What is the clearance you set the 3-4 clutches at? I'm thinking it's too wide and the time it takes to command the shift, fill the drum with fluid and excessive distance the piston has to travel to engage the clutches may be an issue. What was your band clearance? If it's too tight then it may not let go fast enough. Did you reuse the stock pin and stock servo assembly? If you changed anything in the 2-4 servo the clearance needs to set up using a dial indicator. Did you change the green oring in the aluminum drum ? Maybe forget to reinstall it? Did you replace that drum with a new or rebuilt unit? They don't have that oring in them (mistake I once made). You cannot see this oring from the top of the drum. You can only see it through the holes in the side of the drum. Did you replace the shift solonoids? I've made the mistake of not changing them a couple times during a build and it's caused me headaches. I've rebuilt a lot of these transmissions. And I've made a lot of mistakes along the way, leading from it each time.

 

I can't honestly tell you. I recall that at the time I was given a range, but was too lazy to dig out the feeler gauges. I used my calibrated eye. It wasn't until I finished the rebuild and looked at the leftover parts that I realized that the kit came with a few different thickness plates for the 3-4 pack. I used the stock spacer plate, but the clutch was a 9 plate ALTO power pak. It looked OK, be I'm no expert.
After reading this question, and thinking back, it is quite possible that I have the gap out of range.

I used the stock servo and pin. I knew nothing at the time about pin length and travel distance. I later went back and checked it with a pry bar and my calibrated eye. It looked to be 0.090"- 0.100".

I reused the drum, but I don't recall a green o-ring other than the one that goes on the shaft for the TC. I did air test all of the functions and had no leaks. I'll have to go back through the video I went through, and try to refresh my memory. (transmissionbench.com)

The shift solenoids were replaced just before I bought the donor truck, so they are about a year old, and were working fine when the sun shell stripped, so I reused them.

Edit: I went back and looked at the video, and saw the o-ring that you are referring to. I remember replacing that.

 

If it was slow to shift, wouldn't it tend to flare?

And if it's a clue, third gear shift is on the harsh side when all other gears are firm, but smooth

 

Out of curiosity, what is the effect of leaving out that green oring?

 

OK, here's what I'm thinking of doing; I've already got the Sonnax boost valve, and a pan gasket. But while I'm in there, I want to either adjust or replace the PC Solenoid, upgrade the TCC valve with the Sonnax kit, and replace the separator plate and gaskets while the VB is off.
The separator plate has some wear where the ***** seat, and one of them had a small lip all the way around. I flattened it with a hammer, but I wonder if it is still round enough. But rather than have doubts, why not just replace it?
Any advice on which plate to replace it with? Are there better ones than stock? Are there holes I should bore out? (Which ones, and why?)

This is all stuff I can do with the trans still in the truck. Sound reasonable?

 

Should I replace the plastic accumulator pistons, also? They were good, and I reused them. I'm referring to the ones that that you have to remove to get the separator plate out.
I already installed a sonnax pinless forward piston.

 

Replace the accumulators with the sonnax pinless ones.

Replace the check ***** with the plastic ones (torlene)
It will cut down on separator plate getting beat up. They go in every one of my builds. I could not tell you how many of these transmissions I've built. Been building them for about 17 years now. I don't consider myself to be a pro at it but I've had pretty good luck for the most part. Every now and then I'll have an issue but that's going to happen.

 

If installing the Sonnax boost valve I would not adjust the PC Solenoid. You can replace if you like but don’t adjust it until you know what your line pressure is when taken with a manual pressure gauge. It would be a good idea to replace the plastic accumulator pistons.

 

I never mess with the pressure regulator on the solonoid. You run the risk of blowing pistons out or breaking the tangs on the end of the input drum. I don't have personal experience with this but it's an issue that could happen if you pump up the pressure too much.

 

Never heard of Torlon *****. Definitely going to "check" that out.
What separator plate? Transgo? AC Delco?

I'm favoring replacing the PC Solenoid over adjusting it. My scan tool shows that it is returning the amperage that the ECM is calling for. I don't know that that means it is putting out the pressure that is being called for, though.

 

Is there a cheaper way to upgrade the TCC valve without having to by the $135 reamer? I only need to do this once.

 

Sonnax TCC Apply Valve Kit 77805E-K be sure to get the correct one for your year trans.

 

That's the that's the one that goes in the pump. I was referring to the one that goes in the valve body. I figured that's the one that would cause the pulsing at TCC lockup.
Am I barking up the wrong tree?

 

Sorry, my bad. This is what you can use http://www.fitzall.com/supportDetail.php?A74741Q-188

Or the valve in the TransGo HD-2 kit.

 

It took a while to get anything done on this due to eye surgery, but I'm back to give an update.

Still will not shift from 2-3 under heavy throttle, but here is what I have done based on the advice I've been given so far:

I pulled the VB and made sure all the valves moved freely.
I made sure the 3rd shift valve was not in backwards.
I replaced the spring on the 3-2 valve for good measure.
I installed the Fitzall TCC gizmo to get rid of the pulsing at 35mph under light throttle. I would have gone the Sonnax route if it weren't for the expense of the reamer. I can still do that in the future if I decide to.
I replaced the worn factory separator plate with a Transgo. 2nd hole drilled to .06 which is pretty much where it was. No other changes to the plate.
New gaskets. There were no problems with the gaskets that I removed; no bridging or anything that might raise an eyebrow.
torlon ***** replaced the steel *****.
Sonnax pinless pistons in all three accumulators, now.
Two new shift solenoids.
Sonnax boost valve: the one with the o-rings.


My pressure at idle when from 50 to 55, so I am happy with that. All other pressures looked right, so I finally removed the gauge from my mirror. It's been there for the past few months.

At this point, I'm ok with just living with it until I, or someone here, has an epiphany. I am not throwing in the towel, though.

My only thought is that maybe the band is not releasing enough at high RPM to allow it to shift to third. Maybe the problem is in the servo. I recall the travel being right, but maybe I'm overlooking something else? (Stock servo. I re-used the drum, with a new red eagle band.)

Thanks for all the help so far.

 

Post your tune file, let us sanity check it.

 

I don't have HP Tuners. I have a Diablosport Predator. Best I could do is write everything down and type it here.

As for the tune, and all of it for that matter, I keep going back to the fact that it did not do this before I rebuilt the transmission because of a stripped sun shell.

It used to have a 2-3 flare under heavy throttle. Everything else was fine.

Say, is is possible to put the servo together with one of it's parts backward? Trying to recall off the top of my head....

 

I've pulled the trans out of the truck because it was starting to slip out of 4th (to 3rd) when throttle was light, such as going downhill. 4th apply not holding pressure?

I've got it torn down, and am going through it looking for problems.
Band and clutches look fine. Servo travel is .125"
4th piston feels a bit sloppy in the cover, but only in the area where it operates. Fit is good near the edge. I ordered a billet set to replace it. Supposed to have more surface area for better holding. Thoughts on this?

3-4 clutch pack (ALTO) is supposed to have clearance of .025 to .040 but measures .057 Could that be my "no 2-3 shift" culprit?

Have any of you ever seen this?: During the first teardown, I saw that the forward sprag had a worn brass ring, and some matching wear on the overrun clutch hub that it rides against. The brass is cupped, but it should be flat. It allows end play in the sprag assembly.
Being a newb, and in a hurry, I reused it. I reasoned that my only failure was the sun shell, so this was obviously working.
But I am replacing the sprag and the overrun hub this time. Could this cause either of my problems?

 

I built ALOT of these units and I never have this issue, because I guess I do the same things every time. So follow this guide and I’ll try to give you some answers. If you need more info then let me know and I’ll give you my number.

First remove the pistons out of the forward drum. Change the thin green oring in the center of the drum. You have to really look for it. You can see it through the holes in the side of the drum.
​​​​​​​Replace the molded pistons if you haven’t on your last build. Make sure you don’t hVe a damaged lip seal somewhere.

Insoect all all of your Teflon seals. Input shaft and put stator shaft.

I like .045 ish clearance on the 3/4. .065 will not cause you issues. I’ve seen clearances around .090 and they shift fine.

Replce all your check ***** with plastic ones.

Add a sonnax hd 2-3 valve

replace all three accumulator pistons with pinless sonnax ones

do some research on raybestos gpz 3-4 clutches. Better than high energy and red alto

replace your reverse input drum and add a carbon or red alto wide band

do not use the superior billet servos. They bang shift. Poor design because they eliminate the cushion springs. Use the sonnax ones

Use the sonnax high rpm pump spring

I like .075 on the 2-4 band .125 won’t cause you issues but your shifts will be slower.. If you get the sonnax servo kit it will come with a new longer pin with seals on it. You will have to grind it shorter. Be careful and only remove a little at a time.

I don’t think any of what you mentioned is your issue. You likely have a leak somewhere and doing all what I just told you should fix it. It could also be in your tune.

If you follow this guide your trans will shift unbelievably quick. I just built the one in my gto three weeks ago and as soon as I command it, it shifts. As soon as I move the shift lever it shifts. I used to have to shift 400 rpm soon then I wanted it to because of the delay. It’s immediate now. Good luck and if you have any questions you can pm me.

 

Thanks for the quick reply.
Up to this point, I have replaced all frictions, steels, bushings, and pistons.
I have upgraded all three accumulators to Sonnax pinless.
Torlon *****
Sonnax boost valve
New pressure manifold
New shift solenoids
Transgo separator plate, because ball holes were worn.

I have another complete alto overall kit, with band, less bushings.
New reverse input drum
New forward sprag
Overrun clutch hub to replace the worn one.
New billet 4th piston and cover (billet) I'm using the stock servo, but I like the idea of having more holding pressure in 4th because it is a truck.


I considered the Sonnax HD 2-3 valve that you mentioned. I read that it applies the overrun clutch in D3. I'm not drag racing, so it may not benefit me. I haven't ruled it out, but it's 30 bucks I don't need to spend.
I looked at the Sonnax servo, but that is a costly part. Money is snug right now. If I was convinced that it was a worthwhile investment, I would wait my next paycheck and order it.

Since you don't think any of my findings (so far) are the cause of my problems, I hope to find a damaged lip seal or something.
I sure hope I find something obvious.