Front drive shaft

S

sonofa

New member
Hello. I've just had a substantial amount of work done to my '72. After this phase of Scout construction in 4wd at all speeds there is a lot of noise and shaking (like an earthquake), transfer case is difficult to change from 2wd to 4wd, plus it wanders all over the road. In 2wd everything is all good. I have since discovered that if I change from 2wd to 4wd in reverse it shifts real smooth (what is that all about?).

Work done was a SOA (cut & turn), alcan springs (stock dimensions), Dana 44 in front, reverse shackle, high steer, power disc brakes front/rear, 33" tires, t19 wide, Dana 20, 3.54 gears and 304.
From everything I've read so far I'm guessing a double cardan on the transfer case end of the front drive shaft should correct this problem. Does that sound right?

Thanks
 
Last edited:
Well based on what you've told us, I'll assume that you're still running the stock drive shaft and now have the pinion of the front axle pointed at the transfer case. If that's the current situation then yes a double cardon joint at the transfer case will solve the shaking problem.

As to the hard shifting, how did it shift before all the changes?

Wandering??? Need more info.
 
Lots of variables here...
First thing would be to take it back to the shop that did the work and have them drive it with you riding shotgun. Let them explain it.
If that's not an option, then here's a few things to check:

wandering down the road could be bad caster settings. The cut and turn should have left you at 4-6 deg positive at normal ride height and load. This forces the wheels back to center using the weight of the truck. Wandering is usually not a factor if this is set right.

The shaking of the truck in 4wd makes me question weather the gears in the front axle match those in the rear. If 3.54s aren't in both differentials, you'll have one axle turning the wheels faster or slower than the the other. It'll try to buck the truck off the ground.

Also, shifting from 2wd to 4wd will be nearly impossible when the truck is moving if the above situation exists. The speeds of each drive shaft won't match, and you'll have to come to a complete stop to shift.

The mis-match of gears will really cause some serious damage, so I'd make double sure this is not really the case before I tried to drive it.

The only other thing that comes to mind in regards to shifting 2wd-4wd on the fly would be the hubs. Are they locked when you try to shift? If not, then that could cause a mis-match of drive shaft speeds and cause some grinding as you shift. Make sense?

Lastly, changing the front drive shaft to a cv joint won't fix your problems. A cv or double cardigan helps eliminate vibration caused by extreme angles and/or short drive shafts. You'll only sense these vibrations at higher than trail speeds. Doesn't sound like your problem.

Check back in and let us know what you find. The problems are only solved when you find out what was wrong and share it with the board.

Good luck!
 
Thanks for the replies. It is appreciated. Ok I need to verify the gear ratios are the same front and rear. Measure the caster. Can there be too much caster? Prior to work completed the transmission shifted very easy as it does when in 2wd now. Previously the transfer case I could would change form 2wd to 4wd by just getting rolling and easy shift. Now shifting from 2wd to 4wd in a forward direction is near impossible. However, very easy if I shift rolling in reverse.
Now I'm kind of thinking maybe the gear ratios from front to back are different.
 
Last edited:
Is this the same front axle that was original to the truck before the cut/turn mod? Its hard to imagine someone sneaking a gear change passed you without your knowledge (or payment!).

Yes, there can be too much caster. But whoever did the axle mod should have dealt with this. Its axle 101. The shifting into 4wd while reversing is strange. I don't have any other comment yet on that.

Verify the axle gears first. If they match, then there must be something different about the locking hubs. If they are unlocked at speed, then you will have difficulty (grinding) when trying to go from 2wd to 4wd hi. They must be locked to spin the front shaft to match the speed of the rest of the gearbox. You May need to jack the front up and verify the hub functionality. Just because it points to "lock" doesn't guarantee its actually locked.

Keep us updated.

One more thing after re-reading your post:

do you now have difficulty shifting transmission gears? And if yes, is it only when in 4wd hi? Or is it also in 2wd?
 
Last edited:
Thank you so much for all of the response and information. Thank hard shifting only occurs in 4 high. I read somewhere on line about shifting the transfer case while in reverse so I tried it and it works real smooth. The neither axles are original to the truck. Used to have 44 rear and 30 front (3.31). I found a 44 front (had new 3.54 gears installed) found a rear 44 (tagged with 3.54 ). I'm thinking maybe the rear axle May not be 3.54.
 
Okay. The front and rear axles are 3.54 and the hubs do lock and unlock.
How much caster is too much? While talking with the mechanic he told me the caster was 4.5*.
Steering has a little play, but it always has. Never had a problem tracking before.
Wheels are new and balanced.
Transfer case has been recently inspected and I was told it is in good shape.
Come to think of it, there is occasionally a good amount of vibration/grinding at the transfer case. Although for a short period of time. Has never done that before. Is it possible that the increased pinion (?) angle is playing hell on the transfer case?
20141216_110038640x360_zpsf16a20cc.jpg

20141216_105901640x360_zps1f5f9e3a.jpg

http://i1273.photobucket.com/albums...0_zps8295595d.jpg?1418761221864&1418761228140
http://i1273.photobucket.com/albums...0_zpsfab2e81f.jpg?1418761221864&1418761228140
Steering has a little play, but it always has. Never had a problem tracking before.
 
Last edited:
Apparently the gears in the front are 3.31 not 3.54 as marked. Had the gears swapped out for 3.54 a couple years ago. Called the shop that did the work today and apparently they put 3.31 gears in and put a 3.54 tag on the cover. :icon_stare: the rear axle has 3.54 / the front axle has 3.31.
At any rate, mystery solved.

The only thing is... How does a person that owns 4wd shop test drive the truck and not know that something is wrong with this truck?:confused:

I am glad I did not dump more cash in to buying a drive shaft with cardan joint.

Thank you for all the help. It is greatly appreciated.
 
From the pics, it looks like some competent work was done. No shade-tree stuff going on that I can see. Also the elimination of the axle ratios and hubs was good news. Soooo....

The only thing I saw was in one of the photobucket pics. The shot of the front of the truck shows what looks like the front tires toed-out pretty far. Not sure if the truck was still under construction at this point, but the tires should be aligned to be toed in 1/16-1/8". Never out. That could cause wandering.

As far as the caster, 4.5 deg is good as long as that's the absolute measurement (with the truck on a level pad at normal load) and not a number the shop added, and is quoting now.
If you could drive the truck onto an alignment rack and see 4.5 deg positive, you're fine.

As far as the grinding going into 4wd, we've eliminated the obvious things. Not sure where to go from here. When its in 4wd, you say you have major shaking. If your axle ratios were different, you'd really not be able to move it very far before it bucked and bounced you out of the chair. But if its a vibration, and happens above say 25 mph, then that could be your front drive shaft. It doesn't have the cv joint at the top, so you do have quite a bit of angular imbalance. Check this video. Makes it plain as day. Is this what you're experiencing?

https://www.youtube.com/watch?v=gmv4qwlfomy

I don't see how fixing the front drive shaft will cure the 4wd shifting issue, but its possible that your shaking in 4wd will go away.
Another thing is to check the phasing of the front drive shaft. Both yokes need to be on the spline parallel as you look at it from one end. If its off one spline, there would be vibration.

If it were me, I'd look at the toe adjustment. If its good (hard to tell from the pic), take it for a spin in 2wd, hubs unlocked. If it still wanders unacceptably, then you'll have to have someone confirm the caster and toe settings. If it goes down the road ok, then how's the vibration? If its ok, then lock in the hubs and try it again. Hubs locked in 2wd will spin the front drive line and probably give a vibration. Should be more of a buzz and not as destructive as it seemed in 4wd.
If it still bucks and jumps around in 4wd, all I can say is put it up on blocks and verify the front tires spin at the same speed as the rears. Tires are the same size front and rear, right? That would also cause a slight ratio mis-match. Other than that, I'd say you still have a gear ratio that's different in one axle.
Maybe one of the real braniacs will chime in and pour some fresh science on this fire....I think I've covered all of the possibilities I've run across.
Let us know...

Just seeing your reply. I was a little late and didn't see it.
Sounds like you're on the right track now....!
 
Last edited:
That looks like beautiful work! I have had a little driveshaft issue in the past. Your u joint needs a minimum of 1/2 degree operating angle. If the driveshaft points directly at the transfer case and there is not enough angle you can get a light vibration. In this scenario a double cordon will solve the issue.
I have had to run a 3.73 rear gear set with a front 3.54. The ratio was close enough to not cause a vibration like you describe. It is very hard on the transfer case bearings. I did it just long enough to get my broken but to the road. I was on granite so I definitely had the traction to cause a vibration at times.
Did you check to make sure the yokes were tight? I would get under and do a wiggle test to make sure everything is tight. It is a good idea to check the fluid levels as well. Sometimes I forget to check the basics first and run a wild goose chase for something silly.
 
Thank you. Thank you. Thank you. For everyone's replies/responses. Very nice to get a "diagnosis" from several people. Thank you everyone.

Ok. One last question...

I had a gear set changed from 3.54 to 3.31 about 3 years ago. I have had the axle sitting in my garage since. The shop that did the work left the 3.54 tag attached under the cover plate bolt. Being the work happened 3 years ago I did not remember exactly what gear set I ended up going with, I checked the tag and read "3.54". I then picked up a rear axle with 3.54 gears...
I ended up with 3.31s in front and 3.54s is rear. Creating the situation I am having above. Should I take issue with the shop or should I just chalk it up to experience?
:icon_question:
 
I'd be surprised if the shop swaps your 3.31s for 3.54s at this point. Never hurts to ask, but after three years, I kinda doubt it.

The two options you have that are easy and relatively cheap are:

-finding a rear axle with 3.31s
-pitching in with the suspension shop and see if they'll maybe discount you a 3.54 swap back into the front. You do have those gears still, right?

3.31s and 33s are more of a highway set-up, rather than trail. I'd either leave it for now (no 4wd) and save my pennies for a 4.10 front-rear swap w/d-locker and trutrac, or find a 3.31 rear axle and see how that works in the snow and muck you'll be dealing with.

Glad you got it figured out.
 
Having driven a Scout with 3.31s and 33s, I can say its a bit of a slug in between gears. It did fine on the highway, but off road I was in 4-low much of the time. With this setup, you can go 45-50 mph in 4-low, so that May not be a problem for you. You will probably find that in 4wd at any speed above 25-30 mph, that non-cv front drive shaft will start buzzing pretty good. Did you check that video?

I guess it all depends on your usage. You May find this combo is ok for you. I was happier with shorter axle gears, and an eventual overdrive. You've got a solid truck. You'll figure out what it wants.
 
Sounds like I should get a cv drive shaft. I will be making a trip from anchorage thru denali to prudhoe bay then to el paso tx. Going through denali there are some moderate grades at 55 mph on asphalt. Up north gas can run $7 a gallon. I do have a t19 wide ratio transmission I know it only helps for the low end but might be a factor. Any suggestions? I'm debating 3.31 or 3.54? Is there a difference in mpg between the two since they are close in ratio?
I did see the video it cleared thing ups very well. Thanks for that.
 
Last edited:
If anchorage to el paso is in your plans, keep the trans and 3.31s. You'll be a little over 2300 rpms at 70. Good torque/throttle response, and your mileage is going to be 12 if the motor is in good shape. If you have to do 55mph in 4wd, then get a cv joint on the front shaft. That vibration will drive you crazy.

There is no magic formula. These trucks never went as fast as fords/chev/chrys. Never got great mileage. What they did do well was stay running for 300k mi. If you looked after them. Drive it like it is, and see what you think. Jeff has a whole store full of stuff here on the site ranging from cams, intakes, overdrives, and hamilton fuel injection kits. Plenty of mods to take things to the next level. Whatever that level is to you.

Have fun with it and keep posting up as you go!
 
You must log in or register to reply here.
Back
Top