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Discussion Starter #1
In need of some troubleshooting advice for the problem I'm having with my TH400. Here's a list of mods and the current symptoms. Appreciate the help!

-Stock Th400 case
-CK Performance RMVB 1st gear transbrake
-4L80E Direct Drum w/ 34 element sprag
-Dual feed mod with bleed hole in direct drum
-TSR Billet clutch hub

Symptoms (with all four wheels off the ground)
Park, reverse, and neutral all put the car in reverse without the transbrake being applied. Parking lugs keep the wheels from continuously spinning in reverse. I verified that the scheduling valve is in proper positions and not getting hung up in the case. Triple check shift linkage.

1st, 2nd, and 3rd all bind up, as if the transbrake is activated. In 1st gear, 3/4 throttle will begin to move the the tires forward.

As another test, I started the vehicle in 3rd gear. Tires moved forward for a couple seconds, then locked up as if the transbrake were activated.

My assumption is a crossleak into the rear servo, applying the rear band at all times. However, having reverse in P, R, and N also indicate that the direct drum is constantly under pressure as well. Please correct me if I'm wrong.

I've pulled the transmission apart and did not find anything eye catching. A little lost on what to test and troubleshoot next. Thanks in advance!
 

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Discussion Starter #5
Just sounds like the transbrake is on all the time.


Hutch
Thanks Hutch. I was hoping it was as simple as that. This vb is supposed to be designed where transbrake cannot be applied in 2nd and 3rd. Could this indicate that 3rd gear is getting line pressure at all times?


"The selecetion of Reverse range does not require transbrake activation. Built in safety function prohibits transmision brake apply in second or third gear even if the button is depressed."
 

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Discussion Starter #6
Transbrake Scheduling Valve Action

<iframe width="560" height="315" src="
" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

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Discussion Starter #7
Reaction carrier with rear band and servo installed

<iframe width="560" height="315" src="
" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

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Discussion Starter #8
Forward drum pressure check

<iframe width="560" height="315" src="
" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

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Discussion Starter #9
Direct drum pressure check

<iframe width="560" height="315" src="
" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
 

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Discussion Starter #10
Also, would it be possible to bench test the transmission assembled? Possibly 100+psi of constant line pressure through the port on the side of the trans. Or, pressure test with the pump removed?

Ultimately, I would like fully test this thing prior to install. Although I'm now extremely efficient with installing and pulling out a trans from a 4th gen f body, I no longer wish to do it for fun! 😂
 

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Discussion Starter #13
You have an odd problem but somehow you have the direct clutch and band on all the time but are able to manually turn on and off the fwd clutch with the manual valve.


Hutch
Thanks Hutch. I've come to the same conclusion. Would anything mechanically with the low roller clutch or intermediate sprag cause such a symptom? Or is this purely a crossleak issue?

I'm having a blast trying to understand the circuits of this valve body 😅 not!
 

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Discussion Starter #15
Don't think so. Direct clutch is on in park with the band. That points to a major oil volume heading in that direction as it has to overcome the leak in the drum also.


Hutch
Hoping Chris can chime in here too as he will be most familiar with the valve body. Haven't the first idea as to what to test next.
 

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Oil has to be entering the circuit after the shuttle valve in the case. Are there any dents in case, valve body or separator plate faces? Both surfaces must be perfectly flat. .
 

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Discussion Starter #17
Oil has to be entering the circuit after the shuttle valve in the case. Are there any dents in case, valve body or separator plate faces? Both surfaces must be perfectly flat. .
Case, VB, and plate are all flat. Didnt find any dents or damage.

Chris, would you be willing to overnight a scheduling valve if I start fresh with a new case? I can only assume the case is bad if the VB is in perfect order. The only thing that stands out to me is some wear/scuffing on the scheduling valve. Quite possible that this case has seen better days. Unsure if theres anything I can do to fix the bore in which that valve rides in.
 

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Discussion Starter #18
Quick update. Walked through the entire valve body with CK today. All of his necessary modifications are accounted for. We suspect a clearance issue between the scheduling valve and the bore in the case. Might be too much clearance, allowing line pressure past the valve and applying the transbrake full time. I'm shipping him back the vb and plate to verify functionality on the transmission dyno. Appreciate your time Chris! Stay tuned everyone.

On a side not, I couldn't help but buy another transmission today. Scored this working Turbo 400 for $100 😎

82060
 

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Discussion Starter #19
Don't think so. Direct clutch is on in park with the band. That points to a major oil volume heading in that direction as it has to overcome the leak in the drum also.


Hutch
What would occur if I had zero rear end play? Noticed some wear on thrust bearing between reaction carrier and output carrier.

82116


82117
 
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