4L80 leak and converter wear issues

[The_Eric]

Here's a question to all who know the 4L80.. This unit is in a 1996 "short bus" that now sees life as a college ball game with the friends bus..

Owner is complaining of a leak - inspection looked like it was leaking from the front seal area.. pulled the trans pan beforehand to drain and found a fair bit of metal in the pan. Dropped the trans and pulled the converter and found all this loveliness. There is a pretty good step (by feel) from the lower (in the pic)to the upper marks. It's also not even all the way around and neither is the "step" Also worth noting is that I think it's been "rebuilt" at one point.. cleaning tool marks on the pan, paint on the pan (not the case) and a date on the converter of 2/6/15

What in the name tarnation is going on here? I realize this thing needs more attention than I can give, but would like to be able to talk to the customer about it and fill him in

 

[bullwinkle]

May have torn up the front pump-I had a work Savana 2500 4L80E do that (2000), and it took a couple tries before the shop got a front pump/converter combo that wouldn't leak...

 

[wwillson]

If anyone knows @clinebarger will

 

[The_Eric]

If anyone knows @clinebarger will

Agreed. The man is a freaking transmission guru!

 

[clinebarger]

Very common issue on 4L80E's, The Converter has a TON of circular runout., Basically the converter is not in-line with the Crank Centerline.

This is not to be confused with Crankshaft sitting low in the Crankcase which is common on Gen I & II small block Chevies with high mileage or just plain worked hard. OR the Transmission Case/Pump being Offset to the Crank Centerline....
*Both these issues will cause wear all-the-way-around the Converter Hub, But the Pump Bushing will only be worn on one side.

When the Converter Hub (The entire Converter) has Circular Runout.....The Converter Hub will be worn on one side while the Pump Bushing will have wear all-the-way-around.

This is more often than not cause buy the Pilot of Converter being worn, (The Pilot Hub that fits into the Crankshaft.) This is usually cause by running a busted Flexplate too long thus allowing the Pilot Hub to beat itself against the Crankshaft.
Just about EVERY 310mm 4L80E Converter core needs a new Front Cover OR the Pilot needs to be welded & turned down to 1.703".

**I have machined "Go-NoGo" gauges for the end of the crankshaft in .002" increments from 1.703" to 1.709" with a 1.708" inbetween the 1.707" & 1.709".
I find myself asking my converter builder for a 1.705" or 1.708" Pilot Diameter quite often as I like a tighter fit than what's deemed acceptable.

Let's talk specifications....The accepted (Industry Standard) Pilot Hub to Crankshaft clearance is .005", So assuming the Pilot is 1.703", A 1.708" go-nogo gauge shouldn't just drop in, And 1.709" gauge shouldn't fit at all.

The "fly in the ointment"....The Pilot Hub has a very thin work surface that extends into the Crankshaft, You MUST be mindful of this & using a suitable Bore Gauge to make sure there's not a Rut worn in the crank is highly recommended.
The good news is.....A Nodular or Forged Crank is MUCH harder than the thin Mild Steel Converter Pilot Hub work surface.

If you're ever working with a LSx(Gen III)/4L80E combo....The Crank Spacer which accepts the Converter Hub Pilot instead of the Crankshaft itself should be replaced ANYTIME the transmission is removed as it is a lot softer than a Crankshaft!!

 

[The_Eric]

clinebarger, I really appreciate your in depth explanation - thank you! I will relay this to my customer and see how he wants to proceed.

 

[clinebarger]

Bet the pump & gears are completely wiped out & enough metal has ran through the unit to need a teardown & inspection.

The LSx swap craze has caused a severe shortage of "Good/Rebuildable" 4L80E Cores......Though this may be regional?

 

[The_Eric]

That was my thought too. I briefly entertained the notion of pulling the pump and replacing the bushing and pump gears, throwing a converter in it and running it, but the reality is that there still is a bunch of metal in it, so I'm not going to trust it.

Customer wasn't thrilled with the prospect of spending big money on it since "it only drives a thousand miles a year", but the bigger problem proved to be ID'ing the unit (which 3 letter code it is) because whoever rebuilt it tossed the build tag. That meant I couldn't find a direct fit used one and the yard only had one of the 8 possible configurations available for my cost of $700 anyway! So by the time I mark it up, possibly change yokes, lengthen or shorten the driveshaft and whatever else, he's within spitting distance of a rebuilt unit.. Luckily the customer is a reasonable and understanding fellow who agreed with my assessment. So I spoke with an area rebuilder who will pick it up on their route, build it and deliver it within a week from this coming Friday.