So I was driving down the highway yesterday and I come to a stop at a red light. I then go to push the pedal and see the RPM needle screem up to 2200rpm but I'm only doing 20k/hr. I let go a bit and it shifted into place and then it was fine...I started puzzling why the hell it was doing this, so when I got to my place i checked the tranny fluid and it was pretty full.

Now again today, i was driving around and it started to not catch the gear again...something fishy is going on and this wasn't happening up until I put in the new hanger bearing a few days ago.

It's not doing this all the time, it's like it has a mind of it's own or something. It'll do it whenever, there's no set time. What could it be?

Just for info purposes, I have the C6 tranny and 150,000 km's on the truck, and for you american's, thats about 90,000 miles.

Is the tranny starting to crap out on me or what could be the problem? I'm not all too familiar with tranny's and common problems that they have, I'm more of an engine kinda guy. Should I get rid of the truck before it finally decides to crap out on me?

Any comments/concerns would be great!

 

Check a manual for intermediate band adjustment. It'll do that if they're to loose. I'm not saying that that is definately the problem. But it very well could be.

 

Could also be the vacuum modulator. Makes the C-6 do some real strange things when it starts leaking vacuum

 

Who did the removal of the driveshaft.......check the fluid again and top it up to specs, PRETTY FULL does not cut it......sorry

 

I took off the drive shaft and brought it to a friend of mine and they put the new hanger bearing on. What exactly does the vacuum modulator do? I heard it's responsible for your brakes, and my brakes have been kinda fishy too and I just got them replaced. And what exactly is an intermediate band adjustment?

 

If you pull the vacuum line off of the modulator and get fluid out of it, your modulator's dead. Don't lose the pin inside if you pull the modulator.

Has the filter been replaced in the last few years?

 

Uh...where is the vacuum line and the modulator located? I have no idea if the filter has been replaced within the last few years, maybe it's a good idea to change it? Where is the filter located? I've never changed a tranny filter before, as I've said I'm not really a tranny guy. I hear its a biatch to get to the filter?

So what happens if I pull the vacuum line and there's no liquid in there? What could the problem be? And if I do pull the line and there's fluid inside, what will the fluid be? Oil? Tranny fluid? Coolant? So what should I do if I find liquid in there? Just drain it and change the modulator? Btw, what's a modulator go for anyways? Are they pretty pricey?

 

You have to pull the pan off the trans to change the filter, there is no drain plug unless someone has put one in. It's not a hard job, but can be a bit messy.

The vacuum modulator is on the lower, right (passenger) side. It has small vacuum line on the end and is round in shape. It has nothing to do with brakes, unless it's leaking a heck of a lot of vacuum.

Check all the lines for splits, loose fittings ect. Might also want to check the vacuum on the pump it's self. I believe it should hold around 20 lbs, someone will correct me, I am sure.

 

The Vacuum regulator valve is on the drivers side of the ip with two vacuum lines on it. It varies the amount of vacuum going to the modulator to give the trans. an idea of throttle opening. One line comes from the vacuum tee (source), and the other goes to the trans. There isn't a real filter in the trans., just a screen to stop the big pieces. The one I took, and the one I put in were like this.

 

Thanks Jake S, I forgot about the regulator on the diesel. It's one of those nit-picky things to fix when doing a gas to diesel swap with an auto tranny. Whether it's the IH or Cummins swap, you still need to figure how to regulate the vacuum to the C-6.

 

I just got a good look at everything this last week as I pulled the c6 and put a zf in. Forgot how much work it would be....

 

It can also be a sticking governor as well. How is the tranny holding, as in does it seem to be slipping, or is it such that when you let off the throttle, it comes right back down like it was a manual in low gear? Then when it shifts , how does it shift, soft, hard? When it works properly, does it seem to shift a bit late, or on time, and the shift firm or soft?

 

Sounds like the VRV is not adjusted right. Does the RPM drop a ton when you let off or does the motor slow you down? If the VRV is not adjusted right it will hold a gear and act like it is in neutral until you step on it.

 

I guess it doesn't start giving me a problem unless I've been driving for a while. If I've only been driving for about 20 minutes or something, it'll shift just fine. I think if I'm driving for around an hour, that's when it starts to give me a problem. I'm guessing it's having something to do with heat maybe? Because after it's been sitting for a while, it shifts perfectly.

When I let off the throttle, it stays in gear, it doesn't downshift unless I let the speed drop alot, and that's quite normal for a tranny to do. When I start going from a stopped position, and we're assuming it's acting up, if I just push the pedal till its around 1500rpm it'll eventually shift, but if I get it up to about 15mph, and I hammer on it to about 2200rpm and then suddenly let go, it shifts into gear. 2nd gear is a little weirder, I can cruise up to around 2000rpm and it'l shift on it's own. Going from 2nd to 3rd is the one that's a real pain in the butt. First gear and the 3rd gear seem to be the ones that's giving me a problem.

When it actually does shift, I'd say it shifts pretty normally. Not too soft and not too hard. There isn't a huge thud when it does shift...I have no idea what's causing it not to shift properly. Like I said before, it wasn't doing this before I took the drive shaft apart to change the hanger bearing.

And finally when it does work properly, it shifts on time, every time. And the gear changes are really smooth. This tranny is really weird.

As far as the brakes go, they have a mind of their own. Most of the time I have to push the pedal in about 3-4 inches for it to start stopping the truck. It stops fine, it's just I feel that I shouldn't have to push in the brake pedal that far to get some stopping power. Anyways, when it does have a mind of its own, the pedal will become stiff and I don't have to really push much on it to get any stopping power, but this seldomly happens. I'm not saying it happens rarely, and it doesn't happen often, it's kind of in between.

 

No the rpm doesn't drop alot at all, it just naturally declines like a normal tranny would when i let off the accelerator. It's not being "sticky" at all, and it doesn't hold the gear...i'm almost convinced the torque converter might be involved in this.