34mm vs 38mm Idler shaft T-cases... What's the real difference anyways?

[cruisermatt]

Time to stir the pot up a bit.. and hopefully clear some things up. Over the years when it comes to T-cases I have seen and heard multiple times, "Gotta have a 38mm case", "the 38mm case is stronger, better, etc", sometimes from reputable sources. Plus seeing the 38mm versions going for significantly more cash in the classifieds! Well I've had my fair share of these transfer cases apart and nothing stuck out to me as really that different, other then the obvious idler diameter (minimal) and the rear output gears riding on bearings instead of bushings (Again, the first 75% of 60 series transfer cases are setup like that, they're FINE). Well, me being the skeptic I am, and happened to have a complete 34mm T-case come into my shop this week, and a old 38mm T-case on the shelf, decided to put them side by side so we can sort this out once and for all.

Idler shaft side by side. Can you tell which is the puny weak 34mm and which is the massive, larger, improved, 4mm (0.157") larger, idler shaft?

 

[cruisermatt]

That was a bit of a photography trick to help get my point across, which is that a 34mm solid shaft is seriously a heavy duty part for some bearings to spin on. Let's check out the idler bearing differences. Ok, I will concede here that the 38mm idler bearings are significantly beefier. However, who here has seen a 34mm idler bearing wear out?

 

[cruisermatt]

Let's talk about the case itself. I have heard, from more then one very reputable vendor, that there is a strength and clearance difference in the 34/38 case structures themselves. Pictured below are 34mm and 38mm back halves side by side. Can you tell which is which? Lets see how how many differences you can spot between the two.

 

[OSS]

I wouldn't compare the two like comparing a FZJ80 transmission combo to the FJ62 transmission combo (which are radically different) but think of the changes as a sustainable engineering upgrade within a model. Toyota frequently tweaks stuff (upgrades stuff) during mid life of the model to offer some improvements that may or may not impact real world performance or longetivity.

Think of it more as a "bug fix" than a go-no-go difference when comparing engineering changes. Perhaps during long term torture testing, Toyota engineers identified (or suspected) increased wear or longetivity issues with certain components and upgraded them mid cycle to address their concerns.

It may be a culture with them to constantly improve things - so tweaking high load components with upgraded specs would be natural.

Also there was an "important" change to the post '85 transfer case- the oiling provision cutout to snap in the plastic oiler for the 5 speed. Since a new casting needed to be made to do that - they likely threw some other things into the to-do list as well (larger idler & bearings etc) since they weren't expensive changes.

 

[cruisermatt]

I intended for this to be a discussion, so thanks for contributing.

Think of it more as a "bug fix" than a go-no-go difference when comparing engineering changes. Perhaps during long term torture testing, Toyota engineers identified (or suspected) increased wear or longevity issues with certain components and upgraded them mid cycle to address their concerns.

Well this is certain. Toyota wouldn't change their tooling and setup, gear forging, etc for no reason. My point was that while there may be a gain, it most likely isn't drastic. The main thing I had a big issues with was people spouting that there's a case strength difference - there's not.

Also there was an "important" change to the post '85 transfer case- the oiling provision cutout to snap in the plastic oiler for the 5 speed. Since a new casting needed to be made to do that - they likely threw some other things into the to-do list as well (larger idler & bearings etc) since they weren't expensive changes.

Ah, but this is not true. There are oiler provisions in earlier cases. They had H55f's with split cases before 85 you know. In fact, that 34mm case I pictured above has the cutout for the oiler provision.

 

[klinetime574]

Matt, I read the same things you did. “38mm is better,” etc etc. Definitely a weird change during a model. Especially considering it changed many other parts with it, transmission, cross member, shifter, drive shafts, just to name a few. Thanks for the comparison photos. Can’t really tell the case halves apart.

And yes my 5/84 split case (34mm shaft with oiler provision) is compatible with an H55F. Been running great!

 

[Spike Strip]

Many years ago when I got my first FJ60, a 5/85 with a 34mm t'case, and I knew very little about these things but I was in the process of rebuilding everything, I asked this exact question of the Gurus because I was on the hunt for a 38mm case. Their answer was essentially the same as yours, that they rarely see them break and when they do, it's usually from misuse or poor maintenance, not because of any inherent weakness between the two cases.

I've still got that original rebuilt case in the truck and I don't even think about it.

Thanks for posting this!

Should be a FAQ!

 

[cruisermatt]

Thanks for the comparison photos. Can’t really tell the case halves apart.

Neither could I, in person either. Well... my digital calipers could find one big difference (Idler shaft bores)

 

[cruiseroutfit]

Put a 38mm idler shaft and bearings in a 34mm case Seriously, totally doable with the right parts. We ship a set or two a week that way.

I tell people all the time, choose the cleanest, lowest mile case you can find. The 34 - 38mm is negligible for most particularly for the earlier 38mm cases that still use a bushing in the output gears versus the later 38mm with bearings in the output gears (truly better with the bearings). I run a 34mm behind the H55F in my FJ40, have for several decades now. Many broken birfs and rear axle shafts, t-case is fine. It is getting noisier with time, I'll eventually swap a 3:1 or 3.3:1 variant in there.

There is some ongoing discussion that the 34mm cases have some thinner aluminum in locations, I don't disagree but need to spend some more time with them side by side. Perhaps you could weigh the two cases half pairs you have and see if there is much difference? Advance adapters for example won't machine the 34mm cases for low range gears unless they've added additional material. Our machine shop prefers material on both cases so? I've got variants of both here in the shop and just haven't measure those thicknesses yet.

...However, who here has seen a 34mm idler bearing wear out?

Me. It's not the bearings so much as the 34mm ilder shafts themselves do seem to get far more wear (grooves) in the same relative mileage as a 38mm, that is obviously the trend Toyota was correcting with the increasing idler shaft size of the years. It's not so much a strength issue as a longevity situation, I have no doubt the 38 idler will stay tighter in the same 250k miles of service due to the shaft surface area and subsequent larger bearings surface. Poor aftermarket idler shafts exaggerate the situation, we've had customers need to replace their Chinese or Indian idler shaft as the hardening was obviously not up to par and it left them with a noisy t-case. Unfortunately this was common a decade ago. Less of those kits in the US now, most have good Japanese shafts in the kit.

Also there was an "important" change to the post '85 transfer case- the oiling provision cutout to snap in the plastic oiler for the 5 speed. Since a new casting needed to be made to do that - they likely threw some other things into the to-do list as well (larger idler & bearings etc) since they weren't expensive changes.

The oiler cup provision absolutely exists in 34mm cases after ~10/82' fwiw.

Split-Case Versions
8/80' - 10/82' - 34mm idler shaft, unique input gear. No oiler cup provisions. No spacer bolt hole.
10/82' - ~83' - Same as earlier case, with updated input gear. Introduction of oiler cup provision at this time. Middle bolt hole not present.
~83' - 4/86' - 34mm idler shaft. Has oiler provisions. Has spacer bolt hole.
4/86' - 8/87' - 38mm idler shaft. Has oiler provisions. Has spacer bolt hole.
8/87' - 1/90' - 38mm idler shaft. Auto tranny version. Vacuum 4wd. Has oiler provisions. Different gear train, bearings and seals than earlier 38mm cases.
4/86' - 90' - 38mm idler, no oiler (might have been an auto one I had without oiler provisions?)
This doesn't include the many non-US variants out there. At best guess there are 20 different Split Case's used by Toyota?

 

[cruiseroutfit]

This is the troublesome wear on an idler (not my pic, from a customer)

This can absolutely happen to both the 34mm & 38mm but in my experience, it happens faster and more substantial on 34mm shafts. I expect mine to look similar in my own 34mm t-case that hasn't been opened since 2001

 

[cruisermatt]

Put a 38mm idler shaft and bearings in a 34mm case

You guys are opening up the idler shaft bore to 38mm? After looking everything over I don't see any reason that wouldn't work.

There is some ongoing discussion that the 34mm cases have some thinner aluminum in locations, I don't disagree but need to spend some more time with them side by side. Perhaps you could weigh the two cases half pairs you have and see if there is much difference? Advance adapters for example won't machine the 34mm cases for low range gears unless they've added additional material. Our machine shop prefers material on both cases so? I've got variants of both here in the shop and just haven't measure those thicknesses yet.

As you can see in my pictures I have them side by side... After looking very thoroughly I couldn't find any visual differences. I'll bring my mics to the shop and check the case thickness around the low range gear on both versions, but visually they're the same. Weight doesn't seem like a good test to me, the 34mm case should actually be heavier since it has a smaller hole in it.

 

[OGBeno]

Good tech thread. Thanks for this.

 

[cruiseroutfit]

You guys are opening up the idler shaft bore to 38mm? After looking everything over I don't see any reason that wouldn't work.

No, but I suppose that is doable too. We have a Japanese 38mm shaft that steps down to 34mm on both ends. So it uses the bearings/thrust washers (and gears) from the 38mm variants in the 34mm case housing.

You would swap all the later model 38mm stuff in the 34mm case to achieve the desired ratios.

As you can see in my pictures I have them side by side... After looking very thoroughly I couldn't find any visual differences. I'll bring my mics to the shop and check the case thickness around the low range gear on both versions, but visually they're the same. Weight doesn't seem like a good test to me, the 34mm case should actually be heavier since it has a smaller hole in it.

You're right, it should be heavier, but if it's not.... that would definitely be a potential indicator of less material somewhere. Here is what AA has to say on the subject.

"Low gear clearance: This gear requires a bit more modifications to the rear case half for gear clearance. The gear diameter needs to clear 7.353" all the way to the bottom of the case half. The modifications to the case for this gear removes material ,several of the internal bosses, and from the shift rail boss.

34MM cases must have material added to the outside areas of the case. The case must be taken to a welding shop and heliarced. The if this is not done the machine operation will break through. Advance Adapters will not weld or have this procedure done. We will machine cases that have been welded."

@orangefj45 has them machine his cases I believe?, he may know more about their thoughts on the thicknesses. They've done cases for our gears, but to my knowledge they've all been 38mm. As I mentioned our local machinist wants material on all of them and he'll helicarc it before machining.



Actuall building a 38mm case this minute. This is a brand new case with bearings in the hi/low output gears, full spline input gear, etc. We can do all the same stuff in a 34mm case with new/used parts, we stock full 34 & 38mm gear sets in stock ratios or 3:1, 3.3:1 or 4:1 low range and/or 10% OD/UD high ranges. Many many options for the split-case, more then we've ever seen in the market which is neat after so many years and a 40+ year old case technology.

 

[cruisermatt]

so no guesses as to which case is which in the pictures I posted? Or any differences spotted?

 

[Spike Strip]

Wow. Who knew ?

Kurt did

 

[klinetime574]

Post #3: Case on bottom in first pic & right in second is the 38mm variant?

 

[cruisermatt]

"Low gear clearance: This gear requires a bit more modifications to the rear case half for gear clearance. The gear diameter needs to clear 7.353" all the way to the bottom of the case half. The modifications to the case for this gear removes material ,several of the internal bosses, and from the shift rail boss.

34MM cases must have material added to the outside areas of the case. The case must be taken to a welding shop and heliarced. The if this is not done the machine operation will break through. Advance Adapters will not weld or have this procedure done. We will machine cases that have been welded."

@orangefj45 has them machine his cases I believe?, he may know more about their thoughts on the thicknesses. They've done cases for our gears, but to my knowledge they've all been 38mm. As I mentioned our local machinist wants material on all of them and he'll helicarc it before machining.

This is what I would like to put to the test. If it's an issue with one version and not the other then that would indicated that the actual outside dimensions of the case are smaller on the 34.
I am going to take some measurements.
It would be strange for AA to come up with a statement like that out of nowhere. However, I am driven by posted information/data and not just what someone said one time, and I have seen no posted evidence for this claim... We'll find out

 

[cruisermatt]

Post #3: Case on bottom in first pic & right in second is the 38mm variant?

Do you know how I know you're guessing?

 

[klinetime574]

Do you know how I know you're guessing?

The newer one is cleaner. But also I spotted a difference. At the rear output of the transmission the case is thicker and more reinforced there. More material for a bearing and/or load.

 

[cruisermatt]

The newer one is cleaner. But also I spotted a difference. At the rear output of the transmission the case is thicker and more reinforced there. More material for a bearing and/or load.

I see what you're saying, but that's an illusion due to the photo being taken on a slight angle.
I actually know you're guessing because you guessed wrong

The dirty one is a 38mm housing that came out of my rig last summer. The clean one is actually the 34mm unit, taken out of a low mileage truck and then stored for decades.