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TH400 to a NP205

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by **DONOTDELETE**, Apr 21, 2001.

    I am looking at a TH400 w/ TC and its mated to a NP205 w/ slip yoke in the rear out of a 1980 truck. What I want to know is what is the difference between TH400's, I have heard there are some that have a short shaft and some with long or is that the NP205's input shaft? Next question is probably for Shawn since he has done it. What do you have to do to swap out the slip yoke for a fixed and a guesstimate of costs.

    [​IMG]<font color=red>BigBurb[​IMG]
    <font color=purple>IF YOU'RE SCARED, SAY YOU'RE SCARED !!
     
  1. Wheels

    Wheels 1/2 ton status

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    First you'll need the output shaft that has .875" length (measured from the end of the housing to the end of the shaft). If it's already mated to a 205, your good to go and have a priceless jewel. A th400 np 205 has a larger input bearing than a th350 205. (A th350 205 can be machined to accept the larger bearing). To convert a slip yoke to a fixed yoke you need a fixed yoke output shaft. They are no longer in production (I found one at 4xheaven and it was the last new one they had at $245) so unless you get lucky, you'll have to find a good used one. You'll also need a new or used output shaft housing (for the fixed yoke style). You'll need a good set of split ring pliers. Sears, Lisle, Snap On all carry them and get a set the opens up to at least 2". Remove the output housing (aluminum one) and you'll run into the first split ring. Remove this split ring and then remove the bolts that hold the second output housing (metal). Remove this housing and the output shaft bearing. Tip the case slightly back and work the output shaft out. There are roller bearings on the inner part of the output shaft that should be held in place with a retainer clip. Best to take this to a work bench with room to lay the parts out for re-assembly. There should be a spacer, speedo gear, another spacer, a ring and two thrust washers that come off before the output gear. When you take the output gear off, there are two rows of roller bearings that are inside it seperated by a washer. Watch where they go, you'll need them all. after the gear is off. there is another thrust washer held in place by a small pin that should come out with a small magnet. Inside the output shaft at the front, there is a snap ring and washer that hold some more roller bearings. When you get them out, the new shaft is ready to go together. Assembly is reverse of the above. When putting the roller bearings in the front of the input shaft, the roller bearings go in first, put grease on them to hold them in place. Followed by the washer, then the snap ring. Assemble the rest of the components on the shaft (one of the snap rings will not be reused, it's about halfway up on the old shaft). Install the shaft in the housing making sure that it is seated properly. Dry assemble the metal housing (no seal yet) with one or two bolts to hold it in place. Place the aluminum housing on and mark the spot where the oil drain back slot is onto the metal housing (use a pencil). Remove the metal housing and drill an oil drain back hole in it (if it's not there, oil will blow by the seal from what I was told). Now it's ready for full assembly. Torque metal housing bolts to 30 ft lbs, and aluminum housing bolts to 25 ft lbs. Output yoke nut 150 ft lbs. The Chilton manual has a good break down of the internals drawing on the 205.
     
  2. Shawn

    Shawn 1/2 ton status Premium Member Author

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    My slip to fixed yoke 205 was easy. I purchased a used 205 fixed yoke for $230 and was able to sell the 465 adapter for $100 so it reallly cost $130. I then just swapped the tail housings and shafts. Easier than I thought. I did call one place that wanted $150 for just the fixed yoke parts. I was going to put the slip yoke parts on the other 205 and sell it but haven't had the time. Looks like wheels has a good description of whats involved. Watch out for those roller bearings!

    Shawn
    87 K5
    few mods[​IMG]
    <A target="_blank" HREF=http://www.off-road.com/chevy>http://www.off-road.com/chevy</A>
     
  3. I may go ahead and buy this one out of a 1980 truck and run it with the slip until I can find the parts I need to convert it. That for the in depth instructions.

    [​IMG]<font color=red>BigBurb[​IMG]
    <font color=purple>IF YOU'RE SCARED, SAY YOU'RE SCARED !!
     

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