Newly-rebuilt 4L60E lost 3rd gear within 20 miles, sigh...

[jamyers63]

So...after completely rebuilding a '96 4L60E for son's '69 C10
(see this thread for details: https://bobistheoilguy.com/forums/threads/another-4l60e-build-with-questions.371065/
and the clearances / specs are pictured below.)

Last weekend we pulled out the tired 700R4 and swapped in the new trans. Hooked up a USShift Quick4 controller with a stock (5000rpm shift) tune. Checked line pressure, 60 at idle in D, 75 in R. Pressures ramped up dramatically with the throttle, and followed the pressures indicated in the Quick4 - so we concluded the Quick4 was indicating correct line pressures.

Let the engine and trans idle to warm up (engine 180, trans 170), doublechecked the fluid level, Went for an easy test drive, and all seemed well for the first 4 miles - all gears shifted well, nothing seemed slipping, no obvious issues - until I looked down and saw the the trans temp at 210, 215, 220...we pulled over, let it idle in P, checked the fluid level, checked no leaks, etc. It cooled down to 210, so we started easing it back to the shop - and the temps climbed, seemingly no matter which gear we held it in. By the time we got to the shop it was well over 260.

We doublechecked the line pressures, all was in spec, checked the fluid - it wasn't discolored at all, no debris in it, but it smelled like a burned pizza.

Let is cool down while we ate supper, gave it some thought, and wondered if the line pressure curve wasn't steep enough - because the Holley Sniper EFT is set up to use all 4 bores simultaneously, which means the truck drives down the road at 60mph with around 10% TPS, and so maybe there wasn't enough pressure to keep the clutches held while going even 30mph? Surely stock pressures are enough - otherwise I can't be the first to kill a transmission with this setup...?


After it had cooled down below 90F, I raised the static line pressures by about 50psi across the board, and raised the shift firmnesses as well. Went for another test drive, and all seemed well, temps never got above 180F, except the shifts weren't as hard as I'd expect (I'm not sure what to expect, they just didn't seem...)

Knowing that the trans was hurt, I pulled the pan and found tiny black flakes, and both magnets were fuzzy with black debris. No shiny bronze, aluminum, or other non-magnetic debris, looks like just friction and steel materials.

Pulled the filter (which looks good) hooked up a hose from the pump inlet to a jug of new fluid, started the engine and let it push new fluid through the trans and into a large catch pan, then replaced the filter and fluid.

Went for another short drive, and temps never got above 180, all gears work fine except 3rd, which slips badly. Dammit.

Ideas about where we went wrong, other than not maxing the line pressure at the first sign of trouble?

Trans is obviously coming back out, what's the fix?

 

[weaponoffreedom]

take it to a transmission shop.....as is known trannies are a bit special

 

[i6pwr]

Did you confirm the converter locking up in 3rd and 4th? Not sure about the TH700, but the TH 400 didn't lock, but the 4L60E MUST lock.

Make sure you have the converter lock points low enough, I believe around 40 in 3rd and 50 in 4th. Not sure on those numbers but they are likely within 5-7 MPH.

If it's shifting fine but getting hot at cruise, that would be my guess.

Transgo makes a kit that eliminates the PWM control of the converter lockup, maybe that's what is not being controlled and you need the new valve that makes lockup an on and off function.

They don't sell the piece alone, maybe other sellers do, but comes in the kit. Not sure if you are using PWM lockup or not, but I would recommend the normal on/off style of lockup

Looks like this.

With this spring, may or may not be blue.

TransGo - GM 4L60E, 4L65E, 4L70E SHIFT KIT® Valve Body Repair Kit

The TransGo 4L60E SHIFT KIT® Valve Body Repair Kit fits 1993 to 2015 General Motors vehicles equipped with 4L60E, 4L65E and 4L70E automatic transmissions.

transgo.com

 

[jamyers63]

@weaponoffreedom , Thank you for the helpful advice, but if we wanted to just write a check and not learn anything, we would have taken it to a shop to begin with. But since my son and I wanted to learn and do, we got the manuals, researched, asked advice, and rebuilt it ourselves. We've hit a snag, but hopefully we can learn what we did wrong and fix it ourselves.

@i6pwr, the TCC is locking up just fine, as mentioned above we used the TransGo TCC Isolator - Converter Regulator valve (and turned off PWM in the Quick4 controller.

@clinebarger, I believe that something was keeping the 3-4 clutch from holding securely, and now it's toasted.
Ideas on what may have caused that?

 

[i6pwr]

the TCC is locking up just fine, as mentioned above we used the TransGo TCC Isolator - Converter Regulator valve (and turned off PWM in the Quick4 controller.

Whoops sorry, didn't view the link, my bad.

I believe that something was keeping the 3-4 clutch from holding securely, and now it's toasted.
Ideas on what may have caused that?

Could this be a band and not the clutch pack? Something inside the servo housing on the side, maybe the length of the pin? Not sure what the specs are but just tossing out ideas.

 

[Chris142]

@weaponoffreedom , Thank you for the helpful advice, but if we wanted to just write a check and not learn anything, we would have taken it to a shop to begin with. But since my son and I wanted to learn and do, we got the manuals, researched, asked advice, and rebuilt it ourselves.

I get it. You want to do it and you did your best. Years ago I rebuilt a th350 3x in a week or so. Had it in and out of the elcamino 3x before I gave up and took it to a shop.

Some things are best left to the pros and even they have problems. A 4L60E has a lot of things that could go wrong.and is a pretty complicated transmission to try to fix for a beginner.

Maybe a shop would be willing to show you what's wrong?

 

[weaponoffreedom]

@weaponoffreedom , Thank you for the helpful advice, but if we wanted to just write a check and not learn anything, we would have taken it to a shop to begin with. But since my son and I wanted to learn and do, we got the manuals, researched, asked advice, and rebuilt it ourselves. We've hit a snag, but hopefully we can learn what we did wrong and fix it ourselves.

@i6pwr, the TCC is locking up just fine, as mentioned above we used the TransGo TCC Isolator - Converter Regulator valve (and turned off PWM in the Quick4 controller.

@clinebarger, I believe that something was keeping the 3-4 clutch from holding securely, and now it's toasted.
Ideas on what may have caused that?

I hope you can learn. There are probably 20 things that could be wrong. I have been talking to many shops recently about rebuilding my AX15 manual, and the concensus is that "new" rebuild kits, generally suck. You could have a bad new part, and though you did nothing wrong, still be wrong.

I commend you for your gusto to try, but i think without carnal knowledge, you are going to be spinning your wheels, unless it is obvious. Good luck to you on your endeavor.

 

[clinebarger]

@clinebarger, I believe that something was keeping the 3-4 clutch from holding securely, and now it's toasted.
Ideas on what may have caused that?

You could have a leak in the 3-4 circuit, A pretty big one to roast the frictions in 20 miles.

I'm not familiar with US Shift controllers, But with a healthy pump & a Purple Sonnax PR Spring.....Max PSI (No current to EPC) should be right around 220. Assuming pressure ramp was linear with the throttle input? Pressure was likely not the issue.

Start with pressure checking the Input Drum. With the Bleed orifice blocked with your finger.....It should be tight/No leaks.
This is done with the drum loaded, You may need to throw a steel in the burnt 3-4 stack to take up the clearance for testing purposes.

The two leak points are between the Input Shaft & Drum, And the Checkball Capsule (The one in the Input Drum).

 

[clinebarger]

Wondered if the line pressure curve wasn't steep enough - because the Holley Sniper EFT is set up to use all 4 bores simultaneously, which means the truck drives down the road at 60mph with around 10% TPS, and so maybe there wasn't enough pressure to keep the clutches held while going even 30mph? Surely stock pressures are enough - otherwise I can't be the first to kill a transmission with this setup...?

The larger Boost Valve creates a more aggressive pressure ramp, I use stock GM pressure tables on all sub 500HP 4L60E builds. Aftermarket controllers are generally more aggressive than GM with their base files.

Then again......The 2 aren't really comparable as GM uses Calculated Load via a MAP or MAF sensor to command EPC duty cycle while most AM Controllers use Throttle Position.

 

[jamyers63]

@clinebarger OK, finally got the trans out and apart on the bench.

Nothing obviously wrong, apart from the scorched fluid and clutch debris in the pan.

3-4 clutch pack clearance has gone from .025 to around .075-.080.

Air tested the 3-4 clutch pack with the bleed orifice blocked, had good lockup. The checkball capsule seems to seal well, at most some fluid oozed past it when applying and releasing air repeatedly.

Did not observe any fluid, bubbles, or air coming out between the shaft and drum.

Doublechecked the 3rd Accumulator checkball capsule, gasoline will dribble past it but not ATF (although can't pressurize behind it.)

(looking at the fluid path, why is there even an accumulator checkball capsule there - when releasing 3-4, wouldn't fluid exhaust out the #11 orifice and back up the passages towards the valves?)

Looking at the Service Manual, looks like the other possibilities for leaks are:
3-2 Downshift Valve
3-2 Downshift Control Valve
The Servo Case Accumulator Orificed Plug (#11, exhausts accumulator fluid into the case)

Any other ideas or things to check?

(Transmission also had a small leak / drip off of the converter, I'm assuming the pump seal wasn't 100%)

 

[clinebarger]

The orifice in the servo bore lubes the 2-4 Band & Reverse Input Drum during sustained 3rd/Direct operation.

The checkball capsule is to bleed the 3rd clutch circuit during 3-4 clutch apply, Blocking it isn't anything new but causes undesirable 2-3 shift characteristics.

Was the 3-4 clutch already burnt on this unit?

 

[jamyers63]

Nope, all new clutches, bushings, everything.

 

[i6pwr]

I don't know if this would even relate to your issue, but I swapped the OE 2nd apply piston for the vette servo in my buddies 4L60E recently.

Where these two mount had considerable wear and you could wobble them around quite a bit.

The seal was still good but he was having other issues and this with a few other things has breathed some life back into it.

Anyway, it's here where all the wobble was, not sure if this would amount to alot of pressure loss but it was definitely a loose fit.

The ID and OD in red is what had wear on the OE parts, not the new vetted servo pictured. (Web pic)

 

[jamyers63]

We installed a new 'corvette' 2nd piston, along with a Sonnax superhold 4th piston.

 

[i6pwr]

I'm sure you covered this but this check ball went back?

Also, I don't know it this applies to every 4L60E, but there's a small flat metal plate with three 8MM bolts that secure the separator plate under both shift solenoids. You kinda need to tighten them with the solenoids removed or before the valve body gets mounted.

I can see how those can be finger tight and forgetting to torque them.

Just tossing out ideas.

 

[clinebarger]

Nope, all new clutches, bushings, everything.

Was the 3-4 clutch burnt before you built it?

 

[clinebarger]

I'm sure you covered this but this check ball went back?

View attachment 190564

Also, I don't know it this applies to every 4L60E, but there's a small flat metal plate with three 8MM bolts that secure the separator plate under both shift solenoids. You kinda need to tighten them with the solenoids removed or before the valve body gets mounted.

I can see how those can be finger tight and forgetting to torque them.

Just tossing out ideas.

The checkball next to the 4th Accumulator won't cause the 3-4 clutch to burn up, When I block the 4th Accumulator.....I omit that checkball.

Leaving the support plate loose will cause a Slipping Reverse or No Reverse.

 

[jamyers63]

Was the 3-4 clutch burnt before you built it?

Not to my knowledge - we got it as a "running when pulled" core, apart from the wrecking yard letting the pan fill with rain water and some mud in the pan, everything looked like it had been recently rebuilt - the steels and frictions all looked new (apart from water on some frictions making them bubble up)

 

[jamyers63]

Staring at the Service Manual and fluid flow paths...
2nd gear held so I'll assume the 2nd Servo piston and band are good.
4th gear held so I'll assume that either or both servo pistons are good (assuming I'm reading it right and both pistons get apply fluid in 4th).

Makes me suspect something in the 3rd Accumulator, either the new capsule checkball, or the orificed plug (which I never thought to look closely at), or the new seal(s) on the Band Apply Pin?

I'm grasping at straws here...during the rebuild we air tested all the pistons / clutches, double- and triple-checked clearances in the pump, clutch packs, etc. Now that we've gotten it back out and apart, I'm not seeing anything wrong... maybe I need new glasses...

 

[clinebarger]

Not to my knowledge - we got it as a "running when pulled" core, apart from the wrecking yard letting the pan fill with rain water and some mud in the pan, everything looked like it had been recently rebuilt - the steels and frictions all looked new (apart from water on some frictions making them bubble up)

This reason I ask is......If the 3-2 Downshift Valve or 3-2 Downshift Control Valve were an issue....The 3-4's would've been burnt down.

How do the other frictions look, The Band & Overruns specifically? I've seen the Forward Piston inner seal get nicked during assembly causing the Overruns to come on with the Forward Clutch, This causes a bind in 4th gear as the Forward Sprag & Overrun Frictions HAVE to overrun in 4th.

Guessing the Turbine Shaft/Input Shaft sealing rings are in good shape & fit the Stator Support well?

The Stator Support isn't rusted (The Sleeve inside).

You can pressure check the 3rd accumulator checkball for leakage by installing the Servo, Fill the Accumulator with ATF, Placing a short piece of rubber hose down into the 3rd accumulator feed that fits tight, Then apply air.

If you have leakage.....Take a blunt nose punch & reseat the checkball into the Capsule & Capsule into the Case.

The seals on the Pressure Switch Manifold are good & proud?