Bob88GTA

iTrader: (2)

Hi all. I have a question regarding the lock up in my 85 T/A, 56k miles all original.
Back story...a few years ago I had some shift point issues. When starting out, the trans would stack shift through the gears. I remedied that with a TV Cable reset. The trans when cruising would work perfect. but still had some lock-up issues.I took it to a trans shop ( not AAMCO) for diagnosis. The car had sat for several years and I figured it was maybe a sticking valve or maybe something else.

While at the shop, I mentioned to the guys that I wanted the trans to shift from 1-2, 2-3, then lock up. He mentioned a mod to the pressure switches. He done the mod and gave me what I asked for...shifts from 1, 2, 3, to lockup. It seems I have no 1st stage of 4th...it goes straight from 3 into lock up. It will unlock when brake is pressed and I go to accelerate , but goes down to 3rd and not the 4th.
I don't drive this thing at all, but I want the normal configuration back and I want to do it my self. I'm pretty familiar with the pressure switches on the VB and such.
My question, without taking it back to them, is what was the "Mod/Re-wire" that they done??
Sorry so long.
Thanks
Bob

ASE doc

It sounds like they wired the 4th gear pressure switch directly to the TCC solenoid. This way, the TCC locks up in 4th all the time. Normally, in 88 the TCC is controlled by the ECM. The pressure switches, brake switch, and probably a fluid temp switch, are input to the ECM and it locks up the TCC in 4th or in 3rd and 4th, depending on the setup. The ECM would not engage the TCC until a few moments after 3-4 shift and only below about 1/2 throttle. When you press on the throttle or the brake, the ECM would release the TCC. The TCC would also release for a brief period after 4-3 downshift. There are several variations to how the factory setup the TCC controls. Some were real simple, others real complicated. But by 88, most TCC control was done by the ECM.

Some models had the brake switch wired either to pin A or pin D of the 4 pin TCC connector on the outside of the the trans, depending on whether the brake TCC switch was connected to ground or power. This way, when the brake was pressed, it takes away power or ground to the TCC and releases it. You still need either a throttle switch or the ECM to turn off the TCC under throttle, otherwise you'll likely burn up the TCC friction with too much torque and not enough fluid pressure on the stock trans.

Bob88GTA

iTrader: (2)

Thanks Doc, thats exactly what is happening. It will unlock coming to a stop, under braking, and such, but as sone as you start to accellarate, say under 38-40, it goes straight to lock up, instead of hanging in 1st stage 4th. Thanks for the reply!!! I'll check it all out. Whatever the mod was, I hate it!

Pro Built Automatics

He could have put a checkball in the lockup solenoid. Take off solenoid (two bolts) and look for a steel checkball in the tip of the solenoid and remove it.