TH350 K-Case vs HD Case

[merc359]

So I was bolting up my brand spanking new TH350 with K-case to my brand spanking new NP205 transfer case and one of the four bolts to connect the two units cracked the aluminum bell housing. I took it to a transmission shop who welded it as a temporary fix until I could find a new case, but the moment I bolted them back together again, SNAP, the weld broke. The aluminum is really weak on it and I've made the choice to buy another case.

Problem is, up here in Canada, these damn K-case TH350 are as rare as hen's teeth. I've been calling all over town and had absolutely zero luck finding anything. Through this process, however, I've heard of an HD case that is even heavier.

Three part question:
1. Anyone heard of this HD case? Got one?
2. Anyone HAVE a K-case that i can buy?
3. Is there any aftermarket for these cases? Can I buy something beefy and all new?

I am just going to swap out my innards of the existing transmisison to the new one, so I only really need the case.

Suggestions?

 

[merc359]

Ack!

17 views and no one has any input? Is this really that rare an item?

 

[troutbum_mt]

17 views and no one has any input? Is this really that rare an item?

Have you tried checking outside your area a little? Maybe some junkyards over the border or something?

 

[thatK30guy]

K-case and HD-case are the same thing, aren't they? Unless I'm missing something here, I thought there was only a 2wd and 4wd case.

 

[AJMBLAZER]

K-case and HD-case are the same thing, aren't they? Unless I'm missing something here, I thought there was only a 2wd and 4wd case.

That's what I always heard. K cases were the heavier, thicker 4x4 cases and the 2wd ones where lighter and thinner.

 

[tRustyK5]

I recall Russ (BadDog) killing the "k" case myth...the 'K' wasn't any thicker or stronger than any of the non 'K' cases. The difference, if I recall right, was the dust cover was also a cast aluminum instead of sheet tin.

Just to clarify, Russ broke a bellhousing on a 'K' and ended up measuring several 'K' and non 'k' cases...no difference in the areas he checked. He then went with an aftermarket bolt on bellhousing.

Rene

 

[SUB602]

I had a HD case that cracked at the tail section. I did what you are thinking of doing. Replaced the good inards of the HD case into A regular K-Case. The only difference i notice is that the dust cover is aluminum, but there are braces that attach to the Dust Cover from the Motor for added strength.

I thought maybe i could add the Dust Cover to my K-case so i could re-use the braces but it wont work because the bell housing is a little different regarding where the Dust Cover bolts up.

Heres the K-case Bad Pic


Heres the HD-Case

 

[nvrenuf]

Sub602, the first trans pictured had a "K" cast on it?

 

[SUB602]

Sub602, the first trans pictured had a "K" cast on it?

No it did not, The HD case did though. What i am calling a K-Case could very well be a 2wd unit. I got it from a 78 Blazer and it was a rebuild. Actually after looking at my new case it has a "G" cast into the top. Maybe it came out of a 2wd Van. After doing a little research there is only an HD Case and a regular case as previously stated in this Thread.

Heres a better pic

 

[dyeager535]

Man it's been awhile, but the thin sheet metal covers (2WD, right?) use a different bolt diameter than the ones that use the cast aluminum inspection cover (4WD?), correct?

 

[SUB602]

Man it's been awhile, but the thin sheet metal covers (2WD, right?) use a different bolt diameter than the ones that use the cast aluminum inspection cover (4WD?), correct?

Yes thats what it seems like.

 

[nvrenuf]

Ok, just checking. All of the "K", "HD", etc transmissions I've seen had the thicker converter cover.

Fwiw, I'm not sure about th350's but on th400's I have seen the thick cover cases with "K", "HD", "39" and "47" cast in them. They're always referred to as HD cases but that always seems to be generically related to the thick cover type case.

 

[dyeager535]

As I recall the testing, it was mentioned that the only way to truly measure the cases was to break the bellhousing and measure the thickness there, as the edge (where everything bolts up) is meaningless when it comes to strength. That's where it was determined that there was indeed no difference in the thickness of the bellhousing itself.

But from the pics, it appears to me that the larger bolts required the converter inspection cover flange to be cast differently (wider) than the 2wd variants which actually used screws IIRC.

 

[SUB602]

As I recall the testing, it was mentioned that the only way to truly measure the cases was to break the bellhousing and measure the thickness there, as the edge (where everything bolts up) is meaningless when it comes to strength. That's where it was determined that there was indeed no difference in the thickness of the bellhousing itself.

But from the pics, it appears to me that the larger bolts required the converter inspection cover flange to be cast differently (wider) than the 2wd variants which actually used screws IIRC.

I dont believe there is a difference in strength other than having the Aluminum Dust cover, and only because there is extra bracing that attaches from the Dust Cover to the engine.

Heres a pic of the HD Case and the Aluminum Dust cover attached as well as the bracing.

 

[thatK30guy]

I recall Russ (BadDog) killing the "k" case myth...the 'K' wasn't any thicker or stronger than any of the non 'K' cases. The difference, if I recall right, was the dust cover was also a cast aluminum instead of sheet tin.

This quote is true.

I think too many people get the "thick" wording mixed up when they try to identify a K-case and non-K-case.

What they need to know about the word "thick" or "thicker" is that the only area that is thicker is the seating area where the thick dust cover bolts to. Those bosses with the 6 holes for bolts, not screws.

This picture:

...is NOT a K-case. Its the non-K with the 4 screws to hold a thin dust cover. This is the 2wd case. Sorry but this is no way in shape or form a K-case, nor an HD case either.

K-case and HD case are the exact same thing. They are the thick flange boss utilizing the thick 6 bolt dust cover. These are the 4wd cases that use the strut rods to the motor mount brackets.

A 2wd non-K-case is just a thinner boss with smaller holes for 4 screws.

Time for everyone to learn the differences. If I had the 2 different cases right here to take pictures of and point out the differences, I'd do it but sorry, can't show you now so I try to explain it instead.

This is still hard to explain.

 

[thatK30guy]

I dont believe there is a difference in strength other than having the Aluminum Dust cover, and only because there is extra bracing that attaches from the Dust Cover to the engine.

Heres a pic of the HD Case and the Aluminum Dust cover attached as well as the bracing.
View attachment 69854
View attachment 69855

These pictures are ALSO a K-case as well as HD since they're the same thing.

Just because a tranny came out of a K-series truck doesn't mean its gonna have the thick 6 bolt dust cover tranny. I've seen way too many of these trucks with the 2wd cases with the 4wd output shafts in them and having a thin 4 screw dust cover.

Get it right, guys! K and HD are the exact same thing.

 

[thatK30guy]

As I recall the testing, it was mentioned that the only way to truly measure the cases was to break the bellhousing and measure the thickness there, as the edge (where everything bolts up) is meaningless when it comes to strength. That's where it was determined that there was indeed no difference in the thickness of the bellhousing itself.

But from the pics, it appears to me that the larger bolts required the converter inspection cover flange to be cast differently (wider) than the 2wd variants which actually used screws IIRC.

Someone who has the 2 different cases needs to take pictures of the SIDE of the flanges/bosses where the dust covers bolt to.

A 4wd (K or HD) case will show a thicker flange and 6 bolt holes.

A 2wd case will show a thinner flange.

This is the big confusion everyone keeps messing up. Thick has nothing to do with the whole and overall case of the housing. It only has to do with the FLANGE.

 

[dyeager535]

You got it clear, I understand.

Let me try. As mounted in the truck, the vertical portion of the bellhousing face (the piece that seats against the block) is NOT what we are talking about. The portion of the bellhousing that angles back at a 45* angle (or so) and that the inspection cover bolts to, IS where the castings are different. If it takes bolts, it's a K/HD case, if it takes screws, it's a 2wd case.

Post #14 clearly shows the K/HD inspection cover mounting *bolts*. The 2wd case uses small screws, and a stamped metal inspection cover that has no bosses for the support rods which are also installed in that photo.

 

[thatK30guy]

You got it clear, I understand.

Let me try. As mounted in the truck, the vertical portion of the bellhousing face (the piece that seats against the block) is NOT what we are talking about. The portion of the bellhousing that angles back at a 45* angle (or so) and that the inspection cover bolts to, IS where the castings are different. If it takes bolts, it's a K/HD case, if it takes screws, it's a 2wd case.

Post #14 clearly shows the K/HD inspection cover mounting *bolts*. The 2wd case uses small screws, and a stamped metal inspection cover that has no bosses for the support rods which are also installed in that photo.

EXACTLY!

It's the 45 degree boss/flange area where the dust cover bolts to is what makes a 2 or 4wd case. Period.

I never meant the engine mounting areas. Good thing you clarified that, Dorian.

 

[nvrenuf]

Allow me to interject some confusion...

It's not a 2wd vs 4wd difference as I have seen the HD type cases in 2wd applications. Imo, it's a year model change. I believe all cases produced after either 78 or 79 were HD type cases. The 2wd HD cases I have seen (personally owned 2 th400 versions, 1 = motorhome & 1 = Astro van) had the thick flange but still only had the thin tin covers with sheetmetal screws.

Here's my Astro van case -