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1480 u-joint 6000rpm problem

1K views 7 replies 4 participants last post by  cerial 
#1 · (Edited)
I have been piecing together a hot rod for a few years now and am having a bit of a problem that hopefully I can get some advise on.
The car is going to be a tube built monocoque chassis in a mid engine rear wheel drive setup.
Instead of using the traditional(and costly) transverse transmission I have decided to go more low tech and heavier setup which gives me more ratios and cheaper easier to find parts.

The drive line goes like this,
76 500 Cadillac to a sm465, to a propshaft, to a .75/1 reverse case, to 2 prop shafts, to a 3 speed aux transmission, to a 271 transfer case 1/1 drive chain(just the chain and gears), to the pinion of a 14 bolt 4.56 dwr axle turning four 216/70/r16 tires.

If your confused I would be also. I will post some pictures later on this afternoon. I don't have the transfer case chain/gears or smaller tires and just running rollers at this point.

Now all this accounts for 12 speeds and a drive train that can handle engine torque of 800ft/lbs without any need to upgrade anything or buy any specialty parts(t56 guys you know what I mean). While I have 12 speeds I don't see using more then 8.

The sm465 ratios are 6.56(not used), 3.58(Warm up gear), 1.7, and 1.0. The 3 speed aux trans ratios are 1.52,1, .72.

If I leave the 3 speed in low(1.52) and start off in 3rd gear in the sm465 then pull back into 4th I will only need to shift once between 0 and 70 without the engine going over 4500 rpm.

The ratios in this setup are 2.58, 1.54, 1.0, .72. It should provide brisk acceleration with the ablity to drop down into the 2 other gears and cruise once up to 70.




To paint a bit better picture of the layout lets look the single shift 0-70 I am trying to achieve and you will see my issue.
With the engine putting out around 500 ft/lbs with the transmission in 3rd gear at 40mph the 1st prop shaft is turning at 4500 with a torque load of only 850/lbs. Then there is the .75/1 reverser case that reduces the torque by 25% (638lbs)which speeds the drive shaft to a brief 6000rpm before the shift. This then goes through 2 prop shafts to the 3 speed which is in low where the torque is multiplied by 1.52 to 969lbs. This torque is transmitted through the 271 transfer case chain and gears(rated at around 10,000lbs) and is the only part of the drive line that the suspension influences. The chain transmits torque to the pinion which then multiplies it by 4.56 putting 4418 lbs into the shafts(which are cheap and easy to replace), then to the 216/70/r16 tires.

Now while in 3rd gear the 6000 rpm speed is brief when in 4th gear at say 65 the 2 drive shafts between the reverse case and aux trans will be spinning at a constant 5506rpm with a torque load of just 375lbs and increase to a rpm of 6000 with the load remaining about the same meager 375lbs.



In this scene I believe that I can use 1480 u joints(rated at 1,100 continuous) in the 1st prop shaft which is within the max 5000 rpm and torque ratings that are good for 3rd and 4th shift.

Later on I plan on making 650lbs with the engine and that translates to 1105lbs to the 1st shaft :) and 828 lbs to the two faster spinning prop shafts.

A 1310 u-joint has a continuous of 400lbs and a short of 800lbs with a max of 6,000 rpm.
1410 and 1480 are rated for 5000rpm.

I will be at a continuous of around 800lbs in the two faster spinning shafts with who knows what kind of shock loads I may get along the way. Now the 1410 has a continuous of 820lbs. But, it is rated the same rpm as a 1480. It makes sense to go with the 1480 then. But, the added 1000 rpm above the rating has me a bit concerned about the life. It is important to mention that these two shafts have NO angularity. Not a easy feat to achieve longer more reliable u-joint life(hopefully).



Sorry about the book above. But, I had to give a bit of background.
Pictures of the pile of parts that I have been arranging for the last 2 months trying to find a way to make everything work, have a low c/g, easy to work on, and make everything happy coming this afternoon.


I think I will be fine using the 1480 u-joints on all the shafts with the only real downside being decreased life.
But, I would like some feedback if I have any other options.

Thank you for taking the time to read my long description of this issue.
 
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#2 ·
What kind of car will require an output of 800 ft-lbs continuous? Bonneville? No road-driven vehicle would need to put out a continuous load. All those joints are good for intermittent use..

Russ
 
#4 ·
A two speed powerglide with a 1.76 1st gear behind a big block putting out 500ft/lbs would put out 880ft/lbs continuous to the drive shaft until the thing shifted between 55 and 70 mph.

My engine torque should flatten out 500ft/lbs around 3000rpm. From 30 to 45 and from 49 to 73 the u joints will experience the engines max torque. From there I can shift to decrease wear on the engine or I can always shift sooner for less acceleration. But, that's no fun.

I just want to make sure I am ordering the correct parts to avoid needing to order a different set of shafts with bigger joints or lessen my rpm because I did not do my homework from the start.



''''''
 
#3 ·
Ok, here is the setup in pictures.
465 to reverse case there will be a small vertical angle to the drive shaft to keep the high speed rpm at 0 degrees.



Driveshaft passes under the passenger seat


Along side the engine(which will be lowered 6" from this point) to the 3 speed.





Then I will have the transfer case chain between the 3 speed and pinion. The measurement between the pinion and 3 speed is correct here I was unable to move the 3 speed into position due to the uprights supporting the motor.


Here is the 3 speed with the lowest point 6" of clearance off the ground. After playing around with it for a bit. I will clock it slightly which lets me lower everything 4" more.

The reverser case becomes the lowest part at 6" of clearance letting me move the drive shaft/passengers seat down and there for the roofline becomes 54" with 5" of total headroom. Once my chain and gears arrive I will have a better idea where everything will line up and can begin talking to shops about the drive shafts which is where this u-joint issue comes into play.
 
#8 ·
I am thinking 4" OD, .8 wall(standard) dom and a two piece length of 30"(with a carrier bearing/slip yoke) and 27" no slip yoke rearmost shaft. Rough measurements.

After playing around with this and various calculators I believe that 5000 rpm is more of a general number. Many people have run stupid power and crazy rpm's through 1350 joints that have a "safe" rating at 5000 rpm.

I still like the idea of using 1480 joints just so when I hit it I don't need to worry about anything breaking. But, I will have a sit down with a drive shaft shop and see what they recommend.

At this point I am going to put this on the back burner, use lasers to make sure everything is and stays at 0 degrees during the chassis build and talk with DTS in the spring about this.

Thank you all for the help.
 
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