turbo350c

[Canadian 4X4]

i am looking at a truck that has a 355 350c 373. its an 86 2wd shorty. when driving the truck at 50-55 it almost feels like the convertor is locking and unlocking. kind of like a surging feel. it isnt a problem at 30 or 70. the current owner is putting in a new convertor. he said when the driveline was first built it had 2.73s or 3.08s in it and it was never an issue. if the new convertor isnt the right fix, does anyone else have any ideas?
thanks in advance.

[454Man]

My truck still has the original gears that are for a 700r4. I to have the th350c... 55-60 the rpms are well above 2200. I may or maynot be on the right path, but I think if you still have that little lock up vac pod hooked up that may be the issue. Since it senses vacuum there may not be enough vac to lock up the convertor. You can check by bypassing that lock up deal and wiring up your own. Maybe someone else might say somethin diff.also check the rpms at the speed you are saying the problem exist

[bd]

Adjust the brake switch at the pedal arm under the dash.

[bake74]

Adjust the brake switch at the pedal arm under the dash.

      Are you talking about the switch for the brake lights, when you depress the brake pedal and the brake lights come on ?

[bd]

Adjust the brake switch at the pedal arm under the dash.

      Are you talking about the switch for the brake lights, when you depress the brake pedal and the brake lights come on ?

Hi Bake.  TCC is disengaged with brake application.  If the brake switch is right at the edge of its adjustment, pedal vibration at cruise can cause the switch to make and break contact and TCC will drive you nuts disengaging/engaging.  Same thing can happen if a driver hovers the brake pedal with a foot, using it like an ottoman.      The brake switch can be easily knocked out of adjustment if a driver catches a foot under the pedal by accident and lifts slightly.  It's one of those simple things that can burn hours of diagnostic time the first time around.   

Edit:
In fact, if you think you have a TCC issue but aren't sure, lightly step on the brake pedal at road speed to disengage TCC and see if the symptoms go away.

[bake74]

     Thanks for the explanation.

[Canadian 4X4]

i did  as you said and lightly pressed the brake at cruising speed and the surging stopped. the switch i need to adjust is on the brake pedal?[/img] [/img] is that the switch i need to adjust? one picture is the pedal at "home" the other is depressed as far as i could with my hand

[bd]

Your image isn't displaying.  Adjust the brake light switch under the dash, so the brake lights come on with about 4 - 6 mm of pedal movement (you may have to experiment a little bit).  Your switch should be similar to the one pictured, depending on whether you have factory cruise control.