4x4 not working, diagnosis help

Vexarana · Oct 27, 2014

So I had my rear drive-shaft grenade on me after driving through some deep snow. I think it packed it with gritty, icy water and just locked the U-joint up. Made a spectacular pop. Lots of sparks as I limped it home.

So I drove it for a little bit on 4x4 after dropping the rear shaft but only using the front drive-shaft. Well, I was late to work one morning, heard a loud CLUNK, and it didn't go anywhere anymore. The front drive-shaft was still spinning.

After replacing the rear, it drives fine. But obviously no 4x4. I want to get this fixed before winter and am going to be getting junkyard parts, but the closest junkyard is ~45 minutes to an hour away. Not really wanting to do multiple runs.

So, is it LIKELY that I exploded the front diff? It's a 1991 TTB so (I think) a Dana 35? Or is it more likely that I snapped one of the front axle shafts?

It has manual Warn Hubs that I did a full rebuild on when I got the truck 3 years ago (replaced all the gaskets and such).

Hoping to get some time throughout this week so that I can get the truck lifted. My diagnosis thought process is..

1) Lift front of truck up.
2) Lock manual hubs on both sides.
3) Turn one wheel. Other shouldn't turn (since it's broke).

But that doesn't really narrow anything down as far as I can tell. Should I look at pulling a whole new front axle if I can find one? Since it is a 2nd gen does it have to be from a 1989-1992? Or can I go up to 1997?

alwaysFlOoReD · Oct 27, 2014

I'm not the greatest in diagnosis as I jump around from one thought to the next when I'm actually working on my own stuff. Something about shiny, bright objects gets me off path :icon_confused:

You need to do a step by step.
Leave the rear driveshaft off for now. Use jackstands under the front axles.
First is the transfer case OK? Does the front driveshaft spin when the truck is in gear. Perhaps the tc broke. The wheels may [or not] be spinning, one forward, the other stopped or spinning backwards. Look at the drive axles and see if they are spinning. Perhaps a u-joint broke.
There is probably stuff I forgot or don't know about this type of diagnosis so some research on your part will help. Check out the tech pages; at the top of every page in the lighter blue header, third from the right ^^^^
If you decide to get a new front axle, make sure it is the same gear ratio as you have now. As long as the truck is stock you can find the ratio on a tag under a bolt head on the front and/or rear axle pumpkin. Also you can use the door tag and an online decoder. And last the vin and an online decoder will work too.

Good luck,

Richard

Vexarana · Oct 27, 2014

Whoops! You made points on a few things that I forgot to mention.

The front drive-shaft is intact. In fact, it spins freely when 4x4 is not engaged and the hubs are free-spinning.

When the truck is in 4x4, the front drive-shaft spins, but locking the wheels just doesn't do anything.

This is why I am focusing more on the pumpkin and axle-shafts.

If I get it up on stands and lock the wheels, will I be able to tell just by spinning the tires if one of the axle shafts is broken?

I.e. if one of them is broken, will I be able to hear / feel something?

alwaysFlOoReD · Oct 27, 2014

https://www.youtube.com/watch?v=K4JhruinbWc
A vid that will help visualize how an open rear/front drive differential works. Skip to 1:50.

'the front driveshaft' it spins freely when 4x4 is not engaged and the hubs are free-spinning.

When the truck is in 4x4, the front drive-shaft spins

This is what makes me wonder about the transfer case. If in 4x4, the driveshaft should not spin freely with the motor not running.

Edit; Having the truck up on stands will greatly help diagnosis. You can crawl under and look and listen while running in and out of gear. And you can physically move shafts while NOT running to see or hear problems.

Richard

Vexarana · Oct 27, 2014

Richard,

Is it still a problem if the truck is a 5-speed?

If the transfer case is in 4x4, but the transmission is in neutral, and the hubs are unlocked.. What should I expect? Will turning the front drive-shaft affect the rear driveshaft?

4x4junkie · Oct 27, 2014

Are one or both of the front axle-shaft u-joints turning while the driveshaft turns? (but the wheel isn't turning)? If so, it's likely a failed locking hub.

If neither u-joint spins, then there may be an internal problem with the diff (maybe a broken shaft at the splines, or maybe a broken spider gear).

In 4WD, the front driveshaft gets locked to the rear driveshaft so they both turn together as one. So no you won't be able to turn it by hand if the rear shaft is also not allowed to turn (rear wheels are sitting on the ground, etc.). In 2WD, the front shaft should rotate freely (unless both front hubs are locked, then it should not turn more than about 1/16 - 1/8th of a rotation).

adsm08 · Oct 27, 2014

I'd suspect you lost a hub before thinking you blew up the diff.

Systems, like chains, tend to break at the weakest point. The hubs are the weakest point of the front drive line system. They are fine for added traction in bad spots, but aren't really designed to take the full brunt of driving the vehicle by themselves full time. Compared to the splines on the rear axle shafts the spines at the outer end of the front axles are pretty small.

4x4 not working, diagnosis help

Vexarana

New Member

alwaysFlOoReD

Forum Staff Member

Vexarana

New Member

alwaysFlOoReD

Forum Staff Member

Vexarana

New Member

4x4junkie

Forum Staff Member

adsm08

Senior Master Grease Monkey

Sponsored Ad

Sponsored Ad

Staff online

Members online

Today's birthdays

Member & Vendor Upgrades

Latest posts

Truck of The Month

Recently Featured

Follow TRS On Instagram

Latest Album Photos

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals