How Tos / Tech / Tech Articles

Step-by-Step: Installing TCI’s Powerglide Trans-Brake

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This is the TCI Powerglide trans-brake. It comes with a valve body, solenoid, brake valve, and brake valve spring. Disassemble the transmission according to the shop manual and TCI's instructions. You can discard the governor assembly, rear pump gears (1962-66 models), and vacuum modulator and spring. If you have a shorty transmission, you can dump the governor support and use the round support gasket to seal the case.

Enlarge the hole to the lower right of the output shaft opening in the center with a 5/16-inch bit. While the TCI instructions tell you to drill this hole through to the outside of the case, you don't really have to. That saves you the hassle of drilling through a thick ridge of metal, and having to drill the rear case gasket for the hole.

Drill a 5/16-inch hole in the area indicated by the arrow. This hole will intersect the one you drilled in the case in Photo Two.

Drill a 1/16-inch hole in the reverse piston. This bleeds off fluid pressure and releases the trans-brake quicker-and can save your transmission from the extra fluid pressure the trans-brake causes. Install the reverse and high gear clutch plates and bolt in the valve body per the TCI instructions. Button up the transmission and you're ready to go racing.

The most popular automatic transmission in drag racing is GM’s two-speed Powerglide. A lot of those ’Glides have trans-brakes in them. Put those two thoughts together and voila—instant tech story.

So, we decided to show you a few tricks on installing a TCI trans-brake in an aluminum-case Powerglide. We’re not going to take you step by step through the process; TCI’s instructions do a good job of that. Instead, we’ll show you a couple things our installer, Bob, has learned from many years of modifying transmissions.

As an added bonus, we have a trans-brake troubleshooting guide to help you diagnose your ailing Powerglide. If you haven’t torn down an automatic trans before, you might want to farm out the work to a shop that specializes in performance and racing transmissions.

What’s Wrong With My Powerglide?
TCI includes this handy troubleshooting guide in their instructions to help you figure out what’s ailing your Powerglide. It’s so handy, in fact, we figured it was worth repeating here.

Symptom Possible Problem
Transmission slips in all gears • Bad low band
• Bad low band servo
• Bad converter stator
Transmission slips or chatters in first gear • Bad servo seal


Symptom Possible Problem
Car backs up when trans-brake is applied • Worn pump
• Bad low gear servo sealing ring
• Worn or cracked servo bore
• Too much clearance in reverse gear
Forward gears OK, no reverse or trans-brake • Wrong rear case gasket
• Early plate on late model case
• Late plate on early case
• Detent cover reinstalled
• Broken C-clip on detent valve
• Low current to solenoid
• Stuck trans-brake valve
• Wrong governor
• Stuck Low/drive valve
• Case not drilled for trans-brake
• Solenoid has wrong stroke
• Exposed block hole in low/drive valve
• Bad reverse servo
Brake is slow or won’t release • Stuck aluminum valve
• Stuck solenoid
• Improper or too short valve spring


TCI-748200 TCI Trans-Brake for Powerglide, Aluminum Case
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  1. How do you dertermine if the solenoid on a P/G tranzbrake is applying to the proper depth??

    • OnAllCylinders says:

      In speaking with the Summit tech team, it doesn’t seem like this specification is shared in print by any of the manufacturers. We’d start by placing the call to the manufacturer and consulting with them on the exact proper depth.

  2. I have a power glide with a pro brake when I put it in first gear and push the button the transaction goes into reverse. When I put the transaction in reverse and push the button trans. Is very lazy.

  3. Transbrake works fine when applied, but reverse seems not to have a lot of power when reverse is needed by it’s self for backing up seams to slip is this normal is there an adjustment needed.

    • OnAllCylinders says:

      Because “Transbrakes” are not all the same, it would depend upon whose it is and if it was installed properly! You might consider asking your trans builder or the manufacturer of the brake.

  4. I changed sealinoid, but still no tranbrake, hear the clicks but no hold on the brake

  5. Why do I have to drill hole B and what
    Is the purpose or drilling it . I have a TCI 628200

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