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1979 Chevrolet Blazer - Grinds

Little info first. Bought this 1979 K5 Blazer as a toy about year ago. It has a 350 with Dart Iron Eagle heads, quadrajet carb, 350turbo tranny with a NP 203 transfer case with the part-time conversion sitting on 36’s and a 4" lift. It had some engine issues ( a lifter needed replaced general tune up needed) so I parked it to tinker on when I felt like it. Daily driver got repo-ed so I did the work to make it my daily driver about a month and a half ago.

So about 2 weeks ago I was leaving the store and when I shifted from reverse to drive there was a quick ( about a sec) but loud grind noise. I assumed it was my transfer case. I only lived about 6-7 blocks ( which it drove with absolutely no noise or problems) so as soon as I got home I checked my trans fluid which was fine.

There was a small puddle of what looked like engine oil next morning (which it does leak oil a bit from around the timing chain gasket) so I didn’t think anything about it.
I continued driving it like normal (small trips of usually less than a few miles) and it would occasionally make that small grinding it always shifting from reverse to drive.

Here lies the true problem. I went to make a quick run to grab something to eat and got about a block from my house when it suddenly made a small grinding noise and acted like I stomped on the brakes. Besides completely freaking out my 15year old, I let it coast a bit gave it a little gas and it started forward like normal, for about 25-50 feet before doing it again. Thought it must be my transfer case that was leaking and out of fluid.
Best way to explain it is like I shifted the transfer case from Hi to Low.
So I put it in 4wd, locked the hubs and limped it home with no change. Pulled the plug on the transfer case to check the fluid level and it’s still full.

The transmission doesn’t have a history of shifting rough or late, have whinning noises or anything other than the usual “Chevy hard shift into gear” that every chevy I ever owned did.

Really scratching my head here on whats going on but hope someone here can point me in the right direction.

Thanks in advance, Daniel

How about the oil level in the rear diff ?
How are the U-Joints?


U joints are good. Borrowing a pair of Jack stands that are tall enough to raise the truck off the ground to check the differentials in the morning. Changed the fluid and filter today as well as the modulator, checked all vacuum lines, and did visual inspection of flex plate which looked fine. No change after work today.

Should be able to check the differentials without jacking it up if it’s rolling on 36” tires, no?

I can get under it fine but to do any work in it I will need to right?

I was thinking you can check the fluid levels and look for anything obvious without jacking it up. But, you’re right. May be better to put it on jackstands, rotate the wheels, and look/listen for binding, grinding, etc.

Where is the oil leaking from? Pinion seal if so equipped my guess would be shot bearings.

The oil is leaking from the timing chain cover. Not a severe leak. About a quart every week and a half to two weeks. Gonna check the fluid in the diff today, had stuff come up so didn’t get to it before. Should I go ahead and pull the cover or just check from the fill hole? Thinking pulling the cover might be better and put new fluid in it anyway so I can do a visual check and look for teeth or excessive shavings.