C6 transmission on my 1989 Bronco 351W

captsb890

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I still cannot find an answer to my shifting problem after the transmission was overhauled. AAMCO Had it back many times and they stated the miles on the motor 202,000 and tired etc. It has 17 + on the vacuum ----It shifts a little better when it is cold rather than hot-----Has late shifting into 3rd gear - and Gerks but here is what I tried- I can, from a standstill, put it in low gear---accelerates and runs smooth---then shift to D2 still a smooth shift -- but when I get to shift at a higher rpm into drive--it stutters, breaks down, runs rough----What is it-? linkage adjustment-? shift solenoids-? motor inside the transmission? Thsy adjusted the modulator out as far as it would go. Without shifting through the gears manually, it shifts pretty good low into 2nd but hangs up on 3rd? until I let off a little gas pedal and then it shifts with a Gerk-------------any advice would be greatly appreciated----No, I won't take it back to AAMCO as after 4 times, they can't find their ass with both hands and a map!
 

Tiha

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Well it sure sounds like it is still the trans. But we can maybe do some more trouble shooting.

I am not sure if the Neutral safety switch has any effect on your model year, but you can start the truck crawl under it and unplug it. Then go for a drive, see if there is any change. My thinking is if maybe it is telling the ECM to open the EGR valve or something like that when in 3rd gear.

You said it cuts out, or runs rough in 3rd gear, if you pull it back into 2nd gear does it start running properly?

I am pretty sure there are no solenoids in the C6. It should not need any electrical to run. I think you can completely unhook the modulator as well and take if for a drive to check for change.

Off the top of my head sounds like there is a sticky valve in the valve body, or a servo piston that is sticking, could be from housing wear. But after it shifts that would not cause it to run poorly. Might be fighting more than one issue there.

I assume it shifted okay before the trans was rebuilt? And ran okay in 3rd gear?
 
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captsb890

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Well it sure sounds like it is still the trans. But we can maybe do some more trouble shooting.

I am not sure if the Neutral safety switch has any effect on your model year, but you can start the truck crawl under it and unplug it. Then go for a drive, see if there is any change. My thinking is if maybe it is telling the ECM to open the EGR valve or something like that when in 3rd gear.

You said it cuts out, or runs rough in 3rd gear, if you pull it back into 2nd gear does it start running properly?

I am pretty sure there are no solenoids in the C6. It should not need any electrical to run. I think you can completely unhook the modulator as well and take if for a drive to check for change.

Off the top of my head sounds like there is a sticky valve in the valve body, or a servo piston that is sticking, could be from housing wear. But after it shifts that would not cause it to run poorly. Might be fighting more than one issue there.

I assume it shifted okay before the trans was rebuilt? And ran okay in 3rd gear?
Once it shifts into 3rd gear while in drive D it runs fine-- it has always been slow on acceleration, it is just that shifting into 3rd it hangs up and just hangs there until I let a little pedal off then it shifts with a ****. The transmission before overhaul ran ok in 3rd--but I never tried to walk through the gears--wish I had thought of that----Like I mentioned, it does shift a little better when cold--I was told the C6 runs hot and was thinking of putting that F 100% synthetic fluid in as it will not break down when hot. The racing people recommend it. But I could have sworn that Aamco said at first, they put Dextron 2 in it and then when I brought it back, they changed and said Dextron 3? It doesn't make sense as I think because of it getting hot, they may have put the wrong fluid in it. They kept telling me that you got to dive it 100 miles to break it in. I think that is because they have been paid and don't want to be bothered.
Could it be a linkage adjustment that it needs? I don't think it is the neutral switch and that's new. If I step on it from a stop, it downshifts fair but kind of smooth. I mentioned that when it is cold fluid---cold meaning I live in Arizona and it doesn't get that cold here, but it shifts really smooth in D from start to 2 and much better in 3---seems like when it gets hot it gets worse. I put a lot of money in the Bronco 5 coat paint, complete AC, etc and if I could get it to shift smoothly, I would be happy. Any other suggestions? If I was rich, I would take it somewhere else and have it again rebuilt. Any other suggestions? How about that throttle linkage to make it shift earlier?
 

Tiha

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The fluid options we have today for the C6 are limited. The Dex 2 or 3 doesn't matter it most likely came out of the same drum and wasn't even dexron.

Overheating, or running hot, without a trans temp gauge it is just a guess.
Running differently between cold and hot would suggest fluid leaking past sealing rings or apply clutches. When aluminum warms up gaps expand allowing more fluid to leak by. Or sometimes they expand in the direction of closing a bore so valves and serovos hang up.
Also adding a pressure gauge, take reading from the test ports in every gear, cold and hot, that would also help you see where the problem is, or isn't. They are like $45 at harbor freight.

Adjusting the kick down or the vacuum modulator should not affect the way it shifts into 3rd gear. You can completely unhook them and take it for a drive and see if there is a difference.

Completely understand your frustration and I agree the trans shop should be taking better care of you and they most likely do not know what they are doing.

I don't know if it is still the case, but test drives from trans shops used to be free. Maybe call a different shop and see what they say? If they would look at it? If you could get them on your side then you have a good reason to go up a level or two in amco management and maybe get something done. At least have some good technical information instead of just saying "it isn't right" Gives them more to work with, upper level people respond to that much better.

Maybe someone else can come up with some better ideas than myself. Being at wits end at this point, myself, I would probably buy a used c6 of the internet or junkyard and stick it in just to see/prove that was the problem.
 
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captsb890

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The fluid options we have today for the C6 are limited. The Dex 2 or 3 doesn't matter it most likely came out of the same drum and wasn't even dexron.

Overheating, or running hot, without a trans temp gauge it is just a guess.
Running differently between cold and hot would suggest fluid leaking past sealing rings or apply clutches. When aluminum warms up gaps expand allowing more fluid to leak by. Or sometimes they expand in the direction of closing a bore so valves and serovos hang up.
Also adding a pressure gauge, take reading from the test ports in every gear, cold and hot, that would also help you see where the problem is, or isn't. They are like $45 at harbor freight.

Adjusting the kick down or the vacuum modulator should not affect the way it shifts into 3rd gear. You can completely unhook them and take it for a drive and see if there is a difference.

Completely understand your frustration and I agree the trans shop should be taking better care of you and they most likely do not know what they are doing.

I don't know if it is still the case, but test drives from trans shops used to be free. Maybe call a different shop and see what they say? If they would look at it? If you could get them on your side then you have a good reason to go up a level or two in amco management and maybe get something done. At least have some good technical information instead of just saying "it isn't right" Gives them more to work with, upper level people respond to that much better.

Maybe someone else can come up with some better ideas than myself. Being at wits end at this point, myself, I would probably buy a used c6 of the internet or junkyard and stick it in just to see/prove that was the problem.
I do appreciate your time with me---Oh, by the way, what is that shift linkage on top that they said you can adjust of shifting earyl or late--think that has anything to do with things?
 

Tiha

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The cable linkage on top is the kick down cable, so when you hammer the throttle the transmission will downshift. If you unhook it the transmission will only down shift manually while driving.

The vacuum modulator helps control the upshift. So if you are really light on the throttle it should shift earlier, if you are ******* the throttle there is less vacuum so it shifts later.

At least I think I got that right. Haven't done this C6 stuff in years.
It is an all mechanical transmission. Meaning you unhook all of that stuff it should still run, drive, and shift fine. Maybe not shift like you want it, but still give good solid quick shifts.

Edit ******* = H a m m e r i n g Word filter gets a little over zealous.
 

Juan2three

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I still cannot find an answer to my shifting problem after the transmission was overhauled. AAMCO Had it back many times and they stated the miles on the motor 202,000 and tired etc. It has 17 + on the vacuum ----It shifts a little better when it is cold rather than hot-----Has late shifting into 3rd gear - and Gerks but here is what I tried- I can, from a standstill, put it in low gear---accelerates and runs smooth---then shift to D2 still a smooth shift -- but when I get to shift at a higher rpm into drive--it stutters, breaks down, runs rough----What is it-? linkage adjustment-? shift solenoids-? motor inside the transmission? Thsy adjusted the modulator out as far as it would go. Without shifting through the gears manually, it shifts pretty good low into 2nd but hangs up on 3rd? until I let off a little gas pedal and then it shifts with a Gerk-------------any advice would be greatly appreciated----No, I won't take it back to AAMCO as after 4 times, they can't find their ass with both hands and a map!
I have a 1996 Bronco w/351W. I experienced the exact problem you are having. There is an electrical module under the dash that I believe is your problem. When you sit in the driver's seat it is located behind the lower panel below the steering column in front of your right knee position. The module is no longer available and the solution was to install a simple 12volt, fused jumper from a 12 volt source to a Green wire with a Yellow stripe that comes out of that module. I used to know what the module was but my senior memory fails me at this moment. I went out and verified on my Bronco what I am telling you. Let me know if this helps or if I can be of further help. Maybe you could find one in a junk yard.
 
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captsb890

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I'm not sure what you are saying as I don't know transmissions----My 89 Bronco has electric or no electric or strictly vacuum?
 

Tiha

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I'm not sure what you are saying as I don't know transmissions----My 89 Bronco has electric or no electric or strictly vacuum?
He is talking about an E4OD which is controlled by a computer and solenoids. You, the C6 has none of that. So what he is suggesting doesn't apply to your shifting problem.

Unless he is trying to say it is the ECM in which case that would mean the engine is not running right.
 
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captsb890

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I see--My engine does run ok for 202,000---valves were done at 125,000--idle a little rough and at idle sounds like a coffee percolator--that could be glass packs old over ten years or maybe catalytic converters -old--- but if i get money I will put a NEW 351W in it-------I think the engine isn't producing enough vacuum--it does show 17 at idle but when you push on it ---it delays shifting to 3rd and i have to let some pedal off--then it shifts with a ****--so vacuum isn't up there---Where does an engine get its vacuum from anyway? pistons sucking or valves ?? What causes it to lose the vacuum and is there anything that can be done?
 

Tiha

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vacuum shouldn't be an issue for you.

It is created by the pistons going up and down, plus the cam profile. The way the camshaft is grouind has a big effect on vacuum, but in the end it is the butterfly in the throttle body that creates vacuum. It is the restriction that controls the air intake.
So when you step on the gas, the butterfly opens and allows more air in. Lowering vacuum until engine rpms come up and compensate for the new air flow.

Seeing the vacuum drop is normal, but it should recover.

When you let off the gas the bufferfly closes and the vacuum spikes up.
 

L\Bronco

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I see--My engine does run ok for 202,000---valves were done at 125,000--idle a little rough and at idle sounds like a coffee percolator--that could be glass packs old over ten years or maybe catalytic converters -old--- but if i get money I will put a NEW 351W in it-------I think the engine isn't producing enough vacuum--it does show 17 at idle but when you push on it ---it delays shifting to 3rd and i have to let some pedal off--then it shifts with a ****--so vacuum isn't up there---Where does an engine get its vacuum from anyway? pistons sucking or valves ?? What causes it to lose the vacuum and is there anything that can be done?
The vacuum modulator controls shift points and line pressure based on engine load.
Vacuum will indicate engine load if the engine performance is good. High vacuum = low load, so low pressure and early shifts. Low vacuum = high load, so high shifts and high pressure.
It sounds like the root cause might be engine performance. restricted exhaust will **** the vacuum as the engine revs up and it will get worse with load which could explain the late\hard 2-3 shift, but it doesn't normally cause misfiring, so maybe look there too, Cracked plugs/wires, worn exhaust cam lobes (rare), ect.
Id start by checking your vac at idle, you said it was around 17", then rev it to around 2000 in neutral, the vacuum should climb around 1-2" (It will drop as you open the throttle, and then recover as Tiha said.)
(The engine is more efficient at 2000, the vac should be better)
If it goes down but is running smoothly, you likely have restricted exhaust, drop the pipes at the manifolds (I they will come off without breaking all the studs) and check again. If it comes up now, the exhaust is plugged.
If it runs bad at 2000 RPM with low vacuum, chase the engine performance first.
If you pull the vacuum hose off of the modulator on a C-6 it will not shift into 3rd until the road speed is crazy high. (Depending on gear ratio)
Hope that helps
Cheers
 
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captsb890

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The vacuum modulator controls shift points and line pressure based on engine load.
Vacuum will indicate engine load if the engine performance is good. High vacuum = low load, so low pressure and early shifts. Low vacuum = high load, so high shifts and high pressure.
It sounds like the root cause might be engine performance. restricted exhaust will **** the vacuum as the engine revs up and it will get worse with load which could explain the late\hard 2-3 shift, but it doesn't normally cause misfiring, so maybe look there too, Cracked plugs/wires, worn exhaust cam lobes (rare), ect.
Id start by checking your vac at idle, you said it was around 17", then rev it to around 2000 in neutral, the vacuum should climb around 1-2" (It will drop as you open the throttle, and then recover as Tiha said.)
(The engine is more efficient at 2000, the vac should be better)
If it goes down but is running smoothly, you likely have restricted exhaust, drop the pipes at the manifolds (I they will come off without breaking all the studs) and check again. If it comes up now, the exhaust is plugged.
If it runs bad at 2000 RPM with low vacuum, chase the engine performance first.
If you pull the vacuum hose off of the modulator on a C-6 it will not shift into 3rd until the road speed is crazy high. (Depending on gear ratio)
Hope that helps
Cheers
Thank you for that---I believe it could be a combination of exhaust and tired engine. It shifts pretty smoothly from 1-2 even with a heavy pedal but faulters 2-3--also if I manually shift 1-2 smooth--but 2-3 faulters--sounds like vacuum--other wise the car runs pretty smooth and doesn't misfire. Just no pep
 

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i think you have a engine timing issue. You indicated the engine had low power out put. With +200K miles the timing chain can get slopy and or you set the timing and the dampener has spun which moved the timing mark. In both cases the engine would have bad timing and in 3 gear will run very poor. Simple test, advance the timing about 10 degrees and take it for a ride. If it helps you now know where to look for the actual problem.
my two cents. Hope this helps...
 

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Google PSOM { 'Programmable Speedometer Odometer Module } Its on the back of the instrument cluster and after time the solder breaks down causing bad signals to the ECM. My E4OD had the same problem and after a lot of trouble shooting I called a speedo repair shop in Florida and they fixed it.
 
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captsb890

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i think you have a engine timing issue. You indicated the engine had low power out put. With +200K miles the timing chain can get slopy and or you set the timing and the dampener has spun which moved the timing mark. In both cases the engine would have bad timing and in 3 gear will run very poor. Simple test, advance the timing about 10 degrees and take it for a ride. If it helps you now know where to look for the actual problem.
my two cents. Hope this helps...
Thanks, haven't thought of that--The timing normally is what--10degrees? so make it 20 degrees for the test? would just a few degrees make a difference?
I noticed something the other day--I ran it manually through the gears---1-2 good but was around 3000 rpm and shifted 2-3 Nothing? didn't shift? maybe wasn't high enough on rpm?-------------If I get enough money I'm just going to put a new 351w in it.
 

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