4L80E & TH400 Tech.

[clinebarger]

Originally Posted by whitels1

Cost really, I'm getting the TH400/NP205 combo for less than the price it would be for a 4l80E/NP205 Adapter.

Cool, Are you going to tear the TH400 down & rebuild?


Ok, Back to the business at hand.

Separator Plate Hole sizes, We will start with the TH400. These are suggestions. The bigger the feed hole....The quicker & Firmer the shift will be. Clutch clearance affects this as well! A loose clutch stack-up will cause a firmer shift than one that is set-up tight.

2nd Feed Hole, 125" Max.

3rd Feed Hole, 140" is good if your Blocking the 2-3 Accumulator.
If leaving the Accumulator functional, .175" is where I like it.

Before anyone gets their panties in a wad over such a big 3rd feed hole......The plate in the pic is from a '70 Cadillac TH400 that had a factory 6 friction Direct Drum & has a .175" 3rd feed hole stock.

**Note, Removing checkballs will render feed hole sizes useless!

[whitels1]

Originally Posted by clinebarger

Cool, Are you going to tear the TH400 down & rebuild?

Yes, even though it only has 50k miles on it and in good working order, I still feel like it would be beneficial to beef it up now, rather than later. Besides it would make for good video and it's something that I have been wanting to do for a long time.

[clinebarger]

Blocking the 2-3 Accumulator. (TH400)

You will need a 5/16-18 tap & a 5/16" set screw.
Tap it just deep enough for the set screw to seat good.

The red arrow is the accumulator feed hole that needs to be tapped & plugged.

[clinebarger]

4L80E Separator Plate hole sizes. This unit is kinda picky about clutch feed hole sizes & don't need to be as big as a TH400.

If your running a stronger Pressure Regulator spring or a larger Boost valve (Or both)....Be conservative on feed hole sizes.....Mainly 2nd to keep from shocking the Intermediate sprag.

"Stall" Of the converter has a huge effect on shift feel....The Looser the converter...The softer the shifts will feel, Meaning you can run bigger holes.
Using a stock converter....Again, Be Conservative!

2nd Feed Hole, .085" to .125"
3rd Feed Hole, .093 to .150"
4th Feed Hole, .085 to .093"

[clinebarger]

Pressure Regulator & Boost Valve basics, From a Sonnax Tech article.


Raising line pressure is typically done by using a stronger pressure regulator spring, installing a larger boost valve or doing both.

A stronger spring and larger boost valve will both increase pressure, just not in the same way, so it's important to understand the differences before making any changes.

Stronger springs have a "linear" effect on pressure. This means you get the same amount of pressure increase at the low and high ends of the pressure range.

While a stronger pressure regulator spring will raise line pressure, there is a limit to how much you can get away with before troubles surface. A significant pressure increase that tightens upshifts under heavy load can be too much of an increase when shifting into reverse in the garage. This increase also puts extra load on the pump at idle and can result in the TCC clutch dragging due to reduced cooler flow.

Larger boost valves have a "progressive" effect on pressure: they change the rate of pressure increase. Using larger boost valves, it's possible to have a very small pressure increase at the low end of the pressure range and a far greater increase at the high end. This creates an ideal situation: smooth engagements and lower load on the pump at idle, plus a greater increase in pressure as the transmission is worked harder. The significance of changing the rate of pressure increase with larger valves – rather than simply increasing pressure by the same amount with springs – is that higher pressure is created when it is needed most.

[engairuph]

I'm still having a issue

[clinebarger]

Blocking the 3rd gear Accumulator on a 4L80E, Unbolt the 3rd/4th Accumulator housing from the Valve Body. (The Valve body has to be removed)

Remove both Accumulator Pistons, The one without a guide pin is the 3rd gear Accumulator, The Hole near the bottom of the big bore is what needs to be blocked. (arrow).




Using a 5/16-18 tap, Carefully tap the hole deep enough so the Set screw sits below flush, The Hole is at an angle....Try to keep the tap at that angle.




Test fit the set screw so you know it's seating below flush, You can make fun of the Gold Plated set screw if you want, I bought 2 boxes full of them from an Audio install shop that was going out of business.



You can Block the 4th Accumulator if you like (I generally don't unless a high stall converter is being used), It's the exact same method, Just remove the guide pin to tap the hole.

[-TheBandit-]

clinebarger, thank you for the great tech advice!

Originally Posted by clinebarger

Blocking the 2-3 Accumulator. (TH400)

You will need a 5/16-18 tap & a 5/16" set screw.
Tap it just deep enough for the set screw to seat good.

The red arrow is the accumulator feed hole that needs to be tapped & plugged.

When blocking the 2-3 accumulator feed port, should you remove the spring under the accumulator piston?

Originally Posted by clinebarger

3rd Feed Hole, 140" is good if your Blocking the 2-3 Accumulator.
If leaving the Accumulator functional, .175" is where I like it.

Before anyone gets their panties in a wad over such a big 3rd feed hole......The plate in the pic is from a '70 Cadillac TH400 that had a factory 6 friction Direct Drum & has a .175" 3rd feed hole stock.

Regarding blocking the 2-3 accumulator vs. leaving it functional and using a larger 3rd feed hole, do you have a preferred approach? What are the tradeoffs?

[clinebarger]

Originally Posted by -TheBandit-

clinebarger, thank you for the great tech advice!



When blocking the 2-3 accumulator feed port, should you remove the spring under the accumulator piston?



Regarding blocking the 2-3 accumulator vs. leaving it functional and using a larger 3rd feed hole, do you have a preferred approach? What are the tradeoffs?

No need to remove the accumulator spring, Your blocking 3rd gear oil from reaching the accumulator.

Vehicle specifics would help a lot...... HP, Torque, stall speed, gear ratio?

[-TheBandit-]

It's a 70 Nova roughly 3500lbs dynod peak 410rwhp/390ft-lb rwtq. BTE 2,800rpm 10" stall. 3.73so 28" tall tires. It is a street driven car 90% of the time but I want to take it to autocross a few times a year and maybe to the strip a few times too. I'd love to also try road course. It's not the right transmission for that exactly but it will have to do for now. I don't need the transmission upsetting the tires with banging harsh shifts, but firm would be fine.

Thanks for any suggestions.

[picklito]

Originally Posted by clinebarger

Separator Plate Hole sizes, We will start with the TH400. These are suggestions. The bigger the feed hole....The quicker & Firmer the shift will be. Clutch clearance affects this as well! A loose clutch stack-up will cause a firmer shift than one that is set-up tight.

2nd Feed Hole, 125" Max.

1970 TH400: I'm at .125" using a new plate from Superior and all 6 original check balls. I want to go a little firmer... enlarge the hole or start removing check balls?

[clinebarger]

Originally Posted by picklito

1970 TH400: I'm at .125" using a new plate from Superior and all 6 original check balls. I want to go a little firmer... enlarge the hole or start removing check balls?

Do you know what style Direct Drum you have...Roller Clutch or Sprag type???

A Intermediate Roller is quite a bit weaker than a Intermediate Sprag, A '70 model "should" have a Sprag type Drum.

Roller Clutch....NO larger than .125"! If you do.....The risk of Roller Clutch failure is high.

Sprag....You can go out to .140".....With the 2nd Clutch checkball in place & a Active 2nd accumulator.

Do not remove checkballs....The Reverse checkball being an exception when dual feeding the directs.

The checkballs job is to route clutch feed oil through the orifice, If you remove it, Feed oil will freely pass through both the orifice & the hole the checkball is suppose to check. You end up with a effective feed hole size of over .300" or larger.
I have fixed too many broke units with B&M/TCI shift kits (That delete checkballs) to ever recommend doing this on a street transmission.

The ONLY time I omit CB's other than reverse, Is on Reverse Pattern Manual Valve Body (RPMVB) units, And RPMVB with a Trans Brake. However these competition units don't take a standard plate, They only have the Feed holes, The CB holes are eliminated.

Here is a pic of a RPMVB/Trans brake plate to show the huge difference from a standard plate.