TRNW-2: 6T70, SLIP BANG IN REVERSE UNDER HEAVY THROTTLE

[Chris and Cathy Kershaw]

Where did the valve body come from? It's very easy to have a mix up of gen
1 & 2 parts on these. We have had to use a variety of tech info combined
with dealer numbers to sort out a vb mix up on one of these before.

In a case like this at our shop I feel like we have to install a completely
different unit, all new stuff to prove it's not the trans. I had a 6t70 a
few years ago, came in with a terrible tcc shudder, built it and it
randomly wouldn't upshift, went through it a few times & changed lots of
parts only to have the same problem. We put a dealer unit in it, same
problem. It was subbed from another shop to us so I got paid, threw the
keys to them and wished them luck. An alignment fixed it, something about
the steering angle sensor causing traction or stability to kick in. No
codes, no lights.

Since then I'll buy a core and build in those situations. Sometimes it
seems that the unit as a whole is just not going to work. We just went
through a rough trip on a 10r80, 2nd time it came back we built a core and
prayed it would stay out there. We will eventually use all the new parts
out of the first unit we built but only 1 at a time, that way if there's a
bad part in there we'll find it later.

On Tue, Apr 29, 2025 at 11:13 AM Fred Whitaker <ibsprag at hotmail.com> wrote:

> Techm came from the dealer,ordered by VIN.  Remote programmed by A&E
> tools. They sell programming equipment,and usually only charge us the GM
> subscription fee.
>  It was replaced trying to fix this problem,and made no difference.
> ------------------------------
> *From:* Chris and Cathy Kershaw <kershawservicesllc at gmail.com>
> *Sent:* Tuesday, April 29, 2025 10:00 AM
> *To:* Fred Whitaker <ibsprag at hotmail.com>; Direct-Reply Mailer <
> reply at trnw.net>
> *Subject:* Re: 6T70, SLIP BANG IN REVERSE UNDER HEAVY THROTTLE
>
> What techm is in it? How was the techm programmed?
>
> On Tue, Apr 29, 2025 at 10:39 AM Fred Whitaker via reply <reply at trnw.net>
> wrote:
>
>  I am saying the pressure is 10 to 15 LB low at idle in any gear Park or
> neutral. It is a few more pounds lower at full line.
>  If you google 6T70 clutch pulse learn. I think it describes the pulse I
> am seeing on the gauge. (Although I can't see it on any movie)
>  Every 2 seconds the pressure pulses (spikes) 15 PSI  higher and makes a
> click noise. (It stops the pulse/spike when you get above 1/5th throttle
> when pressure gets higher)
>  I don't think it is the problem,but a symptom of the problem.  I think
> the computer is trying to test or adjust pressure,but dead ends with no
> solution or codes.  I think it is seeing the low line ,but has no
> solution,and trips no codes for it. ( YES I have a far fetched imagination!)
>   I think I am going to get a cheap valve body off of ebay,and just slap
> it on. (I really don't know what else to do) (Do something even if it's
> wrong)
>  I had a U code from ABS.  Pulling the ABS fuse has no effect on
> clicking,and it still cuts loose in reverse.
>   250 at full line is just below specs. Shop key shows full line  270-300
> ------------------------------
> *From:* reply-bounces at trnw.net <reply-bounces at trnw.net> on behalf of
> Wayne via reply <reply at trnw.net>
> *Sent:* Tuesday, April 29, 2025 5:25 AM
> *To:* Dan Hogan <danhogan at busterstransmission.com>; Direct-Reply Mailer <
> reply at trnw.net>
> *Subject:* Re: 6T70, SLIP BANG IN REVERSE UNDER HEAVY THROTTLE
>
> Dan, did you see the cut loose in the movie?
> Sent from my iPhone
>
> On Apr 28, 2025, at 9:33 PM, Dan Hogan via reply <reply at trnw.net> wrote:
>
>  Fred,
>
> Did you say you’re getting U comm codes in different modules?  I know from
> experience these modules do some real strange things when they get knocked
> offline even momentarily.
>
> Hard shifts and weird issues.
>
> 250 psi sounds ok to me for max line on this unit, but I’d have to look it
> up for the actual spec.
>
> I’m not following your post well, but you’re seeing 10-20 psi on line tap
> in gear at times?
>
> —-
> Dan Hogan
> Buster’s Transmission Service
> Matthews, NC 28105
> 704-847-5321
> https://busterstransmissionservice.com
>
> On Apr 28, 2025, at 7:47 PM, Fred Whitaker via reply <reply at trnw.net>
> wrote:
>
>  *Date:* Mon Apr 28 16:45:57 PDT 2025
> *Subject:* 6T70, SLIP BANG IN REVERSE UNDER HEAVY THROTTLE
>
> Got a gauge on this thing today. Pressure is a little low across the
> board. Commanding the highest pressure with a scanner,and also with
> transmission fuse pulled. 250 PSI is it. raising RPM makes no
> difference,still 250
> The one I checked last week hit 275 in reverse instantly with full
> throttle. Commanding the lowest pressure this one is 10 to 15 PSI low
> When it acts up the needle drops severely and bounces to about 250 when it
> catches.
>
> One thing I had completely forgot about was right after it was overhauled
> he brought it back for a click noise that happens about every 2 seconds. It
> isn't all that loud. BUT the noise is the pressure jumping every 2 seconds.
> It blips about 15psi.and clicks when it does it! It happens like clockwork!
> I can see nothing on movies either transmission side or engine side causing
> it. It does it with the BCM fuse pulled. I didn't think about pulling the
> ABS fuse,I'll try that tomorrow. The clicking noise stops when you give it
> a little throttle and the pressure comes up a bit. I also unplugged the
> alternator.
> I have no idea where this is going. I want to put another complete
> transmission in it. But shop owner isn't really wanting to go that way and
> I don't blame him. I honestly cant see something hydraulic making pressure
> flick like that timed so accurately apart. But maxing out at 250lb
> unplugged to me proves something isn't right inside. It is a freakin weird
> one fer sure!
>
>
> Fred Whitaker
> Anderson Transmission
> Peculiar, Missouri USA
> TRNW Member Since: 9/10/2007
> 1 inquiries, and 17 answers
>
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> Original Post *Date:* Fri Apr 25 8:13:03 PDT 2025
> *Subject:* 6T70, Slip bang in reverse under heavy throttle
> *Vehicle:* 2015 Chevrolet Impala 3.6 FWD
> *VIN:* 1G1165S3XFU138548
> *Mileage:* 249317
> *Return Visit?* come back
>
> REPAIRS THIS VISIT
>
> *Current Customer Complaint:* Slip bang in reverse under heavy throttle
>
> *Codes Currently Present:* No Codes Present
>
> *Work Completed:* Pulled transmission back out and replaced pretty much
> everything except Bellhousing.,
> Same problem
>
> *Summary:* I have been fighting this problem since last fall. Customer
> has been driving it most of the time,it only acts up under heavy throttle.
> Problem is intermittent,sometimes it does it all the time,sometimes it
> quits doing it for miles.
> I have attached a Movie.
> If you look at frame 16 I go to full throttle. But it doesn't go to full
> line pressure until frame 18.
> Car has a lot of miles but is extremely clean and runs like a new
> one,except for the slip bang in reverse. Sorry I haven't put a gauge on it.
> But seems to work fine forward,and having it back out this time clutches
> all still looked good.
>
>
>
> PAST REPAIRS
>
> *Time Line of Previous Repairs:* I believe EVERYTHING in the transmission
> has been replaced except bellhousing,trying to fix this problem. Has new
> Techm,Central valve body,different pump Etc.Etc.
> No codes,although it has come back with ABS code U0073,(can bus 2 off)but
> hasn't returned since being back this time. And a few BCM codes such as
> headlight circuit and horn relay,which all work.
> Hope someone can spot something I am missing.
>
>
>
> FILE ATTACHMENTS
>
> 2015 Chevrolet Impala 2025-04-25 08.03.47 Transmixer.pids
> <http:///uploads/forum/trnwyear2024/ibsprag_2015_Chevrolet_Impala_2025-04-25_08.03.47_Transmixer.pids>
>
>
>
>
>
> Fred Whitaker
> Anderson Transmission
> Peculiar, Missouri
> TRNW Member Since: 9/10/2007
> 0 inquiries, and 17 answers
>
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