1990 Suburban Manual Transmission Swap Noise

[linux2]

Back in October I bought myself a 1990 Diesel 2500 Suburban 4x4 which had a TH400 Automatic transmission in it. I've owned quite a few 6.2L diesel GM vehicles over the years and I can't stand the 3 speed auto behind it. I had owned another 2500 diesel suburban years ago that had a 700r4 behind it, which I actually liked quite a bit. Despite the negative comments I see about them I never ran into any issues the 40K miles I put on it.

While I was looking to convert my Suburban I was seeing quite a bit of modifications that would be needed to do this. So I started to look into a manual transmission swap. I'll cut the details short, but I now have a remanufactured NV3500 transmission installed in the Suburban.

Everything works great except for a "chatter" or "metallic" noise when the transmission is in neutral. I previously had a used NV3500 installed while I was seeing if everything would fit together. It also made the same ratting noise, but I figured it was something in the transmission. However, the remanufactured transmission makes the same noise. I'm wondering what I may have done wrong.

I put in a brand new flywheel, clutch, pressure plate, throwout bearing, clutch fork, and master and slave cylinder. I'm positive I installed the throwout bearing correctly on the fork. I'm wondering if anyone else has ever had similar issues with an NV3500.

As a note, as soon as you push the clutch in the noise stops. If you let the clutch up slowly, it starts making the noise as soon as the clutch engages with the engine. Again, this is only in neutral. When the vehicle is in gear there is no noticable noise, except if the engine RPMs are on the lower side, then you get a rather noisy gear chattering noise (perhaps maybe another clue as to what is wrong). The speedometer also moves when in neutral, so the input shaft in the transmission is rotating all the way through to the transfer case (where the speedo sensor is) and registering some small amount of movement.

I'd like to note that I didn't have many instructions when installing so I did place grease on the input shaft and on the bearing "guide" shaft (seemed to make sense to have that be lubricated). Otherwise it was a pretty straight forward install.

Any ideas on this? I had a chevy pickup (1500) that had an NV3500 in it stock and it made the exact same noise, but I figured it was the throwout bearing. Perhaps it wasn't.

 

[yevgenievich]

I had the same thing happen, but on a different type of vehicle/trans after puting in a parts stoere clutch/pressure plate/bearing. Chatter sometimes can be normal for certain setups. It might be ok the way it is.

 

[CSFJ]

I've heard many people complain that the nv3500 is a noisy trans. can't recall the specific noise complaints, but if you're hearing the same chatter from 2 different trucks, then that's likely it. Since they're a 1/2 ton truck trans, they're a popular swap into older jeeps, and were the factory installed trans for a few years ending in '04 or '05. I've heard that the nv4500 requires a special gear lube, does the same apply to the Chevy version of the nv3500?

 

[linux2]

Yeah, the NV3500 requires "synchromesh" fluid. I put that into both transmissions. From what I've read the NV3500 can develop a whine, which my used one had quite badly. This whine was in all gears except 4th. Within 400 miles the transmission blew up. Investigating that transmission showed that the read output shaft seal had gone bad, the previous owner kept driving it, and surely enough it ran low on fluid. That in turn ruined the internal bearings and that was the end of that. The rebuild one is nice and quiet (except a little bit a noise, but basically silent compared to the old one). I have a video here somewhere I should upload to show the noise.

I think I'll pull the transmission this weekend and take a look at the throwout bearing. I think maybe the issue is some grease on it or an improperly adjusted/installed clutch fork allowing it to possibly rattle around. I'll let you know my findings once I can take a look.

Thanks for the feedback though. My truck is almost ready to be driven daily

 

[bucket]

If the throw out bearing turns out to be OK and the fluid is clean, I'd just run it. Was the 3500 ever used behind a diesel?

 

[linux2]

Yep, I'll let you know once I have a chance to take a look at it. As far as I know the NV3500 was never offered with the 6.2 diesel or any other diesel, but it's max torque rating is somewhere between 275 and 300ft lbs. The 6.2 engine I have outputs 277 ft lbs so it should work ok. I don't drive very hard and it seems to be fine so far.

 

[bucket]

I agree it should hold up if you don't beat on it. I just wonder if the added vibration of the diesel is what's causing the rattle.