C-6 Modulator:Diagnose and Replace - Ford Bronco Forum
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post #1 of 24 (permalink) Old 04-15-2004, 05:12 PM Thread Starter
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C-6 Modulator:Diagnose and Replace

I started out having shift problems, my tranny wouldnt shift out of first after a dead stop until after 40mph/3K-RPM, and once it did it would shift up and down between 35mph and 45mph, from 2 to 3 and 3 to 2 and 2 to 3, etc.. It wasnt a shudder, it took a few seconds between shifts. Then it started not wanting to shift into 3rd. I would have to manually shift to 2 and back to 3 and most of the time it would kick into 3rd.

Terrified it would cost me a mint, I posted a Q in the tech section at FSB. Got a few ideas, and meanwhile I dropped down to a Cottman's transmission shop for a free checkout. The tech said he removed the vaccuum line from the modulator and oil (transmission fluid) ran out, so the modulator was bad. The modulator simply has a diaphragm that is vaccuum actuated to adjust the shift points (tell the tranny when its okay to shift). If you pull the vaccuum line and fluid runs out, the diaphragm is busted and fluid is getting by. This means the vaccuum on the line is not pulling the diag. and hence the small shaft inside is not moving.

Remove the bracket bolt with a 14mm socket, pull the old modulator from the rear of the C-6 transmission. Be carefull not to loose the plunger, its about a 2 inch piece of metal with rounded ends. Put the plunger into the new modulator, slide it onto the transmission and bolt down the bracket. Remove the vaccuum line from the old modulator and plug up the new, but allow for any excess fluid to drain fron the line.

Failure to replace the modulator could result in bruning up the transmission. I noticed mine not "acting right" since I first put it on the road (2 months), but it was nothing major. Yesterday on my way to work, the tranny's shif went all to hell, nothing was right.

Below, please see a picture of the modulator on the C-6. There is also a before and after video. Notice the MPH and RPM on both the before and after. At one point before, I pushed 3K RPM at 45MPH and it never shifted out of 2ed.

With the new modulator, the tranny shifts like a war hawk, just like its supposed to! And, this may also, most likely be the source of my tranny fluid leak (As verified by the tech at Cottman's).



Video: Before C-6 modulator replacement

Video: After C-6 modulator replacement

Modulator was purchased at Advance Auto for $13.99. Cottman's wanted $140 (parts and labor) for the rapair.


I hope this helps someone out!
Andrew


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post #2 of 24 (permalink) Old 04-17-2004, 11:35 PM
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A few years ago my Bronco wouldnt shift out of 1st. gear, turns out it was the hose going to the modulator was bad.
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post #3 of 24 (permalink) Old 06-08-2004, 11:47 PM Thread Starter
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Quote:
Originally Posted by tigertank
A few years ago my Bronco wouldnt shift out of 1st. gear, turns out it was the hose going to the modulator was bad.

Yup, that would do it too!!

Leaks in that vaccuum line will yield similar results, however if you pull the line from the mod and fluid leaks out, you know of at least 1 thing that must be replaced!


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post #4 of 24 (permalink) Old 06-21-2004, 11:14 PM
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When you remove the modulator do you lose any fluid or is above the fluid line?
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post #5 of 24 (permalink) Old 07-07-2004, 03:22 AM Thread Starter
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When you remove the modulator do you lose any fluid or is above the fluid line?
When I removed mine, no fluid came out. Thats a good question though! If anything, I guess the vaccuum drew it. Dohno.


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post #6 of 24 (permalink) Old 07-07-2004, 12:47 PM
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When I replaced mine a few years ago fluid did come out! Also IIRC there are two types for the C-6 that are ditinguished by the color band on them. Not sure exactly what the difference is...was kinda hoping someone on here might know. it seems like one was striped purple and the other black?

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post #7 of 24 (permalink) Old 03-01-2005, 11:04 PM Thread Starter
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Update: 1 March 2005

1) Some fluid may come out when you remove the modulator, but shouldnt be much. If a bunch pours out, then your transmission was OVERFILLED! If you loose any, chances are you will need to top it off with about 1/2 quard of ATF.

2) There are two modulators avaliable, green and purple band. I do not as of yet have any data or information on the two, although it is suspected that they have different shift points. Though, that may be weak since both are adjustable.

Thats all for now...


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post #8 of 24 (permalink) Old 03-11-2005, 12:27 PM
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don't know about the colors, but- there are two styles. The slip in kind like the one you have shown and then there is a screw in kind that's mostly found on the late 60's early 70's C6

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post #9 of 24 (permalink) Old 03-11-2005, 05:02 PM Thread Starter
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Originally Posted by MyFullSize
2) There are two modulators avaliable, green and purple band. I do not as of yet have any data or information on the two, although it is suspected that they have different shift points. Though, that may be weak since both are adjustable.
I have new information on the modulators, coming from the transmission specialist, and I mean specialist that rebuilt my C6 2 weeks ago.

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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post #10 of 24 (permalink) Old 04-12-2005, 12:43 AM
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im trying this tomorrow, sounds just like my c6 problem right now
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post #11 of 24 (permalink) Old 04-20-2005, 06:00 PM
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Just so you know, I had mine replaced and the used a green band. I believe that different modulators are used depending on the engine. Different size engines will have different amounts of vacuum, hence different modulators. At least thats the way I see it.

-Matt

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post #12 of 24 (permalink) Old 04-21-2005, 02:34 PM Thread Starter
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Just so you know, I had mine replaced and the used a green band. I believe that different modulators are used depending on the engine. Different size engines will have different amounts of vacuum, hence different modulators. At least thats the way I see it.

-Matt

The way the transmission man explained it to me, the band indicates vaccuum settings on the modulator, and there are "car" bands and the one that is black is the "truck" band, based on the weight of the vehicle, and the anticipated/expected pull/haul/tow weight. Hence, the truck is expected to do more "work" than a "car".

Make sense?


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post #13 of 24 (permalink) Old 04-22-2005, 12:24 PM
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Hmm..

Gave me all kinds of options for modulators on my Beast. Green, Purple, Black. Push in, etc..


Gonna have to make sure I got the right one..

1992 XLT, 5.8 w/ E40D transmission, TTB D44 in front, 8.8 rear, 4.88 gears w/ Eaton Posi, Gibson exhaust/headers,cb radio, 4" suspension lift, 33x12.5's on 8" Pro Comp wheels.

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post #14 of 24 (permalink) Old 04-22-2005, 01:23 PM Thread Starter
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Gonna have to make sure I got the right one..
The bottom line is, we use the black band mod.


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post #15 of 24 (permalink) Old 04-22-2005, 01:33 PM
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The bottom line is, we use the black band mod.
Well I dont know about THAT. I had the green band installed on mine, and it works like a demon....

-Matt

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post #16 of 24 (permalink) Old 04-22-2005, 02:06 PM
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The lady's 91 is shifting funny. That is the one I am worried about. I am just gonna check mine to be sure. It it's black, I won't worry, if it isn't, I am gonna get a black to see if I feel any difference..

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post #17 of 24 (permalink) Old 04-22-2005, 02:34 PM Thread Starter
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The essence of it is, the green would be okay, I dont think it would create any damage to the transmisstion, just that the black one is the one that is intended for the F150/Bronco. That is all.


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post #18 of 24 (permalink) Old 04-22-2005, 02:59 PM
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My modulator was installed by a large and well respected transmission shop that I have gone to for years. If the black one was the sworn modulator for trucks, im sure that it would have been installed. Instead, they took mine and weighed it, and came back out with the green band. It works great.

Im not saying your wrong, and im not saying im right. Im also not trying to start a petty argument. Im just trying to say that there may be more into the differences of what types of modulators go into C6 transmissions than we know. i would like to know what those differences are.

-Matt

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post #19 of 24 (permalink) Old 04-22-2005, 05:16 PM Thread Starter
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Matthew, I got your PM... Ill post back the numbers as soon as I can. These come from the book, but not my book, the shop's book.

Be patient, it may be easiest if I just go down and see the guy again, which will be Monday at the earliest.

Cheers..


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post #20 of 24 (permalink) Old 04-30-2005, 01:04 PM
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could this mod. cause reverse to take a couple minutes to get into when just started...?

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