Steering wobble and pull

[1972MaineK5]

First day member and I'm posting like crazy. So yesterday out of nowhere I started to experience wobbly floating steering. Additionally when turning at low speed I experience some resistance to turning the steering wheel. And then when turning against this resistance the steering sort of "gives" and over steers in the direction I was turning. It also gives little pulls to the left as I'm driving. Nothing major but certainly startling when driving. Ok. And here is the kicker. Only happens in 2 wheel drive. If I just engage 4wd from the cab and don't lock the hubs. The truck drives completely normally. If I engage the hub's in 4wd it drives normally and if I drive in 2wd with the hubs engaged it drives normally. Anyway, I haven't really done anything other than visually check the front end. Ball joints, tie rod end's all visually look fine. Plan to put it up on jack stands today and get a better feel for the ball joints and wheel bearings. And plan to pull the front diff cover and see if anything is going on in there. I had read one post of simular symptoms that someoNE had traced back to front diff issues but no mention of when it occurred in relation to 2wd or 4wd. Though and or input would be appreciated.

[jjzepplin]

First of all Welcome to the site! So we need a bit more info here. Is the truck new to you? What year? etc.
You are not supposed to engage 4wd on pavement.(you probably already know this)
You may want to make sure the gearing is equal front to rear. If someone has changed out a differential they may have changed the gearing.
Are you sure of the position of the 4wd shifter? Maybe you are really in 2wd when you think it is in 4wd? Just askin.

[1972MaineK5]

Thank you. Yeah I need to setup my footer with truck information. It's a 1972 k5 4wd. I've had it for almost a year now put maybe 8000 miles on it since ive had it. Solid truck. New motor at purchase and have had next to no issues since I've had it. Runs smooth, drives straight, brakes straight. And yes. I don't usually rUn 4wd on pavement. It was more of a ... a tried shifting into 4wd from the cab and all symposium went away so I got out and locked the hubs. It was a little sloppy yesterday with some snow on the road so I didn't feel too bad about it and only drove about a mile to see how it would behave. And I've driven it enough in 4wd to know that it was actually in 4wd. Then disengaged the 4wd from the cab and left the hubs locked and still had zero symptoms. Really a night and day difference.

[1972MaineK5]

Thank you. Yeah I need to setup my footer with truck information. It's a 1972 k5 4wd. I've had it for almost a year now put maybe 8000 miles on it since ive had it. Solid truck. New motor at purchase and have had next to no issues since I've had it. Runs smooth, drives straight, brakes straight. And yes. I don't usually rUn 4wd on pavement. It was more of a ... a tried shifting into 4wd from the cab and all symposium went away so I got out and locked the hubs. It was a little sloppy yesterday with some snow on the road so I didn't feel too bad about it and only drove about a mile to see how it would behave. And I've driven it enough in 4wd to know that it was actually in 4wd. Then disengaged the 4wd from the cab and left the hubs locked and still had zero symptoms. Really a night and day difference.

[boynton]

I'm still new to the 4wd world but it may also be in your steering box/power steering pump. Just a thought. When was the last time it was greased up?

[1972MaineK5]

Yeah could be a lot of things. I'm asking myself.... what's different when I have the hubs locked and /or shifted inot 4wd from inside the cab vs. Running straight 2 wheel drive? And I keep coming back to the front differential and front axles. And again I'm just speculating but that's where I'm going to start.

[jjzepplin]

The front could have a locker or something and that would pull it all over the place. I would pull the diff covers and check for such things and gearing compatibility.

[hemi43]

The OP mentioned it happens in 2WD, so I'd rule out anything inside the diff.
Crawl under the truck and turn the U-joints by hand at the hubs. Do this on both sides with the wheels pointed forward, and do this with the wheels turned. The stub shaft and axle should rotate freely. If not, then you may have a U-joint that seized most likely to lack of use and corrosion. While you're under there, put a mark on each U-joint and take the truck around the block making sure your transfer case is in 2WD and your hubs aren't locked. The marks should be in the exact same position when you get back. If not, then you have some binding in the front hubs.

[jjzepplin]

Good idea!
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[1972MaineK5]

Alrighty then... here is where we stand today. And thank you hemi43. I think you are onto something. So. 2wd and hubs unlocked. Turn the u joints by hand. They turn about 90 degrees freely then encounter resistance. Cant really turn by hand but can with a screw driver through for leverage. Then hand turnable again for about 90 degrees or so. Mark the u joints and take a quick drive and the u joints are definitely not in the same position after the drive. Jack up the right front to get the wheel off the ground. Turn the tire by hand and it feels smooth no odd noise and the u joint does not move. Rotate it backwards and forwards and maybe get the u joint to move a little but not much at all. Same on the front left.

So... sounds like the axles are turning when they shouldn't be. So put the truck on flat ground in neutral and roll the car forward slowly. U joints turn. Not 1 to 1 with the tirest but clearly turning slowly.

Ok. Then... I take out the differentail fill. Stick my finger in. And... drum roll. Vanilla shake. Nice white and creamy. So unless im.missing something. Not good.

So I've drained it, taken the cover off and sitting at a 7 year Olds birthday party waiting to get back at it.

Oh... and while under there I noticed there is no vent hose. None. Never noticed one way or the other in the past. Might have fallen off. Might never have been there.

Next steps? Clean it out and refill and see where we stand? Other ideas?

[1972MaineK5]

Oh and no noticeable damage in there. No chips no metal flakes. And I do drive it pretty often doesn't sit for extended periods of time.

[hemi43]

Don't refill the diff yet !!
If the U-joints need replacing, you'll have to drain the diff again to remove the axles.
If it was me, I would take both hubs apart and see where it's binding.
Take the large pin out of the differential and remove the spider gears. This will allow you to spin the axle shafts independently of one another so you can see which side causing you problems.
That milky diff lube has definitely been contaminated with water, so you need to decide the next step. Hopefully the water came in the vent hole on top of the housing, or it went by the axle seals. Unfortunately, the axle seals are located inboard and the whole carrier has to be removed to change them. Not sure if this is something you want to take on, but if you do we'll help you through the process. It's not difficult, but you will need a few specialty tools like a dial indicator and a seal installer.
At the very least, I would replace both U-joints and check the locking hubs for signs of damage because that's where I think your problem is.
Dan

[1972MaineK5]

Thanks again hemi43. I really do appreciate the input. So... well yeah... replacedthe diff. Fluid yesterday. What a mess in there. Milky white oIL and milky white sludge. Some of it like toothpaste some stuck and alost like bubble gum stuck to non meshing surfacea. It's definitely been running a while with water in there. So I did clean it out and put in fresh oil. My intent... because I'm sure I didon't get it all was to run this for a couple hundred miles or so and then switch it out again. I'm thinking water through the vent fitting. I blew air threw it when I had it apart and it's wide open. I've been driving around it wet puddles and snow for 3 or 4 months now so I'm sure that's how water was getting in. And... while I dont think that was the solution to my problem mysteriously I had no steering issues at all today.so I'll keep an eye on things and keep investigating as I have time. I considered pulling the locking hubs yesterday... covers at least but just didn't have time. 2 young kids.. work full time. Really do enjoy working on cars, mechanical engineering background. But it's always a question if I have time to do it myself. I've got a great guy who I trust completely and charges $49 hourly. Sometimes it's just easier to pay for a couple of hours work that would take an entire Saturday afternoon. Also in about 2 months the 66 Chevelle convertible will be on the road and I'll be able to leave the blazer to have my guy take it a step beyond what I'm willing and or capable of doing.

My previous car was a 99 range rover. So I spent 9 years with that beast diagnosing and problem solving and fixing. That thing always had something wrong with it. And if I didn't do it myself there was no way I was paying to have a dealer even look at it. I've been enjoying the blazer imensly. Generally speaking very easy to diagnose and remedy problems but also so relatively cheep in comparison. Blow motor $19. Coil and module $45 or so.

So I think I'll pull the locking hubs and take a peak. No grease in there from what I've seen. Light oil. And it doesn't look like there is any way to grease anything in the front end from my inspection. Ball joint, u joints, wheel bearings all closed with no fittings.