BigVin

I have 68 camaro with 350 373 rear a 96 4l60e and a tci 2nd gen computor.It shifts hard from 1st to 2nd at low speed. Ive tried lowering line pressure in 1st to 2nd but that didnt help. trans shifts great otherwise. Do you think its a sensor or a tune or both? thanks

performabuilt

iTrader: (25)

Is the trans stock or a built unit . shift kit ? Larger servos need more info.

mrvedit

First, I would scan the PCM for codes. If there is a trans slip code (e.g. 1870) or a sensor code the PCM might command max line pressure and result in hard shifts.

After that, hooking up a trans pressure gauge is the key to diagnosing this. Either get your own on ebay for $45 or have a local trans shop do it for you.

If the pressure is high, you have a sensor, PCM or tune problem. Or a defective PCS (Pressure Control Solenoid, also called EPC) which is easy to replace.
If the pressure is correct/moderate it could be due to a (excessive) shift kit or a cracked piston in the 1-2 accumulator.

If you want to skip the pressures test, then take off the pan and filter and remove the 3 screws that hold on the 1-2 accumulator - the dome shaped thingy-ma-bob. Take a good picture of all the internal parts and post it. That will tell us if you have a shift kit and which shift kit. The stock piston is plastic and often cracks; check for that too.

BigVin

update worn tcc bore. the fix sonnax reamer and valve.

mrvedit

If you have already done or committed to it, great; it is the proper "OEM" fix. IIRC the reamer is $150 and the valve is $50; of course some trans shops will already have the reamer.

However there is a cheaper alternative - replace the troublesome PCM TCC valve with a on/off valve, e.g. the Fitzall valve or the TCC valve from Trango or supplied with the Sonnax shift kit. Each of these is less than $20.
With an on/off TCC valve the lockup clutch engages more solidly instead of super-smoothly. I think nearly everyone on this forum would prefer to more solid engagement; non-car-enthusiasts don't want to feel any shifts or anything for that matter.
Also, most of the aftermarket converter companies prefer use of the on/off TCC valve.

BigVin

Thanks for the reply I'm going with the transgo code buster this is a 96 stock trans in good shape. With the pan off is there any other upgrades you would do?

mrvedit

Yes, I would also suggest the Sonnax 4L60-LB1 boost valve; it will raise the line pressure across the board and set a higher max pressure of around 230psi. Under $30 and only takes a few minutes to install; you need snap ring pliers.
Shift will feel slightly firmer and is likely to extend the life of your trans.

BigVin

I took pan and valve body off to do the upgrades and there is no spring in 3/4 accumulator. I think the accumulator are shift cushions 1/2 has 1 spring 3/4 none is this ok? Trans shifts good except for hard 1/2 low speed shift.

BigVin

anyone have an opinion on 3/4 spring?

mrvedit

The stock 1-2 accumulator has two springs - a very stiff narrow one (.9" wide) one and a moderately stiff wider one (1.5" wide). I can compress the wider one significantly by hand, but the stiff one just barely.
Which one do you have?

The 4th accumulator spring is very soft. Some builders put in under the piston, some on top and other leave it out. These accumulators are pressurized by the accumulator valve which pressurizes fluid between the separator plate and each accumulator's piston. This accumulator fluid is the critical part, the springs modify the feel.

BigVin

In the 1/2 accumulator I have one yellow spring. I'm no trans expert but I think this trans has a shift kit in it. I put the tcc valve in and boost valve in. I though this was a stock 96 out of an Astro van. Valve body has a 93 cast into it. I would like to find out what year this trans is? Again this is in 68 Camaro with a PCS comp. trans shifted good except the hard low speed 1/2 shift. thanks for the help so far
trans id above pan rail pass side is 6wbd050b thats all I can find

BigVin

anyone?