JT5 and Shortened Tremec 3550 Comparison

The 3550 from Tremec Trading Corporation was a high performance 5 speed designed to replace weaker T5 5 speeds in Mustangs. Tremec Corp. was originally a vendor for Ford and Jeep during the 1970's thru late 1980's. By 1986 they were no longer an OEM supplier for any U.S. auto maker and solely dependant on aftermarket sales of their 3 and 4 speed parts as well as transmission sales to the South American markets as a main source of revenue.

As demand for the gears they were making dropped off, the 3550 5 speed created that extra income boost they needed. They recently ( 1997 ) acquired the rights to manufacture transmissions for U.S. auto makers by purchasing Borg Warner's Automotive Gear Divison. So the T5 and 3550 are now made by Tremec!

Tremec was dropped by the auto makers simply because of poor quality and delivery. When you compare the fantastic engineering of Borg Warner to Tremec units it becomes quite obvious why Tremec purchased Warner and their vast base of technology patents. New units made after the 3550 could prove to be some of the finest combinations of Tremec's manufacturing base along with Warners technology!

A vendor called Waterloo Drive Train decided to shorten the 3550. This was suppose to be an alternative to the JT5 5 speed. The vendor states that the transmission requires no modifications to the floor, drive shaft, and interior. We got our hands on one of these transmissions and installed them at a customers request only to find out that the floor, driveshaft and interior had to be greatly modified. It was a clean shorten of a 3550 but to our standards totally unsafe and we feel the output shaft will fail. The glued together tailhousing is also not acceptable. Also the following problems are now documented with that conversion for a stock E-Type 6 cylinder conversion.

When the concept of putting a 5 speed in an E-TYPE Jaguar was put in front of me I thought of many base platforms. I picked the T5 base simply because it could handle the power and torque of 6 and 12 cylinder Jaguar engines and yield a good life factor. It also was one of the finest shifting transmissions ever built. Many people advertise gearboxes that can handle 600 horsepower and 500 FT lbs of torque. The T5 is rated at 330 FT LBS and the Tremec is now rated at over 400 FT LBS. What does this mean? Even Tremec's test on the T5 and 3550 are not done under the same time / load frame. Gear boxes are rated on what the manufacturer's idea of how much torque a transmission should hold over a specific period of time. If no two tests are done exactly the same it makes it difficult to really say what a rating means when comparing gearboxes. You can apply more torque to the transmission above it's suggested rating but the life factor of the gearbox will decrease. Generally torque ratings are based on what torque the transmission may see in its life time. Most manufacturers will also fiqure on 150,000 miles as a life time. Holeshots or clutch dumps decrease that life factor. It is not uncommon to see a 400 plus horsepower Mustang GT run a T5 at the drags but break it weeks later. The box was never designed for this nor should it be put in that class. Put the same box in a 450 hp road car with little shock loads and to your surprise the T5 doesn't break. If your engine produces 400 FT LBS of torque at 3000 RPM that torque load is split between the transmission and rear. If you have a 1 to 1 rear axle ratio, most of it is absorbed in the gearbox. If you have a 4.56 rear axle ratio the torque load shifts more towards the rear axle. That is why most gearboxes break in cars with "dead rear end gears" such as 2.76 or 3.08 ratios. ( Stock Mustang GT'S) I did not see a need to compromise quality shifting for a highly rated torque load that would never be exceeded in almost all of the conversion applications. If high torque and power ratings are a major factor then the unshortened 3550 is for you.

Ratios for the Tremec 3550 were designed to be compatable with the T5 Mustang version a chart below shows some comparisons. The JT5 is offered with several ratio options. It is not just a 5th gear change. Because the 3550 upper 5th gear is part of the mainshaft and not replacable, there are no optional 5th gear ratios available. Custom gear shops can grind the 5th gear section off the 3550 shaft and weld or keyway a new one in place, but this procedure is not cost effective in my opinion. If you need to make further comparisons download my RPM calculator.

We have spent a great deal of time and money to create conversions that are cost effective, a better driving experience, safe, and install with minimal modification to your existing E-TYPE. Our castings and shafting are own own pieces that are engineered for performance and race proven. XK's Unlimited, Terry Larsen, Vicarage Jaguar, Classic Jaguar, Eagle E-Types, Predator Performance, and Terry's Jaguar have all installed JT5 gearboxes in race applications with fantastic results.

Special offer! If you are a current owner of a TX51 5 speed ( shortened 3550 ) that broke or never received a new tunnel cover, we will give you a $800 credit towards your TX51 5 speed when converting back to a JT5. Contact us for details....