Ask Away! with Jeff Smith: Tips & Advice for Bolting Up a 4L60E Transmission to a Small Block Chevy Engine

I just read your article from 2017: The Great Chevy Auto Trans Interchange Guide.

This is a great article, but my head is spinning.

I have a small block Chevy that I’m trying to attach a 4L60 transmission to. The transmission is out of a 2005 Tahoe, with a 5.3L LS engine. I tried installing the transmission and although it bolted up, the torque converter would not turn. So, I believe I need the adapter plate. Which do you recommend?  Can you please advise the best way to do this?

I believe the Chevy Performance Adapter kit is the way to go but wanted validation.

Also, one other question: How do I attach the manual speed cable to the electronic 4L60E?

B.S.

Let’s go over why the trans bolted up but the converter does not turn. The first version of the GM 4L60E in 1990 (which is an electronically controlled update of the 700-R4) was designed to bolt to a one-piece rear main seal small block Chevy. The small block Chevy was eventually replaced in most GM vehicles roughly by the year 2000 with the Gen III. LS engine.

The LS engines use the same basic bellhousing bolt pattern but the distance from the cylinder block bellhousing flange to the crankshaft mounting flange for the flexplate/flywheel changed. The new LS engines (with the exception of the 1999 all-iron 6.0L truck engine) placed the crank flange approximately 0.400 inch closer to the front of the engine compared to the small block Chevy.

Where the confusion lies with these 4L60E transmissions is that GM changed its design slightly around 2002 with a deeper bellhousing to accommodate a larger torque converter. This is the transmission that you have. This latest design creates three different 4L60E transmissions: the first generation small block Chevy style, the second used with the early LS engines, and the later LS transmission with the deeper bellhousing.

With an older, Gen I small block Chevy, the crankshaft flange extends rearward roughly 0.400 inch more than the typical LS engine. This additional depth pushes the converter into the front pump creating a serious preload that should not be there. It’s good you didn’t try to drive this or it would have failed both the transmission and the thrust bearing in your engine requiring a complete rebuild of both!

This is roughly 0.270 inch too great a distance, which is why the converter will not turn with the transmission and converter bolted to the engine.

To ensure the proper clearance, there are a couple of kits available to adapt the later 4L60E automatics to a small block Chevy. The first transmission adapter kit is available through Chevrolet Performance. The main component is a 0.400 inch thick adapter plate that fits between the engine block and the bellhousing flange on the transmission. The kit comes with two longer dowel pins to accommodate the adapter plate, longer bolts, as well as a one-piece rear main seal flexplate. (We’ve listed the part number at the bottom of this article.)

You didn’t mention which small block you have but if you have an older, two-piece rear main seal small block, then the above Chevrolet kit one-piece main seal flexplate will not bolt up to your two-piece rear main seal crankshaft. Rather than having to spend money on two flexplates, there is an alternative.  Lakewood sells an adapter kit using a similar 0.400 inch thick steel spacer, longer bolts and guide pins but without the flexplate. If you already have a flexplate for your engine then you are almost there.

We say “almost” because you need to check the converter bolt pattern on the converter against the pattern on your flexplate. It’s likely that these two patterns will not be the same.

We’ve listed the converter patterns in a chart below. There are essentially three different converter patterns with a large and small pattern for the older TH350/TH400 converters and a new pattern for the LS that is in between these two. If you have a flexplate with the larger pattern (which is unlikely) the three converter bolt holes can be slightly altered with a hand file or die grinder to open them up roughly 0.020 inch to match the LS pattern. If you need a flexplate, TCI PN 399273 is available through Summit Racing. The converter mounting pad holes will also need to be modified to fit the larger LS converter pattern.

Once the converter and transmission package is bolted up with to the engine, there should be roughly 1/8 inch clearance between the converter and the flexplate with the converter pushed back into the transmission pump. If there is less than this clearance, you may need to machine the converter mounting tabs on the converter or somehow increase this clearance. This is important, since this clearance is necessary to prevent the converter from bottoming out against the front pump which can cause serious damage to both the engine and transmission.

If there is more than 1/8 inch clearance, you may need to add thin AN washers to take up this greater clearance between the converter and the flexplate mounting lugs. This is important because you don’t want to pull the converter out of the front pump more than the above distance.

Adding an Electronic Transmission Controller

You are probably aware that you will also need a separate transmission controller to operate the 4L60E since all its commands are accomplished electronically. There are multiple controllers out there that can do the job—including an all new lineup of TC Transmission Controllers from Edelbrock.

We’ve listed four units from different manufacturers in the Parts List at the bottom of this article. You should probably do your own research since not all the units are currently available due to supply chain difficulties which are becoming a way of life these days.

You can learn more about those Edelbrock Transmission Controllers in this article.

Connecting a Speedo to a 4L60E

As for your question regarding the speedometer, the electronic transmissions do not offer a way to connect the mechanical drive cable. There are companies that make a new tailhousing that will accommodate a mechanical speedo drive. Bowler is one company that offers this kit—but it’s expensive. A company called Speed Hut offers a mechanical drive box that will take the vehicle speed sensor (VSS) output from the transmission and convert it into an electric motor drive that will spin your mechanical speedometer. Or, you can have your mechanical speedometer converted to an electric drive like most new cars use. One company that could help you with this would be our friend Shannon Hudson’s company called Redline Gauge Works. We’ve listed both contacts in our Source list below. Hope this helps.

Torque Converter to Bellhousing Spacing Chart

4L60E-to-SBC Parts List

• Chevrolet Performance Transmission Adapter Kit – NAL-19154766
• Lakewood Bellhousing Adapter – LAK-15901LKW
• TCI Forged Flexplate for 2-Piece RMS – TCI-399273
• Edelbrock TC Transmission Controller – EDL-36212
• DIYAutoTune MicroSquirt CAN Transmission Controller – DIY-S0031
• ATI Performance Products Automatic Transmission Controller – ATI-705506
• Painless Performance PERFECT TORC Transmission Controller – PRF-66501

Contacts:

• Redline Gauge Works – 661-259-8891, RedlineGaugeWorks.com
• Speedhut – 801-221-1400, Speedhut.com