TH350 Solenoid Kit, new and ready to install. Fits the TH350. Ships fast from the USA.
The TH350 never had shift solenoids from the factory - it is a fully hydraulic three-speed run by a vacuum modulator and a governor. So when a racer searches for a TH350 solenoid kit, what they almost always need is a transbrake: a solenoid-operated valve that locks the transmission on the starting line so a drag or bracket car can build converter stall against it and leave the instant the button is released. This listing is exactly that - a brand-new Coan COA-32020 Trans Brake Kit, reversed pattern, for the Turbo Hydramatic 350, with the transbrake solenoid, brake valve and springs.
In a stock TH350 the modulator valve takes a vacuum signal from the engine and turns it into line pressure. A transbrake kit puts its own spring-loaded brake valve and a 12-volt solenoid into that modulator bore. With the shifter in first and the button held, the solenoid moves the brake valve and the transmission applies a reverse circuit at the same time as first gear, so the output shaft cannot turn. The driver loads the engine against the converter, lets go of the button, the solenoid drops out, the reverse oil exhausts and the car launches in first. That is why the bleed rate of the release circuit and the clutch clearances matter so much on a transbrake build - a slow release is a slow reaction time.
This is a reverse-pattern kit. The shifter gate runs Park, Reverse, Neutral, First, Second, Third, so the driver pulls the lever back for each upshift and reverse is never in the path of a hurried shift. Coan's own catalog lists the COA-32020 as a TH350 component in its valve bodies and kits line.
If the car is a street TH350 with a soft or late shift, a transbrake is not the fix - work through our TH350 common problems guide and check the modulator, governor and worn bores first. If you already run a transbrake and it is misbehaving, test the electrical side with a meter at the solenoid before pulling the pan; a bad switch or ground looks exactly like a failed solenoid. Our TH350 valve body testing guide covers sticking valves and debris, which is the other common cause of a brake that will not release.
Built for the GM TH350 used from 1969 through 1986 in Chevrolet, GMC, Pontiac, Oldsmobile and Buick cars and light trucks. Important limits: it is a reversed-pattern kit, so a stock PRND21 column or console shifter must be swapped for a reverse-pattern race shifter such as this 3-speed ratchet shifter. Published TH350 transbrake installs are for non-lockup units, so a late-1979 to 1984 TH350C lockup case needs the lockup circuit addressed by your builder. Pairing it with a reverse-pattern full manual valve body is the common race setup - confirm with your builder which valve body your kit is matched to. Send us your year and VIN or case details if you are unsure, and see every part we carry for this unit in the TH350 parts collection.
This is a teardown job, not a pan-off bolt-in. Typical TH350 transbrake instructions call for removing the transmission, installing the solenoid, brake valve and spring in the modulator bore, drilling and plugging specific case passages, adding a small bleed hole to the direct clutch drum, tack welding the sun gear retaining ring, and replacing the factory intermediate roller clutch with an upgraded sprag. Clutch clearances are set wider than stock and the cushion plates come out. Since every seal is disturbed, rebuild it with a full TH350 master repair kit and fresh frictions. Wire the solenoid through a momentary switch with at least 12-gauge wire, a direct battery feed and a solid chassis ground. Fill with Dexron-type ATF, warm it up, cycle the shifter and check the level - our TH350 fluid type and capacity guide has the refill amounts.
| Fits | TH350 |
| Part type | Solenoid Kit |
| Condition | New |
| Brand | OEM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. The factory TH350 is fully hydraulic and shifts with a vacuum modulator and governor. Only the TH350C lockup version used an electric converter clutch solenoid. This kit is a transbrake, which adds a solenoid for drag racing launches.
No. The COA-32020 is a reversed-pattern kit (Park, Reverse, Neutral, First, Second, Third). You need a reverse-pattern race shifter, and the shifter has to match the valve body pattern.
Not properly. A TH350 transbrake conversion involves case drilling, direct drum and sun gear modifications and new clutch clearances, so the unit comes out and gets fully disassembled. Plan to rebuild it at the same time.
A momentary button or microswitch on a 12-volt circuit, ideally 12-gauge wire, a fused direct feed and a clean chassis ground. A delay box can sit between the switch and solenoid for bracket racing.
Usually not. It is built for repeatable drag and bracket launches and puts heavy load on the clutches, sun gear and converter. A street TH350 with shift problems needs a repair or a shift kit instead.
A Dexron-type ATF is the TH350 factory spec. Many race builders use a high-temperature racing ATF because transbrake launches generate a lot of heat - follow your builder's recommendation.
