TRNW-2: 6L80, Pump & bell housing machining

[Richard Wardell]

I've been machining these things since day 1 in 2014 whe we did the first
5L40 and then our first 6L was a 6L90.   I've purchased only 2 new bells
and no stators.  I checked those bells and 1 had excessive runout in the
pocket.  I machined a stator yesterday that had .006" runout!  From the
factory!  It had 71k on it and the TC was shot.  I did one this morning
that a local shop reused the bell and the TC didn't last 50k.   The photo
is ME, several years ago.  some dick stole it from one of my youtube videos
and uses it on ebay to sell service.  I've cut them on the mill from the
beginning.  With the ideal clearance @ .0015" pump machining and building
is a big deal.  If they are loose fluid leaks into the apply side and drags
the TCC at stop lights.  Tight and you get anything from noise to no line
rise at all.  I cut 3 surfaces on every one.  What is cut from the pocket
is cut from the deck, and what is cut from the stator is added to what was
cut from the deck and that's how much is cut from the case mating surface.
End play is a big deal too.  I don't know of any published spec's. I have
always used the 4L60 spec's of 5-25 and it's worked out well.

[image: image.png]

On Thu, Sep 4, 2025 at 10:15 PM Chris Kershaw via trnw2 <trnw2 at trnw.net>
wrote:

> *Date:* Thu Sep 4 19:15:05 PDT 2025
> *Subject:* 6L80, Pump & bell housing machining
>
> Group, we have had some recent issues with machined 6l80 bell housings.
> I've had a few that would make pump noise under heavy throttle. Seems like
> it would happen once or twice and clear up after the initial 10-mile road
> test. I even pulled pans and inspected filters after 40-50 miles and no
> debris, so we let them go.
>
> Recently pulled a comeback out for noise and found the pocket depth was
> uneven, and the slide was tight in one area when checking clearance with a
> straight edge. Our local guy who originally machined it said the depth was
> off by .001 and fixed it. He machines them on a lathe. He does not cut the
> surface that contacts the case. I've noticed a lot of videos show these
> being cut on a milling machine.
>
> The Machined bells we have gotten from natpro or transtar appear to be cut
> with a milling machine and have a much smoother surface than lathe cut.
> They are also cut at the surface that contacts the case.
>
> Is there a machinist (I'm not one) reason to cut the bellhousings one way
> or the other or with one tool or the other? is it just personal preference?
> Any opinions or experiences on this would be appreciated.
>
> Chris Kershaw
> Kershaw Services Llc The Gear Box
> Mechanicsville, Maryland USA
> TRNW Member Since: 5/1/2023
>
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-- 
Richard Wardell
owner Quality Transmission of Bartow county
1640 JFH PKWY Cartersville Ga 30121
770-315-2544

*In a world full of self centered shallow people, think for yourself, be
kind and generous.  You will take nothing with you and your children will
waste what you leave behind!*
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