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Old 01-30-2012, 06:51 AM
ekacpuc ekacpuc is offline
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c6 vacuum modulator questions

From the day I got the truck the power brakes have sucked, it takes excessive pressure to stop the truck. I've checked pads and such and everythings fine so I figure it's the booster. Just wanted that noted..

My vacuum modulator is hooked up to the same T that the power brakes are on. If my brake booster was bad would that do funny things to the vacuum signal? When I pull off the line at the modulator the engine doesn't speed up or run rough. I hear and can feel the hose sucking alot though..

Should I try move the modulator hose to the manifold? They're currently on the back of the block on a funny T. It's hard to get to and I couldn't really tell what the huge T (it was a little manifold with 4 or 5 fittings) was getting its vacuum from.


Thanks,
Greg 79 F250
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Old 01-30-2012, 10:57 AM
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Look for what is broken,moving the vacuum line from the factory tee at the back of the manifold won't solve a thing. Fix your brakes first, without them you just park! Make sure your rear brakes are adjusted properly, check brake fluid if dirty replace and bleed out system. i made a great little tool for checking booster, just a small tee that goes between the check valve and booster when you stop motor vavuum should remain in booster, i have bad hearing so it works for me just be sure your check valve is good. After that you can start looking at your vacuum modulator line it's rubber at both ends, look for trans fluid in modulator end. Good luck
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Old 01-30-2012, 03:50 PM
ekacpuc ekacpuc is offline
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I like how people know how to skip right around answering my questions and instead tell me what to do with my rig. I just don't see why you people can't just answer my question.

The question was : If my check valve on my booster was bad that would affect my modulator right?


Oh well, doubt I'll be back this is just silly. I'll have better luck just guessing than asking ANY forum. It's annoying really, I can ask how this camshaft does and instead of just answering a simple question you guys all suggest a different one instead.

I'm aware I need brakes but you don't know my rig my situation or my town. I never said the brakes didn't work, I just listed that as a symptom. I was hoping someone fairly smart would see where I was going and confirm what I already think. Not some dummy saying I need brakes and to first fix those first. Clearly I'm looking for what's broken, I've been ALL over the rig.


Greg
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Old 01-30-2012, 04:39 PM
1912barry 1912barry is offline
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Quote:
Originally Posted by ekacpuc View Post
I like how people know how to skip right around answering my questions and instead tell me what to do with my rig. I just don't see why you people can't just answer my question.

The question was : If my check valve on my booster was bad that would affect my modulator right?


Oh well, doubt I'll be back this is just silly. I'll have better luck just guessing than asking ANY forum. It's annoying really, I can ask how this camshaft does and instead of just answering a simple question you guys all suggest a different one instead.

I'm aware I need brakes but you don't know my rig my situation or my town. I never said the brakes didn't work, I just listed that as a symptom. I was hoping someone fairly smart would see where I was going and confirm what I already think. Not some dummy saying I need brakes and to first fix those first. Clearly I'm looking for what's broken, I've been ALL over the rig.


Greg
With an attitude like that you will get lots of help now!
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Old 01-30-2012, 05:51 PM
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Stinky7-11 Stinky7-11 is offline
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Quote:
Originally Posted by ekacpuc View Post
I like how people know how to skip right around answering my questions and instead tell me what to do with my rig. I just don't see why you people can't just answer my question.

The question was : If my check valve on my booster was bad that would affect my modulator right?


Oh well, doubt I'll be back this is just silly. I'll have better luck just guessing than asking ANY forum. It's annoying really, I can ask how this camshaft does and instead of just answering a simple question you guys all suggest a different one instead.

I'm aware I need brakes but you don't know my rig my situation or my town. I never said the brakes didn't work, I just listed that as a symptom. I was hoping someone fairly smart would see where I was going and confirm what I already think. Not some dummy saying I need brakes and to first fix those first. Clearly I'm looking for what's broken, I've been ALL over the rig.


Greg
No, and i don't prescribe your meds either, something else that seems to not be working, take the yellow brick road it's waiting just for you Scarecrow !
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Old 01-30-2012, 07:09 PM
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Answer to your question!!! not unless you have a bad leak through the booster, it would be big enough you could here it.
Moving the line off the tee will not make it better. Just make sure your tee is not clogged, carbon from inside manifold, etc. The tee goes into the back runner of the intake manifold. If you want to diagnois the booster. Check the tee to see if clogged, check the check valve, if valve and tee are ok booster is bad.
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Old 01-30-2012, 07:21 PM
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LOL... where's the popcorn? This could get ugly...

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Old 01-31-2012, 04:46 AM
wdfp wdfp is offline
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Why do you think your modulator is acting up? Because the brakes don't work? You didn't say anything about your transmission and how it is working, so what was the real question here? Well maybe I missed something both times I read it..
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Old 02-01-2012, 12:32 AM
ekacpuc ekacpuc is offline
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Thank you moose4x4. I do hear a leak somewhere but it isn't the check valve or those hoses (replaced em).


Overhauled the C6 and used a SK6 shift kit so I expected nice firm shifts. I ended up with a almost stock 1-2 shift feel and a nice firm 2-3 shift. I shouldn't have used a N servo with a A lever (stock, imagine that when it feels stock huh?). I shoulda used that A lever (PITA to get pin out anyways) with a R code servo so everything was sorta balanced.

Well I put my transmission in then it snowed and then hit 0 degrees so it was really icy. Today it finally melted and I got to finally romp on it and the 1-2 shift really isn't that bad after all.. A little softer that I prefer but not bad.


Looking back now I reacted a bit rash at the first response. When you read just the first 2 sentences it appears that he isn't even making an attempt to answer my question. I didn't read far enough, just saw " look for whats broken and fix your brakes first". I finally looked at it again and noticed he's helping me trouble shoot my brakes (based on my poorly stated question). Problem was I am aware of what's wrong with my brakes (bad booster), but cannot afford it right now. The brakes work BTW just takes excessive pedal pressure to stop, reminds me of my old 74 jeep with manual drums. I do appologize. Remember everyone has a bad day sometimes and when I read the begining of your question I figured you just wanted to add to it... This whole transmission rebuild has been a nightmare, I'm in over my head and have no resource to ask questions too. The few I've found say "Oh don't waste your time ship it out to be rebuilt", well that isn't realistic for me. I live in Ketchikan Alaska and with shipping and trucking it begins to be too much $.


Anyways turns out you could just take the booster check valve off and suck through it to test, should only flow one way. I replaced mine.. I hoped for a change in shift timing (1-2 shift) and for the booster to work better. Didn't help any though. Next will be the booster (to fix the brakes not the shifting).


I saw that the brakes and the modulator where hooked together and both where not working well so I hoped the check valve would fix both..




Greg
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Old 02-02-2012, 12:36 AM
wdfp wdfp is offline
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Have you tried adjusting the modulator? I had a problem like that after mine was done, sloppy shifts and just outright wierdness. Turned out the modulator had never been set at all, the screw was almost out the back of it (where the vacuum line hooks up). I ended up a good 9 turns in or so then it started working like the transmission was built to work. make sure the kickdown is adjusted properly too
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Old 02-02-2012, 11:08 AM
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There exist different length modulator pins as well that might help you. The longer the later/firmer the shift.

It is really easy though to have an internal leak, and that just messes everything up. My vote would be to run a pressure test on the tranny and see what kind of pressures you are working with, that can tell a lot.
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Old 02-03-2012, 02:22 PM
ekacpuc ekacpuc is offline
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There exist different length modulator pins as well that might help you. The longer the later/firmer the shift.

It is really easy though to have an internal leak, and that just messes everything up. My vote would be to run a pressure test on the tranny and see what kind of pressures you are working with, that can tell a lot.


Indeed, I'm going to do a pressure test, have to order the gauge from harbor freight or somewhere like that. Couldn't find one in town . I'm also going to see what pin I used, I can't remember if I used the old one or new one and I didn't check the length.

I went like nine turns in as well and the shifts improved alot.

When I assembled the transmission I checked the lips seals (with air) and I know those are good. When you put it into D or R it clearly goes into gear with a nice thud (plus a leap forward). That's why (other than no money) I havn't worried about the pressures yet.


Greg
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Old 02-03-2012, 03:54 PM
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There are many more places in the transmission you can lose pressure than just lip seals.
Your governor could be out of whack.
Your pump could be faulty. (trust me on this) even if it's new.
The valve body may be the culprit, doesn't matter if you meticulously rebuilt and added installed a shift kit and all that fun stuff, just because you remember doing something doesn't mean you can rule out that circuit.

The list goes on and on but I think you see the point.

90% of the time it seems that when a c6 is shifting poorly or at the wrong time, it's a pressure problem. These things are great when you get them set up right, but when the font shift right it usually indicates an internal problem.

As far as a pressure testing goes, you can get a cheap gauge and use powersteering hose with I believe a 1/8 npt fitting.

I'm assuming you have watched the bad shoe video. (only assuming) while that is an excellent video. It does not by any means cover everything, nor does it make one an expert on automatic transmissions. I was in the same boat years ago (and recently too) shaking my head at the c6 transmission. You just have to be patient and never rule out the replaced part. See image below.



Click the image to open in full size.
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Old 02-03-2012, 03:54 PM
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