Turbo 350 NP205 Leak - The 1947 - Present Chevrolet & GMC Truck Message Board Network

leatherhead63 · 11-30-2008, 09:18 PM

My Turbo 350 trans is loosing fluid and my NP205 is leaking on the
output shaft. No visible leak at the tranny. I have heard that the coupling between the two can be the problem. Is there a path for fluid between the
tranny and the TC

thanks

1-tonmudder · 11-30-2008, 09:29 PM

The seal's in the trans/case adapter are bad and fluid is bypassing them and filling the case.Pull the fill plug in the case and see if the case is overfull with ATF.

Cyclone · 11-30-2008, 09:30 PM

There are two seals in the transfercase adapter, one to keep trans fluid from going to the TC, another to keep the TC fluid from the trans. Sounds like you need to drop the transfercase, remove the adapter, replace those two seals, re-install.

Picture see#37

leatherhead63 · 11-30-2008, 09:37 PM

did a search and found the same advice. Thanks.

hdflstf · 11-30-2008, 11:17 PM

Actually there are 3 seals. Been there done that. There are 2 seals on the outside diameter of the coupler (these are the likely leak path). Pay attention to the direction they are installed since they are backwards from what you would normally see.
Third seal is a thick o-ring on the NP205 input shaft which seals with the inside diameter of the coupler.

Chevy1TonFun · 12-01-2008, 12:49 AM

Quote:

Originally Posted by hdflstf

Actually there are 3 seals. Been there done that. There are 2 seals on the outside diameter of the coupler (these are the likely leak path). Pay attention to the direction they are installed since they are backwards from what you would normally see.
Third seal is a thick o-ring on the NP205 input shaft which seals with the inside diameter of the coupler.

Yep thats true. I just did that on my th350 and 205.

leatherhead63 · 12-01-2008, 01:25 AM

I see I;m not the first. Thanks for the good info. Just got it back on the road. will most likely wait a week or two before tearing it down. Need to fix or replace a leaky power steering gear box first.

shiner · 11-02-2009, 02:30 PM

I've recently got the same problem. Quick question though, today's Monday and I'm planning on going camping/hunting this weekend, about 180miles round trip. What kind of danger am I looking at driving it this way? Its opening weekend by God.

Gene · 11-02-2009, 07:02 PM

Ran into the same problem, took my 205 to my transmission guy to check it out and install new seals while he was changing my output shaft to a shorter one on my TH350, and when he pulled the plug there was more AT fluid than gear oil. He assured me that it wouldnt hurt anything and it's pretty common.

Chevy1TonFun · 11-02-2009, 08:58 PM

Quote:

Originally Posted by shiner

I've recently got the same problem. Quick question though, today's Monday and I'm planning on going camping/hunting this weekend, about 180miles round trip. What kind of danger am I looking at driving it this way? Its opening weekend by God.

You should be fine. I drove my truck for months with ATF leaking into the t case. Its just annoying. Just take some extra AT Fluid with you.

**Thealien** · 11-02-2009, 10:07 PM

Quote:

Originally Posted by Ridin' High

You should be fine. I drove my truck for months with ATF leaking into the t case. Its just annoying. Just take some extra AT Fluid with you.

Been doing this for a year. Don't let your transmission get low!

shiner · 11-03-2009, 11:50 PM

Good deal, thanks for the quick replies.

I pulled the plug on the tc, but had gear oil run out. I'm going to clean up the bottom and see if the fluid is coming from the tranny.

**special-K** · 11-04-2009, 07:13 AM

My`92 K3500 is doing this,but it`s a manual.My NV4500 started whining so I drained the fluid and about a quart came out...no leaks showing anywhere.I left the t-case overall and just filled the transmission back up and all is good until the next time something needs to come out.You can`t hurt the t-case and even if it builds too much pressure it will puke out the vent.I still check levels periodically in case it decides to swap directions.That`s the only thing i`d worry about,is if the gear oil gets into the trans,although the thinned lubricant will leak before the thicker.

fleetmitch · 07-16-2011, 10:54 AM

To follow up, can the leakage problem from Turbo 350 to transfer case also cause downshift problems in the tranny? Admittedly, my trans fluid level got low before I found that it was leaking into the transfer case. But now my transmission won't downshift to first gear at a stop sign. Otherwise, it shifts fine - either manually or if when stopped, I move the lever to first and then back to drive prior to pulling away from the stop sign. I pulled the pan and valve body, and found a very small amount of metal dust (we did a rebuild just a year ago) in the pan and everything in the valve body worked OK. We replaced the detent cable, and even tried adjusting it all the way in. Can there be a pressure issue, whereby not enough pressure (due to bad seals) that the tranny won't downshift?

slider · 07-19-2011, 01:43 AM

I'm going through this right now, turned out my case was bad, found a k case, taking it to my tranny guy in the morning, just hope its a good one.

robs71k5 · 08-24-2013, 02:15 AM

I found this I info here and I believe this to be the issue with my truck Question is can these seals be replaced without totally dropping the tcase maybe just sliding it back a couple inches to get clearance for new seal installation and or would it be an expensive gesture to have it done at tranny shop. Thanks

Quote:

Originally Posted by 1-tonmudder

The seal's in the trans/case adapter are bad and fluid is bypassing them and filling the case.Pull the fill plug in the case and see if the case is overfull with ATF.

Re: Turbo 350 NP205 Leak
There are two seals in the transfercase adapter, one to keep trans fluid from going to the TC, another to keep the TC fluid from the trans. Sounds like you need to drop the transfercase, remove the adapter, replace those two seals, re-install.

Picture see#37
Last edited by Cyclone; 11-30-2008 at 07:34 PM.
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Posted via Mobile Device
Posted via Mobile Device

fleetmitch · 08-25-2013, 01:17 PM

The "adapter" is a short shaft - several inches long, as I remember, and thus you will need to disconnect the transfer case to get it out. In my case (no pun intended), I had Transmission Fluid (which is lighter than transfer case oil), running out of the lever selector rod holes - near the top of transfer case !

DSST_construction · 03-24-2014, 12:31 AM

Does anyone have pictures or part numbers to order the seals? I need to do this asap

Orange Crate · 03-27-2014, 07:56 PM

Here is a post from July last year going over this same issue with answers about the seals.

http://67-72chevytrucks.com/vboard/s...ighlight=NP205

11-30-2008, 09:18 PM	#1
leatherhead63 Registered User Join Date: Jun 2008 Location: Yuma, Arizona Posts: 43	Turbo 350 NP205 Leak My Turbo 350 trans is loosing fluid and my NP205 is leaking on the output shaft. No visible leak at the tranny. I have heard that the coupling between the two can be the problem. Is there a path for fluid between the tranny and the TC thanks

11-30-2008, 09:29 PM	#2
1-tonmudder Modern day Fred Sanford Join Date: Oct 2005 Location: Greeneville,TN Posts: 330	Re: Turbo 350 NP205 Leak The seal's in the trans/case adapter are bad and fluid is bypassing them and filling the case.Pull the fill plug in the case and see if the case is overfull with ATF.

11-30-2008, 09:37 PM	#4
leatherhead63 Registered User Join Date: Jun 2008 Location: Yuma, Arizona Posts: 43	Re: Turbo 350 NP205 Leak did a search and found the same advice. Thanks.

11-30-2008, 11:17 PM	#5
hdflstf Registered User Join Date: Oct 2007 Location: Desert Southwest Posts: 540	Re: Turbo 350 NP205 Leak Actually there are 3 seals. Been there done that. There are 2 seals on the outside diameter of the coupler (these are the likely leak path). Pay attention to the direction they are installed since they are backwards from what you would normally see. Third seal is a thick o-ring on the NP205 input shaft which seals with the inside diameter of the coupler.

12-01-2008, 01:25 AM	#7
leatherhead63 Registered User Join Date: Jun 2008 Location: Yuma, Arizona Posts: 43	Re: Turbo 350 NP205 Leak I see I;m not the first. Thanks for the good info. Just got it back on the road. will most likely wait a week or two before tearing it down. Need to fix or replace a leaky power steering gear box first.

11-30-2008, 09:30 PM	#3
Cyclone Registered User Join Date: Oct 2004 Location: Sonoma, CA Posts: 319	Re: Turbo 350 NP205 Leak There are two seals in the transfercase adapter, one to keep trans fluid from going to the TC, another to keep the TC fluid from the trans. Sounds like you need to drop the transfercase, remove the adapter, replace those two seals, re-install. Picture see#37 Last edited by Cyclone; 11-30-2008 at 09:34 PM.

11-02-2009, 02:30 PM	#8
shiner Registered User Join Date: Jun 2009 Location: Katy, TX Posts: 26	Re: Turbo 350 NP205 Leak I've recently got the same problem. Quick question though, today's Monday and I'm planning on going camping/hunting this weekend, about 180miles round trip. What kind of danger am I looking at driving it this way? Its opening weekend by God.

11-02-2009, 07:02 PM	#9
Gene Registered User Join Date: Aug 2002 Location: Muskogee, Oklahoma Posts: 2,914	Re: Turbo 350 NP205 Leak Ran into the same problem, took my 205 to my transmission guy to check it out and install new seals while he was changing my output shaft to a shorter one on my TH350, and when he pulled the plug there was more AT fluid than gear oil. He assured me that it wouldnt hurt anything and it's pretty common.

11-03-2009, 11:50 PM	#12
shiner Registered User Join Date: Jun 2009 Location: Katy, TX Posts: 26	Re: Turbo 350 NP205 Leak Good deal, thanks for the quick replies. I pulled the plug on the tc, but had gear oil run out. I'm going to clean up the bottom and see if the fluid is coming from the tranny.

11-04-2009, 07:13 AM	#13
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Turbo 350 NP205 Leak My`92 K3500 is doing this,but it`s a manual.My NV4500 started whining so I drained the fluid and about a quart came out...no leaks showing anywhere.I left the t-case overall and just filled the transmission back up and all is good until the next time something needs to come out.You can`t hurt the t-case and even if it builds too much pressure it will puke out the vent.I still check levels periodically in case it decides to swap directions.That`s the only thing i`d worry about,is if the gear oil gets into the trans,although the thinned lubricant will leak before the thicker. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

07-16-2011, 10:54 AM	#14
fleetmitch Registered User Join Date: Dec 2007 Location: Millsboro, DE Posts: 94	Re: Turbo 350 NP205 Leak To follow up, can the leakage problem from Turbo 350 to transfer case also cause downshift problems in the tranny? Admittedly, my trans fluid level got low before I found that it was leaking into the transfer case. But now my transmission won't downshift to first gear at a stop sign. Otherwise, it shifts fine - either manually or if when stopped, I move the lever to first and then back to drive prior to pulling away from the stop sign. I pulled the pan and valve body, and found a very small amount of metal dust (we did a rebuild just a year ago) in the pan and everything in the valve body worked OK. We replaced the detent cable, and even tried adjusting it all the way in. Can there be a pressure issue, whereby not enough pressure (due to bad seals) that the tranny won't downshift?

07-19-2011, 01:43 AM	#15
slider Registered User Join Date: Dec 2002 Location: Oceanside ca. Posts: 26	Re: Turbo 350 NP205 Leak I'm going through this right now, turned out my case was bad, found a k case, taking it to my tranny guy in the morning, just hope its a good one.

08-25-2013, 01:17 PM	#17
fleetmitch Registered User Join Date: Dec 2007 Location: Millsboro, DE Posts: 94	Re: Turbo 350 NP205 Leak The "adapter" is a short shaft - several inches long, as I remember, and thus you will need to disconnect the transfer case to get it out. In my case (no pun intended), I had Transmission Fluid (which is lighter than transfer case oil), running out of the lever selector rod holes - near the top of transfer case !

03-24-2014, 12:31 AM	#18
DSST_construction Registered User Join Date: Mar 2013 Location: Houston Texas Posts: 66	Re: Turbo 350 NP205 Leak Does anyone have pictures or part numbers to order the seals? I need to do this asap

03-27-2014, 07:56 PM	#19
Orange Crate Registered User Join Date: Feb 2011 Location: Under the Truck Dreaming Posts: 755	Re: Turbo 350 NP205 Leak Here is a post from July last year going over this same issue with answers about the seals. http://67-72chevytrucks.com/vboard/s...ighlight=NP205 __________________ 72 K20 Custom Camper, D60, 14BFF, full roller 406 TPI w custom built ECU and yes..it has tow hooks...and a 5 speed



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