Just Fishing's 09 Tahoe Build thread

[Just Fishing]

Random find while looking for more detailed specs related to clutch pack clearance.

Gears Magazine - The Devil's in the Details! A Machinist's Look at the 6L80/6L90 Units

The 6L80 and 6L90 transmissions have become the most popular rear-wheel drive GM transmissions in most of our shops. We have seen several patterned failures, written numerous articles, and found countless fixes to keep these units on the road (and the list doesn’t end). With so many of them in...

gearsmagazine.com

Lots of good info there.

Doing a check on my clearance, I'm a little tight on one, and in the middle range of others.

There does not seem to be any real selective options available.

As it sits, everything should be fine.
But I'm more concerned with the tight clearance of the low rev clutch at the back.

Part of my mistake was saturating the clutch packs in fluid before installing.

Cleaning and drying, i get a good .048 per my dial indicator.
Spec in atsg says around .050.

Per the link, I'm good.
But i would rather have the clearances a little more uniform.

Rest of the packs, I'll see if i can't tighten them up just a little.

But I'll wait until i confirm end play since this will be another order and a wait.

Might as well get shims on order with it.

 

[Just Fishing]

Soon I'm planning to start the pump final assembly.
I'll get some pictures of that process.

This differs a bit from what i learned with the 4l60.
Pump selectives... lol

What i figured out there, is to use the pump slide to confirm clearance.
Those are cheap.

Probably easier if you have the original pump handy, but with me i went with a whole new unit before even tearing down my original due to the pressure gauge suggesting issues.

 

[pwtr02ss]

Random find while looking for more detailed specs related to clutch pack clearance.

Gears Magazine - The Devil's in the Details! A Machinist's Look at the 6L80/6L90 Units

The 6L80 and 6L90 transmissions have become the most popular rear-wheel drive GM transmissions in most of our shops. We have seen several patterned failures, written numerous articles, and found countless fixes to keep these units on the road (and the list doesn’t end). With so many of them in...

gearsmagazine.com

Lots of good info there.

Doing a check on my clearance, I'm a little tight on one, and in the middle range of others.

There does not seem to be any real selective options available.

As it sits, everything should be fine.
But I'm more concerned with the tight clearance of the low rev clutch at the back.

Part of my mistake was saturating the clutch packs in fluid before installing.

Cleaning and drying, i get a good .048 per my dial indicator.
Spec in atsg says around .050.

Per the link, I'm good.
But i would rather have the clearances a little more uniform.

Rest of the packs, I'll see if i can't tighten them up just a little.

But I'll wait until i confirm end play since this will be another order and a wait.

Might as well get shims on order with it.

What wouldn't you check everything with the frictions soaked in fluid? Do they make a thinner steel or pressure plate to get that extra clearance you need? I ALWAYS soak my frictions for a while and then check everything with them saturated.

Generally curious if this is specific to the 6l80

 

[Just Fishing]

What wouldn't you check everything with the frictions soaked in fluid? Do they make a thinner steel or pressure plate to get that extra clearance you need? I ALWAYS soak my frictions for a while and then check everything with them saturated.

Generally curious if this is specific to the 6l80

So what i'm seeing is there are no selectives for the 6l80
but some of the clutch packs have selective retaining rings.

So far It looks like I can tune the 4-5-6 and the 1-2-3-4 clutch packs

And I learned the spec is while the clutches are dry, that could be wrong.
but the assumption would be that the fluid would take up some space.

 

[pwtr02ss]

So what i'm seeing is there are no selectives for the 6l80
but some of the clutch packs have selective retaining rings.

So far It looks like I can tune the 4-5-6 and the 1-2-3-4 clutch packs

And I learned the spec is while the clutches are dry, that could be wrong.
but the assumption would be that the fluid would take up some space.

If it's a little tight, it won't hurt anything. It'll wear in and clearance itself. The issue with too tight is excessive wear and heat. They only pack I set up a little under the spec is the 3/4 stack. Full fluid soak, I set it around .055 IIRC. Spec is .060-.080. That hasn't been an issue so far.

The first one we did was right at the top. I believe at the .080. After after 15k miles, we started get a shift flare and I blame it on that. We've learned a lot since then...

This of course is on the 4l60-65. The 6 speed is completely different beast and will adjust the fluid levels (based on my reading), so I believe if you're a little tight, you won't have an issue. The only thing is prematurely wearing the friction and shortening life. You're plenty knowledgeable with these so don't question yourself based on me. It'll work fine if you're comfortable with it.

I really wish I could get a free core and build one for my dad. They look like such simple units (if there's a way a transmission CAN be simple...). I'm confident I could do it, I just don't want my dads truck being down and then it having a problem if I screwed it up. If my avalanche would've had a 6speed, I'd have given it a shot!

 

[pwtr02ss]

And yes, you 100% gain clearance if you test them dry. When we assembled my 3/4 pack, I tested it full fluid soaked and needed a thicker (selective) pressure plate to get it where it needed to be (.055). After it sat in the shop and most of the fluid ran out, it was much looser. Like 0.20 looser. I left it because if it was fine full soak, it'll be fine when it's soaked in the trans. I double checked the pressure plates to ensure I got what I ordered. They were dead on.

 

[Just Fishing]

If it's a little tight, it won't hurt anything. It'll wear in and clearance itself. The issue with too tight is excessive wear and heat. They only pack I set up a little under the spec is the 3/4 stack. Full fluid soak, I set it around .055 IIRC. Spec is .060-.080. That hasn't been an issue so far.

The first one we did was right at the top. I believe at the .080. After after 15k miles, we started get a shift flare and I blame it on that. We've learned a lot since then...

This of course is on the 4l60-65. The 6 speed is completely different beast and will adjust the fluid levels (based on my reading), so I believe if you're a little tight, you won't have an issue. The only thing is prematurely wearing the friction and shortening life. You're plenty knowledgeable with these so don't question yourself based on me. It'll work fine if you're comfortable with it.

I really wish I could get a free core and build one for my dad. They look like such simple units (if there's a way a transmission CAN be simple...). I'm confident I could do it, I just don't want my dads truck being down and then it having a problem if I screwed it up. If my avalanche would've had a 6speed, I'd have given it a shot!

When i did my vette, i targeted .035 if i remember correctly.
Later i had an aftermarket pump rotor blow up (Came in the "stage 2" rebuild kit)
so, the trans had to come completely apart.

At that time, I found some burning on the 3-4 clutch and blamed having too tight of clearances.
And I had the band slightly too tight as well.

that transmission was super cheap compared to this.
I loosened the clearances, and slapped it back together after cleaning everything with more upgrades, new pump, billet pump rotor, and a better converter.
It has been flawless ever since.

IIRC I ran with a .040 (wet) clearances for all of the clutches.

It has been perfect ever since.

Not a "pleasant" car by any means, but it is very fun and entertaining.
(long tubes, loud, hard and fast shifting (giggity), super stiff suspension...
suspension is normal for that car and there is a fun story related to the history of the C4 for me to tell people because i'm a nerd).

And of course, the Tahoe has to be the "opposite", i don't want headers anywhere near this thing.

for the clutch clearances.
I have in the past gotten away with sanding a clutch down, but it's a massive pita.
You need absolute perfection, must be perfectly level and flat.

Luckly with the vette, the transmission was really easy for me to pull.
this is not that easy because of 4x4

I'm wanting to avoid that if at all possible.

I have been toying with the idea of re-using one or two of the original clutches to loosen the clutch pack up a tad
they aren't bad, but they are old.

 

[Just Fishing]

And as I'm up nice and early preparing for another weekend of fun.
Some images,

First the t-case all cleaned up, this thing was nasty.
Looked like some seeping of oil over the years had attracted lots and lots of dirt.
I really should have gotten a before.




6l80 build stuff.

Here is the rear case bushing before I changed it out.
Still a nice coat of Teflon on there, only mild wear but I replaced it anyways.



Notice the pass through in the rear of the case.
There is no lube feed here, it's just a return to the pan.
Notice the hole in the original bushing being clocked away from it.

I also noticed a mark from the original assembly there, the blue mark.
This was under the rear seal.

This looks like it was marked to avoid placing the bushing hole near the case pass through.

New bushing was installed in the exact same location.
This image was to just keep track of where it was, I have a bunch more of these but I won't clutter this thread with those.


Moving onto the pump assembly,
Snipping this from a PDF version I have of the ATSG manual,

Pump clearances,


Pump and rotor selection,

 

[Just Fishing]

I bought an actual straight edge for this.
I used my handy caliper set to measure pocket depth, then made the selection.
I came out within #2 for both the pump and rotor selection.

I have one that's great for most things, but not for this level of precision.
So I bought a new one.
Iirc this was about $30 on ebay.


With the pump and rotor, I came out right in the spec, so it's gtg for install.

Plastigauge to confirm,


Rotor is the exact same measurement.

Pump ready to bolt together!


I used the sonnax pump spring, helps keep pressure up at higher rpm
otherwise, the rotor likes to move to bleed off pressure causing some slippages.
I had a good experience with this in the ol vette, so I wanted the same.

This thing was fun to get in there.
I did some testing with the old pump using tools.
but in the end I ended up squeezing it in there.

And of course, the other half has all of the other upgrades from transgo.
I didn't get any images of that process, but it's pretty standard.
Looks complex until your actually holding the parts.

 

[Just Fishing]

I also used that straight edge to install my rear engine cover to absolute perfection.


And here we have the pump ready to install and check clearances.
ends taped off for now to keep everything clean.