Adjust Stock Trans Shift Points
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 1,015
Likes: 15
From: Loxahatchee Florida
Adjust Stock Trans Shift Points
I was wondering if anyone knew how to easily adust the shift points on the original transmission for a 1977 vette. I had the trans rebuilt heavy duty to handle the HP and I had them set the shift points at 4500 rpm WOT to play it safe. It does that perfectly, shifts at 4500 at WOT each gear. Now I want it to shift at 5500 WOT and use some more of the cars potential. Any experienced ideas besides bring it back to the shop? Thanks!
Racer
Joined: Jun 2006
Posts: 316
Likes: 1
From: Southern California
I've only done this once in my 73 thanks to someone showing me. It worked for me.
For a TH400 unplug the vacuum hose at the tip of the modulator. It will spill some fluid so be ready to plug with finger. Insert a small flat blade screw driver and feel for a screw. Make 1/4 turn adjustments in or out to adjust shift points. Adjust a little and try it out, adjust some more as necessary.
For a TH400 unplug the vacuum hose at the tip of the modulator. It will spill some fluid so be ready to plug with finger. Insert a small flat blade screw driver and feel for a screw. Make 1/4 turn adjustments in or out to adjust shift points. Adjust a little and try it out, adjust some more as necessary.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
I've only done this once in my 73 thanks to someone showing me. It worked for me.
For a TH400 unplug the vacuum hose at the tip of the modulator. It will spill some fluid so be ready to plug with finger. Insert a small flat blade screw driver and feel for a screw. Make 1/4 turn adjustments in or out to adjust shift points. Adjust a little and try it out, adjust some more as necessary.
For a TH400 unplug the vacuum hose at the tip of the modulator. It will spill some fluid so be ready to plug with finger. Insert a small flat blade screw driver and feel for a screw. Make 1/4 turn adjustments in or out to adjust shift points. Adjust a little and try it out, adjust some more as necessary.
That would mean the diaphram is busted and you are burning trans fluid faster than you can add it!!!!! And your car will smoke bad.
I don't think the modulator does anything to wide open throttle shifts?
I think its weight in the side of the trans.
The modulator only moves low speed shift points about 5MPH.
If you need more up top just shift manually.
Racer
Joined: Jun 2006
Posts: 316
Likes: 1
From: Southern California
It better not spill any fluid out when you pull the vacuum line!!!!!!!!!!
That would mean the diaphram is busted and you are burning trans fluid faster than you can add it!!!!! And your car will smoke bad.
I don't think the modulator does anything to wide open throttle shifts?
I think its weight in the side of the trans.
The modulator only moves low speed shift points about 5MPH.
If you need more up top just shift manually.
That would mean the diaphram is busted and you are burning trans fluid faster than you can add it!!!!! And your car will smoke bad.
I don't think the modulator does anything to wide open throttle shifts?
I think its weight in the side of the trans.
The modulator only moves low speed shift points about 5MPH.
If you need more up top just shift manually.
What I do remember is a much better shift at a higher RPM. Tire chirp was more pronounced after the change. Maybe there was another hose we disconnected for another adjustment point that leaked fluid.
If this is not the correct procedure, please disregard.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 1,015
Likes: 15
From: Loxahatchee Florida
Thanks for the info everyone! I could just shift manually as suggested but with 3:73 to 1 rear end gearing it comes up fast and there isn't any rev limiter like in newer cars. I'll try the modulator screw first and if that's ineffective I'll rebuild the govenor with different springs. I was being lazy and looking for an easy way to move the shifts up. I just don't have a lot of free time to turn a wrench anymore.
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Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
It's been a while and I only did this once under direction from a friend. But I do remember the fluid and his warning that it would leak some. Don't remember how much my shift points changed and I'm not burning any trans fluids. No smoke.
What I do remember is a much better shift at a higher RPM. Tire chirp was more pronounced after the change. Maybe there was another hose we disconnected for another adjustment point that leaked fluid.
If this is not the correct procedure, please disregard.
What I do remember is a much better shift at a higher RPM. Tire chirp was more pronounced after the change. Maybe there was another hose we disconnected for another adjustment point that leaked fluid.
If this is not the correct procedure, please disregard.
One end of the hose is connected to the intake or carb and is pulling vacuum.
The other end is connected to the outside of the modulator.
In the middle is a diaphram and the innerside is a spring bathed in trans fluid.
If the diphram is wet on the outside where the vacuum hose is, this means the diaphram is torn.
Vacuum will pull that fluid to the carb and burn it.
Now I think your friend meant it will leak fluid if you pull the madulator out of the trans.
Anyway it doesn't matter don't touch the modulator to adjust full throttle shifts.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 1,015
Likes: 15
From: Loxahatchee Florida
So, in your experience, adjusting the modulator won't significantly affect WOT shift points? Adjusting it will affect exactly what aspect of shifting? AND, just so I don't screw up, could you tell me where the governor is located on the transmission? Or a picture? Thanks for your patience answering these questions.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
You shouldn't move the screw in the modulator in or out more than a couple of turns.
If you turn it in say 1 whole turn then when you take off normal it will take longer to shift into secong.
If you screw it out say 1.5 turns and take off normal you will be in third gear before you get across the intersection.
You have to remember when you mash the gas that there is no vacuum pull from the intake to the modulator so it does nothing, thats why the mechanical weights are used.
I think really,you haven't got a problem that bad that you would want to tackle the weights in the side of the trans.
Just learn to manually shift and watch the tach or buy a simple shift lite with plug in modules.
If you turn it in say 1 whole turn then when you take off normal it will take longer to shift into secong.
If you screw it out say 1.5 turns and take off normal you will be in third gear before you get across the intersection.
You have to remember when you mash the gas that there is no vacuum pull from the intake to the modulator so it does nothing, thats why the mechanical weights are used.
I think really,you haven't got a problem that bad that you would want to tackle the weights in the side of the trans.
Just learn to manually shift and watch the tach or buy a simple shift lite with plug in modules.
Melting Slicks
Joined: Oct 2005
Posts: 2,056
Likes: 8
From: Redruth Cornwall
Have no idea apart from changing out the springs in the governor, trial and error from what Ive heard...
Also, the 77 will have a TH350 trans and not a TH400 so it may be different anyway.
Also, the 77 will have a TH350 trans and not a TH400 so it may be different anyway.
Instructor
Joined: May 2006
Posts: 221
Likes: 1
From: Albuquerque New Mexico
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 1,015
Likes: 15
From: Loxahatchee Florida
The final answer!
Thanks for the education. I read the whole article on how to adjust the governor. I am now going to go buy a good shift light. Problem solved.
Thanks to all!
Thanks to all!
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
I have a 77 with a TH350 also. I had the trans rebuilt with shift kit etc. It has a new modulator which is gold color with a red stripe on it. I can tell you for a fact that I increased the full throttle upshift points by removing the vac hose (no leaks) and turning a small screw in the modulator about 1/4 turn. I forget which way, but its easy to experiment.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
I have a 77 with a TH350 also. I had the trans rebuilt with shift kit etc. It has a new modulator which is gold color with a red stripe on it. I can tell you for a fact that I increased the full throttle upshift points by removing the vac hose (no leaks) and turning a small screw in the modulator about 1/4 turn. I forget which way, but its easy to experiment.
Its all in your head
