Thought this was a good post from them over on FB.
It's time for another CDS Tech Tip Tuesday!
Today we're going to discuss torque converter spacing. This is the most critical dimension you need to pay attention to when installing a torque converter in your vehicle.
Generally we recommend 0.125-inch (1/8") to 0.187-inch (3/16") of torque converter spacing when installing a torque converter in most combinations. Transmissions that either feature a taller pump gear (like a 4L80E), or that move a higher-than-average amount of converter charge oil (like a transbrake-equipped TH400) can get away with (or even benefit from) slightly more torque converter spacing at 0.200-inch.
So... what is torque converter spacing, exactly? Torque converter spacing refers to the amount of air gap present between the torque converter mounting pads & the flexplate when you have the torque converter full seated into the transmission pump & the transmission bolted up to your engine.
If you have the torque converter spacing listed above once you have the transmission installed onto your engine then you can rest assured that the converter is properly indexed & seated into your transmission pump. At this point, you can slide the torque converter forward to your flexplate & install your torque converter-to-flexplate bolts.
At no point do you ever want to install shims or washers to take up all of the torque converter spacing between the torque converter mounting pads & flexplate!! Doing so will bottom out the torque converter pump hub into the transmission pump leading to premature wear & failure of the transmission pump, typically with progressive damage to the torque converter itself as well.
If you have less than 0.125-inch torque converter spacing then you either do not have the torque converter indexed correctly & fully seated into the transmission pump, or the torque converter height is too tall for the specific combination of parts that you have relative to the crankshaft, flexplate, & transmission. Sometimes you'll run into a tolerance stack-up on all of these components that results in less-than-ideal torque converter spacing. In some circumstances such as with an 8L90 where the transmission features a chain-driven oil pump you can get away with less converter spacing without any issues. In other instances where minimum torque converter spacing is absolutely crucial such as in a transbrake-equipped TH400, running less than 0.125-inch (1/8") torque converter spacing can very problematic with respect to properly managing torque converter charge pressure, thrust issues, etc.
In cases of insufficient torque converter spacing with the converter fully seated into the transmission pump you may need to have material removed via machining from the torque converter mounting pads in order to establish sufficient torque converter spacing, or in some circumstances you may be able to install a shim between the engine block & bellhousing such as those available for GM applications from companies such as ICT Billet LLC.
If you end up with excess torque converter spacing that is significantly wider than 0.187-inch (3/16") then you can generally use some high quality flat washers or spacers between the torque converter mounting pads & flexplate in order to help establish correct torque converter spacing. We do offer different thickness torque converter spacers if needed here at CDS if you ever need a set.
As mentioned earlier in this post, you **never** want to completely shim all of the torque converter spacing so that there is no converter pull-out available to slide the converter forward to the flexplate. You only want to shim a converter if necessary to the correct torque converter spacing dimension range listed above, then slide the converter forward for attachment to your flexplate.
If you run into a situation where you have slid the converter forward to the flexplate & the torque converter mounting pads will not seat flush against the flexplate then the torque converter pilot is likely bottoming out inside the crankshaft pilot.
Pilot bottoming can happen for a variety of reasons including:
1.) Insufficient pilot depth machined into crankshaft.
2.) Pilot bushing for manual transmission is inside crankshaft pilot.
3.) Rust, scale, debris, etc. inside the crankshaft pilot is preventing complete seating of the torque converter pilot.
4.) Torque converter pilot is too long for your specific combination of parts relative to the crankshaft & flexplate.
In any of the above scenarios corrective measures will need to be taken by the installer before bolting the torque converter to the flexplate. We do **not** recommend removing any material from the face of the torque converter pilot in order to shorten the overall height of the pilot without first consulting with the torque converter manufacturer to confirm whether or not there is sufficient material thickness on the face of the torque converter pilot to allow removal of any material for reduction of pilot height.
On the flip side of the above pilot scenario, you may find in rare circumstances that the torque converter pilot is not engaging the crankshaft pilot at all with the torque converter mounting pads fully seated against the flexplate. This type of scenario can come up when fitting a Powerglide, TH350, or TH400 torque converter to an LS or Gen-V LT engine since early torque converter pilot dimension on these styles of converters is shorter than what is needed for pilot length with an LS/LT combo.
Here at CDS we prefer to build these types of converters with an LS/LT-specific length pilot whenever possible in order to help end-users avoid such a scenario. However, if you do find yourself in the above scenario with an LS/LT combo then we do offer a simple pilot extension sleeve that will allow a torque converter with an early short pilot to properly engage with an LS/LT crankshaft pilot.
If you have a non-LS/LT combo where you find yourself with a torque converter pilot not engaging the crankshaft pilot then a pilot extension sleeve / adapter may be available for your combination such as when installing a GM-based converter & transmission onto a Ford Windsor, Modular, Coyote, or 385-series engine. For other combinations with pilot engagement issues you may have to have your converter pilot dimensions modified to suit your specific combination of parts. We recommend contacting the converter manufacturer for an appropriate resolution in that type of scenario.
Under no circumstance should you run the engine or drive the vehicle without the torque converter pilot properly engaged to the crankshaft pilot. Doing so will typically cause a vibration as well as risk potential damage to the torque converter, transmission, or even your engine.
If you'd like to learn more or have any questions please feel free to comment below, send us a DM here, shoot us over an email to ask@cdsftw.com, or give us a call at 713-895-8834. Thanks!!
