Ok so my knowledge is limited here. I know 700r4s are known for 3/4 clutches going out. This build im doin has been a nightmare. Its a 92 s10 blazer v8 conversion. When i bought this thing it was in limp mode with bad wiring and sensors. Fixed everything, 350 started knocking. Replaced with an L05 Lt1 police engine, mated to the 700r4 the vehicle had mated to 350. Idk if its original 700r4 because the 4.3s did have 700r4 to my knowledge. Well 30 miles down road trans blew 3/4 clutches. they were FLAT when i tore down.
Replaced plates, clutches, torque convertor, oil pump, all seals and gaskets, installed complete shift kit with corvette servo, filter and screens, blocked off the right holes, new valve body plate. The oil pump was an upgraded 10vane billet oil pump. The TC was a mild upgrade, not a stall. Dang near 1500 miles on fresh install the 3/4 clutches burn out AGAIN. Its the right tv cable the only issue i had was it was the wrong ecm so it would cycle 3/4 gears at 30mph but i installed ratchet shifter and used it to get to 0D 90% of the time. It seemed like a soft shift from 2to3 occasionally. What did i do wrong? This is a 3rd gen(depending on what you consider 1&2 to be) rainbow cast with aux valve body and lockup 700r4. The blazer has 287,000 miles on it so i doubt if its orig trans.
On a 700 with TV cable, the ECM only controls converter lockup. It has nothing to do with main gear changes. The governor and TV cable control those.
The symptoms you describe are most likely pressure related. The TV cable would be the first thing to suspect. Crosley has already hit the main points. 700's will die a quick death if the cable isn't adjusted properly or moving at the correct ratio. A TBI throttle body "SHOULD" be moving the cable correctly, but that's not a given. I would look at cable adjustment.
The only way to be certain you have good pressure is to hook up a gauge and check.
If the cable is good and you can't get pressure, then something isn't right inside.
Did you pressure check 3/4 clutchs when it was rebuilt/compleat?
New lip seals on all the pistons inside the 3/4 clutch pack?
Most likely to late now but you should of pressure checked it before ever driving it. That port above the the shifter that has a 1/8 threaded plug in it. You can get a pressure gauge at Northern Tools, 300 psi. I bought fittings at Home Depot. Buy 4 ft. of high pressure hose, 1/4 id. I used some cutting torch hose laying around I didn't need. Had the back tires off the ground an ran it thru the gears while watching the gauge. The TV cable is life & death for 700's. A common probulm on 700's is low pressure to the 3/4 clutches, not enough pressure on the clutches & steels then they slip & over heat an fail.
The guys above have given you good advise. The only thing I will add is that once you get the trans torn down again PRESSURE TEST the input drum to see if it is leaking between the turbine shaft and the aluminum drum itself. If the shaft press-fit has been compromised, you will continue to burn up the 3rd & 4th clutch pack. But, this would be the last thing I would be worried about. Most likely a TV cable adjustment, or geometry issue, or other internal issue with the trans.
LO5 and LT1 aren't the same engine. LO5's are GEN I TBI engines with different trims between passenger or cop cars and trucks. The LT1 is GEN II reverse coolant flow engine using injection more similar to TPI. The whole engine that is way different looking and functioning than GEN I engines.
The 700R4 is extremely sensitive to TV cable adjustment, it is best done with a pressure gauge and the service manual, small misses in the adjustment quickly become a disaster and that's easy to do especially on S10 conversions.
The computer has no control on 700R4's except for converter lock. The computer only controls shifts on the 4L60E that came in 1993 and on. The 700R4 behind the 4.3's does not last long behind a V8. If you have a computer controlled transmission it will have a really big connector and cable going into the casting above the pan on the passenger side and no TV cable.
The lack of the 3-4 shift you've experienced also shows something is wrong.
They gave you good advise. Always put in bigger valves in the pump for more pressure and use that gauge. Is cheaper to buy the gauge set and take the time than to screw it up. Its like buying a small insurance policy, and every year or so, put the gauge back on it to make sure it stays right.
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