Hi Dana,
I'd like to turn to you for some advice with my '90 700R4.
After my last rebuild 3 years ago with a number of good upgrades (new pump w/ high pressure pump spring, smart shell, pinless accumulators,.471 o-ring boost valve, corvette servo, servo release check valve, new accumulator sleeve, 7-clutch & thick steels 3-4 clutch with Sonnax backing plate, new clutches, bushings and band, 9.5" 3000rpm vigilante converter).

I have recently experienced again a flare at my 2-3 WOT shift (5800rpm) after having short and firm shifts for the years before that. The engine has approx. 350hp, so nothing crazy.
It shifts fine and firm when I let off the gas a tiny bit at WOT runs. Before I ruin the trans I would like to fix this issue once and for all as this was also an issue that led to the rebuild.

I have two suspicions: first one - the clearance of the corvette servo might be on the loose side, I can't remember exactly what it was back then but it was more than .100 and I plan to check it soon and have already purchased a new Sonnax pin with the longer tip and the o-rings.
The second issue might be my separator plate. I have drilled some of the holes, 3-4 clutch feed etc. according to some of your suggestions in the past, but I haven't recorded the values back then.
I have found a picture that shows the plate and holes. Maybe you can see something out of the ordinary.
Before I drop the pan again to measure everything I wanted to get your opinion what the cause for this behaviour is and why it came back after a couple thousand miles without issues.
Could it be a general mismatch of 3-4 clutch feed and the band release hole sizes in the separator plate?
Any other parts you would recommend adding while the trans is open?

Thanks for your help,
Alex

Those Sonnax Servo Release Check-Valves can sometimes be absolutely horrible!
Most often they will cause a 2-3 Up-Shift Bind.

They manor in which the Separator-Plate Orificing is performed is going to make the biggest decisions on how the Transmission will behave/ perform.

If you have a 2-3 Up-Shift Flair with the the Sonnax Servo Release Check-Valve installed (usually causes the opposite: a Bind) then the Servo Travel must be way too much or there is another Hydraulic change that had occurred and created this new behavior.

There is a far better way to achieve what Sonnax tries to do with their Servo Release Check-Valve.

Most likely Dana/ PBA would tell you the same exact thing.
Your best bet is to visit his Website, give Him a call, and he will offer you any necessary modifications/Parts that you might need, customized to your Transmission Build for a great price!

Thanks!
I would be very curious what the better way ist to fix my problem.
Unfortunately I'm located in Germany, so I have no way to give my transmission to Dana or someone knowledgeable in that regard.
My hope is that the servo clearance is way more than necessary, but I#m still waiting for the new pin to arrive. In case that clearance is way higher than recommended (I read .060 to .075 should be OK?), will this be the permanent fix for my issue?
Also just to clarify, my so-called flare behaves like this: at WOT I reach the shiftpoint around 5800rpm, when it attempts to shift it will jump up the rpm and hit the limiter until I let off the gas.

Thanks
Alex

2-3 shift is about band release and 3-4 clutch apply. Going to a longer band apply pin, won't change much in the dynamics described. Flare is a result mis-synchronization in band release and clutch apply. Sounds like you need to slow down the band release through 3rd accumulator system or speed up 3-4 clutch apply. If everything was working fine, I would look at the 3-4 pack to see if there's excessive play in the pack due to wear.

That info helps a lot.
In order to get that timing right, I would propose to speed up the clutch apply. That would be done by opening up the right orifice in the separator plate, right?
I've attached a picture and would assume this is hole #43.
Would reducing the size of #46 (3rd clutch exhaust) be the right hole to slow down the release of the band?
What would be the right orifice sizes and are there other holes to adjust for this?

BTW, I swapped out the servo pin. The old one was quite worn on the surfaces and had a clearance of .110". I modified the Sonnax pin to a clearance of .065".
I have not yet tested the shift at WOT though.
Thanks
Alex

Sorry, the last two Post are incorrect.

That Sonnax Servo release Check-Valve needs to come out.

You will want to speed up/ shorten the travel of the 2-4 Servo for a 2-3 Shift Flare.

Both the 2-4 Band Clearance, and the 3-4 Clutch Clearance must be within particular measurements for proper 2-3 Up-Shift Timing.
Approx 0.060" for the Servo, and approx. 0.030" for the 3-4 Clutch.

Match the 3rd-Exhaust Orifice to the same size as the 3rd-Feed Orifice.

For finer Control of the 2-3 Shift timing...
There is a 3rd-Accumulator/ Band Release Orifice next to the #2 Check-Ball.
The 3-2 Control Valve needs to be blocked, and the #2 Check-Ball Hole Plugged.
The 3rd-Accumulator/ Band Release Orifice must then be significantly enlarged.

All three of those Orifice sizes will be dictated upon desired shift feel, and fine 2-3 Shift Timing.

Myself and Dana have designed these modifications, and have been using them for about 30 or more Years successfully.

Good luck and have fun!

Thanks for clarification!

Just to be clear: using my last picture - we are talking about hole #43 (feed) and #46 (exhaust), right?
Also looking onto my first pic of my actual separator plate, it can be seen that both orifices are not the same size. The exhaust hole is a bit smaller.
Should I enlarge the exhaust or rather shrink the feed? I read somewhere that .155 is a good number for the feed. Can you confirm?

Regarding these mods - will it be OK if I move forward with the previous steps first or are these steps 100% necessary to fix the issue? I'd prefer to go step by step.

Thanks
Alex

@vorteciroc , could you confirm my last post, so I don't do any stupid moves.
Thanks!

I am very sorry.
I have been backed-up on returning PMs and answering Posts.

I will replay when I have some time... Hopefully soon.

Otherwise, please Call Dana.
He and I talk all the time.
He uses my hydraulic designs, so he can also answer your questions.

Thanks!

First, here is one of my Separator-Plates that we can use to identify the "Orifice-Holes" in the Image Below:



The RED Circled Orifice, marked "A" is: 3rd-Feed (I would normally make it 0.157") so your 0.155" Size here is Fine.

The RED Circled Orifice, marked "C" is: 3rd-Exhaust (I would normally make it 0.157") so your 0.155" Size here is Fine.

Orifice-Holes "A" and "C" are not normally the same size... we make them them same size as part of our Hydraulic Modifications to these Circuits.


Your 2-4 Band Servo Travel/ Clearance issue must be corrected first.
That Sonnax Servo Release Check-Valve needs to get removed with an "Easy-Out" Extractor.
Hopefully the 3-4 Clutch Clearance is acceptable.

Then the Modifications for "Ideal" 2-3 Up-Shift Timing should be done.
Quoted from my Post above:

"There is a 3rd-Accumulator/ Band Release Orifice next to the #2 Check-Ball.
The 3-2 Control Valve needs to be blocked, and the #2 Check-Ball Hole Plugged.
The 3rd-Accumulator/ Band Release Orifice must then be significantly enlarged."

What I am talking about is:
-Plugging the #2 Check-Ball Hole (Black Circle marked: "F" on my Separator-Plate).
-Drilling/ Enlarging the 3rd-Accumulator/ Band Release Orifice (Red Circle marked: "G" on my Separator-Plate).

Last, is blocking the 3-2 Control-Valve.
Keep the Original 3-2 Control-Valve, but Omit the Original Spring.

You need one more item, either:
-The Tiny Spring that goes under the Pivot-Pin of the Slide from the Oil-Pump (GM Part #8634098) (Aftermarket Part #A54540B) (DO NOT BUY ONE NEW FOR CRAZY PRICES, LIKE $14.95)
It's $1.95 at "Global Transmission Parts" (globaltransmissionparts.com).
-A Tiny Cup-Plug that would be used to Plug the 4th Accumulator.

Install the 3-2 Control Valve, Blocked in place, as in the Image below:

Thanks so much for the details and instructions!

You are Most Welcome!!!

Just a short follow up on this thread. After replacing the servo pin with a longer o-ringed Sonnax pin with a clearance of .065 from the old, worn pin with over .100 clearance, the 2-3 WOT shift came back again.
I have not come around to redrilling the holes in the separator plate but plan to do that during winter time.

Thanks
Alex

Do you have any guidelines put together in a link or email? I've been looking for tested servo size/3-4 clearance/orifice size combinations that are proven to work under different conditions.

No.


There are too many variables when Building the Unit that need to be minimized in order to have some kind of recipe...
That is way more than I wish to go over here.
Sorry.