Hi everyone,

I own a GMC Typhoon in the UK and have done a lot of work on it. I thought my transmission would be bullet proof but it looks like I have some issues.

I was driving on the motorway on Friday at about 75 mph and the truck started slipping out of OD into 3rd and just revving really high and not going anywhere. If I lowered the throttle, it would shift back to to OD and then TCC lockup would happen and I was able to continue at 70 and above. Any more than about 40% throttle and I would downshift and the engine would rev.

When I came to a stop, I had lost 1st gear as well and the engine would pull away in 2nd then upshift to 3rd and just rev. If I manually put it in 2, not OD, I could accelerate in 2nd to the point where I changed the lever to OD, OD would kick in and then I had TCC lockup and I was ok again. Slow traffic was a real pain.

I also have reverse.

So, I have REV, 2nd gear, OD and TCC.

The A and B solenoids are used in 1st and 3rd respectively but both need to be on for OD to work. A is applied in Reverse so it appears my solenoids are good.

I am looking at the manual and trying to workout the fault mode..

If I lost the forward clutch, I wouldn't have any forward gears but I have second AND overdrive so I think that the FWD CLUTCH is good.

I haven't driven the truck far - it has 2k miles on the rebuild.

My theory is this... It may have started a few weeks ago...

I thought that my torque converter is lame - it stalls way too high (5000rpm) so I was applying the TCC at low mph to see if I had trans slip or if the TC was actually loose. I have some data logs showing the difference. This led me to believe the TC is way loose. However the RPM at 6mph with such a loose converter was still quite a high RPM so I wonder if the RPM tore up the TC and clutch material worked its way into the valve body and blocked some passages for 1st and 3rd gear.

It's odd that it failed within 100 miles of me doing that.

Anyone got any better ideas or ideally an explanation for what I have experienced?

I have to pull the trans anyway for the TC swap so I guess I'll be taking it apart as well.

Can anyone tell me what I might have missed or how I can verify it's not anything really simple?

Thanks!

Mark

 

Nobody?

Bump!