Upgrading the 3 speed automatic transmission

Got to agree that the wording does not help...

At idle if you brake hard, you do have 100% slippage, whereas if you just release the brake, the converter will slip less. You will experience the same phenomenon if you push the accelerator pedal to the floor, the converter will slip less if the wheels aren't locked.

The quoted stall is the maximum amount of slippage you would get when the wheels are locked and the engine outputs its maximum torque. In real driving conditions our torque converter do slip less than the maximum quoted stall: 1) our wheels are not locked 2) we are not always on the rpm range that delivers maximum torque. So in driving condition the amount of slippage we will see is roughly going to be 600rpm below the quoted stall speed.

The comment I made on the converter size was based on my friend Francisco's experience: our engines do have lots of torque at high rpm, and his small converters kept slipping at high rpm, which he did not like.

Aluminium drums are heavier than steel or titanium. Steel being much stronger than aluminium, less material is required, i.e a lighter part can be made out of steel. If I remember correctly Kilgore 4 pounds drums are steel. As a general rule I would borrow parts from a 4L80 rather than cheaply made after-market parts.

The 10inch 2400 converter looks good to me, the dual bolt pattern, may fit without new holes, but from memory our stock converters do have 6 bolts, not 3. In any case it's just a mater of drilling three holes on the flex-plate (see photo I previously posted)

(new holes on the inner radius)

 

Update: I had a long chat with Kilgore just now, very pleasant fellow and took his time to explain everything.

He will be sending me a "list" of the items he recommends.

What I do not know is the difference between the 400 and 412 torque converter, he said the 400 converter is terrible, and not only due to the stall speed, but it may be that the 412 already has some improvements.

He suggests to use a 9 inch TH350 torque converter, change the gear as well (to 2.75/1.57 ) and the valve body to "tighten up" the shifts.

With regards to light weight direct and forward drums, he said it is only required if one does many high rpm "launches".

 

Good news.

It will be interesting to see what converters he recommends.

I have a B&M shift kit so that would cover the valve body upgrade. I'm just about to order one.

It's no a "racer" so I will probably keep the gearing, albeit 2,75 may be a genuine improvement.

 

He said to "not waste on the shift kit improvers", explaining that the actual valve body needs to be replaced.

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I don't believe that my kit contains the actual valve body but only the steel valve plate, new valves, new springs and aluminum accumulator pistons (I think they are plastic now). I have had this kit for years so that is sunk cost .

A Raybestos full renovation kit is ordered (there is a lot of stuff in that kit) and now I'd love to hear about what converter he recommends. Or if the one (10" TCI) I found is good enough.

There were some suggested mods to the valve body in the kit manual but I won't take it apart myself so the gearbox specialist have to decide if the actual valve body need to be changed.

My shifter is a bit loose (may be the connector) and there is no engine brake on second gear to it is absolutely time to have it refurbished.

 

I have been having a hoot with this thread. If we can reduce the first gear ratio by 10% to 51.8MPH at 6000 rpm, 2nd down by 5.6% from 51.8MPH to 60 MPH. Would (after I ran my rates and it was ugly) the originally stated 0-60 of 8.5 seconds improve to 7.696 seconds? This assumes speed is linear with RPM. If this is correct, what affect would the stall converter have?

 

Not sure if the increase in acceleration can be calculated as such.

The 400 owners manual states the speed at 6400 RPM in each gear, here again it is very obvious that 1st and 2nd are extremely "tall".

In 1st gear, the automatic reaches 94(!) km/h vs 72.5 km/h for the manual.

2nd gear is even more ridiculous, 157 vs 110.

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Does anyone know what size torque converter we have on the 400 or 412? It is by chance the "big" 12 inch one?

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I am getting motivated in doing a 700R4 swap.

Des anyone know if the bolt pattern is the same?

The tail side does not concern me, torque tube and shaft can be made.



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Here are the measurement comparisons. Image Unavailable, Please Login

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Bolt pattern does not matter as there is already an adapter plate between gearbox and engine (which is made to match the manual gearbox, not the auto).

There is a specific tail in our gearboxes, this tail incorporates the speedo cable.

This tail also incorporates the mounting for the "cross member" (that's not a cross member but you get the idea).

The problem with the 400r4 is that it is not meant to sustain the torsional forces induced by the rigid setup, so unless you get a custom made gearbox housing, it will probably crack under stress. For the record, my original gearbox had been so stressed that during rebuild it could not sustain the pressure test and fell apart...

 

Thank you Raemin, as usually very helpful information.

The TH700 then renamed 4L60 was rated for 6000 lbs, hence the name.

It used on very heavy GMC/GM pick ups, with engines that had much more torque than ours could ever make.

Why do you think our cars need so much strength at the transmission?

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It's not the torque but the tortional stress that is applied to the case itself: remember that the rear axle the torque tube housing the gearbox and the engine do constitute a rigid setup, with the gearbox just in the midle. Guess which is going to give-up when upshifting from 1st to 2nd at full rpm.

Regular muscle cars do usally have some flexibility between the gearbox tail and the rear axle (a shaft with a "dogbone" allows the gearbox to move).

Even if you beef-up the gear-train, it's the case that will break. If it's got to be a 4l60 you should use a strong case.

A 4l80 would be probably be more appropriate. But all in all an ultralight switch pitch 3l80 would make more sense.

 

Good day Raemin,

I am not overly familiar with the 400 Auto setup and the connection to the diff and, so I hope you will forgive my question if you answered it previously. What was done to the TH400 and/or its tail housing area to allow for its use with a torque tube and diff? Did they simply create a custom and stronger end tail with the supports, etc? Just curious, as it is not obvious from the parts diagrams.

Cheers,

Sam

 

The TH400 is one of the stronger stock case one can get. In order to adapt it to the engine (which has a bolt pattern for the manual transmission) a thick (~3cm) alloy mounting plate is made which allows to bolt a chevy style gearbox. In order to fit the converter a thinner flywheel is used together with a flex plate with bolt patterns for the converter.

In order to fit the gearbox to the torque tube a specific tail end is bolted to the tail of the TH400. Tthis is this tail that has a specific bolt pattern that allows to attach the torque tube. This tail is probably only suitable to the TH400 (not 100% sure though).

That's all from memory as my conversion was made in 2010~2012... I had a recent look at it though as we changed the converter, but I did not disassembled the torque tube recently.

 

Raemin, did you ever measure the performance of your car after the modifications to the transmission? 0-100km for example?

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Good day Raemin,

Excellent, thank you!

Cheers,

Sam

 

These are no race-cars, even with the manual trans... Not sure there is a significant performance boost.

The cars downshifts and upshifts when required, and the engine revs higher. At least I know it will not shift in the worst possible moment and the engine music is not spoiled. This really allows for spirited driving, and I personnaly drive it much harder than my brother's 365 (I am a bad driver).

Feels like a proper Ferrari...

 

I had a 1992 5.0 Mustang sedan (the lightest version of that car) and I’d say my 365 is as quick as the Mustang was up to around 100. Above 100 the Ferrari would pull away from the Mustang.

 

Yes, at least on paper there seem to be a huge difference in 0-100 times, which is most certainly only attained with dumping the clutch at 5000rpm...something no one would do. In this regard, I think the auto cars can be "pushed" more comfortably.

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It seems there are upgraded cases on the 700R4, the "K" cases. Image Unavailable, Please Login Image Unavailable, Please Login

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The "K cases" are for 4WD applications, so presumably stronger, but with a different output. In any "case", you would have to fabricate a new tail housing and a longer torque tube.

There are some TH400 beefed-up case (see REID racing), but I am not aware of such upgrades for the 700R4.

 

Yes, the tail would need to be adapted anyways. So the "K" casing seems the way to go.

Comparing the manual transmission and the TH400 to the 700R4, it seems just a stout.

The gear ratios on the 700 would be perfect for the 400/412.

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The stock gear ratio is plain wrong even with a "manual" rear axle. 1st way too short, 2nd too long. The Norwood 400 had such a transmission and it was sluggish despite the twin turbos... So you need custom ratios.

A 4l80 with "manual" rear axle would be a perfect match (ratio wise), sadly it is longer than the 3l80 and also wider (in order to accomodate all the electronics). Would probably be an easier swap though (it's probably easier to shorten the torque tube rather than extend it!).

 

I have been looking more into the 700R4, and there are many that come "upgraded" and guaranteed to 500-600 horse power.

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