700R4 shifting problem

Is there a transmision builder here that can help?

The problem is assosiated with the TCC but is some what deeper then the basic control perifials, although the TCC should have nothing to do with gear shifting times as that is a hydraulic funtion. The 1-2, 2-3, 3-4 shift timing all changes back to normal when I disconect the TCC wiring. With the TCC connected it will shift 1-2-3-4 and then engage the TCC as low as 20 MPH and then you have to beet on it to get it to down shift, Its killing the engine and trany.

Its a good diognostic clue for someone who really knows thier transmisions, that wouldn't be me! quite frankly I am baffled at how the TCC being hooked up electrically effects the other hydraulic functions of the valve body?

I will go into detail if there is someone here that really knows the inner working of the hydralic system in these machines.

M1D

[This message has been edited by m1dadio (edited November 08, 2009).]

Everthing is exactly all from the donner car. All wireing harness, computer, same engine trany (never seperated) factory TV set up, all the emision controls in place, Everything!! its a 1988 pontiac trans am GTA same as the iroc camaro for that year, the trany had been a rebuild installed at some time. It is a 1992 700R4, not so different from the original 1988. I did not get very much chance to drive the donner car before stripping it. I drove it about 10 miles high way and city and did not notice any prablem then but the engine was running real bad at that time so I cant be sure.

The only thing different is rear end gear and tires. only by 4.6% actual.

My computer needs certain information from the transmision to tell the TCC when to engage and disengage and to manage the fuel and emision systems. That is the only control it has over the trany. I have a scanner for drivbility tests so I can see when the fourth gear switch is activated,( the fourth gear switch is only a ground to tell the computer we are in forth for fuel and emision control) what speed the trany thinks I am doing and when the TCC system is activated as well as when the TCC is engaged.

I compaired the scanner speed reading to a good hand held GPS. MY computer thinks I am doing 4.6% slower then I really am. Not enough to cause the degree of problem I have and in the oposite direction as well. When I'm doing 100 it thinks we are going 95.

Electrically speeking the TCC system is active when it should be and deactivates with quick closing of the throtle or touching the brake as it should. The TCC engages in the correct sequence as it should (always after the final gear has been reached) The fourth gear switch is telling the computer when and only when the trany is in fourth gear as it should.

With all that unpluged the trany hydraulicaly shifts nice, smooth and at the right speeds acourding to the GM shop manual for the donner car. At light acceleration I get 1-2 at about 10 MPH then a 2-3 shift at about 25 mph and a 3-4 shift at about 40 mph which would be followed by TCC lock up if it was connected. If I accelerate the down shifting is all normal. This is all normal as the shifting is a hydraulic function controlled mainly by the govenor vs TV cable.

Now here is where diognostics gets crazy. The only part of the transmision controlled by the computer is the TCC lock up and dissengagment. The VSS speed input and the forth gear switch are imputs the computer uses to make other fuel and emision decisions. With all wires connected to the transmision, the trany wil # 1. alow TCC lock up at any manual gear shift position. low 1 I get 1st gear then TCC lock up, low2 I get 1-2 shift then tcc lock up, in "D" I get 1-2, 2-3 shift then TCC lock up and in OD I get 1-2, 2-3, 3-4 then TCC lock up.
AND # 2 in all the above casses the shifting is extremly early, I mean in "OD" light acceleration (simular to above description of shifts) I get 1-2, 2-3, 3-4, then TCC lock up all before 20 MPH. Then of course the engine is seriously lugging and wont downshift without a dangerous anount of throtle.

The question for me is how is it that the TCC electric solinoid can cause the hydraulic shifting of all the gears to go so early??


My system is a complete GM engineerd system that has a problem(or two) I intend to fix it, not attach some aftermarket band aid to it. All the trany shops around here just want to sell me a band aid out of a box that seperates the trany from the computer, I know there is a place for that Most hot rods need a stand alone trany TCC control but my machine also needs these imputs to control fuel economy and emisions so I need to fix the factory set up.

I am begining to think there is more then one problem here. Its posible my computer chip is messed up causing the TCC to lock prematurly and that can be easily replaced, but how is it posible that the gear shifting times get changed? when they are hydraulicaly controlled?? That is where some one who really knows these beasts can help.

One other note to the electric side. MY VSS feeds to a "4 out buffer" before it gets to the computer because the donner car had a digital dash. Even though my scanner plugged into the diognostic conector is saying something close to the speed I am traveling, that does not automaticaly mean the computer is getting the same signal my scanner is, OR is it ???

Its possible all I need to do is a small change to the buffer wiring or replace a solinoid or something like that. It usually is just a small thing but a large task to diognose it. You guys who have worked on vehicles for a living know what I'm talking about, hours of diognosis and you arive at one poor electrical connection or something equally as small.

M1D

LAL !!

OK it sounds like a couple guys on that site really know thier stuff. I will have to go there and see what comes of it

Thanks Don

donivan65 wrote:Sometimes when you run into a problem, you need to back up and try a different angle instead of just spinning your wheels,,,,,at least thats how I operate,,,,,,,,,

I put it in 4x4..............................that usually fixes it..lol

Gitting there:

I finally found a local guy who knows what hes talking about.

Both problems, trany upshifts too early, and goes to TCC lock up no matter what posision the shifter is in because the TCC is "ON" all the time. It turns out my thansmision has differnt internal wiring them I am suposed to have for this computer. Easy to change. My Mannual shows nine different internal wiring set ups for the 1988 firebird 700R4(donner car) and I know what mine is suposed to be and I know it is not that. I will pull the pan and change it up next weekend.

M1D