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Eating ujoints in just a couple of miles

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kingturdherder

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Was wondering if anyone else has had problems with eating ujoints in the rear after adding big horspower and big tires without a gear change. I have around 12" of lift in the rear with aprox 500hp. The shaft with the drop of transfer case ended up at 12 degrees which a stock heavy duty ujoint should support just keeps emolsifing within a few miles. I'm in the proccess of ordering gears as with 39" I'm having to run in 4 low to keep from burning the tranny up (front drive dropped). The joint that is being eaten is the one at the transfer, the dif joint runs cool. Anyone have any ideas? Could it be there is just to much torque on the joint with the tall gears? thx for any ideas. /forums/images/graemlins/confused.gif
 
I ran stock u-joints (Saginaw S44 Brute force) with 500+ HP for about a year with no problems, six inch lift on a K5. The angle is close to what you have. I had 308 rear gears and 37" tires. I ran in 4 low on the street with the front hubs unlocked. I could grab rubber in all three gears. I have since switched to 410 gears. I broke the rear u-joint only once when I twisted the front drive shaft in half at full throttle in a mud bog. I would recomend the brute force non greasable variety u-joint.
 
My guess is that either you're:

A) overtightening the u-bolts, thereby squeezing in on the caps too hard and burning up the bearings or

B) pressing the u-joint caps into the yoke and leaving them pressed in tight against the ends of the cross shaft so that the caps rub against the shaft ends and burning the bearings up. /forums/images/graemlins/eek.gif

Too much power will snap the u-joints, not melt them. /forums/images/graemlins/wink.gif
 
[ QUOTE ]
My guess is that either you're:

A) overtightening the u-bolts, thereby squeezing in on the caps too hard and burning up the bearings or

B) pressing the u-joint caps into the yoke and leaving them pressed in tight against the ends of the cross shaft so that the caps rub against the shaft ends and burning the bearings up. /forums/images/graemlins/eek.gif

Too much power will snap the u-joints, not melt them. /forums/images/graemlins/wink.gif

[/ QUOTE ]

Also I read your at 12* on your rear shaft. Are the two ends of the driveline within 2* of each other? example:
12* at the pumkin and 14* or 10* at the xfer case? Thats why I use CV style drive line.
Bill
 
I bet your U-joint angles are mismatched. Maybe you aimed the pinion up to minimize the angle, which would be much worse for the U-joint. The pinion and T-case output must be parallel unless you have a CV joint.
 
i run 500+hp outta the 454 with 10" lift and 5.13 gears and mine has done fine for close to the 3000 miles that i have had it. im going with mismatched driveline angles too

NITRO
 
[ QUOTE ]
I bet your U-joint angles are mismatched. Maybe you aimed the pinion up to minimize the angle, which would be much worse for the U-joint. The pinion and T-case output must be parallel unless you have a CV joint.

[/ QUOTE ]

UMMMM, No it does not. When I first built my 89 Jimmy I had bad vibration problems with just 4" lift and setting the driveshaft angles to within 1/2 degree of each other. No matter what I did it would not go away. I chatted with tRusty (Rene) and he told me his pinion was pointed up just like it would for a cv shaft and had no vibrations or u joint failures. I did it on mine and it cured my problem and never trashed a joint.
 
Check and make sure the yoke is not damaged. I had a problem with u-joints failing because the yoke had a bit of damage on it. Check and make sure that there is a good amount of surface area on the yoke that is touching the u-joint when its all bolted up...if that makes any sense /forums/images/graemlins/crazy.gif
 
[ QUOTE ]
[ QUOTE ]
I bet your U-joint angles are mismatched. Maybe you aimed the pinion up to minimize the angle, which would be much worse for the U-joint. The pinion and T-case output must be parallel unless you have a CV joint.

[/ QUOTE ]

UMMMM, No it does not. When I first built my 89 Jimmy I had bad vibration problems with just 4" lift and setting the driveshaft angles to within 1/2 degree of each other. No matter what I did it would not go away. I chatted with tRusty (Rene) and he told me his pinion was pointed up just like it would for a cv shaft and had no vibrations or u joint failures. I did it on mine and it cured my problem and never trashed a joint.

[/ QUOTE ]

I agree. I know it seems like it doesn't make any sense, but my driveshaft is the same way, no vibes. My friend that had a 12" lift on his K20 had the same deal. Point pinion at driveshaft, no more vibes.

I still can't understand why though. My truck runs smooth all the way to 80 mph, at which time I'm afraid to go faster, and it's unnecessary!
 
/forums/images/graemlins/crazy.gifThanks for the replies fellas, even though we all have different opinions of the problem. My pinion angle is up as I had welded the spring perches and installed the rear and then decided to do a reverse shackle. To cure the pinion angle problem I am going to turn the blocks around so the taper is backwards as I think this will bring the angle pretty close to within a couple of degrees of the front of the shaft. /forums/images/graemlins/smile.gifYour thoughts on the u bolts being to tight could be a possibility, I had never thought about that as being a problem as I have always tightened them up as tight as I could with a stubby wrench. The more I think about it I have probably always tightened them up to much, heck there are tabs and lock washers there for a reason I guess I should haven't had over looked that bit of common sence. I will try a new u joint in the morning with a bit less torque on the nuts and see if it cures the problem before I turn the block around. As for the caps that are in the press and c clipped part on the shaft they're just fine it is the u bolt ones that are melting. da /forums/images/graemlins/rotfl.gif
 
Just to give you an idea of how tight is tight enough... The factory service manual for a '74 lists the torque for the u-bolt style of retainer as 18-22 ft. lbs. /forums/images/graemlins/shocked.gif (For the strap style they list just 12-17 ft. lbs.)!!!!
 
I would like to thank trucksR4me member as you hit my problem on the head. Because of your reply the last time I went to change the u-joint with thoughts of not tightening it quite so much this time I took a good look at the yoke and yes there was a chip missing out of one of the corners. I replaced it today and tightened the straps as I always have done not wanting to change anything that I had done in the past as I wanted to find the problem without changing several things and not knowing the true culpret.... It was the yoke as I was finally able to put some miles on my new motor. Still have some bugs to work out ie alt belt being thrown anytime it gets near 5000rpm (thinking about doing a surpintine conversion to solve that problem) but at least now I can get the motor broke in and move on to the gearing and some traction control.

Once again I would like to thank all members who took the time to give me their imput /forums/images/graemlins/cool.gif
 
As for the belt coming off around 5000 rpms+ < Check the alignment of the pulleys, If the Alternator is off a little it will throw the belt at hi rpm.
Bill
 
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