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Car Corner
Transmission Swap

December 1, 2002
By Scott Lewis

This month I will provide details about my swap of a TH350 three speed automatic in place of the stock Powerglide two speed automatic in my 67 Camaro. It was not as easy as I expected, especially since I did a Powerglide to TH350 swap once before on a 70 Chevelle. Read on to see what complications I came across, and see if I am driving my convertible before the cold weather sets in.

Removing The Powerglide

This actually turned out to be one of the hardest parts of the swap. I disconnected everything from the transmission. I removed the driveshaft, disconnected the throttle kick down linkage, shifter linkage, vacuum modulator hose, transmission fluid lines and speedometer cable. I removed the inspection pan, unbolted the torque convert from the flywheel and unbolted the transmission from the engine. I unbolted the trans from the crossmember and unbolted the crossmember from the frame.

That's where my trouble began. The crossmember goes above the frame rails and it's wide enough to make it very difficult to remove from the car. It is humped for dual exhaust, and so is the floor pan above it to only allow minimum movement. Not enough to slip it to one side and wiggle it out. I even tried to remove the starter in case I could possibly slip the transmission forward, but the tranny would not move enough to get it past the crossmember. The crossmember had to come out.

I had to remove a plate that went below the driveshaft and the exhaust, and I had to lower the exhaust on the passenger's side of the car. I removed two of the frame rail bolts on the driver's side to separate the floor from the frame enough to give me the clearance I needed to remove the crossmember. Finally it came out, and the transmission slid down on the floor jack.

Installing the TH350

I checked the transmission line fittings on the TH350 with the Powerglide. They were the same with just a slight difference in the angle they protruded from the transmission. A little bending should take care of that, and I should be able to use the lines already in the car.

At this point I did not have the linkage conversion kit that allows a 67 Powerglide shifter to work with a TH350. I figured I would get as much hooked up as possible, and hook up the linkage when it arrives.

Time to take a trip to the auto parts store. I needed to pre-fill the torque converter, so I picked up a case of transmission fluid. Also, when I removed the starter, the stud/bolt holding the battery cable to it broke off instead of coming off properly. I had to pick up a new starter solenoid. $40 for a starter solenoid. Ouch, I can remember when the entire starter for an old Chevy cost $40.

I checked the flywheel that came with the transmission and determined it would not work. I would need a new starter ($90 or more). I checked that the torque converter would mate up with the original flywheel. It did, so I filled it with three quarts of fluid and put it on the end of the TH350. With my brother-in-law's help we heaved the tranny onto the floor jack and raised it up to bolt it to the engine. All went fine. We had the usual trouble getting the dipstick tube in place but it went reasonably well.

Does It Really Fit?

Now was the time to put the crossmember back in place. This was not as hard as removing it. I left a wrench wedged between the frame rail and the underbody to maintain the room I needed, and I still had the exhaust hanging on one side. The problem began when I tried to slide the crossmember under the transmission. It would not fit.

I jacked the TH350 up as high as it would go, but there was not enough clearance to slide the crossmember under the transmission mount. I looked at the mount on the original Powerglide and saw it was thinner. I took the new mount off the TH350 and installed the mount from the Powerglide. I was able to slide the crossmember in place, but the transmission didn't come down any. Part of the transmission was touching a small bulge in the floor pan where the stock shifter was. It was clear that the there would be some kind of clearance problem with any linkage that would try to connect the shifter to the side of the TH350.

Initially I checked a couple of restoration catalogs. They list one part for the transmission mount for all transmissions for 67-69 Camaros with the lone exception being the TH400 (a big heavy duty automatic). They also list one crossmember for 67-69 Camaros except for... you got it.. the TH400. So apparently they will not be able to resolve my issue with a mount or crossmember.

A Blast From The Past

I called my mechanic in New York. I had not spoken with him in about 7 or 8 years. The last time I called him from Texas with a car problem he knew exactly what I needed to do. He has always been a wealth of information. Unfortunately, I finally stumped him. He is a huge Ford fan, so this "Chevy" problem was out of his reach. He called a buddy of his in Georgia that is a Chevy fan, but he didn't have an immediate answer having not worked on this specific car in a long time. Both of them agreed I needed to take both mounts to a GM dealer and see what parts they list for this combination. It is possible that GM made more than one mount, but the aftermarket restoration places only care what is most common, and works most of the time. It couldn't hurt.

67 Camaro With TH350

Part of my problem is that they never offered the TH350 in the 67 Camaro. In 1968 they offered the TH350 in the Camaro and it used a CABLE shifter, not the ROD AND LINKAGE setup from 67. This probably eliminated the "box" protruding into the tunnel. I wondered if I needed to switch to a cable shifter. That would mean one of two options. 1) Remove the factory console and install an aftermarket shifter that uses a cable, or 2) get a 68-69 console and shifter combination that uses the cable. I prefer the second choice since I want to maintain a stock appearance with this car. However, a new console/shifter would set me back at least $600 from prices I have seen.

I also wondering how much clearance I was loosing to body mount bushings. When I unbolted the frame from the body the bushings were is pretty bad shape. New bushings should get the body off the frame more. But how much? I felt that I could only gain a 1/2" or so with new bushings. I priced these bushings at around $90 a while back.

Conversion Kit

Wait a minute. They make a conversion kit for this swap. Shouldn't they know about this. I can't be the first person to have trouble making this swap. I contacted the company that makes the conversion kit (SHIFTWORKS), instead of the restoration company that sells the kit. I should have looked for the company that makes the kit first, they charge $4 less than the restoration company does. Oh well.

I received an e-mail reply the next day directing me to a page on their web site showing how the box must be trimmed for clearance. At last, I am not going crazy!

My brother-in-law helped me grind off the "excess" material from the box. I also trimmed the bracket for the neutral safety switch. Finally we bent the flat lever that protruded through the floor a little more than the original bend to gain a little more clearance on the side of the transmission.

While the shifter was apart I noticed that the shifter button did not return to its full height. When using the shifter while driving the car I noticed that I only needed to press the button to shift in and out of park. I assumed they didn't have detents for all the gears in 1967. Wrong assumption. The spring and washer inside the shifter did not have the range of motion necessary to "push back" the button all the way. I picked up a nylon insert and modified it to fit. All was working with the button and the detents. I even grinded the detent to allow me to shift down to 1st gear. (Remember the new transmission has three gears, but the old one only had two. In its stock form the gated detent would only let me shift down to 2nd gear in the new transmission.

I assembled the shifter and installed it in the car. I went to install the linkage kit and found that it did not reach. The main rod in the kit was threaded on one end for adjustability. However, it did not have enough threads to get itself in place. I ran a tap over the rod and extended the treads another 3/4". With that done the linkage hooked up with no trouble.

Final Assembly

Time to bolt everything up. I got some help from my wife putting the dipstick tube in place better. It was still too loose from the initial transmission install. Then I installed the bolt the top of the transmission that also holds the dipstick tube in place. It took me about an hour for that one bolt. Another 15 minutes had all the other tranny bolts in and tightened down.

I installed the throttle kick down cable and bracket. This took a while. Note to self: next time attach the cable to the transmission BEFORE installing the transmission in the car. At this point the light was finally showing in the tunnel. Of course that means something else needs to go wrong. I bolted up the crossmember, installed the starter, attached the speedometer cable, etc.

When I removed the driveshaft I taped the universal joint closed... just in case. I untapped it and went to install the driveshaft. I knocked one of the caps off for the U-joint and it spilled out all over. Off to the parts store for another U-joint. $20 later and a huge effort to get the old U-joint out and I was again ready to put the driveshaft in the car.

The First Drive

Upon first try the car did not start. I tried switching the wires on the starter. Still wouldn't start. I returned the starter wires and took the console apart on the chance I misaligned the neutral safety switch. It was broken. I don't know how or when, but the switch came off its bracket. I ran a wire inside its harness to override the switch. (I know, I shouldn't do this... but I didn't want to wait for a switch.)

The car started. It went into forward and reverse gears (still on jack stands). I lowered the car, topped off the fluid and hit the road. Once around the block and all seemed well. All forward gears were working. I took it down the main road near our house. I got it up to speed and went to turn around. The car stalled and smoke was billowing from under the hood. I opened the hood and the main battery cables were smoking like crazy and melted all over the place.

I had my wife come and get me. I borrowed a tow chained and my wife towed me home.

How Stupid Am I?

Apparently I installed the starter with the positive battery cable touching the exhaust manifold. When the exhaust heated up it melted the cable and then shorted the car out. I am lucky the engine didn't catch fire.

I put a volt meter on the battery and it still had 12 volts. Back to the parts store for a pair of battery cables. It was late, so I had to wait until the next day. I worried plenty if I could have shorted anything else out.

I installed the new battery cables and made sure the cables were not touching anything. The car started right up.

I repeated my little run down the main road... all with no drama. I did notice one thing. That car was down on power. The first trip I made with no air cleaner. I had not found the nut for the air cleaner, and figured it was under the car somewhere. But when I installed the battery cables I also installed the air cleaner. And it was dirty. I am sure that this is the lose of power I felt. This only confirms that I am in need of a good tune-up on the car. But that will have to wait.

Cost

The cost of this "simple" conversion was not too expensive in reality. However, since I initially figured this out to be around $600 it felt like it was very expensive. The final figures are as follows:

Rebuilt TH350                             $635*
Throttle Kick down Cable for 68-69 Camaro  $24
Throttle Kick down Bracket                  $6
Dipstick & Tube                            $15
Shifter Conversion Kit (67 PH to TH350)    $59
Starter Solenoid                           $40
Transmission Fluid                         $20
Rear Universal Joint                       $19
Battery Cables                             $10
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Total                                     $828

Note: The rebuilt TH350 transmission included: the transmission (no core charge), a shift kit, adjustable vacuum modulator, new inspection pan, new 14" flywheel, new torque converter, new generic throttle kick down cable, new generic dipstick & tube, new transmission mount and new hard lines (not bent) with fittings.

I am going to return the flywheel to my transmission mechanic and see if I can get that money back (about $35). He already took back the generic throttle kick down cable and dipstick tube ($12 & $8, respectively I think). Hopefully I can get some of this money back, but he was doing me a huge favor in the first place so I am not sure I should be begging for a few dollars back.

How Does It Drive

Great. The deeper fist gear (2.52:1 vs. 1.72:1) provides a good deal more punch off the line. I came across this piece of data: a Powerglide absorbs 18 hp, and a TH350 absorbs 38 hp. That means I should feel a loss of 18 horsepower at the seat of my pants. However, the 2:52 first gear provides a "theoretical" increase in torque of 68% over the Powerglide's 1:72:1 first gear. That torque increase is more than enough to overcome the 18 horsepower loss. However, I may see a slight drop in highway mileage because of that 18 hp.

Overall I really enjoy driving the car now. I can fling the car around corners with confidence knowing the transmission will grab a gear... any gear... as I hit the throttle coming out of the corner. I could tell the old transmission was "soft" after about a week of driving. I was always worried it would downshift wrong or just not grab one of its two gears coming out of a corner.

I have a slight exhaust leak. The car is a little louder than before, but not noticeable. I can't even hear it on the highway. When tightening the nuts on the exhaust one of the nuts stripped, and won't tighten anymore. I am not sure what it would take to fix, so I am going to drive it as is until I can get headers.

The speedometer is off. Before the swap the speedometer was off. It would show 65 mph when the car was going about 80. Now it is showing 80 mph when it is going about 70. The transmission mechanic told me there wouldn't be any trouble getting a different gear. So that is something I want to get right pretty soon.

Bottom line... I can drive the car in a spirited manner now. It will squeal the tires off the line, which it couldn't do before. I will need to spend a little time adjusting the vacuum modulator for the best shift points, and get the speedometer on target.

Now, I can't wait for a four barrel carb, headers, camshaft and free flowing cylinder heads. Too bad my wallet isn't ready for all that. The extra power off the line and coming out of corners has made me realize just how bad the shocks are. I think that will be the next upgrade.

Conclusion

The total of $828 is not that bad. I spent three weekends under the car. That was not fun. However, the car is running, and I still have some nice South Texas weather left this year to enjoy driving with the top down.

I will enjoy what little time I have left this fall driving the car. But come Spring I will definitely give the car a full tune up and replace those shocks. I might even get headers.

Until then...

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