C6 automatic Transmission

[Benteketeza]

I will be sorry if this is a wrong post. Hey gurus I need help in regards to my two C6 automatic transmissions that have same problem not shifting/ engaging to drive, 1 and 2 gear. However, parking, neutral and reverse gear works fine.
I have replace the vacuum modulator valve, new type F transmissions fluid and filter. All this issue started after I rebuild the 390fe cid. Could it be the aftermarket intake manifold, or not getting enough vacuum to the modulator? I don't think so, but it could. Please help a guy out before he gives up on this project.

Thanks in advance.

 

[Broncobowsher]

If it isn't low transmission fluid, it is a internal fault to the transmission. There is probably a pressure tap on the case for the forward clutch. If you get pressure when shifting into a forward gear, the clutch failed. If you get zero pressure, it may be a stuck valve in the valve body. Some (but not enough) pressure is probably a blown seal in the clutch pack.

Not a modulator/vacuum/intake issue. They will still go into gear, just harshly, if there is any issues with those items. Won't shift at the right time, but won't stop actually going into a forward gear.

 

[Chiclassics]

@Benteketeza C6 operates on neutral band and intermediate bands, where as C4, C5 operates on reverse and intermediate bands. It sounds your nautral is ok. Try to see how much backing your lock nut has on intermediate band, it should be 1.5 turns out from snug, its less than that it means bands are too tight for you to engage. Lmk how that goes.

 

[Broncobowsher]

Neutral band in the video refers to the band not dragging, Not a band that gives a neutral gear. The C6 only has a single band where the C4 has 2 bands. C6 does this by using a clutch pack to ground the planetary to the case instead of using a band.

An out of adjustment band won't stop it from going into forward gears. Going into the correct forward gear, yes. But you will still some forward gear even without a functional band.

 

[Chiclassics]

An out of adjustment band won't stop it from going into forward gears.

Is it? I had this issue on my C4 a 1/8 extra turn made my transmission not go into gear.

 

[Broncobowsher]

You can take the band out and throw it away it it will still drive, just won't have 2nd gear. In a C4, delete both bands and you loose reverse as well. But since this is C6, and for the most part this site is more based on the C4 version. Let me add a link https://drive.google.com/file/d/1fOMvcNoxettzh4hjNrh7MzrSf2Meru_1/view Go to page 32, it has an apply chart

ALL forward gear require the forward clutch apply. But not reverse. If reverse works, the low reverse and high reverse clutch both apply. Working reverse proves that both of those are functional.
First gear requires only the forward clutch to apply and the one way clutch to hold. Manual 1st gear, forward clutch and the low reverse clutch. So no 1st gear you either failed both the one way clutch and low reverse clutch. Manual 2nd gear, that forward clutch again and the intermediate band applied. You can get 2nd gear in a C6 from a dead stop by manually selecting 2. If that doesn't work, you either failed the band, or the forward clutch failed. Catch a theme? All of this requires a functional forward clutch.

Working park, you have a working linkage and the parking pawl is functional on the output shaft. Convertor, input shaft, all that is proven to be good because you have a working reverse. Working convertor, input shaft, pump, gears are at least functional.

Every single thing in the description of no forward gears and everything else works, points to the forward clutch not working. Thus look at if there is pressure going to the forward clutch. If it is getting pressure, the valve body is functional. No pressure, something is up with the valve body not allowing fluid to the forward clutch.

Adjusting a band won't stop a transmission from going into gear. It might lock a transmission up if too tight. 1/8 of a turn won't matter. Complete coincidence.

 

[Chiclassics]

It might lock a transmission up if too tight. 1/8 of a turn won't matter. Complete coincidence.

Who knew , thanks for throwing more light.

 

[SLOWnEASY]

You can take the band out and throw it away it it will still drive, just won't have 2nd gear. In a C4, delete both bands and you loose reverse as well. But since this is C6, and for the most part this site is more based on the C4 version. Let me add a link https://drive.google.com/file/d/1fOMvcNoxettzh4hjNrh7MzrSf2Meru_1/view Go to page 32, it has an apply chart

My google foo is failing me. Do you have a link to a C4 service manual?

 

[Chiclassics]

OH ya me too...I would love to see a C4 manual.. i always try to send it shop for transmission stuff i like get into this myself.

 

[thegreatjustino]

My google foo is failing me. Do you have a link to a C4 service manual?

As this thread is regarding a C6, the link is to a C6 manual which I've attached here.

 

[Broncobowsher]

My google foo is failing me. Do you have a link to a C4 service manual?

I don't. Post a new thread asking for a C4 manual. That will make future seekers an easier find than one buried in a C6 thread. That C6 manual was a tough find.

 

[Chiclassics]

@Benteketeza whats the word