Chris Knight

iTrader: (2)

Took the Iroc out for a drive today on the same loop I always takes. It appears the transmission has developed an issue in 4th gear of some sort. The first I noticed I was under load going up a steep incline at about 40-45 in the ~2500rpm range and it acted like it was bouncing off a rev limiter. I let off the gas and it stopped doing that. It may have been trying to upshift from 3rd to 4th (I didn't count the gears it went through).

Pulled over and double checked the fan (which was on) and then continued (loose fan relay connection). I kept driving and it was like any time I got over 45ish mph if I took my foot off the gas it would bounce down to ~1200rpms for a second and felt like it was mechanically braking, then shoot back up where it had been between 1700-2500rpms and roll like normal for a second or two. It would alternate doing this every few seconds until I added gas. As long as I was putting some type of fuel in the system, didn't try to do this going up or down hill. When I did put throttle hard, it almost acted like it wasn't in gear and the motor was revving up but was lower in rpm a bit. Needless to say, I was light on the throttle going forward.

I stopped, shifted from O/D to D and went again. Still seemed to have the same weirdness but at higher rpms. I was hoping that it was just an issue with the O/D but I'm not sure it is. Pulled over a 3rd time, parked for a minute and check the fan (still working yay!) and took a couple pictures of the car while running (bc why not?). So back into O/D it went, and I eased out of a stop sign. I was light on the gas as it was a down hill slope and counted it hit every gear. When I got up to 50mph it was around 1700/1800 rpm and I let my foot off, started doing the odd braking slowing down and all. I took a video of the tachometer at the next stop sign which was on a flat bit of road (how can I show this?).

After driving through town under 40mph and having zero odd braking, I hauled butt down an on ramp to 60 and it seemed to up shift through all the gears fine while I was applying gas (unlike what happened in the first paragraph). On the interstate as soon as I lifted off, the braking thing happened, and it slowed from 60 to 50 in only a few seconds which wasn't great being on an interstate. Tried the Cruise Control which worked fine but it did it the braking thing a couple times on the down hill sections when I suppose CC wasn't applying gas. When I was getting off the interstate I lifted off at 50ish mph and never applied the actual brake. I repeated the on/off interstate again with similar results. It seemed to cease doing the braking thing around 40ish mph. I drove through town back to my place at 40 or less and there was no issue.

The only other thing is it seemed like there was a bit of a whine from the back of the car and a bit from where I think the torque converter is. I'm not sure if this whine in either spot has been around or I just noticed from actively listening for once. Just a little over a year ago I have the transmission fluid changed and the rear end re-greased (at least that's what I paid for). It's the original 700R4 in a 1986 Iroc with a G80 3.23 rear end. Doesn't seem to be leaking anything underneath the car either.

So the nut shell is shifts up and down through gears fine, no issues apparent under 40pmh, feels like braking at 45+ mph when in 4th gear.

My initial thoughts are:
- Solenoid tied to 4th gear and O/D
- Torque converter

Any thoughts? Is it safe to drive still?

Jorlain

iTrader: (4)

I'm not a transmission repair professional, but it sort of sounds to me like it's the TCC solenoid or something in that system. I guess it could the torque converter itself, too, but it sounds like the torque converter isn't locking and unlocking properly.

Chris Knight

iTrader: (2)

Thanks for the reply! Did a bit of reading up on the TCC, I could see how that might be the issue. Transmission wouldn't be trying to lock up around town in the lower gears, so if it was the TCC it would only show up at higher cruising speeds. Is there any way to diagnose this? I'm not mechanically inclined so would need some step-by-step directions for it.

Last time I took a transmission to the shop it took 3 months to get it back, I cringe at the idea of doing that again lol!

Jorlain

iTrader: (4)

As a first step, I'd unplug the round wiring harness plug from the transmission and take it for a drive. If the problem is still happening, then the issue is likely mechanical. If it stops happening, then the problem is likely electrical in nature.

Chris Knight

iTrader: (2)

I'm not that mechanically inclined (working on it) so if I get the car up on jack stands, can I access it from the underneath? I found a picture online, is the plug labeled C the one you're talking about? It would be on the driver side of the transmission. Let me know if this is correct. Don't want to mess up the transmission even more!

https://st.hotrod.com/uploads/sites/...nd%7C596%3A398

With the TCC not connected, that would basically eliminate lock up and eliminate O/D correct?

Jorlain

iTrader: (4)

Yep! That's the one.If you can weasel under the car you don't even need to jack it up. If you're a bigger person like me, you might need to. lol Overdrive should continue to work as usual - it just won't try to lock or unlock the torque converter.

Chris Knight

iTrader: (2)

That should be reasonable the reach then. So O/D on the transmission is just 4th gear then. Everything makes a bit more sense now. Before this in my mind I thought that when the torque converter locked it had "entered" O/D. Looks like I learned something good today!

I'll try getting that plug disconnected on the 4th. Have to make a 45 minute drive that day so would be a good test. Would it damage the transmission to drive it with this issue?

Jorlain

iTrader: (4)

It will build more heat as the torque converter will be in a constant state of slipping without lockup, and your converter isn't designed for that (most probably - some are but they're not stock replacement type stuff). Frankly I'd just disconnect it and then go for a 10 minute drive to see if it still exhibits the same symptoms.