[15bhardwick]

About finishing the build on a 1967 GTO. Drag race only. Measured for a driveshaft with weight in car and car at ride height. 59.25" This is with stock location solid motor mounts, TH350 trans, 12 bolt rear w/4:56 gears. I expect the motor to cross at 6400-6500 RPM.

Strange would not make a driveshaft that long with that RPM range.
Precision Shaft Tech. will sell me a 4" aluminum for about the same price as the strange 3.5" chromoly.

Since the rear is up in the car and I had to shim the trans up for pinion and driveshaft angles I am out of clearance. Do I really need the 4" shaft? Stock driveshaft is already about hitting front driveshaft loop. No way I can get a 4" to fit without really cutting up the floor which I don't want to do. Any recommendations?

[Dave Polichena]

You should be fine with a 3.5" chromoly shaft.

[15bhardwick]

Strange wouldn't sell it due to the critical mass and the RPM. They said with that length it was only good for about 5000 RPM which I did not fully understand because we have always used a stock shaft at 6,000 for 30 years. But I don't want to spend 600$ on a driveshaft that comes apart after a few passes due to it not being to spec.

[tom s]

What engine are you going to run 4.56s with?Tom

[Sirrotica]

Some good info here about selecting driveshaft materials, if you haven't read it before:

https://www.dragzine.com/tech-storie...for-your-ride/

[15bhardwick]

Originally Posted by tom s

What engine are you going to run 4.56s with?Tom

455 ci 3450lb car with me in it.

[Mike Davis]

Have you thought about using a Carbon Fiber shaft?

[15bhardwick]

Originally Posted by Mike Davis

Have you thought about using a Carbon Fiber shaft?

Wasn't planning to have to shell out 1000$ on a driveshaft for a mid 10 second car. If its an absolute must I can. I would probably spend some time and do floor work and get the 4" aluminum to work before spending 400$ more. What RPMs and driveshafts are other A body guys using? Was using a stock 3" shaft at 6000 for years that never came apart. Just time to upgrade.

[Mike Davis]

I went the CF route for safety and damage control
Seen too many steel shafts break and tear everything up. I shift at 7200-7400 and cross the stripe about 6900. I ran a chrome moly 3.5" for about 10 years with solid U Joints that I would replace every 3 years.

[Mike Kasparian,Sr.]

Originally Posted by Mike Davis

I went the CF route for safety and damage control
Seen too many steel shafts break and tear everything up. I shift at 7200-7400 and cross the stripe about 6900. I ran a chrome moly 3.5" for about 10 years with solid U Joints that I would replace every 3 years.

Mike , what was the length on your gto driveshaft? I'm going CF for safety also , I broke a steel one probably 20 years ago and it was bad .

[bluegoat65]

Originally Posted by 15bhardwick

Wasn't planning to have to shell out 1000$ on a driveshaft for a mid 10 second car. If its an absolute must I can. I would probably spend some time and do floor work and get the 4" aluminum to work before spending 400$ more. What RPMs and driveshafts are other A body guys using? Was using a stock 3" shaft at 6000 for years that never came apart. Just time to upgrade.

Once you get the material sorted out and driveshaft in hand, for added safety to this is making sure the joints are parallel to each other. When they don t hum together is when the troubles start. A good reference is Rosslers site if you don t know this already. They have a tech sheet that shows how to lay it out. Do whats best for your safety. Peace.

[Dragncar]

Thinking about a CF shaft myself. I have seen cars about half destroyed. Breaking a steel one, it would sure put a problem in whatever race program you have going on. Might end it.
Finding floor pans for some of our old cars might be tough. Then you have all the labor.

[Mike Davis]

Mike, I am not sure of the length off the top of my head. I used PST (Precision Shaft Technologies). Made a huge difference in the car on the top end. I had 2 Chrome Moly shafts from 2 different makers, they both had a slight vibration about 130-135mph. After the CF it was super smooth. I drive it on the street as well with no issues. I can get a measurement over the weekend. All suspension is stock location with a TH400 trans and 12 Bolt so length was stock but will measure.

[Mike Davis]

Originally Posted by Dragncar

Thinking about a CF shaft myself. I have seen cars about half destroyed. Breaking a steel one, it would sure put a problem in whatever race program you have going on. Might end it.
Finding floor pans for some of our old cars might be tough. Then you have all the labor.

I watched a 67 GTO break a shaft on the top end and a piece punctured the tire. Slick blew out at 130mph and he went for a ride. CF would have turned to dust.
$1K is a very minor amount when you look at what is already invested.
At minimum it beats your floor pans up and you're lucky.
Usually it's the floor pans, exhaust system and transmission case that gets destroyed.
I bought 2 and keep one in the trailer for a spare.

[Mike Kasparian,Sr.]

Originally Posted by Mike Davis

Mike, I am not sure of the length off the top of my head. I used PST (Precision Shaft Technologies). Made a huge difference in the car on the top end. I had 2 Chrome Moly shafts from 2 different makers, they both had a slight vibration about 130-135mph. After the CF it was super smooth. I drive it on the street as well with no issues. I can get a measurement over the weekend. All suspension is stock location with a TH400 trans and 12 Bolt so length was stock but will measure.

Mike , the reason I asked was because I think 66 A body driveshafts are longer than 68-72 and was wondering what they said about critical speed with CF . I can go to there site for info . Thanks , good to know it's working for you .

[lust4speed]

I've run 4" driveshafts in two of my 67's. Crowded but did have a little room to spare. Both had 12 bolt rears and 400 transmissions.