Tales From the Bench - June - 2018

Saving Headaches: Toyota Solenoids and Valve Bodies

After a rebuild, Toyota transmissions can have shifting issues and TCC complaints that drive you crazy. If you take a few precautions, you can cut down a lot of the headaches. Some of the main causes for these issues trace back to the valve body, solenoids, and contamination.

For this article, we’re going to talk about Toyota transmissions as a general group. Toyota five- and six-speeds have a lot of common operating components. The linear style solenoid control pressure, shifts, and lockup operate almost identically in each model.

The valve body also has some general issues across the Toyota transmission group. We’ll point you in the right direction so you know where to look for wear in these valve bodies.

RADIATOR AND TRANSMISSION COOLER

When a car comes in with 120,000 miles, we all know some parts are at the end of their lives. The radiator is one of them.

Over time, the radiator gets buildup inside the cooling system and isn’t able to cool the engine as well as it did when it was new. When the engine is running hotter than normal, the transmission runs hotter too. And, as we all know, heat cuts into the life of a transmission.

The other thing a lot of techs don’t think about much is the transmission cooler inside the radiator. We all flush the transmission cooler to get the debris out of it. That works well sometimes.

Many Toyotas come in with case wear and planet damage, and most come in with TCC converter issues. These different issues cause a lot of very fine debris that we don’t always see or get out of the coolers.

This fine debris can cause a lot of headaches, usually when on a road test and the transmission gets hot. This is when that fine debris shakes loose from the cooler and finds its way into the valve body and solenoids.

I know what you’re thinking: “We can’t afford to install a new radiator.” Maybe the better point is, how can you afford not to change the radiator? If you have to remove valve body to free up valves or replace solenoids because of fine contamination, that’ll cost way more than a radiator. Often replacing the radiator will eliminate reworks or no-goes on your lift.

SOLENOID ISSUES

Solenoid issues can cause line pressure, lockup, and shift issues. One of the main problems with the solenoids is contamination. The solenoids you need to clean and inspect most are the SLT, SL1, SL2, SL3, and SLU solenoids.

There are a few different tools on the market to take the solenoids apart for cleaning. One is by Omega Machine and Tool, they offer a tool for the larger can SLT and SLU solenoids (figure 1). They also sell the bushing for inside the solenoid. These tools and bushing may also be available at your local transmission parts supplier. After you have repaired two solenoids, the tool will have paid for itself.

After you get the SLT or SLU solenoid apart (figure 2), look at its snout. Make sure the valve is free in its bore. If you have to take the valve out of the snout, make sure you mark it and count the turns to remove it. You need to make sure it goes back in the same position and depth when you put it back together.

On the can side of the solenoid, you’ll need to make sure the plunger is free. Some of the solenoids will have bushings in them and some will have just a plunger. The point is to make sure the plunger is clean and free so the solenoid can operate correctly.

The plunger clearance is very tight: If any fine debris gets into the solenoid, it’ll stick. This is why a new radiator is so important.

Now let’s look at the SL1, SL2, and in some cases, the SL3 solenoids. These solenoids control clutch apply-and-release timing and shift feel. To get these solenoids apart, you need a different tool because the size of the can is different.

Cottingham Engineering is another company that sells tools to get these SL solenoids apart (figure 3). They’re in the UK but there are U.S. suppliers. These solenoids have the same issues: sticking solenoid plungers and the valve sticking in the snout.

Let’s look at an SL1 solenoid from an A750 transmission (figure 4). The technician who was working on the transmission had the valve body apart three times and found nothing wrong. I got the valve body and started taking the solenoids apart.

The SL1 solenoid had a stuck valve due to contamination. They bought a new valve body with solenoids and fixed the issues. If they had the tools to clean the solenoids, the transmission would have left the shop working great the first time.

With the use of these tools, you can tear apart, clean, and reassemble the expensive solenoids with great success. If you aren’t into fixing your solenoids, you can still use the tool to prove you found a sticking solenoid.

VALVE BODY

Valve body wear is very common, and Toyota is no exception. Some of the areas on these valve bodies you need to check are the lockup relay valve, TCC control valve, solenoid regulator valve, boost valve, and the clutch apply control valves.

On a Toyota A750, lockup issues are a big problem. Let’s take a look at a couple areas that need to be repaired on this valve body (figure 5).

On this valve body, the lockup relay valve bore is part of the valve body casting. When this bore wears (figure 6), you have problems with control lockup slip, TCC chatters, bump on shifts, and erratic lockup apply and release. Sonnax and Transgo both have tools to repair this. The main thing is to address this valve bore and repair it.

The solenoid regulator valve is almost always worn on Toyota transmissions. You’ll need to inspect the valve bore for wear and repair it. Sonnax and Transgo both have simple repairs for this bore (figure 7). Most of the repairs are drop-in parts and require no special tools. If the oil to the solenoids isn’t correct, the solenoids can’t operate correctly. That’s why this bore needs your attention.

Always check the boost bushing in Toyotas. They love to stick and wear and cause all kinds of issues with the pressure regulator boost valve, lockup valve, and the clutch boost bushing (figure 8).

The procedure is simple for Toyotas: Clean or replace the linear-style solenoids, along with repairing worn areas in the valve body at the solenoid regulator, TCC relay valve, and the boost bushings. Follow it up with a good clean rebuild and replace the radiator.

Address these few areas on your Toyota rebuilds and your Toyota headaches will be reduced dramatically.