TranSynd Transmission Fluid

Get The Best Price on TransSynd 668 Transmission Fluid

Released in 2004 TranSynd transmission fluid became the go to transmission fluid for all Allison heavy duty transmission applications. TranSynd was designed for extreme abuse, and the ability to perform under the harshest of situations.

TranSynd was specifically designed by Allison to be meet the highest of standards, and is sold by Castrol to meet demand.

TranSynd Features:

  • Better protection
  • Fully synthetic
  • Improved gear protection
  • Extended transmission life
  • Longer oil & component life
  • Extended anti-shudder durability
  • Outstanding cold-flow properties
  • Upgraded clutch-friction durability
  • Prevents deposits & oil thickening
  • Optimized frictional characteristics
  • Excellent corrosion & foaming resistance
  • Formulated from pure synthetic lubricants

Vehicle Applications

2001Chevy6.6L LB7 Duramax
2002Chevy6.6L LB7 Duramax
2003Chevy6.6L LB7 Duramax
2004Chevy6.6L LB7 Duramax
2004.5Chevy6.6L LLY Duramax
2005Chevy6.6L LLY Duramax
2006Chevy6.6L LLY/LBZ Duramax
2007Chevy6.6L LLY/LBZ Duramax
2007.5Chevy6.6L LMM Duramax
2008Chevy6.6L LMM Duramax
2009Chevy6.6L LMM Duramax
2010Chevy6.6L LMM Duramax
2011Chevy6.6L LML Duramax
2012Chevy6.6L LML Duramax
2013Chevy6.6L LML Duramax
2014Chevy6.6L LML Duramax
2015Chevy6.6L LML Duramax
2016Chevy6.6L LML Duramax
2017Chevy6.6L L5P Duramax
2018Chevy6.6L L5P Duramax
2019Chevy6.6L L5P Duramax
2001GMC6.6L LB7 Duramax
2002GMC6.6L LB7 Duramax
2003GMC6.6L LB7 Duramax
2004GMC6.6L LB7 Duramax
2004.5GMC6.6L LLY Duramax
2005GMC6.6L LLY Duramax
2006GMC6.6L LLY/LBZ Duramax
2007GMC6.6L LLY/LBZ Duramax
2007.5GMC6.6L LMM Duramax
2008GMC6.6L LMM Duramax
2009GMC6.6L LMM Duramax
2010GMC6.6L LMM Duramax
2011GMC6.6L LML Duramax
2012GMC6.6L LML Duramax
2013GMC6.6L LML Duramax
2014GMC6.6L LML Duramax
2015GMC6.6L LML Duramax
2016GMC6.6L LML Duramax
2017GMC6.6L L5P Duramax
2018GMC6.6L L5P Duramax
2019GMC6.6L L5P Duramax
2003Chevy Kodiak / GMC TopKick6.6L LB7 Duramax
2004Chevy Kodiak / GMC TopKick6.6L LB7 Duramax
2004.5Chevy Kodiak / GMC TopKick6.6L LLY Duramax
2005Chevy Kodiak / GMC TopKick6.6L LLY Duramax
2006Chevy Kodiak / GMC TopKick6.6L LLY/LBZ Duramax
2007Chevy Kodiak / GMC TopKick6.6L LLY/LBZ Duramax
2007.5Chevy Kodiak / GMC TopKick6.6L LMM Duramax
2008Chevy Kodiak / GMC TopKick6.6L LMM Duramax
2009Chevy Kodiak / GMC TopKick6.6L LMM Duramax
2010Chevy Kodiak / GMC TopKick6.6L LMM Duramax

TranSynd Transmission Fluid Questions

Is TranSynd Discontinued?

TranSynd transmission fluid is not discontinued and can still be purchased. It’s not the most common transmission fluid based on the applications it’s used in, so it’s best to get it online.  

Shop for TranSynd transmission fluid here.

What Is The Best TranSynd?

In our opinion, the best TranSynd transmission fluid is Castrol.  Since Castrol TranSynd is the most common version, it’s easy to get and meets all Allision specs, it’s the go to in most cases since it can be purchased in large quantities for fleet use.

The most common version of TranSynd is 668, which is backwards compatible with the older versions that include TranSynd 468, however, does not work with TranSynd 295. 

What Transmission Fluid Replaced TranSynd?

TranSynd is still very common in Allison transmissions, and has been updated a couple of time since it’s inception. 

What Year Did on TranSynd Come Out?

Allision TranSynd transmission fluid was introduced in late 2004 as the replacement to Dexron  3. While Dexron 3 was used in Allison applications for a long time, TranSynd is the better transmission to use long term.

Highlighted Features
  • Delivers improved gear protection.
  • Delivers extended anti-shudder durability.
  • Delivers extended clutch-friction durability.
  • Excellent corrosion and foaming resistance.
  • Excellent thermal and oxidative stability that helps to prevent deposits and oil thickening.
Castrol TranSynd 668 transmission fluid performance charts and information

How Much TranSynd Do I Need?

The amount of TranSynd transmission fluid needed for your application varies, so it is best to consult your owner’s manual.  In most cases, reading the transmission dipstick will give you and idea how much fluid you need when you do routine maintenance. 

What Temperature Does TranSynd Fail At? 

Like all transmission fluids, TranSynd is best when it’s temperature is between 160-200 degrees F. This common range is best for longevity of both your transmission fluid and transmission itself.  The below transmission fluid chart shows how long transmissions last when fluid reaches various temperatures.

Transmission Fluid Temperature Chart

Can Dexron 6 Be Mixed With TranSynd? 

In many cases, yes, Dexron 6 can be mixed with TranSynd. In fact, Dexron 6 is the recommended transmission fluid in GM applications with the Allison 1000.

Since TranSynd may be harder to buy, you can use Dex 6 in it’s place. 

What Color Is TranSynd?

TranSynd transmission fluid is a bright red when new and should be a similar color if your transmission is maintained properly.  The below transmission fluid color chart shows common transmission fluid colors depending on use and give you an idea of what to look for over time. 

Transmission Fluid Color Comparison - Transmission Cooler Guide

Can TranSynd Be Used In All Automatic Transmissions?

TranSynd is not a common transmission fluid in terms of applications and it Allison specific, so no, it cannot be used in all automatic transmissions. It’s always best to consult your vehicle’s owners manual to learn what transmission fluid is recommended for your application.

Can TranSynd Be Used As Power Steering Fluid?

Yes, it is common for transmission fluids  to be used as power steering fluid.  The two fluids are similar and both work in power steering systems.

However, we don’t recommend using TranSynd as a power steering fluid because it’s much better suited to be used in your transmission.  TranSynd is expensive, so it’s best to not waste it.

Where Can I Get TranSynd?

The best place to get TranSynd is online. Like we’ve said, TranSynd isn’t a common transmission fluid, so it’s easiest to order online and shipped to you..

How Much Does TranSynd Cost?

Unlike Dex 6 that can be used in Allison transmissions, TranSynd is more expensive. Just to compare, a gallon of Dexron 6 may be $30, where as a gallon of TranSynd may cost anywhere from $45 – $55 depending on where you get it from. 

  • Delivers improved gear protection.
  • Delivers extended anti-shudder durability.
  • Delivers extended clutch-friction durability.
  • Excellent corrosion and foaming resistance.
  • Excellent thermal and oxidative stability that helps to prevent deposits and oil thickening.


Allison transmissions deserve the highest quality fluids, that’s why the Allison approved TES668 synthetic transmission fluid was engineered. TES668 is a modern formulation with many advantages over mineral-based non-synthetic fluids.

This next generation transmission fluid is specified for Allison 1000 2000 3000 and 4000 series automatic transmissions. TES668 outperforms mineral-based fluids in several key areas such as:

  • oxidative stability
  • anti-wear performance
  • friction modifier durability
As mineral-based fluid ages, noise ,vibration, and harshness increase, so owners and operators who choose TES668 get better friction performance which provides more consistent clutch application regardless of temperature variations and loads.
TES 668 (TranSynd) used the  previous TES 295 specification and built on it to deliver a better and higher performance fluid you’re going to have the ability to go those longer drain intervals and your transmission is not going to be the thing that’s holding you back.
The robust formulation of TES668 meets the most demanding specs related to fluid stability lubrication and cold operation this allows Allison to support long drain intervals even when operating under heavy loads.
TES 668 is specified for Allison products to ensure ideal operation unapproved fluids produce a range of durability problems including seal and friction issues.
Using genuine automatic transmission fluid from an Allison approved or Allison authorized partner is key to optimum performance and the long lasting durability of Allison products get extended drain intervals, enhanced transmission performance, lower operating cost, and optimal transmission protection with Allison’s TES 668 transmission fluid.