Upgrading the 3 speed automatic transmission

My idle is about 1200-1500 RPM when in neutral or park then drops (crashes) to 750 RPM or so when shifted into gear. I hate the loud "clank" and jerk when shifted from park to drive. Does everybody's do this? The shop said it would stall out when put in gear if the idle is set at 750 RPM in park.

I also hate how it takes almost full throttle to have the trans shift from third to second and then too it's a lurch and a huge change in engine speed but not much more acceleration. I had a mid-90's V-6 Chevy Malibu out pull me coming on the freeway on ramp this afternoon, totally embarrassing....

Is the transmission on the manual a torque tube also? As I understand it, the torque tube basically transmits the drive power back up the tube to the engine/trans mounts instead of a "regular" transmission transmitting the drive thru the rear suspension. If so, what are the differences between the two models suspensions? What I'm getting to is to get rid of the torque tube. This would allow a number of other transmission combinations (a ZF24 comes to mind, awesome trans!) if we could eliminate the TT via some sort of suspension changes like in the manual car, if this is the case. The only other "conventional" car I know of with a TT is a Corvette. Anybody loo into that equipment?

 

Your idle is too high which will make it harsh to engage. Mine idles at 1000 RPM and doesn't do that and the kick down is controlled by a micro-switch by the throttle linkage on the engine which is adjustable. They all have torque tubes and if you eliminated the tube I agree a swap would be much easier. The cost and work involved in doing that is a hurdle but so is killing resale value, in my opinion it becomes a double negative.

 

To eliminate the torque tube you’d have to fab a crossmember at the tail end of the transmission to have a mounting point for a transmission mount to stabilize the transmission and engine. You’d also have to have a similar set up for the differential.

 

Fix your idle first, seems like you have a major air leak. Idle should be around 900RPM.

 

Finally have my car back with new rebuilt transmission and a new Hughes GM25 torque converter. Ater a week of driving, the wait was well worth it. Low end acceleration is vastly improved. Not sluggish at all and feels very responsive. The tranny was adjusted for tighter shifting and the shifting is firm but not "banging" My idle was low in the past at 500-600 rpms and now is where it should be at 1000 rpms. Comes off the line very well and the torque curve appears to be paired better with the higher stall Torque Converter. In retrospect, really no need now for changing the gearing, the higher stall torque converter changed everything.

 

Fantastic news. What stall speed did they end up using?

You should do some 0-60 pulls to get a good comparison.

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This is it.

How did you deal with the bolts? 3 vs 6? Image Unavailable, Please Login

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Go to your favorite machinist and ask him to drill three (properly centered) holes in the flexplate. My guy did it for free.

No point in being restricted on the converter sizes due to odd bolt pattern.

 

Correct. The flexplate needs to be redrilled to accommodate the smaller diameter of the Torque Converter about 10 1/2 inches compared to the 12 inches on the original. Typically, as stall speeds rise, requires a smaller diameter torque converter. the shipping weight for the new Hughes TC was 25 pounds versus the original at 36 pounds.

 

The 10 lbs weight difference alone is enough to make a difference.

 

So 0-60 time is 15 seconds now instead of 16? Sorry I couldn't help myself. I'll do a converter swap in the future but skip the gear change.

 

Ha Ha Ha The last time I measured mine with my wrist watch stop watch and my GPS it was between 8.8 and 9. That's when I sent a transmission to Kilgore in March (lower gear ratio, torque converter). Don't have it back yet. I dig these cars at highway speeds. I think when Ferrari set these cars up they wanted off idle 500 rpm starts in first (easy stop and go driving) and they wanted the shift to second under acceleration to match max torque. They achieved both goals. I will report back when I get my transmission back.

 

I have had my transmission for a bit, but work and family have taken priority. This is from Kilgore with 2.75/1.57/1 gearing and an L88 valve body. He provided a 2200 rpm stall converter. In the process of sealing the backend of the motor with the transmission out. Waiting on a bearing and a seal for the Ferrari tail shaft. Will let you know how it goes. Should have it together in a couple of weeks. John said that I would feel more improvement from the torque converter than the gearing.
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I agree about the Torque Converter making a larger difference than the gearing. I used a 2500 RPM TC and the difference is remarkable. A better match for the torque curve of the V12. A new valve shifter made the shifts tighter but not a sharp banging. A good tranny shop will know how to adjust the TH400 to make for very smooth shifts.

 

Did you measure any acceleration runs?

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No I didn't, but what is apparent is how much quicker it is off the line. That's where the old TC and tranny were sluggish.

 

Could you do a 0-60 mp/h test?

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