# Weird shifting between 2nd and 3rd



## Cmeyer9424 (May 5, 2020)

I’ve been driving the car a good bit lately since I finally got it tuned right and I’ve noticed it does a weird shifting thing between 30-40mph. So I’m cruising with my foot on the pedal and if I let off a little it will down shift into 2nd and then when I easy back on the gas, just a bit, it will shift into 3rd. As you can imagine this is rather annoying during city driving. I’ve messed with the vacuum module on the trans and turned it all the way in which made the trans shift at higher rpm but still having the issues of up and down shifting around this speed. 
Thanks for any help!


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## armyadarkness (Dec 7, 2020)

Did I miss what trans you're running? I assume it's a TH400. Are you watching a tach when it down shifts? Or do you just feel it? I'm going though/ went through some shift issues, myself.


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## Cmeyer9424 (May 5, 2020)

Sorry, yes it’s a th400. Currently do not have a tach so just by feel and sound mainly


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## armyadarkness (Dec 7, 2020)

When was the trans rebuilt last? When did you change the filter last? Do you check the fluid regularly? I would make sure that the fluid was full and that the filter/ pickup tube were in place. 

Also, have you verified the kickdown switch operation? Maybe unplug it to take it out of the equation.


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## Cmeyer9424 (May 5, 2020)

Unsure when it was rebuilt or the filter changed. Got it about a year ago and just recently got it to be able to reliably drive. Checked the fluid and it was low so I add some and the problem still was there. 

The car does have a few leaks here and there so I try and keep an eye on all fluid levels. 

When I bout the car the lockdown switch was actually unplugged. Just got it hooked back up and it made a huge difference in the power feeling department


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> Unsure when it was rebuilt or the filter changed. Got it about a year ago and just recently got it to be able to reliably drive. Checked the fluid and it was low so I add some and the problem still was there.
> 
> The car does have a few leaks here and there so I try and keep an eye on all fluid levels.
> 
> When I bout the car the lockdown switch was actually unplugged. Just got it hooked back up and it made a huge difference in the power feeling department


There are a lot of things to discuss, in your post. 

Running an auto trans low, to the point where it only picks up fluid intermittently, could cause a jerking feeling, which could seem like shifting.
The fact that the kickdown switch was unplugged, seems suspect. Yes I'm sure it's helping, but if its operation is erratic, then maybe thats why it was unplugged. I would test it and the kickdown solenoid.
As for leaks, I just put this on. It cost $130 and took an hour to install. I think it adds 2 quarts and it's aluminum, so it dramatically drops temps. More importantly, it's very thick, so if you use Ultra Grey when you install it, you'll cure all off your trans leaks, once and for all.









Summit Racing SME-1001 Summit Racing™ Aluminum Transmission Pans | Summit Racing


Free Shipping - Summit Racing™ Aluminum Transmission Pans with qualifying orders of $99. Shop Automatic Transmission Pans at Summit Racing.




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## Cmeyer9424 (May 5, 2020)

Thanks for the info! The trans was a pint low according to the stick.

How do I check the downshift solenoid? I tested the wire with a test light and when I depress the peddle a good bit the light turns on.


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> Thanks for the info! The trans was a pint low according to the stick.
> 
> How do I check the downshift solenoid? I tested the wire with a test light and when I depress the peddle a good bit the light turns on.


"They say" that if you activate the switch and listen at the pan, that you can hear the solenoid. Personally, I was never able to. But Im curious if in your case, the low fluid was causing a surge, which you interpreted as down shifting. In any event, since you don't know the history of the trans, I think it should be a serious priority for you to drop the pan and change the filter. If it's clogged, missing, has fallen down, etc, it could be a very costly repair. A TH400 may be bullet-proof when right, but they're very unforgiving when they're neglected.

Once that's done, you'll have very cheap peace of mind, and you'll eliminate the fluid level as a culprit. Use Ultra Grey and torq to spec and youll solve your leaks, too.

A shift modulator and solenoid are cheap and easy to swap, so you can always swap them too, but I'd do a search for testing procedures, and see if you have luck there.


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## Cmeyer9424 (May 5, 2020)

I’ll do a filter and fluid change soon and update. Thanks!


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## Cmeyer9424 (May 5, 2020)

armyadarkness said:


> "They say" that if you activate the switch and listen at the pan, that you can hear the solenoid. Personally, I was never able to. But Im curious if in your case, the low fluid was causing a surge, which you interpreted as down shifting. In any event, since you don't know the history of the trans, I think it should be a serious priority for you to drop the pan and change the filter. If it's clogged, missing, has fallen down, etc, it could be a very costly repair. A TH400 may be bullet-proof when right, but they're very unforgiving when they're neglected.
> 
> Once that's done, you'll have very cheap peace of mind, and you'll eliminate the fluid level as a culprit. Use Ultra Grey and torq to spec and youll solve your leaks, too.
> 
> A shift modulator and solenoid are cheap and easy to swap, so you can always swap them too, but I'd do a search for testing procedures, and see if you have luck there.


Should I use the gasket that comes with most filters plus the ultra grey? Or just ultra grey


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> Should I use the gasket that comes with most filters plus the ultra grey? Or just ultra grey


I've done both and have had 100% success, both ways. Clean both surfaces free of gasket material, wipe down with acetone, lacquer thinner, or whatever... apply evenly and torq to 11 foot lbs. 

If you do splurge for the Summit pan, it comes with the Delco filter, extension tube, and gasket, plus it has a drain plug and will run cooler. With that pan, I did not use any gasket.


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## Cmeyer9424 (May 5, 2020)

How much oil should I pick up to replace what’s lost when I drop the pan?


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> How much oil should I pick up to replace what’s lost when I drop the pan?


Stock pan, a gallon, to be safe. It took me six quarts with the Summit aluminum pan.


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## Cmeyer9424 (May 5, 2020)

Got the new filter and gasket in, still doing the weird shift thing. Tried to adjust the vac and if I turn it all the way in it will make a pop sound and keep turning. I adjusted it out half way, well after the popping sound, and it didn’t seem to change the shift point. I have a video I will upload and if you watch the oil pressure gauge you can see when I let off the throttle and get back on it right in 2 and shift to 3 instantly.
Shifting Video


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## armyadarkness (Dec 7, 2020)

Sucks that it didn't fix your issue, but it's good insurance, cheap and quick, glad that's out of the way. Sounds like your modulator isn't doing its thing. I hate to tell you to buy one because it might not be the issue, but theyre cheap and easy to replace, too. I think $35

I'm no trans expert, but I do know what blows them up and a few other basics.


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## Cmeyer9424 (May 5, 2020)

Yeah I was thinking the same thing. At least my trans leak is fixed as well! I took some pics when I had the pan off because it had some writing on it that didn’t look factory. Also, I degreased the trans and found the red strip so I believe it to be the upgraded one.


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## armyadarkness (Dec 7, 2020)

Trans looks nice and clean! Leaks fixed is priceless!!! Did you use ultra grey?


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## Cmeyer9424 (May 5, 2020)

I went with the gasket since it came with the filter. Cant beat the price, $10 for both
Just order a new vacuum modulator. Found one for $15 on Amazon


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## Mine'sa66 (Oct 30, 2019)

I suggest purchasing a new stock vacuum modulator. Verify the vacuum line to the modulator has no leaks, isn't shared with any other device, and is on a manifold vacuum source. If the stock one you purchase is adjustable (it may or may not be), do not adjust it at this time, just install it as is out of the box. Assure your trans fluid level is correct. Check it warm, car running. 

It sounds to me (36 year master tech) like your vacuum modulator is malfunctioning. I'm not surprised by what you say of how you've been adjusting it. 
The course of action I've laid out should be cheap and easy and give a baseline to diagnose what the issue is should a new mod not cure it as there's a host of other issues that could be causing your symptoms.
Vacuum modulators really rarely need adjusting unless you're operating your transmission well outside of typical parameters.
Turning an adjustable one's screw all the way in and all the way out will likely puncture the diaphragm.


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## Cmeyer9424 (May 5, 2020)

Mine'sa66 said:


> I suggest purchasing a new stock vacuum modulator. Verify the vacuum line to the modulator has no leaks, isn't shared with any other device, and is on a manifold vacuum source. If the stock one you purchase is adjustable (it may or may not be), do not adjust it at this time, just install it as is out of the box. Assure your trans fluid level is correct. Check it warm, car running.
> 
> It sounds to me (36 year master tech) like your vacuum modulator is malfunctioning. I'm not surprised by what you say of how you've been adjusting it.
> The course of action I've laid out should be cheap and easy and give a baseline to diagnose what the issue is should a new mod not cure it as there's a host of other issues that could be causing your symptoms.
> ...


Thanks for the advice. From what you mentioned I bet the diaphragm is busted just from the sound it makes. I have one coming in next week and will give an update. It is an adjustable one so I’m glad you said to not adjust it haha


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> Thanks for the advice. From what you mentioned I bet the diaphragm is busted just from the sound it makes. I have one coming in next week and will give an update. It is an adjustable one so I’m glad you said to not adjust it haha


The general consensus is that the adjusting doesn't do a whole lot. My 67 is through 2nd gear, 20 feet off the line.


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## Cmeyer9424 (May 5, 2020)

Got the vacuum module on and it seems have help a bit but it’s still there. Should I try and lower the shift point so that when I let off the throttle it doesn’t come back down into second? It just needs to stay in third rather than coming out and going into second only then to turn right around and shift back into third.


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## Mine'sa66 (Oct 30, 2019)

Cmeyer9424 said:


> Got the vacuum module on and it seems have help a bit but it’s still there. Should I try and lower the shift point so that when I let off the throttle it doesn’t come back down into second? It just needs to stay in third rather than coming out and going into second only then to turn right around and shift back into third.


The issue is not likely the modulator. Have you verified your transmission kickdown is properly adjusted?
Letting off the throttle should cause the trans to freewheel.
If letting off the throttle always causes a downshift, then something is shifting it.


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## Cmeyer9424 (May 5, 2020)

Mine'sa66 said:


> The issue is not likely the modulator. Have you verified your transmission kickdown is properly adjusted?
> Letting off the throttle should cause the trans to freewheel.
> If letting off the throttle always causes a downshift, then something is shifting it.


Is the kickdown different from the downshift module on the pedal? Because if the kickdown is the bar connected to the neutral safety switch it’s not hooked up at all. I believe the previous owner broke or disconnected it and lost the parts.


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## Mine'sa66 (Oct 30, 2019)

Cmeyer9424 said:


> Is the kickdown different from the downshift module on the pedal? Because if the kickdown is the bar connected to the neutral safety switch it’s not hooked up at all. I believe the previous owner broke or disconnected it and lost the parts.


Yes, the passing gear kickdown on the TH400 is on the pedal. It works in conjunction with the solenoid on the transmission.
Something is causing your trans to downshift when it shouldn't. There are only so many things that can cause that.
Downshift solenoid is a very common one.


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## Cmeyer9424 (May 5, 2020)

Well I installed an aftermarket pedal since mine broke and I made the factory downshift solenoid bracket work with it. Maybe it’s too close but I really have to put it to the floor to make it actually downshift. Could the solenoid itself be bad? Is there a way to test it


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## armyadarkness (Dec 7, 2020)

Yes, the solenoid could be bad. I posted about it in the begging of this thread. It's easy to test if it's working, however, with your condition, it sounds like it's working... even more than it should, which would mean that the wire harness had a short.that would cause it to activate. Check the harness between the pedal switch and the solenoid.

And, what were you saying about your gas pedal? You went aftermarket and rigged a switch?


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> Summit Racing SME-1001 Summit Racing™ Aluminum Transmission Pans | Summit Racing
> 
> 
> Free Shipping - Summit Racing™ Aluminum Transmission Pans with qualifying orders of $99. Shop Automatic Transmission Pans at Summit Racing.
> ...


Does the original shift cable mount fit and clear with that pan? Did you have to tweak anything? 

Bear


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> Does the original shift cable mount fit and clear with that pan? Did you have to tweak anything?
> 
> Bear


Everything was a direct swap, and they even include new bolts, a gasket, and a Delco Filter and extension tube. I couldnt be happier... Especially since the new pan flange is about 1/4" thick, so using no gasket at all and permatex ultra grey, I have no leaks! The whole job took less than an hour, and now it has more capacity, a heat sink, and a drain plug.


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## Cmeyer9424 (May 5, 2020)

armyadarkness said:


> Yes, the solenoid could be bad. I posted about it in the begging of this thread. It's easy to test if it's working, however, with your condition, it sounds like it's working... even more than it should, which would mean that the wire harness had a short.that would cause it to activate. Check the harness between the pedal switch and the solenoid.
> 
> And, what were you saying about your gas pedal? You went aftermarket and rigged a switch?


Yes I got an aftermarket adjustable pedal since mine broke. The kickdown switch mounts on its own bracket that used to work with the old pedal. I just drilled separate holes to mount the kickdown bracket and made it work with the new pedal.


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## armyadarkness (Dec 7, 2020)

Cmeyer9424 said:


> Yes I got an aftermarket adjustable pedal since mine broke. The kickdown switch mounts on its own bracket that used to work with the old pedal. I just drilled separate holes to mount the kickdown bracket and made it work with the new pedal.


Well it definitely sounds like your kicking down, when you shouldnt be. I would unplug the kickdown solenoid, on the drivers side, and then see if it still does it. That should quickly define this issue.


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## Dave 68 (Nov 18, 2018)

I'm just wondering if the vacuum line is plugged into a ported instead of manifold source. It seems like that would create this type of issue.


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