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Trans cooler issues 4L60, 4L65 & 4L70

Dave’s Tech Tip from Larry Cleeton,

My Hot Rod Buddy, Pierre was having issues with his brand new GM Performance 4L70e transmission and LS3 525hp crate engine this summer having shifting issues.  I had driven it locally when we went to our favorite joint for lunch, Jersey’s Mikes in Sammamish and seemed like it shifted great.  On Pierre’s return trip from Everett, he had problems once he got into stop and go traffic and at low speeds, it just wasn’t shifting right, Pierre called the local transmission guy, had them check it out and it still had problems.

Just by chance I was talking to Larry Cleeton and mentioned it and Larry not only had the same issue, but had solved the problem.  It turns out that these electronically controlled transmissions have a built in safety that locks up the torque converter when it gets too hot.  GM figures that by reducing the slippage of the torque converter (which produces heat)  it will protect the transmission from failure and get you home in more or less “limp mode.”  I had experienced the same type of issue on my LT4 engine which had a oil cooler attached to the engine sump, but was cooled by radiator fluid.  Larry said that the cooling in the front mounted engine radiator was insufficient to cool down the transmission enough to prevent lockup.

Most of the aftermarket swap radiators have an option for transmission cooling in the bottom or side of the newer style aluminum radiators.  This is a separate coil that is cooled by the radiator fluid.  As is the case with the supercharged LT4, why would I want to try and cool down hot oil or hot transmission fluid with a radiator that was at 200 degrees or more?  Most of the Gen IV and Gen V engines run at or around 200-208d before the fans kick on.  I thought that was a poor idea and plumbed in an external oil cooler in the front of the vehicle.  My thinking was why not take a clue from the off-road buggy guys that run the Baja 1000.

I’ve been looking at these compact Derale fan cooled radiators for sometime now thinking that I might want to upgrade and try them out, they also come in a single fan configuration.  I suggested this to Pierre and he jumped on it and solved the issue right away.  Here’s a few pictures for your review:

’64 Chevelle LS3 upgrade

After building the car in 2015 I decided to swap out the cam, upgrade the rockers, valve springs and lifters from Comp Cams.  In Reno last year I saw the new “Sheet Metal Fabricated Intakes” and decided they would look pretty good.  This is the low rise model and uses the 92 mm opening instead of the 102mm.  The Holley engineers explained that it doesn’t matter what size the opening is if you use the stock 90 MM throttle body.

The serpentine system is from CVF racing.

This is what it used to look like:


ZR1 Top Speed Run at Papenburg

Watch closely at the 0:40 second mark when the transmission shifts down 4 gears from 8th gear to 4th gear, the direct injected engine revs almost instantlySame bottom end as the LT4, just a bigger supercharger gets you another 100 hp.  Ligenfelter has pushed the LT4 engine up to 1,400hp with the stock bottom end.

Gen V LT5 – the newest member of the GM High Performance Engines

Article courtesy of David Kimble who is famous for his detailed sectional 3D views of cars and engines.  They’ve taken the LT4, beefed up all the internals and added a much larger supercharger with more boost.  You can also see from the top of the engine that they’ve increased the intercooler size substantially.  This engine is much taller than the LT4, which will present a challenge for engine swaps.

Gen V L83 Truck Engine Swap

More and more L83/L86 truck engines are available now from wrecking yards at reasonable prices, some including the 6 speed 6L80E transmission. These are great solutions for drive-train swaps because they are plentiful, powerful, priced far less than the LS3 and Gen V LT1 takeouts and come complete with everything you need.  ICT Billet has just released brackets that allow you to easily add hydraulic power steering to these engines.  Reference my installation guide for vendors who provide reflashed ECUs.

Gen V LT1 install from StreetRodder Magazine

“Let’s start by saying that swapping in a Gen V gasoline direct injection (GDI) engine won’t be quite as easy as its immediate predecessors, like the LS1 or LS3. While initial concerns were focused on the GDI-specific high-pressure fuel delivery system, that’s really just a small and relatively easy piece of the puzzle. What we’re going to cover with this story are all the other little details that nobody else talks about yet are essential to make this engine run. There are no shortcuts to doing this correctly”.

GEN V LT1/LT4 VSS and tach signal generation

I’ve had quite a few inquires lately in regards to how to power and drive your conventional mechanical or electronic speedometer from the new GM 8L90E 8-speed transmission.  After talking at length with GM Performance and Powertrain they have provided a few solutions that should work.

The 8L90E transmission is a second-generation model that uses an electronic controller built within the transmission itself.  If you’re using the GM “Connect and Cruise” system it includes a separate controller (black rectangle with blue connector above right) that communicates back and forth between the engine ECU and the transmission itself.  This system is part of the CANBUS or GMLAN electronic control system and is for all practical purposes standalone, they don’t want you piggybacking off the system because you can potentially disrupt the network transmission protocol.  For the 8 speed automatic transmissions, the vehicle speed information is fed to the transmission controller through a pulse signal. The Vehicle Speed Sensor connector (on the wiring harness) is not used because there isn’t one on the 8L90E to plug into (see below). The ECM is programmed and looking for 40 pulses per revolution.

I have successfully piggybacked off the VSS signal from a T56 manual transmission and generated the correct speed using the Dakota Digital VHX gauge package with their BIM 01-2 module.  Using the VSS signal from an ECM requires a single wire input into the Dakota Digital bus.  Since the signal is generated outside the GMLAN, a simple pulse generated inductive signal from a magnet, I believe it doesn’t disrupt the signal going to the ECM (see my LT1/LT4 installation guide for more guidance).  This is necessary because both the LT1 and LT4 Gen V engines require a VSS signal, without one they go into ‘limp mode’ and run at 1/3 throttle. Set up this way my engine and transmission function correctly because they do not generate any check engine codes or MIL lights.

GM Powertrain recently brought to my attention that pin 14 (grey/blue wire) out of the transmission will provide a non-CANBUS raw signal (pulse generated) that should drive a conventional electronic speedometer. This is an inductive type signal so voltage output is dependent on speed.

This is the plug that connects to the 8L90E transmission, if you look closely you can see the grey wire.
The plug goes into the transmission here.










One simple solution available is a conventional shaft mounted VSS signal generator like this:
Summit Racing sells this part: This is a VSS magnet kit with pick up coil. Normal rear wheel drive domestic installation takes four magnets on the drive shaft with a pickup coil mounted approx 5/8″ away.  It seems odd that you would use old school mechanical magnets spinning around on the outside of your driveshaft to get a signal that your speedometer can read, but it’s a least a solution.











A little bit more elegant solution is this split-collar speed-sensor that is used on data-acquisition systems
Another option is a GPS driven signal like this:






The best solution seems to be the recently released STA-100 ODBII interface that not only handles the speedometer issue, but also provides a tachometer signal.  There is also pin C (white wire) output from the bulkhead connector on the GM wiring harness that provides engine speed, but it’s a CANBUS signal and will not drive an aftermarket electronic tachometer unless it’s OEM.

The STA-1000 plugs directly into the OBDII diagnostic connector, providing a user-adjustable traditional Speedometer, Tachometer and Check-Engine output for your choice of aftermarket instruments.


  • Fully compatible with common aftermarket electronic speedometers 
  • User selectable output of: 4k, 8k, 16k PPM signals, Sine or Square wave options 
  • +/- 35 percent speed signal correction, compensating for tire size or gearing changes
  • Adjustable 4, 6 or 8 cylinder tachometer signal output
  • Check Engine light output provides a grounded (-) output to activate a check engine light of your choice
  • Automatically calibrated output for an aftermarket cruise control can be activated by making connection to the higher-resolution fixed VSS sensor
  • Small footprint measures 4-3/4″x 3″x 1″ making it easy to hide
  • Compatible with J1850 and CAN OBDII protocols

Stay tuned for more….


Gen V LT1/8 speed “Connect and Cruise” install on a ’55 Chevy 2 door post

I have made a wee bit of progress, the two steps forward part.  Motor is in, small amount of cutting and grinding and welding…well, ok, a lot of that.  Note I cut off a bit of the motor mount to have access to the oil port for my oil pressure gauge.  Put on the Drive Junky belt system today.  Found out that I can use a rack and pinion steering which takes care of the header clearance problem. 

The fuel tank is ready to be TIG welded (Rick’s Tanks).  However the 500 # gorilla is still in the room, that’s the 8 speed, and yes, you are right, 1st gear is like 4.56,  I found out that the rear end is 2.20:1.  Not sure if that is within the parameters of the ECM, might have to swap gears later.  I have to get the steering in before I can move the car back over to the lift side and slide the tranny under the car.  Then I can see how much of the 60 year old floor I have to cut away.  Anyway it is some progress. – Harry Abbott, Oak Harbor, Wa.

Latest photo from Harry -12/5/2017

DriveJunky serpentine system

Rick’s tank bung to be welded into Tank’s Inc FI tank

Dirty Dingo engine mounting plates adapted to frame