examples of trucks or vehicles with that span of mounting and use a similar sized driveshaft to overcome this....however you probably will be getting/making a new driveshaft to accomplish this.

All good
Coley

[demian5]

Next support bearing break, i'm gonna invest in the upgraded solid one for $100.

Thinking about this, how long is the driveshaft on a 1992-1999 suburban 2wd? I know the one in mine was hella long (but fiberglass with aluminum ends).

[69 MOD]

Those weren't 2 piece?
I have a hart time believing they were 1 piece in that length...

[brown7373]

What is the disadvantage of the 2 piece with carrier bearing? I did have to replace my carrier, but at 45 years old, it didn't really bother me.

[MARKDTN]

Originally Posted by biketopia

There is a different yoke available for those trans. My brother has TH400 from a vette in his big block wagon and had to get the correct yoke so it would slide and work with the different spline set up in the vette as stated since it doesn't need to slide in the original application. .

Different animal. Corvette yokes have bolt on u-joints like the rear end because there is very little movement in the short driveshaft since the carrier is fixed to the frame and so you couldn't physically get the driveshaft in the car without dropping that out which requires taking the suspension partially apart. The actual splines on a 'Vette transmission are the same as a "regular" TH350, TH400, etc. so a "regular" yoke works fine.

[biketopia]

Originally Posted by MARKDTN

Different animal. Corvette yokes have bolt on u-joints like the rear end because there is very little movement in the short driveshaft since the carrier is fixed to the frame and so you couldn't physically get the driveshaft in the car without dropping that out which requires taking the suspension partially apart. The actual splines on a 'Vette transmission are the same as a "regular" TH350, TH400, etc. so a "regular" yoke works fine.

Not on the one we have, the splines stop only a few inches down so a th400 yoke out of an other car doesn't slide in but two inches or so. The yoke my brother car is smooth the first few inches and obviously oversized, then the splines start about halfway the inside of the yoke.