C6 TRANSMISSION WOES

[2NDTOUR89]

So I have a 1989 Big Bronco with a 5.8 and a C6 and am having transmission issues. When I got my Bronco it had been neglected and the trans fluid was black and the trans would not shift unless you manually went through the gears. I changed the fluid and filter once and then ran it with cleaner and flushed it completely. Still had the issue so I changed the vacuum modulator but did not adjust it or check for vacuum. Still had the problem and the shifter felt stiff and a transmission shop thought it sounded like valve body so I had one built and installed it last night and now the shifter works fine and the trans shifts beautifully but still does not want to kick down to low when coming to a stop. Am I on the right track checking the modulator vacuum and adjusting the modulator if the vacuum is correct? If not, where do I go next. The trans does not slip at all and when it is shifting through the gears after I either mash the gas pedal or manually put it in low and then shift up do drive after I start rolling.

Any insight???

 

[bidibronco]

Did you check the kickdown lincage?

 

[miesk5]

yo,

by Andrew:

"The different color bands indicate the diamater of the rubber diaphragm inside the modulator. The two COMMON colors from auto parts suppliers are PURPLE and GREEN. These are for CARS. TRUCKS like OURS REQUIRE the BLACK banded modulator, likely from a transmission shop or dealer. This is reguarding the mid/late 80's models, maybe more... Id venture to say any C6 with a slip in modulator.

Again, PURPLE and GREEN are NOT the correct units to use, BLACK is the intended modulator as was designed for TRUCKS.

Hope that helps!

Andrew"

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C6 Trouble Shooting Flow Chart Source: by jasperengines.com via web.archive.org

LATE OR NO DOWNSH = Clean governor; Replace valve body (done by you!)

NO KICKDOWN = Adjust kickdown rod or cable; Throttle linkage not reaching wide open throttle; Replace valve body (done by you!)

http://www.autozone.com/az/cds/en_us/09008...irInfoPages.htm

http://www.autozone.com/az/cds/en_us/09008...irInfoPages.htm

http://www.autozone.com/az/cds/en_us/09008...ges.htm#hd1-1-4

hope some of the diagrams from Chilton via AZ help or are totally correct...memory of c6's is fading here...others here have better info I'm sure!

 

[miesk5]

more;

C6 downshift problem

July 4 2007

Engine - 351w Trans - C6 w/ Coan converter

Symptom - Upshifs fine when it downshifts (automatically), but not always downshifting to 1st gear when come to stop sign

Problem - Not consistent -- 80% of the time it won't downshift to 1st at a stop, 20% of the time it will.

Any thoughts on what might be the cause?

PS -- 10 miles on new Broader transmission.

Jay

Response to C6 downshift problem

High engine idle.

Vacuum block.

Governor valve hanging up.

Try this.

You need an assistant.

Disconnect the kd linkage at the top.

Start the vehicle and place the transmission in Drive.

Push the kd linkage down to the stop several times.

Connect the linkage and try it.

Stuart A

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The vacuum modulator controls upshift, based on intake manifold vacuum when your foot is on the accelerator pedal. Ford calls this the primary throttle valve. This valve is adjustable, which determines upshift and downshift points.

http://64.233.169.104/search?q=cache:HhfXf...cd=17&gl=us

Stock factory modulators are pre-set and most are sealed. TCI

 

[2NDTOUR89]

Thanks for the help. I will double check the color on the modulator that I put in but if memory suits, it was the black one that I installed. I will also check the kickdown cable to make sure it is correctly adjusted. Hopefully this will fix it, after the E4OD woes I have had with my F350, I was hoping that a full mechanical C6 would be easy...

I was just reading the rebuild info on the post and was checking out the info on the intermediate band adjustment. Last night when I had the valve body out, I noticed that you could grab the band and move it, seemed sloppy to me and this tells me how to set the adjustment on it. Great article. Thanks for the link.... This could be it...

 

[2NDTOUR89]

So I worked on the Bronc last night and checked the vacuum at the modulator and it had 15 in of merc at idle and the same was found at the intake so I am assuming that the manifold vacuum is the same between the two spots and is correct. I adjusted the intermediate band (way out of adjustment) and the modulator and it still had the issues. I got frustrated and parked it for the night and then drove it to work this morning and when I started out, it still had the issues but when I got into town (8 miles away from home) it started shifting totally normal ie downshifting to first at a stop etc... Could it be that the adjustments particularly the band adjustment needed to seat or am I wishful thinking? Any other help before I take it to a tranny shop?

 

[miesk5]

well now... I am supposin' that the tranny needed a little warmimg up and the intermediate servo was a little gummy and hotter fluid and a few thousand ops got it all going.

got this info from my old site's notes;

check servo operation using compressed air at the fluid passage. The servo works fine; all is good..... If there

 

[2NDTOUR89]

I was going to drive it just now but was blocked in by a couple of guys that work for me... Had to take the company truck to lunch instead. I will keep posted but if not, i will check out the servo. If I have to get too far into it, i may just buy a new one. That finally worked for my E4OD in my F350 but I hate to have to spend the money if not needed.

Thanks for all the help.

 

[2NDTOUR89]

So I drove it home last night and it shifted fine after the engine warmed up however when I came to a stop and it shifted to first, when I started rolling without giving it throttle, it had a chatter feeling but still shifted properly. Once I got on the gas, the chatter went away. I only have about 400 miles on the rig since I got it back on the road after sitting for about 4 years with the black nasty fluid in it. I am thinking that most of this will clear up with time and more fluid movement but it could still be a sticky or gummy servo. I guess time will tell. I will let you know how it turns out.

Thanks again for all the help.....

 

[miesk5]

yw

-if it stays a little rough w/noise, think about the servo/another tranny flush. GL!

 

[2NDTOUR89]

With every mile it is getting better. Chatter is going away slowly and it is now downshifting normally about 98% of the time. I will probably do another flush shortly to make sure all the gunk is out. I really do appreciate all the help...

Thanks.