Making a coupler shaft to connect transmission to divorced TC

[Brian R]

Perhaps you read my post about the status of my 1981 MBZ diesel wagon on the 1984 Nissan 4x4 chassis project in which I referred to a vibration problem. Here are some more details:



Shaft #1



The first shaft I made to couple the MBZ transmission to the Nissan divorced transmission used standard u joints with no slip yoke or provision for length changes. The main reason is that the entire shaft is only 11" long and there was little room for one. I figured this would be allright since both the engine/transmission and transfer case are both rubber mounted. I knew I was supposed to align the u joints but I didn't and by the time I had the shaft welded together the u joints were slightly out of time and the entire shaft was out of round by probably . 025". I figured it was at least something to get the car to move so I could test out other things. Undesirable symptoms included a low frequency rocking of the TC and a vibration when you back off of the pedal around 40 mph.



Shaft #2



Next, I made a shaft using a Constan Velocity joint on the transmission end. Yes, I used a tulip style CV joint from the front end of the Nissan 4x4 chassis (1984 King Cab pickup). The CV joint has provision for about 1. 8" of length change. I then used a standard U joint on the TC end. The CV joint is running at an angle of around 20 degrees while the u joint is probably running around 5 - 8 degrees. The symptoms have been significantly reduced. Along the way I also added another mount to the TC which eliminated its rocking. The transmission now wants to move to compensate. Also, the higher speed vibration is still present, though lessened. This shaft is true within . 010".



My question:



I think my problem is that by having a u joint on only one side I have introduced a relative velocity change between the shaft and the TC input flange which is not compensated for by the CV joint on the other end of the shaft. I am probably going to put a CV joint on the other end of the shaft. My understanding now is that u joints almost always come in pairs so that the inherent velocity difference at one end is compensated for at the other end. However, if this is the case, why do I see so many lifted trucks with the back axle rotated to lessen the u joint at the axle without altering the u joint angle at the TC? It seems like this would present a similar vibration to the one I am experiencing, if indeed this is the source of my problem.



Incidentally, this work is all done on my lathe with a dial indicator to measure trueness.

 

[Brian R]

In the first sentence under Shaft #1 I meant "Nissan divorced transfer case", not "Nissan divorced transmission".

 

[Uncle Joe]

what do you mean "u joint on the transmission side"????

am i missing something???

all m/b i ever seen had nothing but the stupid rag joints which i constantly had to replace... ... ..... joe

 

[Brian R]

When I built the first of the two shafts I put a u joint on both ends, including the transmission end. In the second shaft I used a CV joint on the transmission end and a u joint on the transfercase end.

 

[drees1]

Sounds like your working through your problem ok. You can get a male slip yoke to female slip yoke (no shaft) and get down to about 8" long and still have the slip in it. I did that on an auxillary job years ago. But I do not believe the slip is needed as you say, nor is the lack of it your problem.



The best is to try to align all shafts as straight as possible. Also, any vibration from any source requires something to initiate it and degree of softness in the system to allow it to resonate and carry on. The balance of the shafts, and Ujoint angles can initiate it. And the rubber mounts can supply the spring in the system. With that in mind, making your mounts twice as soft or flexible will lower the resonance point of the shafts by 4 to 8 times. So if your vibration is strongest at,say 45 mph, and you soften your trans mounts by twice, then it should drive through the vibration at around 10mph or less. You would not even notice that. Soft mounts can solve a lot of problems.



You are right about phasing the u joints on the shaft, it is important. A cv will work with a u joint on a shaft if the u joint is at 3 degrees or less.



Angles over 10 degrees should have cv joints ideally.



I think you will ike the cv's. You can get away with mismatched angles and they will alvays be smooth.

 

[Brian R]

Somehow I missed your post but I seemed to have arrived at (stumbled upon, perhaps) the same basic conclusion you state. After raising my transfer case 3" my joints are running at what looks like zero degrees and I can't see being any more than 2 or three degrees. Voila! The vibration seems to be gone after a couple of test drives. The main reasons I used the CV joint was that the bolt circle on it was exactly the same as the bolt circle on the MBZ transmission flange. I am a bit concerned about the weight of the joint hanging on that flange but compared to the shaft weight that was in the car originally (from the transmission to the carrier bearing) it is probably not much more of a load. Maybe even less. At any rate, I'm a happy man. That dual slip yoke idea is great. I'll keep that in mind for the future. Thanks for your input.



Brian

 

[cjohnson1]

BrianR,

Sounds like your hitting the nail on the head with a blindfold. Not criticizing cuz I'm not an expert. But I did learn this much.

Last year I built one of those BIG tired, lifted to the moon, rock crawlers. You know the ones with 20 forwards and 4 reverse gears. High enough you can crawl under it all the way through on you hands and knees. Well anyway, when I was calculating my drivelines, I too used cardians at the rear transfer case. (Front shaft too!) and "U"joints at the diffs. My driveshaft expert told me that I needed to rotate my pinion angle so that it is at "0" degrees static. (Sitting still) at the rear diff housing. The cardian would do all the work as far as drive angle. He told me that I could be off as much as 1 or two degrees without any adverse effects. He must have been right as I don't have any driveline virbation at any speed.

I would think that as far as your transmission to TC was concerned, it would work as long as your "U" joints are parallel, balanced and in sync. I spent about a grand on custom drive shafts from Jesse at "High Angle Driveline" and they are working perfect.

Course, I could be outta my tree, buy hey, it worked for me.

Curtis J

 

[JTMcCracken]

It sounds like you have solved your problem but I'll throw in 2 bits, the only truck I havbe owned with a divorced trans. case was a 1972 International Travelall w/ divorced 205 and a strong 392. The driveshaft was all slip joint, regular U joints, phased properly, and it would run over 100mph with no driveline symptoms. I miss the truck. JTMcC.

 

[Brian R]

I guess I now know how these trucks run around with these rotated axles. I was wondering how they do it without a comparable angle at the transfercase. I'm assuming that cardian means CV joint.



I still have a little bit of vibration that could be from the shaft or maybe not. Currently, I am in the midst of a boot war. I have had the boot come off the CV joint twice. The first time I had used the clip supplied with the boot. Without a crimping tool, I crimped it with a hammer and screwdriver. It seemed pretty tight but came off after about 30 miles. I then replaced it with a plastic tie which lasted about 1 mile. Then I got the type of clip which uses a special tool to wind it and get it really tight. I drove it and it did not come off but I heard a noise in the drive shaft tunnel which sounded like the boot had disintegrated. What had happened though was that the gear shift linkage had come unlinked. I think the boot expanded because of the centrifugal force and snagged the linkage. I read that this was a problem with Formula cars when they first started using CV joints in place of double H joints. The book said that putting plastic ties in the crevices of the bellows to limit expansion will solve the problem. My joint is turnign at 4. 11 times its designed velocity so I can see why the boot might expand quite a bit. I think I'll try the plastic ties. Thanks for the input and keep the dialogue going if you have any more. I want to start driving this thing to work. It looks so cool.

 

[cjohnson1]

Cardians serve the same purpose as the "CV'S" only they are double "U" joints.



I don't blame you Brian. That is one sweet truck. I just wish mine was finished too!



Your vibration may just be a balance problem.



Curtis J

 

[Brian R]

Now I know what a cardian is! I've seen them. What is your project?

 

[cjohnson1]

I've got a 37 foot Fleetwood Motorhome I'm repowering with a 98 12 v 5. 9 l cummins. I've already bought and bombed Engine up to 250 HP, an Allison AT 542, the intercooler, radiator , coolers, and just about everything else for it. My biggest obstacle is summer is my busy season and it's hard to put in 12 to 14 hours a day and then have the inclination to work outside in the mosquitoes.

The Ford 460 and C5 are removed as I type. In fact I'm sitting in it now typing this.

As soon as I get the motor mounts fabricated then I'll be shoehorning the Cummins in through the front grill.

After I get it driveable I'll pull the rear end and take it to Fort Worth Gear and Axle for the right R&P ratio.

The story is on page two I think.

Curtis J

 

[Brian R]

I did look at those pictures. I like motorhomes, too. I converted a 1966 Flxible 30 diesel pusher transit to a motorhome. It had a Cummins triple nickel V8 and a 540. Your coach is going to be pretty cool with that motor.