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Old Nov 19, 2022 | 09:55 AM
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C6 woes

I just replaced the linkage seal in my 79 Bronco. Had the pan and valve body off. Everything seemed good for about 10 miles but now it seems to slip as I start out from a stop until about 15mph or so then seems to operate normally. If I get hard on the gas as it slips I can feel it grab. I kept adding fluid but now it's a little over the high mark with no change. I didn't change the filter as the one I ordered arrived late. I did add a drain plug and lube locker gasket so it would be easy to drain and get back jnto it.

Ideas?
Thanks!

 
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Old Nov 19, 2022 | 10:00 AM
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Oh boy that rig looks GREAT! Just keep er going
 
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Old Nov 19, 2022 | 10:10 AM
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Did you put new valve body gaskets in, and if so, was all old gasket material removed?
 
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Old Nov 19, 2022 | 11:07 AM
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Thanks!
I did not replace the valve body gasket. My first time opening up an automatic. I also notice that it seems to grab in reverse like it should. Just not in first very well. It looks like you have to split open the valve body to replace that gasket?
 
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Old Nov 19, 2022 | 04:37 PM
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Originally Posted by frdbronco8
Thanks!
I did not replace the valve body gasket. My first time opening up an automatic. I also notice that it seems to grab in reverse like it should. Just not in first very well. It looks like you have to split open the valve body to replace that gasket?
​​​​ Hello from Arlington. Nice looking Bronco.
 
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Old Nov 19, 2022 | 04:46 PM
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Originally Posted by frdbronco8
Thanks!
I did not replace the valve body gasket. My first time opening up an automatic. I also notice that it seems to grab in reverse like it should. Just not in first very well. It looks like you have to split open the valve body to replace that gasket?
​​​​ Hello from Arlington. Nice looking Bronco.
 
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Old Nov 20, 2022 | 10:21 AM
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You're either not getting good apply pressure on the forward clutch, or the clutch was worn and the new fluid isn't grabbing as well. You could probably put a pressure gauge on and watch the pressure as it shifts to see if it's slow to rise and follows the slip. If that's the case you may need to replace or remove the gasket on the valve body. Yes you do need to split it. A lot of times builders don't even run a gasket there. Did you torque the fasteners for the assembly when you installed it? Fluid type?
 
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Old Nov 20, 2022 | 10:42 AM
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Originally Posted by aldridgec
You're either not getting good apply pressure on the forward clutch, or the clutch was worn and the new fluid isn't grabbing as well. You could probably put a pressure gauge on and watch the pressure as it shifts to see if it's slow to rise and follows the slip. If that's the case you may need to replace or remove the gasket on the valve body. Yes you do need to split it. A lot of times builders don't even run a gasket there. Did you torque the fasteners for the assembly when you installed it? Fluid type?

I did torque the valve body (don't remember what torque i used but it was very low... 100in/lbs?). I just ordered a new gasket. If I recall the old one looked metal?
I put mercon/dexron fluid in.
also it feel like when I go past about half throttle it grabs. Would that be the kick down lever being activated? Again, sorry for the ignorance with Automatics and thanks for the suggestions!
 
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Old Nov 20, 2022 | 11:16 AM
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Originally Posted by frdbronco8
I did torque the valve body (don't remember what torque i used but it was very low... 100in/lbs?). I just ordered a new gasket. If I recall the old one looked metal?
I put mercon/dexron fluid in.
also it feel like when I go past about half throttle it grabs. Would that be the kick down lever being activated? Again, sorry for the ignorance with Automatics and thanks for the suggestions!
If by grabs you mean the transmission is downshifting @ WOT then yes it's grabbing. There should be a rod that runs from the linkage on driver's side of carb to driver's side of C-6 shift linkage. Their is also a vacuum modulator on the passenger side of the C-6 that has a vacuum line running from it to the vacuum tree at the back of the intake manifold and controls the shift points of the C-6.
 
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Old Nov 20, 2022 | 11:51 AM
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Not downshifting (cause it's still in first from starting out) but slipping less? Now that I think about it it almost feels like it's starting out in 2nd gear....
 
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Old Nov 20, 2022 | 12:00 PM
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Originally Posted by frdbronco8
Not downshifting (cause it's still in first from starting out) but slipping less? Now that I think about it it almost feels like it's starting out in 2nd gear....
Are you saying you physically have the shifter selecting low gear while you observed the slippage? Sorry if you're having to repeat yourself. I'm first reading the thread.
 
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Old Nov 20, 2022 | 12:11 PM
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Not uncommon to replace the fluid and filter in your transmission and experience slipping. All of the friction material went out with the old fluid and the new fluid is really slick so you may need a friction modifier to add in and help the clutches grab again. If that doesn't work the tranny might need surgery.
 
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Old Nov 20, 2022 | 02:37 PM
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Originally Posted by redroad
Are you saying you physically have the shifter selecting low gear while you observed the slippage? Sorry if you're having to repeat yourself. I'm first reading the thread.
No its in D. But almost feels like im starting in 2nd. Really sluggish and slow until i get some speed then it behaves normally.... would a break in the valve body gasket cause this?
at this point I'm planning on replacing the valve body gasket and filter and seeing what happens.
 
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Old Nov 21, 2022 | 08:56 AM
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Put it in manual low.Still sluggish,feel like slippage? If not,might be instantly shifting to 2nd in D.Turn the tiny flat blade screw in the modulator vacuum hole clockwise to see if it helps.If sluggish in manual low,replace that gasket(metal thing is the separator plate).Keep the casting on the bottom as there is a lot of stuff in there.I really doubt it's the gasket.You might try type F fluid.It gives the clutches a little more grip.One more thing...Make sure the kick down is in the correct slot on the valve body since it is the only thing you messed with,going from good to bad.
 
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