[Alwhite00]

Uphill out of tranny means diff pointing down makes it exactly same.

Uphill out of the trans you have to add the uphill angle to the driveline angle, downhill out of the trans you subtract the angle. Big difference.

 

[O'Man]

The thing about the driveline angle threads is the confusion between “up” and “down”.

This indeed is an issue with many of the "explanations" of setting / adjusting driveline angles. I recently went thru this adjustment exercise. After looking at various "how to" directions I had a discussion with a fellow who could clearly describe the process. One key aspect of his explanation was defining what is "up" and what is "down" in terms of the components in the driveline.

A lot of people who describe this process fail to define the critical elements of this activity. They just launch into a "do this" dialog. Ya gotta know where you are starting from before you can get to your destination! Some descriptions I read made me wonder if the author could clearly write down instructions for blowing your nose!!! It is one thing to know how to do a given task. It is something else to use the written word to accurately describe performing said task.

 

[chaze]

Pugsy linked a PDF in post 14 that tells you all you need to know in no uncertain terms. IT IS SO EASY !!!!

You can lead a horse to water.....................

 

[Alwhite00]

Pugsy linked a PDF in post 14 that tells you all you need to know in no uncertain terms. IT IS SO EASY !!!!

You can lead a horse to water.....................

I hear ya' 🙄

 

[Kopfjaeger]

Ok, driveshaft angle is 1.2*. (Sloping down from transmission)
engine/trans is at 2.7*
pinion yoke is 2.1* (yoke pointing up)
my front operating angle is 1.5*
rear operation angle is 0.9*

Operating angles are with in 1* and no more than 3*

Looks like I’m golden. New MW 3.5 chromoly shaft in route.

Joe

 

[Kopfjaeger]

56.75”, 3.5 chromoly, with 1350 U-joints, and forged Sonnax slip yoke.
Joe

 

[123pugsy]

Sweet.

 

[Lew540]

Here is my story and it might help others in the long run. First, I have a 1965 Chevelle with a Turbo 400. The issue there is they never came with the Turbo 400 so you have to drill holes in the frame. The issue here is that where you have to drill them (the frame slopes down from the frame perch area) lowers the rear of the transmission 1/2 and inch so you need to add spacer washer to mimic the height of say a 1967 Chevelle which has the holes/perch for the Turbo 400. The guy above is correct the engines have a 2 to 4 degree slop down so say for every 12-15 inches in length the slope drops and inch or so. So I put a Gear Vendors overdrive in this lengthens the whole drivetrain another 12+ inches so what happens is my tail shaft was now like an inch lower than it was because of the mentioned slope. So what was once (tail shaft) say 1/2 inch above the rear pinion yoke I was now 1/2 inch below it. This caused drivetrain vibrations above say 3,000 rpm. I raised it up an inch and the problem went away. What happened was by going below the pinion created a higher driveline angle for the U Joint to handle that is why I see on some cars a CV joint which has much higher operating angles. Make sure your car is on flat ground measure the U joint from the ground on the rear end and then the tail shaft and just make sure the transmission tail shaft U-joint is above the pinion U-joint. The Spicer U-Joint catalog has an operating angle chart and 3 degrees is outer limit. This has nothing to do with the slope of the drive shaft by my introducing the GV overdrive I created an additional change of direction angle by going too low.

 

[427L88]

After years of looking at asses, my eyes confirm BADD64's observation about the rear angle being "flatter" than 3 in pitch. So I think you got that part right Joe, and you can dial in the rear at will.

As far as critical speed, I;d defer to a shaft expert. Our shafts are friggin long, and yours is even LONGER! I think that means you need to bump up the dia. I'm fine with a 3" Denny's that sees 3000 rpms all the time. ( only ought have bumped yokes out to 1330 or 1350 is all)

EDIT: PS I missed your last few posts. Yeah man, you ought be golden!

 

[Kopfjaeger]

Yeah Gene, at nearly 57” that is a long-ass driveshaft! The member I purchased the LGT700 from, raced his 67. He had a 4” Denny’s in the car with an extended pinion yoke, which was .75 longer, which shortened his driveshaft length. When, I was building the rear, I contacted Mark Williams and told him I needed the .75 longer yoke. He talked me out of it, so now I was .75 short (driveshaft). The 4“ is a beast!! Heavy as hell and didn’t play nice with my driveshaft loop.
I’m sure I can sell the shaft, since I can’t use it. She has 1350 joints and I imagine the driveshaft ends are forged, as his 496 was a torque best and loved to mangle drivelines. Even though I paid for the 4” as part of the package, it still was a good deal. LGT700, McLeod RXT dual clutch, forged externally balanced flywheel, and the shaft.
I’ll be able to sell the shaft and flywheel all day long.

Joe

 

[RifRaf]

My drive shaft will need to be 56.75” long. I was planning on a 3.5” diameter driveshaft but I’m not sure if that’s going to be enough with 3.73 gears, a .80 5th gear, and 26.65 diameter rear tires.
Thoughts?

I'm a little late to this discussion, but just wanted to reply to the OP's original question.
With your current set-up shown above, your top "safe" speed would be about 119 mph. At this speed, your driveshaft will be spinning at about 5600 rpm (80% critical speed of your driveshaft). Even though your overdrive trans will drop the engine rpm at this speed when in 5th gear, the driveshaft's is still spinning faster than the engine.

80% Critical Speed

1/2 Critical Speed
At about 74 mph, the driveshaft will be spinning at "half critical speed". This is not dangerous is by any means... but if you cruise at a steady speed of 74 mph, you may notice a vibration.

 

[Kopfjaeger]

Rif Raf, thanks for posting all of this info. Where is this site? So, my 3.5 may not be enough at 5000+ rpm in 5th gear. That is disappointing for the times I plan on being at the track. Perhaps I’ll hang onto the 4 inch shaft.

So, they list 80% of critical speed, why? Does the driveshaft begin to become unstable above 80%. And grenade at 100? The tech at Mark Williams advised me not to exceed 5600 RPM while in 4 th gear. According to the 80%, it’s far lower than that.

Joe

 

[RifRaf]

Where is this site?

Gearing Calculator | RPM and Tire Diameter to km/h - mph with Shift Tracer

www.blocklayer.com

So, my 3.5 may not be enough at 5000+ rpm in 5th gear.

As previously mentioned... the overdrive trans slows down the rpm's of your engine in 5th gear, but does not slow down the driveshaft's rpm's (since the driveshaft's rpm's are only based on differential ratio, rear tire diameter, and vehicle speed). If your engine was spinning at 5000 rpm in 5th gear (.80 overdrive), your vehicle speed would be about 133 mph, AND the driveshaft will be spinning at 6250 rpm. At 6250 rpm's, your driveshaft would be spinning at about 90% it's critical speed.

So, they list 80% of critical speed, why?

Short answer... liability.
The chart I posted lists 80% critical speed because that is the recommended "safe" rpm that the driveshaft should be spinning... based on it's build specs. Mark Williams seems to be on the same page as the chart I posted.
So, how much can you go over the 80% critical speed rpm before your driveshaft explodes... I do not know (and would never take a chance to test the limits). I guess that is why driveshaft manufacturers express a safe operating range for their products.