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Old 06-18-2024, 01:26 AM
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Default Turbo Hydro 400 Vacuum Adjustment

I had my TH-400 professionally rebuilt with upgraded internals that I provided. I also provided a new torque converter,Trans-Go shift kit and adjustable vacuum module. The car runs well and flashes great when hard accelerating but off-idle feels like it it needs to overcome the weight of the car to "get going". Other TH-400 cars that I have had felt brisk or wanted to almost surge forward when put into gear. This one does not. I know this doesn't sound technical in my description of how the trans performs but it is the best I can describe. Engine vacuum is 13.5-14 at idle.
Is the vacuum module what I need to start with for adjustment?

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Old 06-18-2024, 02:38 AM
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Not a "vacuum module". It is a vacuum modulator.

The modulator controls the shift firmness, and to some extent the rpm needed for the shift points.

If the trans has problems that don't involve shift quality, it's not the modulator.

If you have a sloppy "high stall" torque converter, they're known to reduce or eliminate "creep" at idle, and they'll soften the perceived engagement when going from Park or Neutral into gear.

You paid a "professional" to deal with this. You should have him test-drive the vehicle.

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Old 06-18-2024, 06:18 AM
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You supplied the torque converter so I can see how that conversation is going to go.

What you describe sounds like a loose torque converter maybe one that's not as efficient as it could be.

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Old 06-18-2024, 07:14 AM
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Car weight, gearset ratio, and converter dia please. Loose converter is suspected.

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Old 06-18-2024, 08:00 AM
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All the modulator does is control the firmness of the two shifts, not when the two shifts take place when left in drive to shift on its own.

If the modulator is not hooked up then a TB400 set in drive will not shift out of first gear.

A stock converter locks up at 1800 rpm and the car will creep no matter how hard you stand on the brakes.

As mentioned above it sounds like your chosen converter is too loose for your liking.
It may not lock up until 2400 rpm and this depends on how much torque the motor is making.

Also the less rear gear you have the less low speed reaction to applying throttle you will have.

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Old 06-18-2024, 10:23 AM
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Not to hijack, but my TH400 is full manual shift. Last time driving 5 years ago, I started to notice really hard 1-2 shifts at light to moderate throttle. Let off gas and shift like a manual, OK, shift when WOT OK. Anywhere else feels like the trans almost hits both gears at once. Could that be my modulator???

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Old 06-18-2024, 01:54 PM
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Sounds like a loose converter. I actually like them a little loose, which eliminates the creeping at idle.

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Old 06-18-2024, 06:03 PM
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Next time you have the car out disable the downshift solenoid and drive the car till it reaches high gear, then coast along about 25-30mph. STUFF the throttle to the floor as hard as you can (leave it in "D") and observe the tach, report what happens?

Then stop, hold the brakes as hard as possible and slowly apply throttle. Watch the tach once again and note when the engine overcomes the tires and/or how high you can get the tach to go without the vehicle moving forward, report what happens there as well.......

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Old 06-18-2024, 07:51 PM
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Can do both tests after the rains stops here.
Quote:
Originally Posted by Cliff R View Post
Next time you have the car out disable the downshift solenoid and drive the car till it reaches high gear, then coast along about 25-30mph. STUFF the throttle to the floor as hard as you can (leave it in "D") and observe the tach, report what happens?

Then stop, hold the brakes as hard as possible and slowly apply throttle. Watch the tach once again and note when the engine overcomes the tires and/or how high you can get the tach to go without the vehicle moving forward, report what happens there as well.......

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Old 06-18-2024, 09:24 PM
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Cool. Both of these tests will tell us how efficient the converter is.

Another very good test but more difficult is to do some track testing. 60' time? RPM at the finish line and what was the MPH as you crossed the stripe......

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Old 06-21-2024, 03:00 AM
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Quote:
Originally Posted by steve25 View Post
All the modulator does is control the firmness of the two shifts, not when the two shifts take place when left in drive to shift on its own.

If the modulator is not hooked up then a TB400 set in drive will not shift out of first gear.
I suppose it depends on how the valve body is set-up. "Shift kit" maybe affects this.

A thousand years ago, I had some water in the modulator of a TH400 I'd just rebuilt. My first TH400 rebuild in trade school, but my own vehicle.

As it happened, it was winter. Start up "cold", and the trans would shift out of first at high RPM and exceedingly harsh. At some point, the modulator warmed-up enough to melt the water, and everything worked just great. Until the next morning, when the modulator froze in the no-vacuum position overnight.

Point is, the modulator does influence shift points, in combination with the governor and the valve-body valves 'n' springs.

I don't remember about the 2--3 shift when the modulator froze in the no-vacuum position.

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Old 06-27-2024, 04:25 PM
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In the meantime, can anyone tell me any info on the old converter that was removed? It is dark blue, has 605 stamped on engine side rim and black magic marker ( faint) PER B3 written. No other markings.
Thanks.
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Old 06-27-2024, 04:51 PM
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What diameter is it?

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  #14  
Old 06-27-2024, 08:45 PM
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13 inches outside diameter.
Quote:
Originally Posted by steve25 View Post
What diameter is it?

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Old 06-27-2024, 08:58 PM
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https://www.buffaloengine.com/catalo...rque-converter

Common generic GM3 (B3) 13 converter.

Google is your friend.

Commonly paired with most all rebuilt 3-speed automatic transmissions.

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Old 06-27-2024, 10:10 PM
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My first thought was a loose converter

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Old 06-27-2024, 10:30 PM
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I never thought to research Google to find out the specs of a torque converter even though I personally believe Google is not really my friend. Thank you for the answer.The old converter was in the car when I purchased it. I am going to try Cliff's suggestions regarding road testing the converter when the rain here stops and I can get a dry road day. I am also going to try to video the tests and post if that is possible here.
Quote:
Originally Posted by b-man View Post
https://www.buffaloengine.com/catalo...rque-converter

Common generic GM3 (B3) 13 converter.

Google is your friend.

Commonly paired with most all rebuilt 3-speed automatic transmissions.

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Old 06-27-2024, 10:42 PM
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You can find good information on non-controversial things on Google and I’ll leave it at that, plenty of questions are easily answered with some simple input.

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Old 06-27-2024, 10:42 PM
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I'd put the old converter back in and see if you like it better.

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