GM 700-R4 questions.....

ss wannabee · 08-05-2010, 10:05 AM

Sorry for the non-performance questions...but my street vehicle ('88 s10 Blazer-2.8) lost both TCC and overdrive a few months back. When I say "lost"...they both come back from time to time....but VERY intermittent...Yeah, the truck should be in a boneyard...it has about 265K on it but still runs.... The other shifts seem ok...trans doesn't seem to be slipping...but I try to avoid highway driving...it's tough in 3rd gear...also the "check engine"
light comes on when doing over 50 with that high-mileage V6 screaming...but I think that's the vehicle speed sensor asking the computer...."where's overdrive?" I adjusted the TV cable with little results.....

I've been driving the truck anyway with mostly city driving and it does ok...but eats a bit more gas...Want to fix for highway diving...and want to try a "fix" WITHOUT complete over-haul.

Was thinking replace the TCC solenoid...and do a valve body cleanout...am I headed in right direction? Not sure if I want to drop the v/body....(too many pieces to lose)....how about a pour-in cleaner in this case? How about a product called "Sea-Breeze"...anybody use this stuff?

Alan Roehrich · 08-05-2010, 10:42 AM

Do not put Sea Foam in a transmission. Sea Foam is a good product, used in your fuel system. You might try a can of Trans Medic, followed by a complete fluid and filter change (if you do that, please make sure the old filter seal is removed before you install the new filter).

Have the computer scanned to see exactly what codes it has.

If the rest of the shifts have a normal feel and occur at the correct time, the TV cable is adjusted close enough that the cable is not causing a problem with OD and lock up.

Fourth gear, AKA over drive, should occur around 38-48 MPH under normal conditions on a level surface, followed shortly afterward by lock up, there are two separate events. Fourth is normally supposed to happen first, then lock up at around 45 MPH. Sometimes, on certain vehicles, lock up can happen first, leading to a somewhat harsh 3-4 shift. They also sometimes happen at the same time, leading to a stacked shift feeling.

Fourth gear is strictly a mechanical and hydraulic function, there is no electrical signal involved. Fourth gear is a combination of the 3-4 clutches and the 2-4 band, so if you have 2nd gear and 3rd gear, you have the friction materials to have 4th gear. If the vehicle will take off from a complete stop with the gear selector in D or OD, the over run sprag is good. So, if you have 2nd gear, 3rd gear, and do not need manual low (L1) to take off from a standing stop, you have what is necessary for OD or 4th gear. At that point, 4th gear becomes a valvebody problem, or possibly a servo problem. The servo is on the passenger side of the case, behind the filler tube, in front of the TV cable. It's the large round piece. I would not advise you fool with it if you are not well versed in transmission work.

It is possible that, the TCC solenoid is bad, the o-ring on the end of the solenoid is bad, one of the pressure or temperature switches that is in line with the TCC solenoid is bad, the brake light switch is bad, a fuse is blown, or you have a bad ground.

I would start with the fuse panel, then check the brake light switch (the part that controls the lock up solenoid is on the end, not on the side, there are two, 2 wire connectors). Any slight pressure on the brake pedal, or adjustment problem, can open that switch and stop lock up from happening. Then look for a vacuum switch on the firewall. Check power to the vacuum switch, and then check vacuum.

Rob Petrie E395 · 08-05-2010, 12:00 PM

When you pull the pan off disconnect the TCC solonoid and measure it with a ohm meter. If its more than 30 ohms its junk. Not a real uncommon problem and cheap to fix. To adjust the brake light switch start the truck and push the pedal down there will be a little *** hanging down off the switch push the *** back towards the seat and let the pedal go and its adjusted. The switch can be the problem too but if the truck has antilock brakes it will usually set a antilock brake code before it will start overriding TCC lockup. If the light on the dash stays on even when the emergency brake is off start with the switch adjustment and clear the code before pulling the pan it might save you some work. Another common problem on these trucks is 2 foot drivers (using one for the brake and the other for the gas) if you drive like this it will cause all kinds of problems with TCC & antilock brake codes.
Hope this helps
Rob

One more thing I just thought of check the fuse for the cigerette lighter. On some of these trucks the cig lighter and the tcc solonoind are on the same fuse. I know its stupid but its the way they did some of the trucks back then.

Alan Roehrich · 08-05-2010, 12:19 PM

Thanks Rob. I never can seem to remember it all. I always forget some of the stuff I should remember, no matter how much I remember.

Rob Petrie E395 · 08-05-2010, 04:29 PM

Quote:

Originally Posted by Alan Roehrich

Thanks Rob. I never can seem to remember it all. I always forget some of the stuff I should remember, no matter how much I remember.

Hey I forget more than I can remember LOL! I just work on alot of trucks being in farm country and if you could see some of the stuff that comes into my shop you would know why I remember the older stuff better than the newer stuff. Some days I would kill to do a oil change on a nice new one.

ss3011 · 08-05-2010, 08:01 PM

This is a cable operated transmission, and shifts based on road speed and throttle cable position. As an engine loses power, when it is old and worn out, or out of tune, you have to step on the throttle more to get the vehicle down the road. Sometimes we have seen this happen if the catalytic converter gets plugged. Many times these old vehicles are so weak, the throttle position needs to be opened so high that all the upshifts feel delayed, the fourth gear shift is at a higher mile per hour then you are going. Does the transmission shift into overdrive if you backoff the throttle but downshifts back into 3rd if you step back into throttle , to maintain road speed ? Same could be happening with the TCC. There is a throttle position load release for TCC. So once the TP is higher than a calibrated number, say 30% then TCC will not come on.

08-05-2010, 10:05 AM	#1
ss wannabee Senior Member Join Date: Jun 2005 Posts: 663 Likes: 0 Liked 7 Times in 7 Posts	GM 700-R4 questions..... Sorry for the non-performance questions...but my street vehicle ('88 s10 Blazer-2.8) lost both TCC and overdrive a few months back. When I say "lost"...they both come back from time to time....but VERY intermittent...Yeah, the truck should be in a boneyard...it has about 265K on it but still runs.... The other shifts seem ok...trans doesn't seem to be slipping...but I try to avoid highway driving...it's tough in 3rd gear...also the "check engine" light comes on when doing over 50 with that high-mileage V6 screaming...but I think that's the vehicle speed sensor asking the computer...."where's overdrive?" I adjusted the TV cable with little results..... I've been driving the truck anyway with mostly city driving and it does ok...but eats a bit more gas...Want to fix for highway diving...and want to try a "fix" WITHOUT complete over-haul. Was thinking replace the TCC solenoid...and do a valve body cleanout...am I headed in right direction? Not sure if I want to drop the v/body....(too many pieces to lose)....how about a pour-in cleaner in this case? How about a product called "Sea-Breeze"...anybody use this stuff?

08-05-2010, 10:42 AM	#2
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,118 Likes: 1,573 Liked 1,837 Times in 417 Posts	Re: GM 700-R4 questions..... Do not put Sea Foam in a transmission. Sea Foam is a good product, used in your fuel system. You might try a can of Trans Medic, followed by a complete fluid and filter change (if you do that, please make sure the old filter seal is removed before you install the new filter). Have the computer scanned to see exactly what codes it has. If the rest of the shifts have a normal feel and occur at the correct time, the TV cable is adjusted close enough that the cable is not causing a problem with OD and lock up. Fourth gear, AKA over drive, should occur around 38-48 MPH under normal conditions on a level surface, followed shortly afterward by lock up, there are two separate events. Fourth is normally supposed to happen first, then lock up at around 45 MPH. Sometimes, on certain vehicles, lock up can happen first, leading to a somewhat harsh 3-4 shift. They also sometimes happen at the same time, leading to a stacked shift feeling. Fourth gear is strictly a mechanical and hydraulic function, there is no electrical signal involved. Fourth gear is a combination of the 3-4 clutches and the 2-4 band, so if you have 2nd gear and 3rd gear, you have the friction materials to have 4th gear. If the vehicle will take off from a complete stop with the gear selector in D or OD, the over run sprag is good. So, if you have 2nd gear, 3rd gear, and do not need manual low (L1) to take off from a standing stop, you have what is necessary for OD or 4th gear. At that point, 4th gear becomes a valvebody problem, or possibly a servo problem. The servo is on the passenger side of the case, behind the filler tube, in front of the TV cable. It's the large round piece. I would not advise you fool with it if you are not well versed in transmission work. It is possible that, the TCC solenoid is bad, the o-ring on the end of the solenoid is bad, one of the pressure or temperature switches that is in line with the TCC solenoid is bad, the brake light switch is bad, a fuse is blown, or you have a bad ground. I would start with the fuse panel, then check the brake light switch (the part that controls the lock up solenoid is on the end, not on the side, there are two, 2 wire connectors). Any slight pressure on the brake pedal, or adjustment problem, can open that switch and stop lock up from happening. Then look for a vacuum switch on the firewall. Check power to the vacuum switch, and then check vacuum. __________________ Alan Roehrich 212A G/S

08-05-2010, 12:00 PM	#3
Rob Petrie E395 VIP Member Join Date: Dec 2007 Location: Woodlawn IL Posts: 1,092 Likes: 162 Liked 216 Times in 77 Posts	Re: GM 700-R4 questions..... When you pull the pan off disconnect the TCC solonoid and measure it with a ohm meter. If its more than 30 ohms its junk. Not a real uncommon problem and cheap to fix. To adjust the brake light switch start the truck and push the pedal down there will be a little * hanging down off the switch push the * back towards the seat and let the pedal go and its adjusted. The switch can be the problem too but if the truck has antilock brakes it will usually set a antilock brake code before it will start overriding TCC lockup. If the light on the dash stays on even when the emergency brake is off start with the switch adjustment and clear the code before pulling the pan it might save you some work. Another common problem on these trucks is 2 foot drivers (using one for the brake and the other for the gas) if you drive like this it will cause all kinds of problems with TCC & antilock brake codes. Hope this helps Rob One more thing I just thought of check the fuse for the cigerette lighter. On some of these trucks the cig lighter and the tcc solonoind are on the same fuse. I know its stupid but its the way they did some of the trucks back then. Last edited by Rob Petrie E395; 08-05-2010 at 12:03 PM. Reason: added last part

08-05-2010, 12:19 PM	#4
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,118 Likes: 1,573 Liked 1,837 Times in 417 Posts	Re: GM 700-R4 questions..... Thanks Rob. I never can seem to remember it all. I always forget some of the stuff I should remember, no matter how much I remember. __________________ Alan Roehrich 212A G/S

08-05-2010, 08:01 PM	#6
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: GM 700-R4 questions..... This is a cable operated transmission, and shifts based on road speed and throttle cable position. As an engine loses power, when it is old and worn out, or out of tune, you have to step on the throttle more to get the vehicle down the road. Sometimes we have seen this happen if the catalytic converter gets plugged. Many times these old vehicles are so weak, the throttle position needs to be opened so high that all the upshifts feel delayed, the fourth gear shift is at a higher mile per hour then you are going. Does the transmission shift into overdrive if you backoff the throttle but downshifts back into 3rd if you step back into throttle , to maintain road speed ? Same could be happening with the TCC. There is a throttle position load release for TCC. So once the TP is higher than a calibrated number, say 30% then TCC will not come on.