C-6 Question
C-6 Question
Senior User
Joined: Jun 2003
Posts: 439
Likes: 0
From: Burnsville, MN
C-6 Question
Then why would you want to adjust it?
The vaccum modulator is a device that translates changes in manifold vacuum into changes in transmission oil pressure to modify shift points/characteristics.
When you look at your transmission you will generally see three tubes going into it. Two of them go into the side of the transmission case and connect it to the oil cooler in the radiator.
The third tube orginates in the engine compartment and carries vacuum from the intake manifold to a cylinderical (sp?) unti that screws into the transmission.
It it is adjustable, the adjustment screw will be inside the vacuum port of the modulator. Remove the tube to gain access, don't modify unless you want to really hose up the transmission.
When it is failing/out of adjustment the tranny will not shift up until the engine is really wound up, or the transmission will shift early cutting your performance.
The vaccum modulator is a device that translates changes in manifold vacuum into changes in transmission oil pressure to modify shift points/characteristics.
When you look at your transmission you will generally see three tubes going into it. Two of them go into the side of the transmission case and connect it to the oil cooler in the radiator.
The third tube orginates in the engine compartment and carries vacuum from the intake manifold to a cylinderical (sp?) unti that screws into the transmission.
It it is adjustable, the adjustment screw will be inside the vacuum port of the modulator. Remove the tube to gain access, don't modify unless you want to really hose up the transmission.
When it is failing/out of adjustment the tranny will not shift up until the engine is really wound up, or the transmission will shift early cutting your performance.
Thread Starter
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Junior User
Joined: Jun 2003
Posts: 79
Likes: 1
From: Neptune Beach
C-6 Question
GR
iesel,
Thanks for the help. I probably wasn't too clear as to what I needed. The problem I am having is the tranny is shifting early and I think is lugging the engine. I hope that is the term I am looking for. I barely get the truck rolling and it shifts the first time and before I reach 30MPH it shifts again regardless of the load I have on the truck.
Thanks so much for your help.
iesel,Thanks for the help. I probably wasn't too clear as to what I needed. The problem I am having is the tranny is shifting early and I think is lugging the engine. I hope that is the term I am looking for. I barely get the truck rolling and it shifts the first time and before I reach 30MPH it shifts again regardless of the load I have on the truck.
Thanks so much for your help.
Senior User
Joined: Jun 2003
Posts: 439
Likes: 0
From: Burnsville, MN
C-6 Question
Change the modulator, fluid, and filter.
Then see where you are.
Shifting early is not as common as shifting late for a bad vacuum modulator.
Does that transmission do this even when floored?
The reason I ask is the downshift linkage overrides the vacuum modulator.
Then see where you are.
Shifting early is not as common as shifting late for a bad vacuum modulator.
Does that transmission do this even when floored?
The reason I ask is the downshift linkage overrides the vacuum modulator.
Senior User
Joined: Jun 2003
Posts: 439
Likes: 0
From: Burnsville, MN
C-6 Question
Change the modulator, fluid, and filter.
Then see where you are.
Shifting early is not as common as shifting late for a bad vacuum modulator.
Does that transmission do this even when floored?
The reason I ask is the downshift linkage overrides the vacuum modulator.
Then see where you are.
Shifting early is not as common as shifting late for a bad vacuum modulator.
Does that transmission do this even when floored?
The reason I ask is the downshift linkage overrides the vacuum modulator.
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Senior User
Joined: Jun 2003
Posts: 439
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From: Burnsville, MN
C-6 Question
I suspect you may have a sticking valve in the valve body.
When you change the oil in the transmission it is not a difficult task to remove the valve body to clean it up.
Before you do:
Get a chiltons or other manual on the C-6.
Have a clean, clean, clean and well lit place to work.
Work slowly, carefully and make sure you keep track of every ball bearing (used as check valves), spring and valve go. Errors are not tolerated. You may want to put in a Shift-Kit at this time.
Not only will it give you directionrs for removing and disassembling the valve body, you'll get a new modulator and better shifts.
Good luck, let us know how it works out.
When you change the oil in the transmission it is not a difficult task to remove the valve body to clean it up.
Before you do:
Get a chiltons or other manual on the C-6.
Have a clean, clean, clean and well lit place to work.
Work slowly, carefully and make sure you keep track of every ball bearing (used as check valves), spring and valve go. Errors are not tolerated. You may want to put in a Shift-Kit at this time.
Not only will it give you directionrs for removing and disassembling the valve body, you'll get a new modulator and better shifts.
Good luck, let us know how it works out.
New User
Joined: Jul 2003
Posts: 24
Likes: 0
From: east coast
C-6 Question
Pull the hose off the modulator and tee in a vacuum gauge. You could be experiencing trapped vaccuum. Should have @ 16" to 21" of vaccuum at idle. Jazz the throttle and should flash close to zero. If it stays at high vac. and or drops slowly, suspect trapped vac.
Senior User
Joined: Jun 2003
Posts: 439
Likes: 0
From: Burnsville, MN
C-6 Question
Usta,
I agree with you, I'm just suggesting a quick way to triage the tranny or not. If he gets late hard shifts, then we know we have an issue like what you have described. I certainly don't want to have tripticker go pullin the valve body out for what appears to be a sticking valve unless we can rule everything else out. Your suggestion is wonderful in that it reminded me of a necessary step, that of operating with zero vacuum. I don't know if he has a vacuum gauge or all the necessary plumbing required by your more definitive test, but I can be he can lay his hands on a screw to plug the line and do it quick and dirty.
Tripticker,
I expect a status report - you have two people here very interested in a successful outcome :-)
I agree with you, I'm just suggesting a quick way to triage the tranny or not. If he gets late hard shifts, then we know we have an issue like what you have described. I certainly don't want to have tripticker go pullin the valve body out for what appears to be a sticking valve unless we can rule everything else out. Your suggestion is wonderful in that it reminded me of a necessary step, that of operating with zero vacuum. I don't know if he has a vacuum gauge or all the necessary plumbing required by your more definitive test, but I can be he can lay his hands on a screw to plug the line and do it quick and dirty.
Tripticker,
I expect a status report - you have two people here very interested in a successful outcome :-)