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Old 05-11-2022, 03:37 PM
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Default Transmission experts??

Any transmission experts here? I'm having issues with my new trans. Just finished reinstalling it.... 2nd time...The new issue is no gear braking when I down shift from 3rd to 2nd. It does when going down to 1st though. I called the builder and he doesn't know why. He said he used 4L80 2nd gear bands so it should be stronger than before. Are the bands interchangeable from a 4L80 to a TH400?
It seems to shift under power like it should but
I couldn't make a full hit anywhere around here my trans has never in the past had the no gear braking option.

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Old 05-11-2022, 05:10 PM
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It's most likely going to be related to the apply pin and servo. This assumes the seal on the servo is there and the pin is engaging the strut on the band plus the band effectively anchored onto the pin in the case.

On the TH400 there is a half moon clip that slides on the pin to so the servo can apply force to the pin to engage the band. Not really a good set-up as a built in shoulder on the pin is a far better idea. The clip can slide off during assembly leaving the servo inoperative.

If you have my TH400 book the parts and order of assembly are on page 105........

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Old 05-11-2022, 06:38 PM
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Cliff, would what you are saying allow it to shift into 2nd gear like it should but not "down shift " to 2nd? Admittedly I only assume it will shift under full throttle. Around town I could not make a full power hit. I just ran it up in 2nd pretty hard to about 5500 and shift to 3rd. It seemed pretty tight, but that was far from a full on drag pass

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Old 05-11-2022, 06:41 PM
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What kind of valve body is in there?
I had a manual valve body that had no 2 gear braking.
(was for racing)



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Old 05-11-2022, 07:01 PM
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Turbo Action forward pattern manual valve body. Same one I have had for many years. It's always had the gear braking when I down shift.
I thought about that and asked the guy if he had to change the valve body when I took it back to him the first time after the rebuild.

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Old 05-11-2022, 07:13 PM
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"Cliff, would what you are saying allow it to shift into 2nd gear like it should but not "down shift " to 2nd?"

Without the band apply you loose engine braking.

If it's a "manual" valve body you should be able to select which gear it will be in, so "normal" upshifts just no engine braking if you let off while in 2nd gear.......

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Old 05-11-2022, 08:00 PM
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Check this post out for no engine braking in second gear on a recently rebuilt transmission:

https://www.dieselplace.com/threads/...-brake.986067/

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Old 05-11-2022, 08:03 PM
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Quote:
Originally Posted by Cliff R View Post
"Cliff, would what you are saying allow it to shift into 2nd gear like it should but not "down shift " to 2nd?"

Without the band apply you loose engine braking.

If it's a "manual" valve body you should be able to select which gear it will be in, so "normal" upshifts just no engine braking if you let off while in 2nd gear.......
Thanks Cliff. I will see what my builder has to say.

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Old 06-10-2022, 08:08 PM
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Update...or lack there of .. I pulled the car back from the transmission shop. They have had it for 2 weeks and out of the car. I drove it 2 times after they thought it was fixed. Still the same thing. They wanted to just start replacing parts until it's fixed. Started with torque converter then said it's the valve body itself. So I gave up on them. I bought Cliff's book. And am going to tackle this myself now. Also the shop said they used a 4L80 band as an upgrade but when I asked them if they changed the pin to a longer pin he said no. They just shimmed the existing one. So I will check that out and the valve body gasket.

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Old 06-10-2022, 10:37 PM
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Assuming the Band is properly set on the Case pin (ground), then the Apply pin circuit is suspect eh.

Drop pan, and Valvebody, and inspect the 2-3/3-2 piston. Bored yet. Then just plain do this modification;

In the GM Automatic Valvebody: Carefully remove E-clip (C-clip), remove piston, toss the "valvespring", flip piston and reinstall E-clip (C-clip) so the VB piston basically doesn't Accum (move up nor down) anymore. A new seal ring might be nice if you have one, but rarely needed.

In the Case: inspect the Apply puck, seal ring, apply pin, spring and case bore. Bore should appear like perfect. A new seal ring might be needed, and reinstall that assy like stock.

Reinstall Automatic VB sep plate using only the 3 checkballs the run straight from front to rear.

See if it plays a lot better, or even fixed, but may still have the same problem due to something else undiscovered.

Well assumes you are willing to toss the Manual VB in the creek, and use the GM VB with the Gov, and Vac Modulator.


Last edited by Half-Inch Stud; 06-10-2022 at 10:53 PM.
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Old 06-10-2022, 10:49 PM
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I have same Turbo Action manual valve body in mine. Trans was rebuilt many yrs ago with hd best parts. I dont think I have problem with braking in 2nd gear,I'll have to fire car up and really check though.

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Old 06-11-2022, 07:07 AM
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I'm not quite understanding the "shimming" the band part. The 4L80E band requires a pin nearly 1/4" longer to effectively apply it. If you are wanting the band to work for engine braking might be best to go back to the TH400 band and TH400 apply pin or remove whatever shimming they did to try to make it work.

To check the band apply you can simply push the piston down to make sure it applies the band before it bottoms out in the case, it's not fussy and never a problem area in the TH400.

Many full manual and TB VB's don't use the band due to possible binding on the release.......Cliff

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Old 06-11-2022, 08:07 AM
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Quote:
Originally Posted by Cliff R View Post
I'm not quite understanding the "shimming" the band part. The 4L80E band requires a pin nearly 1/4" longer to effectively apply it. If you are wanting the band to work for engine braking might be best to go back to the TH400 band and TH400 apply pin or remove whatever shimming they did to try to make it work.

To check the band apply you can simply push the piston down to make sure it applies the band before it bottoms out in the case, it's not fussy and never a problem area in the TH400.

Many full manual and TB VB's don't use the band due to possible binding on the release.......Cliff
I may go back to the TH400 band, but I really don't feel the rebuilder did anything to the pin. I think he told me he shimmed it because I surprised him with the question. This valve body has been in my transmission for many years and the engine braking has always worked. I'm really fine with it not working, but am concerned something is not right and will fail prematurely because of whatever is going on.

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Old 06-11-2022, 09:35 AM
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Scott, Can you post your valve body model or part number. Turbo Action forward pattern manual valve body. Is that these guys? https://www.turboaction.com/vbxa.htm

https://www.turboaction.com/24141%203-06.pdf

Reason I ask is that I was under the impression that when you go manual valve body you loose engine breaking. They also tell you not to shift out of 3rd gear till pretty much stopped.

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Old 06-11-2022, 09:56 AM
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Going by memory (because I don't have them in front of me) the apply pin is apprx .200" longer for the 4L80E. IF they used the TH400 pin and 4L80E band the piston will bottom out before it effectively applies the band.

As mentioned it's not a "fussy" area with the TH400 and I can't ever remember having to do anything to the piston or pin in a TH400 build other than push the piston down to make sure it applied the band before it bottomed out .......

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Old 06-11-2022, 11:57 AM
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Quote:
Originally Posted by chuckies76ta View Post
Scott, Can you post your valve body model or part number. Turbo Action forward pattern manual valve body. Is that these guys? https://www.turboaction.com/vbxa.htm

https://www.turboaction.com/24141%203-06.pdf

Reason I ask is that I was under the impression that when you go manual valve body you loose engine breaking. They also tell you not to shift out of 3rd gear till pretty much stopped.
I'll have to wait to get the pan off to see. I bought it so long ago I don't have a clue. But it has always had the gear braking in 2nd and 1st previously. The rebuild started because it broke the sprag in the trans. I will hopefully get the car on my lift this week and start the dissembly process.

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Old 06-11-2022, 12:42 PM
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Did the sprag "break", roll-over, or push the retaining ring off and come loose? Was it a smooth drum and 34 element sprag set-up?......

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Old 06-11-2022, 02:48 PM
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The sprag rolled over. It was a 34 element sprag. I don't know if it was a smooth drum. Or is that the only way a 34 element sprag is used?

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Old 06-11-2022, 03:36 PM
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Quote:
Originally Posted by Scott Stoneburg View Post
The sprag rolled over. It was a 34 element sprag. I don't know if it was a smooth drum. Or is that the only way a 34 element sprag is used?

Yes it is the smooth drum for the 34 element sprag. Get yourself a 4L80E drum and install an after market piston so you can add additional steels and frictions. Check the 34 element retainer plate on the drum and make sure the tabs are new looking. They sometimes are chewed up. I install the spiral snap ring on the drum to hole the retaining plate Cliff book page 77. I also set the drum up for dual feed.



Can I ask you Scott how you were doing your burn outs at the track?

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68 Firebird. IA2 block, 505 cu in, E-head, Solid roller 3650 weight. Reid TH400 4:11 gear. 29" slick.
Best so far 10.12@133 mph. 1.43 60 ft.
76 Trans am, TKX .81 o/d, 3.73 Moser rearend,
468 with KRE D-ports, Doug headers, 3" Exh.
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Old 06-11-2022, 03:58 PM
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Something else you could do before tearing your transmission apart is take a pressure reading on the Tranny see where it's at. The port is on driver side by shifter. Tells you what the pump is putting out.

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68 Firebird. IA2 block, 505 cu in, E-head, Solid roller 3650 weight. Reid TH400 4:11 gear. 29" slick.
Best so far 10.12@133 mph. 1.43 60 ft.
76 Trans am, TKX .81 o/d, 3.73 Moser rearend,
468 with KRE D-ports, Doug headers, 3" Exh.
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