I should preface this with it could fall either under the axle tech or transfer case tech. That’s why I’m writing this: I have a 72 pickup with an automatic, NP205, and Dana 44’s at each end. I get a heavy clunk along with a short gear grinding noise after about 5 minutes of driving. It’s more prevalent during/after a turn and decelerating. Doesn’t do it all the time. I think I ruled out from the front of the transfer case on because I removed the rear driveshaft and drove around for about a 1/2 hour - didn’t do it. So, in my mind it leaves me with the rear output of the transfer case or the axle. I don’t know, I popped off the diff cover and there was no spec of metal or anything … almost too clean. Did the same with the TC, stuck my magnet up in there and pulled maybe two specs of metal - not enough to convince me it’s the problem. Oh yeah, and there’s very little play in both yokes. Before I start tearing things apart I’d like to solicit some opinions. I’m not convinced that because the diff was so clean it’s NOT the problem. May very well be … which I’m hoping it is because I’m really not in the mood to drop the TC, but I digress …
Clunking Noise
- Thread starter Mike DQ
- Start date
Scoutboy74
Moderator
What's your history with this rig? Has it got any kind of a locker in the rear or is it open diff?
Ah yes, should have mentioned that: open diff - no posi, no locker. To answer the first question, the truck is a bit of a Frankenstein ... I've had it for 20+ years as a 2-wheel drive, I then converted it a couple months ago. So, the Dana 44 front and transfer case came out of a wrecked '75 pickup sitting at Pick and Pull; the rear end came out of a '70 Travelall. Both 3.73 geared. Long story short, I don't really know the history of the 4x4 components.
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Scoutboy74
Moderator
Ok. So did you drive it all before you did the conversion?
Scoutboy74
Moderator
Re-reading through your last answer after having now consumed some caffeine has me realizing my last question was stupid. Have you examined the diff and pinion gear surfaces for abnormal wear patterns? You might need to get some gear pattern marking compound in there after thoroughly cleansing the gear teeth to see what the mesh is.
Welcome to the NP205 life. They usually sound like a grain mill. The cross-members tend to crack. The bushings are also probably wiped out on the cross member. Could also be the shift linkage. Saggy body mounts also cause the cab to hit the t-case cross member at times.
Based on your response, it seems you're leaning toward the differential being the culprit and I'm also leaning that way. I've done a little searching and the most popular answer is that the spider gears are having issues.
Thanks Zaedster - I know of the weak spots on the crossmembers so I reinforced this one. The bushings are good because I got them from you guys. There's about 1 1/2" clearance above the crossmember so there should be no banging against the floor. The one flimsy reason I'm focusing more on the differential is because when you do a slow turn in a parking lot, let's say, you can hear a rhythmic light clunking through the whole turn - the same timing as if you're in 4-wheel drive turning on dry pavement, if that makes sense. So it makes sense to me that it's fighting the wheels going at different speeds.
Anyway, I'm assuming you have a bunch of Dana 44's at the yard?
Thanks Zaedster - I know of the weak spots on the crossmembers so I reinforced this one. The bushings are good because I got them from you guys. There's about 1 1/2" clearance above the crossmember so there should be no banging against the floor. The one flimsy reason I'm focusing more on the differential is because when you do a slow turn in a parking lot, let's say, you can hear a rhythmic light clunking through the whole turn - the same timing as if you're in 4-wheel drive turning on dry pavement, if that makes sense. So it makes sense to me that it's fighting the wheels going at different speeds.
Anyway, I'm assuming you have a bunch of Dana 44's at the yard?
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If it is an early Dana 44 with tapered SET7 axle bearings, that would make sense. Possibly someone has been in the axle before and botched the assembly and proper pre-load of the axle bearings and did not reinstall the thrust blocks in the carrier.
We don't have any good axles in the yard at the moment. We build Dana 60's in 5-lug all the time for the 1/2 ton guys. If you are interested, contact us for a quote. It is the way to go if you plan on not having to rebuild your rear axle every year.
We don't have any good axles in the yard at the moment. We build Dana 60's in 5-lug all the time for the 1/2 ton guys. If you are interested, contact us for a quote. It is the way to go if you plan on not having to rebuild your rear axle every year.
As a follow-up for anyone who cares ... going over it extensively with the guys at the gear shop and it looks as if it's the NP205 and the internal front drive gears banging around wanting to engage. Obviously some wear on something. The axles are fine. I'm going to give rebuilding it a shot.
DarylBrooks
New member
Rattling and crunching noises after driving for a while can be related to powertrain components, be it the rear output of the transmission or the shaft. Since you've ruled out the front end of the assignment case and checked for differences and TCs with minimal findings, that's a bit confusing. Playing in the yoke is minimal, which is a good sign.