So I finally rebuilt my NP208 T-Case with one of the last few remaining overhaul kits from Yukon Gear. The real issue was the oil seals were just old and cracked, and the RTV gasket on the rear output cover had failed. It was leaking so badly at the end that it would loose a quart a week.

The whole thing went pretty smoothly, and was alot easier than I expected. Once back together I let it sit for a week just to let the new RTV cure, and bolted it in Saturday morning.

This was the first "major" mechanical repair Ive ever done, so I was a little hesitant when starting up for the first time. I turned the key and it fired right up, put the truck in reverse and nothing. Absolutely Nothing.

After shifting through the gears, and 2H, 4H, 4L a few times it hooked up and backed out. Ok, now on to Drive....again nothing. I revved the engine to 2500ish (wish I had a tach) and it hooked up going forward.

I was really hoping to finally get to use my truck again, but she is stuck in the garage for the time being until I can figure out whats going on. Here is what I have so far:

1 - No grinding noises - Would assume that a t-case full of gears would grind if I did something that wrong.

2 - Does it in all gears, including Reverse

3 - Transmission fluid level is high, but no higher than its ever been

4 - The adapter between the C6 and NP208 was full of oil when I pulled the t-case...not really sure if it came from the transmission, or the t-case, or if it is supposed to be there (but the shop manual makes no mention of re-filling it)

My best guess - The torque converter is either shot, or partially empty and not refilling. Possible solution - Replace Torque Converter. If not refilling, consider new / rebuilt transmission at the same time as its part of a larger issue.

Anyone else have any thoughts?

 

If you determine it's a tranny problem, don't try to do surgery on it, like "just replace the converter". If the old converter went bad, it sends it's metal shavings throughout the tranny, and it will never work right again unless the whole thing is taken apart and cleaned up, and this is usually the time it gets a rebuild also(the whole tranny). You also have to be careful about the oil cooler in the radiator. A local tranny shop I use will not warranty their trannies unless they install them, because they properly clean out the oil cooler in the radiator which most people don't do when installing a rebuilt tranny. The filth in the oil cooler from the original tranny grenading itself ruins the new rebuilt tranny.

 

Was the trans acting up before you removed the NP 208?Was the np 208 rebuilt only because it was leaking,or was there a problem with it?I had a converter let go in a GM turbo 400 and it was noisey.From the description you give of having to bring the RPMs up to go forward or back,it sounds like the trans is going.Pulling the trans from a 4x4 is a PITA unless you have a hoist.You might want to get a transmission shop to do a diagnosis,and then do the R&R yourself.I've done three c6 4x4 R&Rs.The second time I bought a transmission jack adaptor that goes on a trolley jack,and that helped a little.

 

Can't think of any reason the t-case could do that, so it must be the tranny. But big vann's question re whether the tranny did that before the t-case rebuild is the key.

 

Seems like a little more background information is needed.

I pulled and rebuilt the t-case only because it was leaking. It started out as a slow occasional drip in the fall of 2010. By the fall of 2011 is would loose a quart a week and I knew it was due for an rebuild.

Last time the truck really got driven anywhere was Columbus Day weekend when I took it 3 1/2 hours to and from Vermont for the Harpoon Brewery Oktoberfest. Since then it has done nothing but 15 min trips to and from the dump or lumber yard when I did some work on the house the week before Christmas. Due to the leak, and my indecision on what rebuild kit to buy the truck didn't do much other than sit the rest of the time.

During those few trips I did notice that there was an issue when getting moving from a dead stop at a traffic light. It would occasionally hesitate a second or two, but then get going along like nothing was wrong. Nothing like now where Im dead in the water till the rpm's get up.

While the body and frame on my truck are good and solid, I knew the driveline is old and tired. The plan was (is) to replace the motor with a 95/96 roller (Franklin, I will be most likely asking you about a cam & intake setup for a holley 4 bbl in a few weeks) and rebuild or replace the transmission in the April/May.

The only issue is that between now and then is that Im supposed to take the last week of March off to work on the house again, and will need the truck for dump & lumber yard runs.

Ultimately this is more of a confirm it is not the t-case & figure out if and how it can be band -aided to get me through my home renovations. If it were up to me, I would swap the week on the house for a week on the truck, but the wife might (read will) take issue with that.

 

I doubt anything has failed while sitting still. More likely is that varnish or some other debris is blocking a passage in the valve body. I will pull the shop manual out in a bit and go through their diagnostic chart to see what it says. However, if it were mine I would be trying an inexpensive fix like running Sea Foam's tranny conditioner in the lube. And, others on here have said that a run in reverse at the highest speed you feel comfortable doing may help.

But, I think you said something about the fluid level being high, although no higher than it has been. How high? I'm not sure I'd add to that problem by just dumping the Sea Foam in. If it is very high maybe you can pull some of it out by putting a hose down the dip stick tube and draw some out - either syphon or with a bulb.

 

Out of 7 pages of transmission diagnostic guides in the factory shop manual, the only one that comes close to applying is the following. But, I'm assuming that once you get the transmission to engage it works reasonably well. However, making assumptions isn't a good procedure on diagnosis of problems, so please advise.

Slow Initial Engagement:

• Improper fluid level
• Damaged or improperly adjusted linkage
• Contaminated fluid
• Improper clutch and band application, or oil control pressure
• Damaged 2-3 accumulator

Thinking about what has transpired since it last worked properly, I don't think the clutches or bands have changed, nor that the accumulator has been damaged.

You might have messed up the linkage when you pulled the t-case, so you could pull the bolt that secures the link from the tranny to the shift linkage and recalibrate that by ensuring both the shift lever and tranny are in park and then tightening the bolt down. As for the kick-down linkage, you could actually take it loose from the carb for a test to see if it is returning to the forward position, which it should. In fact, you can leave it loose for a brief test.

That gets us back to the fluid, and its level. If it is high, then why? What might be in it to raise the level? Has the cooler in the radiator leaked coolant into it? Or, has it just been over-filled? I'm thinking this has something to do with the fluid and/or its level. And, depending on how long it has been in there you might want to change it, although that can be messy and it does have a cost due to the quantity of fluid required. However, I have seen fluid changes make a transmission that wouldn't function well at all work properly immediately and continue to do so for years.

And, if you just want to go quick and dirty there is Sea Foam. I've seen it work to make a transmission shift properly after it sat for years and apparently had gum or somesuch in it.

 

But, remember... statistically speaking, there is WAY more of a chance the problem exists in or around the component that was just changed.

 

Very true. But, the t-case is a very mechanical component, meaning it shouldn't be able to finally engage after revving the engine - not without horrible grinding noises I would think. The only thing I can think of that could do this is the C6 with the pump not bringing the pressure up enough to bring the clutches/band in initially.

 

Right, I tend to want to agree, given all else being equal and unmolested.

But, has anybody verified this?

It would be extremely coincidental (although not impossible) for a transmission problem to emerge at just the time the transfer case was dorked with.

Of course, it could be thing sat for 18 months during which time the transmission leaked out all its fluid, or the innards glued together, or whatever, the transfer case was then rebuilt which added 6 months, put everything back together and now there are weird problems. So, it is certainly possible.

But, statistically, the problem was instigated by a recent change....

 

The fluid level has always been high since I bought it, about an inch above the top mark on the dipstick, but I have always heeded the advice of my HS shop teacher that if its not broke, don't fix it applies double to auto transmissions.

I followed the shop manual step by step when pulling the t-case, so anything that I meant to disconnect was reconnected when it was bolted back in. That said, I and also inclined to agree with Tubutis that statistically there is a good chance I screwed something up on the transmission when either removing or reinstalling the t-case.

When I get home I will check all the linkages and hoses to see if anything jumps out at me. If there is nothing obvious I will try draining all the fluid I can, look over the valve body, and refill with new fluid and some seafoam. I have a new gasket and filter sitting on the shelf so all I need is the fluid.

Are there any rookie mistakes that I should be careful of in a drain / fill or cleaning a valve body?

 

First, I hate to differ with your shop teacher, but 1" above the full line is way too much fluid. That will cause aeration of the fluid. But, if it has always been that way it doesn't sound like something has leaked in.

As for having done something incorrectly on the t-case, if you followed the steps closely I doubt you did anything wrong. But, check the linkages as well as the vacuum modulator hose, making sure it is connected and that it isn't leaking.

Concerning rookie mistakes on draining a transmission w/o a drain plug, the mistake would be to expect that you can do so w/o making a big mess. YMMV, but I haven't done it cleanly yet and I've had some practice. The book will say something like "loosen the bolts all around and pry down one corner". In my experience when you do that the pan will come loose on all four sides at the same time, drop down, and fluid will go EVERYWHERE. I would recommend figuring out which corner is the lowest by using a level. Then loosen those the most and the ones on the opposite side just a teeny bit to allow the pan to move but not drop down.

Also, I would get one of the big drain pans from the parts store, the ones that are something like 2' x 3'. They don't really hold all that much, but they do contain the inevitable spills. However, you are also going to need a larger container into which you hope to get the bulk of the ATF. And, don't forget to pull the inspection plate on the torque converter and drain that as well. You'll have to turn the engine some to find the 1/8" drain plug, but it is there. And, the TC holds quite a bit of fluid so it is a must to change if you want new fluid.

As for the valve body, I have never done that. I leave that alone. Change the filter, but leave all the rest alone.

And, follow the directions on the gasket. If it says to put it back dry, do so. If you elect to use RTV you will have to let it set until it sets up, maybe over night, or your gasket will try to slide out between the bolts due to the lubricity of RTV.

 

Rookie mistake #1. Overfilling the tranny. If it gets too full, the oil gets up into the spinning parts above, and gets stirred up and foams. The foamy fluid doesn't work right when it gets in the hydraulics of the valve body and the pump.

 

I looked everything over when I got home, couldnt find any obvious issues. Shift linkage as tight as its ever been, shift points are accurate, vacuum line is in good shape and connected. Pulled the truck out and was hoping or one of those walk away for a day or two and com back to find the problem having resolved itself type situations, but no luck there. Same sort of delayed engagement.

Took the wife's blazer to NAPA and became aware of another symptom. When I put her (working) auto into Reverse or Drive I felt a subtle surge as it got into gear. The truck used to do this as well, but not now. Engine running and foot on the Brake I can go from P to R, D, 2, or 1 and feel nothing.

Back home I dumped the trans pan, converter (drain plug was right there between 5 and 6 o'clock. Good thing too, with the Y pipe right there it would have not been much fun to try and turn it over looking for the plug. I also used 10 psi of air to clear the cooler and lines. In all got about 9.5 of the 11+ quarts of fluid out.

Everything inside looked good. No sludge, no burned smell, no chunks of material (i put a screen over the hole in my drain pan to catch anything that might come out for examination). Only thing I noticed were a few steel filings on the bottom of the pan where I routinely stick I light with a magnet (is there a reason the t-case has a magnet in it, but the transmission does not? If not Im going to stick one in there next time its open)

I cleaned up the gasket surfaces, put everything back with a new gasket, and started refilling. I knew I was high with the 9.5 i got out, so I went back with 7 to start. With the truck in P I started it up, and let everything come up to temp and shifted through the gears. Still felt dead. Added 1 more quart, shifted to D and felt a bit of a surge, and felt a little bit of hope.

Did a quick loop in the condo parking lot and was pretty disappointed. I still have to rev the engine pretty good in order for anything to happen. Up to that point it really just feels like the motor is not connected to anything. Im going to try again when I get home this afternoon, see if it was just an air purge issue from the fluid change, but my hopes arent to high.

 

Sounds like you have done everything correctly, with the possible exception of the amount of fluid you put back. Where does the fluid level show on the dip stick? That is important.

Also, the one I had with shifting problems looked very clean inside. However, there must have been something, like gum or whatever, somewhere in the innards that kept it from working correctly. So, don't give up quite yet. Put the Sea Foam in and drive it awhile.

Also, once it does "connect" does it shift properly? I think that is what you meant by "the shift points are accurate", but does it shift quickly or slowly when it reaches the shift point? And, after the first "connect" does it stay connected?