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Not two engines though.



Two differentials. And it appears I got in there JUST in time to install my LSD. It was already eating up my tailshaft housing. I'll get pics up later, but I just got it apart, and am about to pull the Diff out. I'll use this topic to detail the install since I didn't shoot pics of the teardown.

Wow, that's good timing!!!

Love it when things work out like that!

When I saw the word differential, i was thinking, no... it couldn't be his new one!!! Thank god that wasn't the case... came just in time, eh?

Note the shiny score mark all around the inside is from the pinion shaft shifting out the cage/gear assembly and trying to cut the tailshaft housing in half (again):



Here you can see the pin hanging out one side (bottom). It appears (I have to check still) that the retainer pin broke this time, not the aftermarket hardened pinion shaft (ok, I found another weak spot by beefing up another part), allowing the pinion to walk out. This could have been far worse. And it would have been in time. Hoping the LSD solves this:

Wow, that was indeed lucky. You going to do a trans flush to get the shavings out?

The pan drop and filter change are now on the menu. They weren't an hour ago. Although there is very little risk. These very fine aluminum shavings aren't much danger, and are far more likely to be trapped by the filter than steel or any other metal. This is why I saw no evidence of it. FYI, I barely have 1500 miles on this one. And it was beefed up in my trans build. Certainly less than 5k miles, but I haven't been tracking it. The car hasn't left the State of Oregon since the new trans went in though. All local, less than one-hour trips, mostly my very short (3 mile) commute. The SLEeper is my out-of-towner and CA driver.

After further autopsy.....

I drove the pinion shaft farther out the diff cage to get a visual of the pinion shaft where it rides inside the gears, and I can tell you one thing for sure. Even with a rebuilt diff with a hardened pinion shaft, never run drag slicks without an LSD on a built Series 1 L67 with a 4T60E(HD) trans. This diff was custom built for me and it still failed in a very short period of time. The roll pin holding the pinion shaft sheared due to the friction between the pinion shaft and gears, most likely coming out of the burnout box at the dragstrip at the very moment the tires 'chirped' with traction.

I'll take it out of the car tomorrow (getting late now and I have to be up early), but I've now seen enough to know if I hadn't had the hardened shaft, I'd have broken another pinion, and I already have significant wear on this hardened shaft, and very likely the gears.

For safety, I'm considering drilling the opposite end of the pinion shaft on the LSD for another pin, just on the odd chance I break another pinion (which isn't likely, considering the way an LSD is designed to work).

Wow, that's nuts!

Hope the new diff solves the problems!

To get all this info in one place, here's the long history of the issues. My first trans failed back in 2005 and was completely rebuilt. My pinion sheared in half, and the stub that broke off began cutting my tailshaft in half. The debris went through the trans and trashed it:






The other end of the pinion, still retained by the roll pin in the cage, was UGLY as well, and was about to break inside the spider gear on the opposite end as well. It was going to break, it was a race to see which end went first.

The diff was rebuilt with a new cage, gears, and a hardened Pinion. Since it's install, I have at the MOST about 5k miles on the trans. I'll verify that later when I look at my trans warranty paperwork (warranty is expired due to time, not miles).




New EP LSD ready for install:


Next to the my original failed Diff for comparison:



At this point, I began my teardown, and found the damage posted above in the first post of this topic. The hardened Pinion is damaged inside both spider gears, and the roll pin that normally holds the Pinion in place has snapped. It began cutting the tailshaft housing in half again.


The path forward is tentative, pending further discussion/investigation. Here's the roll pin in the new LSD:


For an added margin of safety, I'm considering adding another pin on the opposite end to hold it better in case the pinion snaps (even though the LSD by design should prevent this from happening), and to possibly double the shear strength and prevent another roll pin from shearing. There's an ideal spot on the opposite end of the Pinion for another pin:


Thoughts?

that sounds like a good idea to me.
I'm not to sure how sensitive things are in the diff as far as weight, but I'd worry about drilling that close to the outside on the rotating mass and throwing off the balance..

It shouldn't be too sensitive, but it is a balanced cage assembly. I'd already planned to remove an equal amount of material off the opposite side. (minus a little to make up for adding the pin)

I say go for it. Is there any added strength in the LSD overall compared to your broken one?

There is added strength in the fact that the LSD equally loads both sides at the same time, which should help prevent this type of failure in the future.

Unfortunately, there will be no pin on the opposite side without a wire EDM. The Pinion is far too hard for any type of drill bit. It goes in like it is, and I'll pull it after WCBF to see how it's doing.

More doom.....maybe.

Look here:

You're looking at the just-removed output shaft and the new one I modified to work with the LSD. The bearing race shown will be replaced, as it won't easily snap and hold together as I insert the shaft....just for safety. I'll get or order that tomorrow. That other thing you see is the input carrier/reaction carrier oil dam. If you look closely, you'll see a little ridge remaining around the middle of it. Think of what you see as saturn, and the piece that's missing is the rings. I see no evidence of it down in the trans, and the damage looks old. It came out on my output shaft, and should have (if it were still intact) remained back in the trans. It cannot be replaced without tearing the trans apart.

Considering I had no trans issues before this teardown, I'm going with it as is. Assuming the dam was to divert fluid to the proper place, I'm going to play angel's advocate and assume that my raised line pressure might be enough to make up for it, since the damage seems to be 'aged' and I've had no issues so far.

BTW, I checked my trans warranty mileage and discovered that since 11-05 I've put on more than the 5k miles I've estimated. I actually put 18k on the trans between then and now. But that Pinion is UGLY in the diff.

Anyway, you can see I've torn in as deep as necessary, I'll get a couple parts I need (including a thrust washer set for the diff in order to set my endplay correctly) and the car will probably be running by this weekend or mid next week at the latest.

Tomorrow, I need to press a new lip seal in my replacement tailshaft housing. After work, the output shaft and diff will go in. From there, I'll check the endplay and adjust if necessary.....assuming I can get the bearing I need (pictured above) tomorrow at lunch. From either NAPA or the dealer.

You dont need that bearing on the output shaft. GM did away with it in later years. When you said your diff was custom built, several posts up, what all was done?

Hey Bill,
First off, good catch and sorry for your troubles.

That oil dam, they always break, the washer is nearly 2" across, I'm talking about the thing your calling the Saturn ring. Its probabely still in there. The thing is you have to pull and replace it from the other end of the trans. Did you tear the trans down that far? You can roll without it for a while but I wouldn't. your smart enough, more then capiable.. tear that trans down and rebuild it.

If you have an engine stand then make a bracket to hold the trans, mount the trans on it and get-er-done.
by being able to rotate the trans its a fairly easy job, it just takes a long time to keep track of the bolts and torque spece.
if you need a manual I might have one for you.
- or go to faxonautolit.com and they usually have trans rebuild manuals at great prices.

Good luck brotha.

That dam broke some time ago. It's obvious from the damage, and it's been floating up and down my input shaft for awhile from the evidence on it.

Bear in mind I don't drive this car much. And it only goes to the track 2-3 times a year. For the time being, I'm going without it and see how it does, on the premise that it broke before 20k on the trans, and if it was a REALLY critical part, it wouldn't be some dang flimsy.

If I have to rebuild later, I will. But I'm at the point now that I have to know if the LSD is going to hold the torque or not, which will determine if the intercooler goes back on the car.

You know, I almost coulnd't belive it the other night when you told me what happend. Now that bearing? Wow. The last few trips it made were on an hour glass, and I think you tore into it just as the last grain of sand fell through.
Good Timing.

dirtracr95 wrote:You dont need that bearing on the output shaft. GM did away with it in later years. When you said your diff was custom built, several posts up, what all was done?

Custom diff? New gears, hardened Pinion to prevent my earlier failure, and a stronger roll pin.

As far as leaving the bearing out, that's very bad advice and I don't suggest anyone ever try that. 93 was a split year between first and second design. Mine is first design, where the two farthest ends of the shaft are supported by bushings, and the center by needle bearings.

The second design deleted the center needle bearing, and moved it to the far, or deep (sun gear) end and retained the bushing at the output (diff) end.

Needle bearings are positive contact devices. Bushings rely on a thin film of lubricant between them and the spinning part to provide placement, which allows for a slight amount of movement, and therefore vibration (harmonics) and slop. Deleting the center bearing on a first-design (mid-93 and earlier) 4T60E output shaft is NOT a good idea. ESPECIALLY on a car with raised shiftpoints, seeing far higher output shaft RPM's than OEM. Those harmonics and vibrations transmit to the output end of the shaft where the differential hangs out. This all happens on a car that eats differentials for breakfast. Ummm......no thanks. I'll keep the 15 dollar bearing.

In addition, with the obvious loss of my reaction drum oil dam, that center bearing will serve as a 'downstream replacement' for the time being. If you look at the illustrated component breakdown in the ATSG manual or FSM, you'll see what I mean. Backing up the flow with that needle bearing at the center position will allow more oil to the planetary gears on the reaction drums farther back in the trans that are normally serviced by the oil dam that apparently failed some time ago in my trans.

This is a big difference in the 4T65E, which has no center support. That oil dam is far more critical on the newer transmissions.

In addition, regardless of the explanations I just posted, why on earth wouldn't I replace a $15 bearing that might reduce harmonic vibration in an output shaft supported only on the ends by BUSHINGS?



Back on task, the bearing, a couple new clips, and some misc other consumables are on order and will be here tomorrow afternoon. Tonight, I'm deleting my 5% underdrive WP pulley that had a hard time keeping up with the IC front core installed last summer. I'm also pre-assembling the output shaft and LSD to check final drive endplay so I can get the right thrust washer in there.

The next couple days will be fine tuning that endplay, and the car should go into final assembly by the weekend. Assuming the LSD performs as advertised, the intercooler will go back on the car with a smaller front core. After WCBF, the LSD will be removed for inspection to see if it's holding up.