Car is an 1984 corvette, 700r4 transmission
issue: drives in netrual, feels like binding in reverse
Forward clutches burnt last time i had it apart.

If i remove the boost valves, clean, and reinstall with assembly lube it works great until i shift gears back and forth.

Last year i blew a pump rotor in my transmission, i replaced the pump with a rebuilt pump with an 86 date code, and installed a billet rotor for good measure.
put the car back together i had this issue, since it worked if i removed the boost valves and flushed everything i figured it was just pump debris choking things up.

So i fully tore down the transmission, cleaned and checked everything including the valve body.

I found my forward clutches were a tad burnt/dark so i replaced them, i also found a few clutches in the 3-4 pack were a little dark in the center, i replaced those and backed my 3-4 clearance from .36 to .42 for good measure.

only metal i found was in the pump it self, seemed to support my theory of pump debris.

So fully cleaned trans, flushed the cooler lines with mineral spirits and compressed air, and brand new torque converter for good measure.

Everything was great for about 10min, neutral worked great, as did reverse, shifted the gear shifter up and down, still great, did it again and the issue reappeared...

So now I'm thinking crossleak, i know my forward clutch was burnt when i had it apart last time.

i also air yested every piston in the trans before assembly.

Thing that confuses me is the low reverse boost valve, if i remove and clean it and the bore in the pump with brake clean it works great for a few minutes.
however i have never been able to find a cause when apart.

Any thoughts would be very appreciated before i pull this thing again.
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Have you checked the pressures according to the chart in the FSM? Driving in neutral and binding in reverse is definitely pointing to one of the forward elements being applied/partially applied when they shouldn't be. When you remove the boost and clean it, you are somehow relieving this apply pressure and all is good again until the next cycle. Are you sure the pump you put in is compatible with your model trans? My 92 FSM troubleshooting guide says this:

Drives In Neutral

Forward clutch not releasing
Manual valve link disconnected
Case face not flat
Internal leakage

 

Thanks, and yes i believe the issue is the forward clutch is not releasing once it's applied.

I also have a pressure gauge permanently installed in the car, but it maxes out at 200psi.

Forward gears have good expected pressure at idle, but reverse and neutral are over 200psi

I keep thinking something is wonky with the new pump, that or i managed to crack the input drum somewhere that last day i had it driving.
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Also that 86 pump, the pump has the same fluid path holes as my 84 pump, but i have noidea if the stator paths are different or something weird...

I'm thinking about going back to the old pump, but it did take some damage when the pump slide snapped in half, the rotor area is still usable tho.

Pretty much there is a good solid nick where the pump slide snapped, but with some cleanup i think it may be ok...
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Your input drum is probably fine. You said you airchecked all the packs. The problem is before the input drum. The clutches can't apply until they get oil.

 

Depending on your model, at 1000RPM, you should have between 90 and 120PSI(based on my FSM) at minimum TV. Your pressure indicates you may have a TV problem as a possibility. 200 PSI at 1000RPM indicates close to max TV

 

The weird thing also is the pressure is only crazy high in neutral, park, and reverse.

Also before putting it back together i checked all the valves in the valvebody to confirm free movement, including the tv.


I keep thinking blockage, it screams forward/reverse boost issue...
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Disconnect your TV cable and see what the pressure is at idle(1000)

 

I'll check it tomorrow, i have open headers right now.
i'm surprised the cops have not been called yet as it is.
​​​​​​​(i have stories related lol)

​​​​​​​Thanks for helping with my head scratch'n

 

Ok tv disconnected, not a huge difference unless i put it in drive, there i can see it rise and fall by pulling the cable.

Possible i just pinched a seal on the input shaft, while i pressure tested the pistons, i forgot to apply air to the circuits with the valve body off.

So I'll pull the transmission later on, and take a really good look at the stator, and the input shaft when i have it apart.

Not much of a hurry until march comes along anyways.
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Well i got a wild hair today after two energy drinks...

Transmission pulled, and i did a detailed wet air test following instructions on sonnaxs website.

I found the forward passage way in the pump totally blocked.

The culprit was a cup plug that the rebuilder at transstar, the cup plug for the forward passage way was way to far in.

Resolved by drilling a hole, inserting a screw down the center, and then pulled out with my slide hammer.
I pulled another cup plug from my old pump and reinstalled, the staked it in place.
i also noticed some weak staking in the new pump compared to the old pump, so i gave all of the cup plugs a once over.

Tomorrow I'll do a detailed check, and then get it back together.


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Not sure if this is visible, but the old pump on the left, new pump on the right.

Cup plug was pushed to far in, redirecting fluid...

I have noidea why removing the boost valves fixed the issue for a few minutes, super weird affect.

Small hole to the left of the filter seal.
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Close up of missing cup plug.
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I spent much of saturday comparing the new pump to the old one.
i found a few other slight issues and corrected them.
biggest other issue was a missing cup plug/air vent for the "line" circuit that's connected to the forward circuit.
I looked like that area was enlarged so the cup plug from the old pump would not fit, however the old pump had another vent plug that did fit after i enlarged it slightly.

I could not find much about cup plug locations for the pump.

And I'm super happy i had not turned in my pump core yet!

When i do turn it in, I'm going to ask transstar if the pump was rebuilt in house.

if yes, I'll suggest drug testing the assembler!!!
​​​​​​​@##$!&!
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Got to give you an A+ for perseverance.

 

No kidding lol

Overall rebuilding one of these was not as bad as it seems at first.
First go around i lost the 3-4 clutch i believe due to a damaged lip seal, second run i upgraded to the bonded pistons.
That made a huge difference, especially due to ease of install.
I had some other headaches along the way that were worked out, i now have every weak spot taken care of short of the input and output shaft...

And i just finished testing on stands, everything looks great!
​​​​​​​Next the exhaust goes back on and then a road test.

I can't wait to get back to tuning the thing

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