Michael Czap
December 31, 2013

If you’re lucky, said owner hopefully was an intelligent fellow and installed his new Tremec transmission with care, while heeding to the strict transmission fluid and 500-mile break-in requirements. Again, this was probably not the case. Your author knows of at least four personal acquaintances who hurt their T-5s at the track one week, then melted the plastic on their credit cards the following week by buying and installing a new 3550/TKO, only to drive straight back to the track once it’s all buttoned up.

These folks are the first to complain about the Tremecs having poor shift quality, which was the primary complaint about this series of transmission. The heavy-duty internals also mean that the larger gear mass is just not going to be as quick to shift at high rpm compared to the owner’s previous T-5 transmission. Break-in was not meant to be 500 miles of highway driving, but 500 miles of city-style driving—up and down through the gears giving the brass blocker rings a chance to properly break-in. The shifting would indeed become easier if you followed the directions—go figure.

This author recently picked up an early Tremec 3550 and bellhousing to rebuild. These transmissions have inspection covers that are a lifesaver when buying used transmissions. Although being very clean externally, this unit had signs of heavy wear on the 1-2 and 3-4 sliders, denoting a generally abusive life. Purchasing a used transmission is a huge gamble, especially if you do not know what you are looking for. Never ever take a seller at their word. How often do people sell perfectly good transmissions? Performance parts have been removed from service for a reason. Simply spinning and wiggling the input shaft, while rowing the shifter through the gears is not an indicator of the health of the transmission. Internal inspections are a must. Parts for Tremec transmissions parts are about twice as expensive as for T-5 transmissions, so take that into consideration when striking a deal on a damaged box.

Tremec transmissions may seem daunting to work on, but they actually require fewer special tools to rebuild than a T-5 does. Simple handtools and a pair of expanding ring pliers are about all that is usually needed. The only press-fit part is usually the tailshaft bushing, but a machine shop can make quick work of that task. Follow along as we show you some of the highlights of rebuilding this Tremec 3550.


The early TKO mainshaft can be retrofitted into a 3550 by simply machining the tailshaft housing to utilize the larger C-6–style tailshaft bushing


17. The input shaft gets its new bearings and it’s installed through the front of the box.
18. The new input shaft seal gets installed next. Another nice thing about these transmissions is that they all have steel bearing retainers from the factory, unlike the stock fox T-5s.
19. At the back of the transmission, Fifth gear, along with its shifter fork and the speedometer drive gear, are installed next.
20. New shift fork pads are installed throughout the transmission. A few vendors sell aftermarket brass shift fork pads. If you think you will be putting the transmission through some abuse, they might be a good option for you.
21. Clean the surfaces well and lay down a thin bead of a premium, firm-setting RTV. These are precision machines surfaces, so a little dab will do you.
22. Rub the RTV across the width of the sealing surfaces with your finger. It goes a long way toward preventing leaks. Try not to get any down into the bolt threads. When you install the bolts, the excess can fill all the available space and prevent the fastener from being torqued down properly or even damaging the case threads.
23. Once the shift forks are lined up, install the cover and torque to 20 ft-lb.
24. This tailshaft bushing was quite scored, so we will be replacing it with the one provided in the kit.
25. A fresh tailshaft seal gets installed after pressing in the new bushing.
26. For the final assembly, it’s easier to have the transmission installed into a fixture. This author is lucky enough to have a vise large enough to tackle this job.
27. Once sealer is applied, the tailshaft housing can be installed and torqued to 50 ft-lb. Remember to install thread sealer on the top two bolts, as they protrude into the main case.
28. Mainshaft endplay is checked and brought into spec with the aid of shims installed into the input shaft bearing retainer.
29. The stock shifter parts are cleaned and installed onto the tailshaft. One complaint people have with the early Tremecs is the lack of a breather in the top cover. As the transmission warms up, they complain of leaks out of the input and output shaft seals. The factory shifter has a rubber seal that vents this pressure, but once an aftermarket shifter is fitted, that pressure relief is removed and it makes the seals the next path of least resistance.
30. Here, the transmission covers are installed and this unit is ready to be put back into service. A frequently heard Internet myth is that the early cases have weak mounting ears because they don’t have as much ribbing as later models. This author has seen just as many, if not more, new-style cases cracked compared to the early ones. One could attribute it to poor installation techniques and general abuse that no case would be able to withstand. We’ve seen a high-horsepower car with solid motor mounts, a poly transmission mount, and a weak chassis that has cracked the heck out of a Tremec case—hardly a design flaw.