Converting the 4L60e Tailshaft Housing to a Mechanical Speedo Drive - bonus episode

Episode one, purchase and bodywork.

Episode two, mechanicals and interior.

Episode three, final details and the finished car.

Bonus episode, LS conversion.

Double bonus episode, converting the 4L60e tailshaft housing to a mechanical speedo drive.

Triple bonus episode, the details leading up to the purchase of this car and what it meant.

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My decision to do an LS swap on my 1967 Camaro convertible (the rest of the swap is covered here) brings up a number of challenges. One of those is the electronic speedometer drive on the 4L60e. The 4L60e has a reluctor wheel on the transmission output shaft which signals the electronic sending unit. I wanted to use my original speedometer, so I needed to convert it to a mechanical drive.

There are people on eBay and elsewhere who will convert your housing for $350, or sell you a converted housing for even more. I'm too cheap, so I wondered if I could do it myself. After studying the issue and doing some measuring, I decided I could.

This is the task that is been the hardest part of the LS conversion so far. I searched the internet quite a bit for someone who had done this conversion and lived to tell the tale, but couldn't find anyone. It may very well be that I am the very first to chronicle the process. A real living legend.

Actually, I did the task twice, once without the reluctor wheel and once with it. I thought the reluctor wheel wasn't needed, but it turns out it is needed for more than the speedo signal. It also is used for the VSS to tell the PCM how fast the car is going so that the transmission can be signaled when it should shift. 

I figure that if it's worth doing, it's worth doing twice...

Removing the Reluctor

The first thing to do is to remove the output shaft housing. You'll see this:

First I pulled the sheetmetal piece, which holds an O ring that seals the yoke. I then made a light mark on the output shaft with a hacksaw blade where the edge of the reluctor is. The reluctor will need to be returned to the same position it was. That is 3 3/4" on center from the flange on the transmission. I then pulled the reluctor using a puller cobbled together from some of my son's tools: 

USE A PULLER, DO NOT HAMMER THESE PIECES. 

The New Gears

As you can see above, the TH350 speedo drive gear fits the output shaft of the 4L60e. You can find all sorts of drive and driven gears on eBay. I got mine from greater dimensions engineering for $23.50 and free shipping. It was the whole package: The drive and driven gear, the bullet, the retainer clip and retainer bolt:

You can calculate what tooth count you need for your application by plugging in some figures into an online calculator like this. In my case, with my 25.5" tall tires and 3.08 gear ratio, I needed 19 tooth driven gear and an 8 tooth drive gear. You can find information on your stock rear end ratio here.

The drive gear will locate against and forward of the reluctor. The drive gear and driven gear need to mesh properly, so a critical measurement is the vertical axis of the hole you will drill in the housing. I needed to find the distance between the rotating center of the driven gear and the rotating center of the output shaft. I carefully laid out the drive and driven gear on a piece of paper, allowing for just a little bit of space at the teeth engagement point. After finding the center point of each gear, I drew some lines, like this:

For my application, the space between the rotating centers of each gear is 1 1/4". That means the rotating center of the driven gear needs to be that distance below the rotating center of the output shaft.

From here on out I needed to keep everything plumb and level. Sometimes it was a challenge, since I own no precision equipment.

So I set my housing on a couple of small pieces of wood on the transmission mount surface. That surface is a handy flat plane representing the level position of the transmission on the side-to-side axis, making it parallel to my workbench. I then put a piece of wood under the seal area of the housing and added shims until the front of the housing checked square with the workbench. It looks like this:

Then I measured to the top and to the bottom of the rear seal, subtracted the two numbers, divided that in half, and subtracted that from the long measurement. Now I have the centerline of the transmission output shaft centerline, and its distance above the surface of my workbench  You can faintly see the center line I drew on the side of the housing. It pretty closely aligns with the one housing bolt hole.

Next, I cut a piece of wood from an extra shim, 1 1/4" shorter than the distance from the work bench to the center line. Remember, 1 1/4" was the distance between the rotating center of the output shaft and the rotating center of the speedo drive.

I used that piece of wood as a gauge, putting one end on the workbench and the other vertically against the housing. Then I made a mark. This should be the rotating center of the driven gear. I then measured horizontally from the flange to where the center of the drive gear is, and made an intersecting mark. This is the preliminary location of the hole. I don't want to be forward of this mark, because the transmission's output shaft reduces in diameter and the speedo drive gear cannot be located there.

Creating a Bullet Holder

The next step is to determine how to hold the bullet in place. I bought a piece of hollow round from metalsdepot.com (Item T21058, 1" OD x .058" wall x .884 ID DOM round steel tube, $25.84 with shipping). I selected this size because the ID is slightly larger (.14") than the 7/8" bullet, which will allow space to accommodate the bullet's O ring. It turned out to a slightly tight fit, but the bullet will ease into the hole just fine with some lube.

Holding the end of the hollow round up to the housing, it looks like I have plenty of room to bore the hole in the housing at the measured location without invading the bottom curve of the housing. Looks like I'm good to go.

So again it was necessary to plumb and level the housing, this time rotated 90 degrees clockwise. The way I did this was to screw the housing to a piece of 2 x 4, allowing the side mounting boss to just touch the drill press table. Putting a square against transmission mount surface, I loosened the screws just slightly and rotated the housing until it was plumb, then tightened the screws. Another scrap of 2 x 4 with a mix of thick and thin washers to shim the housing, which leveled it front to back.

It's time to bore a 1" hole where I made my marks.

This part was easier than I thought. With light pressure, the hole saw cut through the thin housing quickly and without incident. You can see where I put a ratchet strap around the housing. Steady as a rock.

With the hole bored, I can now locate the final position of the drive gear assembly. Here's what the 2 foot piece of hollow round looks like inserted, again leveled to the level and plumb housing. This allowed me to check the fit against the far side of the hole. I marked the hollow round for length and cut the piece.

Because of the curved radius of the inside bottom of the housing, I ground a little relief in the hollow round.

The next thing to do is create an open area in the top of the hollow round so that the driven gear is exposed. I needed to find the center of the hollow round. I put some masking tape vertically in the exact center of both the front and the back opening, and used a straight piece of shim, front to back, and just touching the edge of the two pieces of masking tape, to create the centerline of the housing on the hollow round, where the center of driven gear will be. 

I actually tried to make a mark with a sharpie before I thought of painting it. I spritzed some paint on the hollow round to mark it.

I extended the mark all the way around the circumference, just in case. Then some acetone to remove the paint.

I drew a rough outline of the recess I wanted on the hollow round with a sharpie and took my angle grinder to it. Nothing too fancy, just a clean cut on each side and some filing to touch it up and deburr it. I then cut a tiny scrap of sheetmetal and bent it into a retainer clip that prevents the driven wheel from pushing too far into the hollow round.

A couple of spot welds and it looks like this:

Putting it all together, and we've got an assembly:

I should note that I ruined a reluctor wheel because the cutout was not big enough. Make sure you remove enough material to clear the reluctor.

It's time to dry fit the assembly into the housing, which means I plumbed and leveled it again. Here's the assembly dry fitted:

Then a little bit of JB Weld to lock everything into position and seal the gap against leaks.

Next I installed the assembly to see where I need to tap a hole in the case for the retainer bolt and clip. Lastly, I temporarily installed the housing to see how well the gears mesh. Everything looked good. 

Originally, I drilled a shallow hole in the output shaft to put in the retaining clip for drive gear, but I should have used one of these:

This is a 28mm shaft collar. One side of the drive gear is held in place by the reluctor wheel, and this shaft collar goes on the other side.

Ok, time to put it together. My first try meant putting the retaining clip in the hole, the loop facing towards the front, with the gear slid over it until it seated. The grease shield housing slipped on by hand. 

But on the second attempt I put the shaft collar, the pin, the speedo gear, and the reluctor last.

If you're not running the VSS, Like if you're setting it up for manual shift, you won't need the sensor hole. A Dorman 555-016 expansion plug from O'Reilly for $.59 fits just right. Otherwise, you'll need to buy the VSS sensor.

It took three tries to get the right VSS sensor. The dang thing wouldn't shift right. The wrong sensor confuses the PCM. 

The first one they sold me was the wrong one:

The bracket has an extra piece at an angle which interferes with the housing. Physically, the sensor itself looks the same as the others. O'Reilly's website says it fits, but it doesn't. And it doesn't work. It appears to be the sensor that fits the the late 90s 4L60E.

Sensor number two was this one:

It's got the virtue of a simple bracket, and the sensor itself looks exactly like the other one. But it doesn't work either.

Here's the right sensor (at least the right one for me) from O'Reilly's:

This one works perfectly. I don't know why. 

Here's the completed project:

This picture shows attempt number one, without the VSS. Attempt number two places the speedo drive assembly about 1/4" forward of this location.

Summary

Overall, the conversion itself wasn't terribly difficult. With careful measuring and a bit of skill, this is achievable. And, instead of $350, doing it myself cost $49.34 and about 6 hours. Not bad.