Grinding from transfer case when first off and back on the gas at speed

[AZ77Bronco]

Hi All... thanks for having me. I searched this forum and the web, only to find a couple similar problems that dead ended with no solution given.

I recently bought this 77 bronco with auto trans and dana 20. It was an original auto just shifter moved to floor. This bronco had a lift on it when I bought it and I did not notice this sound at the time, under these same conditions. The owner did not drive it much.

It has an approximately 5" bastardized suspension lift with blocks in the back. Rear drive shaft was lengthened and balanced by previous owner. All U Joints are good.


when driving at approximately 40mph, and let off the gas, I get a grinding sound coming from the transfer case that can also be felt in the shifter. This can also be heard and felt in the T Case shifter, when first getting back on the gas at this speed.

Noticed this about a week after owning and driving it more.

This happens in 4wd or 2wd. Hubs locked or not.

I took the front drive shaft out, drove it, and still does it. U Joints are all good. Angles look good.

I had the transfer case rebuilt, put all new mounts, and still does it only quieter and grind not as severe now. This stumps me a bit because something made it slightly better.

Anyone have any Ideas.. Thanks in advance.

 

[markperry]

Check the angle of your pinion, if the angle is to much it will chew up your CV and or Ujoints.......if you have a smart phone you can down load an app that you can use to find the angle.

 

[AZ77Bronco]

thanks for the reply mark..... U Joints are tight... angle looks good.. and I have never heard a grinding sound, like gears trying to mesh, that can also be felt in the transfer case shifter that came from a U Joint... Am I missing something... Weird how the sound got better with the T Case rebuild and new mount bushings.. If anything that would make the pinion angle steeper right?

Im lost unless it has something to do with axle wrap when letting on and off the gas at first and something binding, but it doesnt do it at low speeds. If it was pinion angle it would do it all the time as well when I get on it at any speed wouldnt it?

Someone must have had this problem.... I just dont want to throw parts at it... any help would be greatly appreciated..... thanks

 

[broncnaz]

Could be more of a issue with the shifter itself. The J shifters tend to have some issues with age. It may not be fully going into 2hi

 

[AZ77Bronco]

thanks for the reply. I looked at that but will check it again. It is an after market shift arm. I tried moving it when it acts up but did not change the grinding sound or feel. It is really stumping me that after the TC rebuild and new bushings that the grind and sound got considerably better but is definitely not gone.

 

[JackHoleRacer]

Maybe try removing rear drive shaft, lock in hubs and test drive in front hi. possibly help isolate prob....

 

[AZ77Bronco]

thanks for the reply, that was what I was going to try next. I did it with the front and didnt change. dont know why I didnt do rear right after. Instead I drained to TC and when I inspected it, I found a little bearing slop and contributed the grind to that. Again I just dont get why it got a little better after the rebuild.

 

[Hozr]

It could be the transmission or even differential gears as well.

You say it happens when you get back on the gas which means there is some play in the gear mesh somewhere. Drivetrain vibration will transmit all the way through the entire setup. You need to isolate exactly which end it is then inspect every part of the system.

 

[69red]

I think its the pinion angle made worse by the nasty lift setup. when you let off the gas the rear axel could be rotating forward and down, putting the Ujoints too far out of line.

if you put it in reverse and floor it, does it grind?
(disclaimer -- make sure wife has not sneaked up and parked her car behind you before attempting this test)

 

[DirtDonk]

Define "good" please, with regard to your pinion angle AZ77.
What you describe is a classic case of pinion drop during deceleration causing a harmonic vibration in the u-joints that is simply traveling up the shaft and rattling the gears in the t-case.

Not that this is a guarantee of course, and you may know exactly what the correct angle should be, but with the unusual lift you're describing, it's still very possible.
And I bring up what's already been asked again because it's very common for new owners of EB's to be more familiar with the alignment of a standard single-cardan shaft than with the double-cardan shafts that almost all EB's use.
So if you look at the rear pinion from the side, it should point almost straight up into the driveshaft's centerline. Just a degree or two below that is optimal, but much more than that will give you deceleration vibrations.

Since the t-case was recently rebuilt and it got better, that's a good sign that you at least tightened up things inside an old gearbox.
By the way, what lubricant did you use in the t-case? Not looking for another cause of the noise here, just wanting to make sure it's the right stuff. Certain gear lubes that are still available will deteriorated the bushings and thrust washers prematurely, and some are just thicker than our t-cases need.

That amount of lift is always a borderline situation with a short wheelbase EB anyway, so any of these things being just a tiny bit out of perfection can lead to issues. And even though the PO had the driveshaft lengthened and supposedly rebuilt, do you know for a fact that the centering ball and yoke of the double-cardan (CV) section was addressed as well? Some of the strangest sounds and feelings will come from a deteriorating (or just dry) CV centering yoke.

Good luck.

Paul

 

[DirtDonk]

What 69red said!

By the way, we'd love to see pics of this beast. Not only because it helps to see things like suspension and pinion angles, but because we like to see pics of new-to-the-forum rigs!;D

Since you can't post pics up directly to the forum unless you become a contributor for 13 bucks a year (or whatever it is) you can still post pics by either using another image hosting site on the internet and then linking it here, or just e-mail one of us the images and we can post them up here for you.

Either way, it's just way more entertaining to see pics.

Paul

 

[AZ77Bronco]

Thanks Horz, Its possible I thought as well. I have always had jeep TJ's and put ARB's in. This gal has a Detroit, no spin, locker in the rear. I was amazed at the backlash and thought something was wrong at first, until I read the info on their site on install. I dont know where to go if thats it, other than take it out, and Im not at the point to get into that right now if its not hurting anything.

 

[AZ77Bronco]

Hozr, thanks for the reply. I have not tried that. It only seems to do it at 35-40mph plus going forward, but when I get time to put it back together, I will and let you know. I will also keep the rear shaft out and drive it just with the front to see if I can loose it.

Dont know why I didnt since I did it with the front. Just got hung up on what I thought was a 40 yr old slopply TC. I will check though.

 

[AZ77Bronco]

DirtDonk.. thanks for the reply as well. I was definitely thinking of the pinion angle. Again I have had a lot of TJ's I built with long arms, so I could easily adjust all that. I have a angle finder for it and everything. I just seem to find my way down the hard road first, and when I saw the TC I just went for that instead of following the rational flow chart. I should know better. I have been looking at shims ect... also been thinking about possible axle wrap, but again with work right now and no helper Im stuck. Im working on it next week.

I also put in 75/90W. This is what I read most run now. Hope I didnt screw up or start a lube debate.. I hope Im not making this sound like a mad beast. I dont think its that crazy from what Im use to, but I will work on putting pics on a site with a link for now. Thanks again all, and I will keep you posted when I am able to give it some time again.

 

[AZ77Bronco]

tried to upload photos.. let me know if it worked.. thanks


http://s1374.photobucket.com/user/AZ77Bronco/library/?sort=3&page=1

 

[AZ77Bronco]

BTW these are pre purchase pics... not my doing, and its not all bad.. Im working on it, so be gentle. I will check the suggestions and get back asap.. I do appreciate all the help and ideas.

 

[AZ77Bronco]

Oh boy Paul. I just got a chance to look at my rear suspension with work and other things getting in the way. Truck is at a buddys shop. Again, I just bought this thing and drove it for a week before all the above, and associated work, started.

The rear drive shaft did not have a CV joint. I found a receipt from the previous owner, who had it extended and balanced after the lift. No mention of CV joint. I also found the blocks under the axles did not have any shims. I could not check the angle because we took the transfer case back out thinking we didnt put something back together right since the sound got better but didnt go away.

I figure Im going to put in the shims and save for a drive shaft. There is no way a U joint only shaft, that I have, would work after I corrected the angle for a CV shaft would it. Really weird part is that this thing drove straight down the road with no shake or shimmy at any speed prior, hands off the wheel and drove itself. I really dont have the 400 bucks for the CV shaft right now if it wont work.. guess we will see.

 

[AZ77Bronco]

again, I know how the angles are suppose to look for a CV and U joint only shaft. Just wondering if I will be able to get by for a bit or will it shake apart and detonate..

 

[bax]

That the guys are telling you is absolutely correct. From the pictures I can tell your pinion angle needs to come up. By your own admittance you do not have a C/V joint in the rear. Thats good because it would hurt. Now without the c/v joint you are creating a vibration that is taking taking it out on the rear output of the 20. some pictures off the Tom Woods web site.

 

[DirtDonk]

And the correction at the rear end is the easy part, so whichever shaft you're using at the time, aim the pinion according to bax's diagrams. Once you get the chance to put the double-cardan shaft back in you can change the pinion angle to be correct again.

In some cases you could just add a CV to the existing shaft, if the one you have is compatible with the proper components. Save money that way maybe. Hard to say though, as local driveline shops are usually more expensive than an off-the-shelf shaft would be.
We sell replacements from $260 to $315 (to $600 for the super duper wazoo High-Angle stuff), so it's not quite so bad as you might think.

In the meantime, depending on the individual Bronco, a single-cardan shaft is perfectly serviceable at least for the street. Not as versatile for a short wheelbase rig as a double-cardan perhaps, but with the right angles and enough length, can get you where you want to go for years.

Paul