High Pitch rattle from Transmission or T-Case when letting off throttle

[chrisok5]

Hey all - First post in years! I just purchased a 72' and stoked!
Its got the following already done before purchased:

• 5.3
• TH350
• NP205
• 10Bolt Front
• 14Bolt FF rear
• 4:11s
• B&M floor shifter

I noticed when I get to 30 or above and let off the throttle, there is a high-pitched rattle coming from the Tranny/T-case area. It gets louder when I let off the throttle at higher speeds.

So far my searches rendered:
- Check pinion angles and u-joints
- TCI Transmissions having some missing parts causing a rattle

I'd like to run a list of things to check. Any help would be greatly appreciated. I'll post a photo soon!

Thanks
Chris

 

[Babaganoosh]

I just found my issue that sounded the same, the rear yoke has stretched and allows the cross shaft in the u joint to move back and forth.

Pinion bearing? Can you move the driveshaft?

 

[ekajkrats]

Welcome to the First Gen Blazer club! Looking forward to your pics.

Also, did you check the fluid levels? My seals are shot between the transfer case and transmission, so the transfer case stays full, and I have to keep an eye on the transmission fluid level.

 

[skunked]

Are you sure it's a np205?

 

[chrisok5]

I just found my issue that sounded the same, the rear yoke has stretched and allows the cross shaft in the u joint to move back and forth.

Pinion bearing? Can you move the driveshaft?

Thanks - I'll check tonight!!

 

[chrisok5]

Are you sure it's a np205?

Are you asking because you don't think that combo will fit? I haven't verified with my own eyes but sure as hell will now (flame on for not verifying before buying!!). We did talk about some of the mods he did to make it all fit but that was a few weeks back. I also have receipts for the shop he got some of the work done. I'll comb through as well.

 

[skunked]

Are you asking because you don't think that combo will fit? I haven't verified with my own eyes but sure as hell will now (flame on for not verifying before buying!!). We did talk about some of the mods he did to make it all fit but that was a few weeks back. I also have receipts for the shop he got some of the work done. I'll comb through as well.

That combo will fit and work fine. I ask because if it's an NP203 the symptoms you describe are also symptoms of a stretched NP203 chain.

 

[chrisok5]

That combo will fit and work fine. I ask because if it's an NP203 the symptoms you describe are also symptoms of a stretched NP203 chain.

Ah, got it. I'm 90% sure that it is a 205 but thanks for that one. I'll be pissed if I found out it wasn't. One of my major considerations for getting this one was the 205.

 

[chrisok5]

Welcome to the First Gen Blazer club! Looking forward to your pics.

Also, did you check the fluid levels? My seals are shot between the transfer case and transmission, so the transfer case stays full, and I have to keep an eye on the transmission fluid level.

Thanks - fluid levels look good. I do have a small tranny leak but it looks like its the cooler line. Everything appears to be relatively new.

 

[chrisok5]

I just found my issue that sounded the same, the rear yoke has stretched and allows the cross shaft in the u joint to move back and forth.

Pinion bearing? Can you move the driveshaft?

No play in the rear drive shaft at all and the angles look fine. I'll take photos and measure when I get more time

 

[Babaganoosh]

No play in the rear drive shaft at all and the angles look fine. I'll take photos and measure when I get more time

Only way o found my issue was setting the ujoint into the yoke and pushing it back and florth. I believe I had a weird scenario though.

 

[sponsoredbydad]

Sometimes the only way to find those sounds is to put it up on jack stands and run it. Unless you have access to a lift (Which is a safer method)

 

[chrisok5]

Only way o found my issue was setting the ujoint into the yoke and pushing it back and florth. I believe I had a weird scenario though.

I did find the front shaft with major play in the slip yoke so the front is shot. I don't think that would cause a consistent rattle at decel, would it?

 

[chrisok5]

Sometimes the only way to find those sounds is to put it up on jack stands and run it. Unless you have access to a lift (Which is a safer method)

I probably won't be putting it on stands to idenitify it because I'd have to get it up to 30mph to replicate. That'd be too sketchy! I have a buddy with a lift. Dude is at Disneyland though so I gotta wait.

 

[Babaganoosh]

I did find the front shaft with major play in the slip yoke so the front is shot. I don't think that would cause a consistent rattle at decel, would it?

I don't think in 2wd the front shaft would be spinning but I have no experience with a 205. Wouldn't hurt to remove it just to narrow it out and give it the attention it needs.

 

[chrisok5]

Here's that pesky rattle. I didn't get the chance to pull the drive shaft yet. This was around 40mph. It gets louder and deeper when I get up to 50.

 

[SpeedlabDan]

Here's that pesky rattle. I didn't get the chance to pull the drive shaft yet. This was around 40mph. It gets louder and deeper when I get up to 50.

I have a similar noise and about the same situation. I didn't think it was the front driveline as a np205 does not turn the front in 2h. I did have poor (too much) pinion angle in the rear (6" lift).
I ended up losing that shaft a couple weeks back, corrected the pinion angle with new perches and I'm presently awaiting a double cardan 1350 u-joint shaft from high angle driveline. I'll keep ya posted