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700R4 help please

F-ingrob

F-ingrob

Wheres the mud
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Jun 13, 2013
Posts
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Location
san francisco ca.
today while driving home from my ranch (4 hour drive at 75 MPH)
i noticed that my trans temp started going up
the censor is in the return line from the cooler and it went up to 170 and normally runs lower than 160
out side temp was about 45-50 degrees
i slowed down and put it in 3rd and cruised at 65 and the temp dropped down to 130-140
after while i put it back in 4th and it slowly went up again
my converter doesn't lock up cause i have it disconnected as i now run a carb instead of TBI
its a 87 with 4.10 gears and 315/75/15 Yokohama mud tires which are about 34 inches tall
after a couple hours driving i stopped for gas and when i started to drive again it now takes longer to shift out of 1st and second but still has a firm shift
any help from would be great thanks
 
Kinda sounds like that OD with no lockup is heating up the fluid. Any way to put that back in?
 
i was planning on it i had to order a new harness for the trans to make it stand alone and i also ordered a new corvet servo to help with 4th gear pressure
im just hoping its not going out
 
Sounds like a fluid/ pressure thing. 3rd gear or the whole tranny going is the typical death of a 700r4. Yours should be ok. Are you in sf or near it?
 
i am in SF
2 trips ago to my ranch i towed a 7000 pound trailer and the temps stayed at 160
just seem kinda strange
im going to change the fluid and filter this week end and check the TV cable as well as install the new servo and converter lock up kit
 
wow, 170 is cold lol but I'm not sure how to judge that. My sensor is in the pan and I've wheeled entire days with it over 200, sometimes a couple hours over 220. Truck seems fine but the trans is built and I run Amsoil. If you are super concerned, change the fluid out and have a look see. :)
 
No lockup and lots of highway driving will result in the fluid heating up. Yours doesn't seem hot enough to be concerned about, but anything outside of what you know as normal for your truck merits some inspection.
 
a little off topic...I have an 83 K5, with a 700R4 w/ temp gauge and lockup switch. I admittedly rarely use the switch. Even on the highways where I am, I hardly get to cruise in 4th long before hitting traffic, and then I drive myself crazy worrying that i'll forget to shut it when I do.

So... if I'm not using the lockup, should I drive in 3 instead? I do about 50 miles each way to work, and maybe drive in 4th for one steady 15m clip each way, aside from that it's stop&go, slow, fast, etc
 
The thing to do is use the complete factory setup for lockup control, with the brake pedal switch and vacuum switch. There are aftermarket solutions (i.e. speed based), but all are inferior to the factory setup.
 
Firmer plus holds the gear longer under hard throttle. It's crisp under lite throttle.
 
Blue85 said:
The thing to do is use the complete factory setup for lockup control, with the brake pedal switch and vacuum switch. There are aftermarket solutions (i.e. speed based), but all are inferior to the factory setup.
Click to expand...
I have the brake switch, (so that the lockup disengages when the brake's applied) but not sure about the vacuum switch, what does that do?
 
F-ingrob said:
how did you find out?
Click to expand...

Took my Suburban out for a 400-mile towing adventure. 700R4, no T/C lockup. Tranny stopped shifting properly 1/2-way through, shortly after a series of steep grades. By the time I got home it was manifesting failure signs.

Story in my Suburban thread, tranny discussion starts here:
ck5.com/forums/threads/313869/page-10#post-3566233

Very light clutch engagement, shifting is spotty/fickle, when it warms up 4th gear completely disappears.
Fluid is still full, and nothing outside the tranny appears to have changed. I have driven it around a few times since then, and it's almost undrivable now. I haven't pulled the pan yet to see what's in there, but at the very least I had an unfun trip. And there's a pretty good chance that I toasted the tranny. :doah:

My advice: Don't be stupid. :haha: I mean, watch your temps (I didn't have a gauge, perhaps it would have told me to stop :dunno:), and get the T/C working. I would not have thought that a trip across mostly flat ground with almost no downshifting would have caused problems. But I don't think it's coincidence that it failed after the steep section of road. The truck was definitely working harder to climb those grades.
 
prolinews said:
Firmer plus holds the gear longer under hard throttle. It's crisp under lite throttle.
Click to expand...
The 'vette servo is a mixed bag. Obviously the reason people use it is the increased band holding power. Since it's bigger than stock it engages and disengages slower. So in some cases the 2-3 can bind if you make this change without any other mods. Ideally you will match valvetrain mods at the same time.

RobTav63 said:
I have the brake switch, (so that the lockup disengages when the brake's applied) but not sure about the vacuum switch, what does that do?
Click to expand...
The vacuum switch is normally located kind of underneath the brake booster and looks like this:
VacuumSwitch.jpg


It makes the TCC unlock at heavy loads (like passing). There are several variations of internal wiring for "carb" 700's, but in general the transmission has a hydraulic circuit that looks at vehicle speed (i.e. governor) and throttle position (i.e. TV) to provide a lockup signal. That combined with the vacuum (i.e. engine load) and brake switch wiring makes the whole setup work pretty well.

For the "TBI" 700's, the ECM controls the lockup directly, but in series with the brake pedal switch. If you can source a vacuum switch and also put a pressure switch on the 4th gear test port and put both in series with the brake pedal switch, that should work OK.
 
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