Torqueflight- rebuild or go manual?

[Jesse B.]

So I just got my rebuilt 392 running in my 1975 Scout II that has a rebuilt 727 and Dana 20 (tera low gears) combination. The axle gears are 3:54 and I am running 32x11.50 tires. I was working the bugs out of the engine and as I got it dialed in, I decided to give it a little bit of gas. I have a quadrajet on top the 392. When the light turned green, I gave it about 1/3 of the pedal and bam!! The truck did not even start to roll when the explosion occurred. The engine was still running and I tried forward, reverse, and nothing. I figured I had destroyed a drive shaft or yoke or something, so I jumped out, looked underneath, didn't see anything, locked the hubs (while people are honking their horns), and tried four wheel. Nothing. So I put it in neutral and pushed it to the side of the road and called a tow truck.

Once I got the truck home I figured I had destroyed the tera low kit, so I pulled off the output shaft tail housing and the gears looked fine. So I put the transmission into park, crawled back under the truck and I was able to spin the bull gear by hand. So, it looks like I broke my transmission output shaft.

I am very surprised by this since the torqueflight is supposed to be a strong tranny. They put these in heavier trucks and chrysler put them behind their 426 hemi in the 70s.

My question is now what? I spoke to Jeff about putting in another 727, but I am nervous about blowing it up as well. It is possible that the tranny was stressed to begin with, but it was behind a tired 304, so I doubt it. Any thoughts on what to do now? Is there a way to build up the 727 to handle more power? Would it be safer to go a manual gearbox? Thanks,

 

[ihpartsjeff]

Hey Jesse,

I was chatting to Darren about this and he brought up a few good points. One will be balancing. You May lose that perfect balance with the swapping in of a flywheel and clutch. Two would be that the cam you spec'd out was setup for an auto trans. Switching that would kind of change things around. Not much but something to consider. Third if you're going to spend the money to go manual why not go with one of our nv4500 swaps and a Jeep Dana 300. Having overdrive and a very low crawl ratio is absolutely the best of both worlds.

 

[Michael Mayben]

I agree regarding the balance issue. Only workaround for that would have the complete rotating clutch assembly "neutral balanced" at considerable expense.

There is no way to determine what May have failed regarding the tf 727 without tearing it down. How did you turn the bull gear by hand, did you remove the transfer case to do that? Is the bull gear retaining nut still torqued in place?? I've never seen an output shaft "broken", even behind the strongest hemis and 440s back in the day. But the planetary system May have given up.

Even the most mild 727 used behind a low output chrysler or amc 6-banger is strong enough to take anything that motor will dish out unless ya rev it to 5k and then drop into gear.

When ya say "rebuilt" 727, when was it done and by whom??? And pro tranny builders can scruu up just like anyone else. I'm dealing now with two similar sii transmissions for forum members built by pros with less than 3k miles on 'em...the "pro" simply did a bogus build!

 

[ihpartsjeff]

Michael,

from what Jesse describes it sounds like the output shaft broke after the parking pawl since he can rotate the output shaft of the tranny with it in park. As for the tranny we sold Jesse the tranny back in nov, 2006 so yes it is from a reputable builder.

 

[Jesse B.]

hey Jesse,

I was chatting to Darren about this and he brought up a few good points. One will be balancing. You May lose that perfect balance with the swapping in of a flywheel and clutch. Two would be that the cam you spec'd out was setup for an auto trans. Switching that would kind of change things around. Not much but something to consider. Third if you're going to spend the money to go manual why not go with one of our nv4500 swaps and a Jeep Dana 300. Having overdrive and a very low crawl ratio is absolutely the best of both worlds.

Darren is correct. The engine was balanced and set up for an auto. So I would lose something there. I don't know what would be involved in getting the flywheel balanced or how necessary it would be. That will have to be one of the many items I'll have to take into account when making a decision. Thanks,

 

[Jesse B.]

I agree regarding the balance issue. Only workaround for that would have the complete rotating clutch assembly "neutral balanced" at considerable expense.

There is no way to determine what May have failed regarding the tf 727 without tearing it down. How did you turn the bull gear by hand, did you remove the transfer case to do that? Is the bull gear retaining nut still torqued in place?? I've never seen an output shaft "broken", even behind the strongest hemis and 440s back in the day. But the planetary system May have given up.

Even the most mild 727 used behind a low output chrysler or amc 6-banger is strong enough to take anything that motor will dish out unless ya rev it to 5k and then drop into gear.

When ya say "rebuilt" 727, when was it done and by whom??? And pro tranny builders can scruu up just like anyone else. I'm dealing now with two similar sii transmissions for forum members built by pros with less than 3k miles on 'em...the "pro" simply did a bogus build!

With the transfer case in neutral and the transmission in park, I can reach through primary gear and rotate the output shaft nut (I.e. Bull gear retaining nut) with my fingers. The nut is not loose, the nut turns with the shaft. Regardless of what actually broke, the problem is what do I do now? If the consensus is something was just plain bad with the tranny, not necessarily related to the new engine, then I'll probably stick with the auto. But if not, I'm going to cut my losses and go manual.

 

[Robert Kenney]

This is just my opinion and I don't have a bunch of severe off road experience in very low gearing to base it on but here it is anyhow.

An auto has a much more easily controlled pedal. The tc slipping gives you an almost unlimited gear ratio and torque modulation when trying to crawl over obstacles and rocks at 0 mph or stopped. To me a clutch is just cumbersome to manage.

I would rebuild the tf 727. I have seen upgraded 727's survive inback of blown hemi's season after season with little more than a service or sprag inverting. Your 392 won't break a good tf that has beed built/ rebuilt right.

 

[Jesse B.]

Thanks Robert. After thinking about it last night and reading through some books, I am going to stick with the 727. However, this one is going to be built with knowledge it is going behind a larger engine....

 

[ihpartsjeff]

The verdict is in. The output shaft was broken aft of the speedo drive gear. From the way it looks the shaft was definitely fractured for quite some time and all the 392 did was finish it off. Will post pictures next time I'm doing downloads.

 

[Michael Mayben]

the verdict is in. The output shaft was broken aft of the speedo drive gear. From the way it looks the shaft was definitely fractured for quite some time and all the 392 did was finish it off. Will post pictures next time I'm doing downloads.

Now that is as freekeedeekee as they come!

I can see that when ya pump 800+ hp through the slushbox (and other shit is gonna break also)...but not a stocker IH motor!

That segment of the output shaft where you describe the break is right in the heart of the heat-treated segment of the output shaft. See the heat draw points about 3.5" on either side of the break? You will see the blue/yellow heat bands denoting the heat treated area.

Check the output shaft bearing behind the bull gear, you know...the "special"! That is a huge bearing for the load it sees, but it could be a contributing factor if it's rough or shows any discoloration or was being turned into a "thrust" bearing if the output shaft end play was fucked up.

And the other common possibility...the bull gear is bottoming out in the transfer case against the inside of the rear output shaft. That puts a tremendous load against the shaft as it tries to drive the tranny output shaft back up inside the planetary. That comes from having a tranny set up with the wrong "end play" on the output shaft (very critical), the incorrect bull gear, or the setup on the d20 transfer case rear output shaft is fucked. I've seen this same "lockup" situation three times since the first of the year on a Dana 20 setup behind a tf 727. In those cases...it was because the stoopid fuckers that put the system together, used fuckin' rtv instead of the proper gasket that serves as a shim between the transfer case adapter/tailhousing, and the mounting boss on the s20. The bull gear and the rear output shaft were trying to "resistance weld" themselves together!

 

[Jesse B.]

Pics Jeff, please!

 

[Jesse B.]

Check the output shaft bearing behind the bull gear, you know...the "special"! That is a huge bearing for the load it sees, but it could be a contributing factor if it's rough or shows any discoloration or was being turned into a "thrust" bearing if the output shaft end play was fucked up.

And the other common possibility...the bull gear is bottoming out in the transfer case against the inside of the rear output shaft. That puts a tremendous load against the shaft as it tries to drive the tranny output shaft back up inside the planetary. That comes from having a tranny set up with the wrong "end play" on the output shaft (very critical), the incorrect bull gear, or the setup on the d20 transfer case rear output shaft is fucked. I've seen this same "lockup" situation three times since the first of the year on a Dana 20 setup behind a tf 727. In those cases...it was because the stoopid fuckers that put the system together, used fuckin' rtv instead of the proper gasket that serves as a shim between the transfer case adapter/tailhousing, and the mounting boss on the s20. The bull gear and the rear output shaft were trying to "resistance weld" themselves together!

From what I know about putting this setup together, it could have been the output shaft end play. The bull gear is from teraflex because the case has the 3.15 teralow setup, and both times that transfer case was removed it mounted to the tf with a gasket. (IHOnly installed the teralow, but I remember looking at the case and seeing a gasket between it and the tf.)

 

[Scouty]

the verdict is in. The output shaft was broken aft of the speedo drive gear.

Does the tranny have a speedo drive gear somewhere that isn't used if the Scout has 4wd? I thought the speedo gear was in the t-case?

 

[Michael Mayben]

All tf 727 units have a helix cut into the output shaft to drive a speedo pinion of some sort.

But there were many different tailshaft lengths and configurations used depending upon oem application. Some tailhousings had a speedo drive pinion system installed that mate with the helix on the output shaft. Some had the speedo pinion drive in the transfer case so that the speedo reading would be correct depending upon which "range" was selected.

In the case of a 727 with d20 married inna Scout II, the speedo drive pinion hole in the tailshaft housing/transfer case adapter is "blanked" with a dummy speedo pinion with no pinion gear installed and cap installed.

Here's a pic I've posted in another thread of three different types of 727 output shafts, ya can see the speedo helix is present on all three.

 

[Michael Mayben]

This pic shows the area of the output shaft under discussion, this one is not damaged and is still in operation three+ years after I built the trans, it's a very early chrysler 383 tranny being pushed by a warmed over 383, and has a Scout II output shaft and tailhousing grafted on.

Rig belongs to our supplier of the "special" output shaft bearing used only on a dam Scout II tailhousing, terry davidson of precision bearing fame. He custom builds those bearings only for ihon.

 

[Michael Mayben]

This is a shot of the tailhousing used in ihc pickalls, either 2x4 or 4x4. Also used in 2x4 Scout II.

The pickalls use a divorced np 205 transfer case if a 4x4 app. This is what we refer to as the "short" tailhousing with the bolt-on yoke (not a slip yoke as used in many 727 apps).

Note the speedo drive,...if the tranny is a 2x4 version, there is a pinion installed in the adapter like this one. If it's a 4x4 app, then there is no pinion installed, a cap is placed on the adapter, and the speedo drive is out of the transfer case.

A different version of this tranny was used in ihc-produced motorhomes/chassis, that one was a long tailhousing with an extra mount added, same as the app for a dodge motorhome app. Still used a bolt-on yoke though, a slip yoke system was not strong enough.

 

[Michael Mayben]

This pic shows a speedometer drive port in the Scout II transfer case adapter/tailhousing along with the blockoff used for the speedo drive area. This is all oem stuff.

 

[Jesse B.]

Drum roll please:

although the other half of the shaft is still in the tranny, it sure looks like this shaft has been busted for some time. It appears about 2/3 of it has kind of a polished buffed look to it, like it had been cracked but just barely being held together. The last third is freshly broke.

 

[Michael Mayben]

Thanks for finishing out this thread Jesse, that's the only way we can learn what works and what don't! And what's strange.

Robert is much more into damage analysis/metal fatigue due to his training and background...but I'd have to say from what I can see in the pic, that no doubt some existing damage would have been revealed inna magnaflux process on that shaft. But nobody would ever do that unless building a super-high end race box.

But no doubt Darren can fab ya up a really nice hood ornament or juju ta hang from the mirror outta the stub.

It would be really kool if Darren can remove the output shaft bearing from the adapter housing and send it up here with Jeff when he comes up for the Binder Bee. It's best to heat the case in the oven to about 350* and the bearing will fall out, but of course ya gotta learn some new cuss words to git the fuckin' retainer ring out. Terryd of bearing tech will be working with us at the bee all weekend and he can take the bearing back to his shop and do an analysis on it.

Also...was there any sign that the bull gear was thrusting hard against the rear output shaft of the d20?? Under load, there needs to be at least 0.050" clearance between the parts when the tranny and tc are bolted together. That can be checked when assembling by using some wadded aluminum foil placed between the parts, then doing a trial assembly and then remove. Measure the crush of the foil with a caliper or micrometer. Also, that special material available only from the ihon kidz...pink play dough! They gave me a can years ago and I still use it all the time!

 

[Jesse B.]

Also...was there any sign that the bull gear was thrusting hard against the rear output shaft of the d20?? Under load, there needs to be at least 0.050" clearance between the parts when the tranny and tc are bolted together. That can be checked when assembling by using some wadded aluminum foil placed between the parts, then doing a trial assembly and then remove. Measure the crush of the foil with a caliper or micrometer. Also, that special material available only from the ihon kidz...pink play dough! They gave me a can years ago and I still use it all the time!

Michael,
I took a look at the bull gear and I see no sign of abrasion or heat. Looks nice and clean.

Also, thank you very much for the valve body. I now have about 400 miles on the engine and I am very happy with the firmness of the shift. 1-2 and 2-3 are nice and tight. Thanks again.