Wheel Alignment, Carb Tuning And Transmission Fixing

It's been a while since I last fiddled with my Corvette so it was time to go back to business. I drove the car about 130km to Tampere to see my car mechanic friend. We had a few tasks on our list: check the wheel alignment, see if the carburetor was tuned correctly after my rebuild and open the transmission to check the shifter linkage.

The drive to Tampere went fine except for the heat. The cabin of the car got pretty hot after a while and it was quite noisy. The Corvette also didn't seem to like the highway. If driving over 100km/h (62mph), the temperature of the engine rose. Not enough to overheat but enough to limit the speed to about 90km/h (55mph)...

Carburetor tuning

We began from the carb as the car was hot after drivin it to the garage. I had rebuild my Holley 80457-S during winter so I had no idea if it was tuned correctly. We placed the probe in both exhaust pipes individually and checked the readings. Idle HC was about 100ppm on both sides and CO about 1%. This meant the engine was running pretty lean!

We loosened the idle screws and got the HC values to about 300-350ppm and CO to about 5% - 5,5%. This was much better.

Next we tested the engine at 2200 RPM. CO dropped to 1% again. I guess this means the carb needs larger main jets. This could also be the reason why the engine gets hot on the freeway as a lean mixture burns hotter.

Left exhaust reading

Right exhaust reading

Wheel Alignment

Next on the list was the wheel alignment. I drove the car on a lift and my friend set up the gear. I didn't know how to use the equipment so I just stood out of the way and looked. It took some time but finally we had the results: both front and rear alignments were within specifications! This was surprising as a lot had been done to the suspension since the last alignment: front springs had been cut, rear had been risen a bit, rear bearings had been changed etc. Oh well, I'm not complaining as this was a much easier job than expected.

Transmission Surgery

I already opened my TH-350 transmission once during winter to tighten the shifter shaft nut. This cured the missing first gear for a while until the nut loosened again. So I knew the transmission was working but the shifter was not.

We drained the oil and dropped the pan. After some examination, my friend had a revelation. Here's the old photo from winter.

It's a bit hard to see but there is a washer on the shaft. But not between the nut and the plate but between the plate and the clip that holds the shaft in place! We removed the clip, opened the nut and pulled the shaft out. Quickly we saw that with the washer in place, the plate never locked to the shaft but just rotated around. We switched the washer to the other side of the plate and put the transmission back together. Wow, even after working with the car for this long, we still find surprises like this...

Finally we decided to switch the speedo driving gear too. The only one I had found before had 10 teeth but after driving a while, I learned I would need a 8 teeth one. The speedometer was showing way too high. Changing the driven gear would not help as I would need a 24 teeth one, but the largest one for TH-350 had 22.

So we pulled the end of the transmission and removed the old, blue gear. I got the correct black one from US-Parts again but something was wrong! The gear was really loose on the transmission shaft. The old one was really tight but this new one was about 1 millimeter larger in diameter. This also meant that the clip that should hold it in place didn't work.

We had to cut the gear up a bit and push a split pin under it to hold it in place. We could only hope it would work and put the transmission back together. Unfortunately it didn't work as the speedometer didn't work at all after this... *uck!

On the return trip the engine still got hot on the freeway and cooled after a few kilometers of slower driving. I need to adress that issue later and go back to the speedo gear too...

Loose TH350 Shifter Shaft

UPDATE 10.01.2013: Seems that the loose bolt was not the only problem: Transmission fixing

There had been a problem in my transmission for a long time. I could not force it to first gear with the shifter. I tried adjusting the shifter cable many times but it just did not work. The shifter lever in the transmission felt somehow loose when turning it by hand and just didn't go to first gear. I searched the net for possible causes and found that a loose nut at the inner end of the shifter shaft could be the problem. Oh well, at least that's pretty simple to check and I needed to change the oil and filter anyway.

Unfortunately I had to work in my really small garage again. To get some room under the car, I bought a pair of ramps. With them, I had just enough space to remove the oil pan. So I drove the Corvette on the ramps, added some wedges behind the wheels and got to work.

I drained the old oil to a container and removed the oil pan. It was exiting to see what it would look inside the transmission. The last time that I opened it up with my friend, it had probably been standing for a while. We were a bit worried how much crap had been stuck in the fluid passages and if it had loosened up after the car had been driven for a few hundred kilometers. The oil didn't seem too bad but there was some crud in the pan. The magnet was clean so at least it was just dirt and not metal.

I cleaned the pan and removed the old gasget. Next it was time to crawl under the car again and check the filter. I removed it and couldn't see any dirt. Hopefully most of the crap was now out of the transmission.

Finally I got to the part that I wanted to see: the nut at the end of the shifter shaft.

I tested the nut with a wrench and it did feel a bit loose. There was not much room but I could turn the wrench enough to tighten it. I tested the shifter lever and the play was gone! Perhaps the transmission was now fixed!

It was time to put the transmission back together. I screwed in the new filter, used some silicone to keep the new pan gasget in place and finally bolted the pan to the car. Lastly I filled the transmission with new oil and took the car for a test drive.

And what a difference this small fix made! The shifter was no longer loose and the transmission was much quieter. Previously there had been a jerk and clank when changing gears between reverse and drive. Now the shifts were smooth and quiet. It was hard to even notice when the transmission went in gear.

I still could not get the first gear activated as I had forgot to adjust the cable. While doing that, I noticed a small mistake. When tightening the shaft nut, it had turned the lever a bit. This meant that the cable had to be adjusted to its maximum limit and even that was barely enough. I still could not always get the shifter to first gear. It worked about half of the time.

Oh well, I'll have to tighten the nut again during the next oil change. At least the transmission works much smoother now.