C6 Transmission Issues

[dakotajeep]

Update:

I am back to hard shifts again. Looked at the lines that I could find and saw no significant causes of a leak. (I was more concerned with my 1997 Olds 88 that was leaking coolant!)

Plan to dig into it tomorrow. I got a vacuum tester/guage and will see what going on. I hope its just a line. I might just replace them all as preventative maintenance.

Thad

 

[duke3478]

Don't forget to take a look at the hard line, which runs from near the modulator to the driver side of the engine. Follow the soft line from the VRV. Mine had a big hole from vibration/friction in it. I cut and bent a new one from a $6 hard brake line, which has worked perfectly.

 

[dakotajeep]

I disconnected the line on the rear of the trans (modulator?) and fluid dripped out.

I did some reading but it is inconclusive as to whether fluid coming out that tube is bad or not. It didn't pour out but more so dribbled out.
I checked this again...not an issue. Just a few drops of fluid.

Any thoughts?

Thad

 

[dakotajeep]

I checked the vacuum and its pulling 24" constantly. So its not the vacuum pump.

I verified everything else that is run off vacuum and they are all at 24" ish. No leaks...

When I connect the vacuum gauge to the trans side of the VRV it shows 14" at idle. If I run the throttle the vacuum decreases to less than 14" the more I increase the throttle.

Is that normal? I am starting to think it could be the VRV? Should I adjust the modulator on the rear of the trans?

Thanks
Thad

 

[Wyreth]

Actually it sounds like your VRV is working, or at least mine read that way back when it was playing nice.

As far as the fluid out of the modulator, that doesn't sound right at all. But I haven't done any research on it. Seeing as the Modulator is a $10 part, it might be worth throwing anther one in to test.

also: http://www.intellidog.com/dieselmann/idi2.htm

bout half way down the page is the guide I used to test my VRV.

 

[itsacrazyasian]

There should never be fluid in the modulator. EVER.

Replace it with a black stripe diesel modulator. The new one will have an adjustment in the vacuum port to adjust should it be incorrect when installed.

 

[IDIDieselJohn]

Is there a difference in the diesel modulator vs. the gas one?

 

[Wyreth]

Is there a difference in the diesel modulator vs. the gas one?

I know the different color bands have different throws, so they trigger differently. The black one prolly has the lowest range, as to reflect the diesel's lower power curve.

 

[itsacrazyasian]

Is there a difference in the diesel modulator vs. the gas one?

well the colors really denote the differences between the modulators.

The black one is for the heavy vehicles. INside the diaphragms are different sizes between the colors.

If fluid comes out from the vacuum line, it means the diaphragm inside has ruptured and no longer moving the pin on the back side correctly. Cheap part. 10 bucks. Check tranny fluid level afterward as you may lose some when swapping the modulator out.

Be careful when swapping, theres a pin on the back side. Don't lose it!

 

[IDIDieselJohn]

double...

 

[IDIDieselJohn]

Yes defenently change it if you found fluid coming out of it!


That silly thing cost me the C6 in my camper last summer..... very last trip of the season, about 3 hours from home, noticed it wasn't operating normally.


RPM's went alot higher before shifting, shifting it's self was still pretty normal though, at the time, I taught it was just the kickdown rod stuck down again, like it was when I bought this thing 12 years ago... so didn't mind it to much.

2 hours from home, started smelling something burning, couldn't for the life of me figure it out what it was, stoped in a truck stop, open hood, checked around, under, no signs of leaks, and no smoke.....


Carryed on, and off the highway, heading towards home (i'm about 2 miles off the highway, 3 sets of lights from highway to home) that's when I noticed a big problem.

Hard high RPM shifts, taking off in 2nd gear, weird shifting. Odd thing is, never slipped....


At the time, had no idea a bad modulator can cause this.....sure learned the hard way.

So I bought a new one, dropped the pan, can't believe I didn't drop dead by how bad that oil smelled, but anyways, fresh filter, and fresh fluid in hopes to save it, but when I came to do my running engine flush, disconnect the feed while, fired it up, nothing coming out..... pump died.


So I left it like that, and drove it like that to winter storage (10 miles) and got me there no problem, hard high RPM shifts, but still no slipping...


Next season I have to drop the trans and rebuilt it though.... poor thing, a short life of only 150k miles. Even if it has been pulling 12k lbs since new.....

 

[6.9poweredscout]

well the colors really denote the differences between the modulators.

The black one is for the heavy vehicles. INside the diaphragms are different sizes between the colors.

If fluid comes out from the vacuum line, it means the diaphragm inside has ruptured and no longer moving the pin on the back side correctly. Cheap part. 10 bucks. Check tranny fluid level afterward as you may lose some when swapping the modulator out.

Be careful when swapping, theres a pin on the back side. Don't lose it!

yeah put a pan under the trans, i didn't know fluid comes out when i changed mine, and i had about 2 quarts down my arm and across my driveway...

 

[dakotajeep]

So the only modulator Oreilly's had was the purple stripe. I plan to get a black stripe but I want to see if this one will help.

The real issue is that when I pulled the modulator out I got 5-6 pea sized pieces from inside the transmission...kinda worries me but I guess I should expect that from a 25 year old rig that cost $400.

Any thougths?

Thad

 

[itsacrazyasian]

pics?

the purple modulator will need adjustment to shift correctly.

 

[6.9poweredscout]

i got a black stripe off rock auto for $11, had to turn it in 1/2 turn when i installed it, and tweaked my vrv a little. it shifts pretty good, if i lean into it it shifts firm and good, sometimes it goes into second quick but if i push it down a little it downshifts and takes off....