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66 Chevelle SS396 & 66 Chevelle 327 Convertible.
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Discussion Starter · #1 ·
This is on a 2004R rebuilt about 500 miles ago. With BowTie Overdrive EZ TV cable . Lokar shift linkage on a 66 chevelle. Lockup in 4th gear only. Power from fuse box to a brake switch to a vacuum switch and then to the transmission.
With power disconnected, trans works fine and engine runs great. The problem happens only after trans has shifted into OD on light to moderated acceleration car misses and rpm drop, then back to normal, then miss again and so on until I get over around 50 mph. Converter is locked. Also this does not happen at WOT.

Adjusting the vacuum switch up or down when lockup is suppose to happen either up or down doesn’t solve the problem. Switch is suppose to be adjustable from approx12* to 20* of vacuum. Mild cam. I was thinking of running the car with power directly to the trans. If it acts as it should then it must have something to do with vacuum switch or engine vacuum. If problem still exits I would think it has something to due with the converter or the trans rebuild. Any thoughts on this? Or has anyone else had this problem?
 

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Your test of manually controlling the lockup is a valid one. But if it's only happening in 4th lockup, under 45 mph, that's low RPM/moderate load, then I think the issue is with your tune. Try knocking a few degrees back on the timing, even if temporarily just for testing. You might need to do some limiting on your vacuum advance.

-Dave
 

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My motor did not like shifting into fourth then
Immediately engaging the lock up at about 45 mph. Lugged & chugged. Added a simple manual on/off switch to the control circuit. Now typically engage the lock up above 55 mph. Much happier.
 

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I'm guessing the problem has to do with the vacuum switch. I don't use one on mine and let the 4th gear pressure switch lock up the converter. Mine locks immediately after shifting to 4th gear at about 40 or so mph. Not a problem with my stock cam and Q jet carb but if you want a higher rpm, install an on off switch like 68fbird did. I wouldn't run it too much in 4th without lockup though or (I've heard) the trans can overheat. Maybe some trans pros can elaborate on that. I got that info from someone that was a GM dealer service mgr years ago.
 

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I’m running a big B&M stacked plate cooler bypassing the radiator cooler. Trans temp rarely exceeds 160 degrees unless I’m repeatedly thrashing on the car from stop lights. Will run all day at 60 mph without exceeding 160 degrees when not locked up. Once converter is locked up, temp drops 25-30 degrees when cruising down the highway.
 

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66 Chevelle SS396 & 66 Chevelle 327 Convertible.
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Discussion Starter · #6 ·
Thanks guys, I really don’t know much about this system. One question Von, are you saying that if trans is not locked up the trans will run hotter, so I should make sure the trans locks up? I messed with the switch a little last night. The adjustment is suppose to be from 20* to 12* according to the instructions. There are 9 full rotations . I turned in all the way, thinking that will lockup at 20*. When cruising on a level road it seems to lockup and I see the rpm drop around 200 rpm. With the slightest addition of more throttle I can feel the converter unlock and see the rpm go up. I first thought this was an carb or ignition problem. I plan to turn the adjustment back 1 turn and see how that works. Then 1 more turn and so on. If that doesn’t get me to a good feeling, the addition of a on/off switch sounds like a good idea no matter what. A friend wants to test the switch, that will likely happen this winter.
 

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I'm saying it might -- I'm basing that on my experience with a mild 350 and a 700r4 lockup. I had a Holley Sniper on there controlling ignition and the default ignition map had a setting of 40 in certain areas which was too much, and I had the same kind of symptoms you describe. I lowered the timing in some of those areas and it helped. Granted, it was a lot easier to do that on EFI. But that is the experience I'm basing my comment/suggestion on.

-Dave
 

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What is happening is that your car doesn't like a locked up drivetrain at low rpms like this.

Think of it as if you had a manual transmission, in the highest gear, at low rpms, and you just hit the gas. It will buck and fuss with you, until you downshift.

What you have done is created the same scenario by locking the converter. The reason that it gets better then worse then better then worse is because, after you lock up the converter with the vacuum switch, you hit the gas, and it bucks/misses, then vacuum drops, the converter unlocks, allows the engine to rev up into a more friendly powerband and it starts to accelerate. Then it builds vacuum up again, the converter locks, and knocks you down into your bucking/missing area of your powerband again.

When you have it set to lock at the highest vacuum setting possible, you are just blipping the throttle, dropping just a little below the on point, it unlocks, and gets you out of it. If you lower the vacuum further, you will probably make the problem worse, not better, as it will take more throttle to get the converter to unlock, which in turn will cause more bucking/missing until it unlocks.

What you are describing driving on a smooth, level road, seeing it lockup and RPM drop, and then slightest touch of throttle causes to unlock and RPM to go up is behaving exactly as it should if you have the vacuum switch set really high. If you lower it, you will be able to give it more throttle before it unlocks again, but it seems like your car doesn't like to run in that powerband with a locked drivetrain, so you will probably increase your bucking/missing if you do that.

Unfortunately, I don't have a good solution to your catch-22 situation you are in. I run all my 2004r transmissions setup for non-lockup and have no issues with any overheating or anything. But, you can't just run them non-locked up all the time (so I've been told) - you have to make some mods and run a converter with no clutch in it.
 

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Thanks guys, I really don’t know much about this system. One question Von, are you saying that if trans is not locked up the trans will run hotter, so I should make sure the trans locks up? I messed with the switch a little last night. The adjustment is suppose to be from 20* to 12* according to the instructions. There are 9 full rotations . I turned in all the way, thinking that will lockup at 20*. When cruising on a level road it seems to lockup and I see the rpm drop around 200 rpm. With the slightest addition of more throttle I can feel the converter unlock and see the rpm go up. I first thought this was an carb or ignition problem. I plan to turn the adjustment back 1 turn and see how that works. Then 1 more turn and so on. If that doesn’t get me to a good feeling, the addition of a on/off switch sounds like a good idea no matter what. A friend wants to test the switch, that will likely happen this winter.
See post #5.
 

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Discussion Starter · #11 · (Edited)
Thanks again everyone. This I the cam kit I put in if that means anything. Cam K-Kit CS RF-V262HR12. With my limited experience I am not sure if I accurately explain the issue. I friend is going to test the switch to see if it is operating as it should. Unlikely but you never know. I have. To drive it a bit more to look at the rpm’s when it’s happening.

as I understand the switch, it’s suppose to allow lockup at say 18” of vacuum, then if the vacuum drops to say 14” of vacuum it will unlock. Correct? Seems like lockup happens, then about 1/2 a second later it unlocks, then happens 2-5 more times. Mostly occurring around 18000 to 2000 rpm. Again, never happens when no power to switch.
 

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Added a simple manual on/off switch to the control circuit. Now typically engage the lock up above 55 mph.
This is exactly the way I have my 2004R lock-up wired (manual switch). My trans shifts into 4th gear at about 45 mph... but I do not engage the lock-up until I am above 55-60 mph. I also run a very large "stacked plate" trans cooler.

If you like having the lock-up functions controlled by the brake and vacuum switches and don't want to have to remember to manual lock-up the converter above a certain speed (and manually disengage when you drop below a certain speed), you could add a B&M controller to your existing set up that would let you choose the mph that the lock-up function on the converter automatically engages/disengages.
 

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I had similar problems with my 700R4. It would hunt between locked and unlocked. Also it would lock as soon as it shifted to 4th gear, and at to low of RPM.
I had 3.31 gears and it would shift to 4th at 38 mph in town and hunt. I tried different vacuum switches and could never get it just right. So I put a switch on my shifter tee handle that is actually a line lock button so I could control the lock up manually through a latching relay. But to stop the hunting, I put a time delay switch in the circuit.
See the file I have attached.
If you have any questions I'll try to answer, but it's been a few years since I had that 68.
Schematic Font Slope Parallel Rectangle
 

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Discussion Starter · #15 ·
Sounds like I have the same exact problem. I have a column shifter. I think a switch under the dash would work for me. And the time delay sounds interesting. Did you leave those low shift points. I have been trying to get mine to shift around 2400,:2400, and 2400. I have a 3:55 speeds would be around 18, 36, and 52 mph.

I just have a single terminal at the trans for 4th gear lock up only. So would my wiring be different.
 

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Sounds like I have the same exact problem. I have a column shifter. I think a switch under the dash would work for me.
Yes a switch anywhere will work.

And the time delay sounds interesting. Did you leave those low shift points. I have been trying to get mine to shift around 2400,:2400, and 2400. I have a 3:55 speeds would be around 18, 36, and 52 mph.
My trans would be in 4th gear TCC locked at 38mph when taking off as soft as I could. and of course you know what that would do. I had a 3.31 gear 700R4 and a ZZ454.

I just have a single terminal at the trans for 4th gear lock up only. So would my wiring be different.
The wiring would be different. I mostly posted that drawing for ideas. Many ways to skin a kat.

Quite frankly a toggle switch that disables the TCC till you get up to 45-50MPH is much more simple. If you have a trans cooler there is no problem with overhearting.
 
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