700R4 overheating...???

Just had a thought... A while back my K5 started overheating. It had been off the road for many months. After I got it running again, I had the transmission rebuilt. I didn't ever drive it before rebuilding the
tranny...
After that, it overheated quite a bit, while driving. At first I thought it was happening at idle, and posted here stating exactly that. I flushed the radiator with store-bought products, pulled it out and did the vinegar thing...even took the heater core out of the equation.
On the trip when the (rebuilt) rear axle gave up the ghost, I paid better attention. It was doing the overheating while I was driving. When I'd actually stop and let it idle, it would eventually cool down. Now since the tranny lines connect to the radiator, is it possible that it was to blame?? That maybe it was heating up while I was driving and transferring that heat to the radiator faster than the radiator could shed it?
It does have an auxilary tranny cooler on it, something that cost like $30 from Auto Zone or a similar parts store--that's not a new addition, been there for a while...
Also, since I lost the electronic TC lockup harness in the fire, they claimed that they'd built the tranny so that it would lock up on its own in 4th gear. I never could feel it lock and I felt that the engine RPMs were too high for the speed I was traveling with my axle ratio...
Thoughts? Ideas?
~jp
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wrote:

Well is the TC lock harness is missing, it is not likely locking and with a .70 OD gear ratio, unlees you have pretty deep gearing when it is in OD and the converter is not locked it will be riding on the edge of the stall making extra heat. Espaecail if you are pushing some rubber too. If you use link below it will calculate torque converter slippage. For gear ratio just plug in axle ratio times .7 for OD if you are check slippage in 4th.
http://forum.snoman.com/slippage.php ----------------- TheSnoMan.com
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Well I can't check it now, but I was pulling roughly 2000rpm @ 75mph, with 31" tires and a 3.73 gearset in the axle... (3.73 * .7)
So...the link gave me a slippage percentage of -6.17%.
Keep in mind, I told them about the missing TCC harness up front, and they said it wouldn't be a problem, as they were going to build it to lockup without electronics. The manager at the shop said he'd put 700R4s into a lot of older muscle cars without the aid of electronic lockup.
I just question how well it actually works or whether they indeed did that. So what does the slippage percentage mean?
~jp
SnoMan wrote:

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As far as the shifting/lockup without the electronics, I can vouch for that. I had a 700R4 rebuilt and put it in my Blazer. It broke 4-5 times but they eventually got it straightned out and has worked fine for the lase several years. I never did look into exactly how it shifts but I think it's the position of a valve hooked up to the cable to the carb linkage. I do recall that's the only shift point adjustment I had to play with. LD

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Was it overheating on you too? The cable running to the carb is the throttle valve cable. I know that controls the pressure of the fluid in the tranny, but exactly how it does it internally in the tranny is beyond me as I haven't yet delved into the world of tranny repair.
~jp
LD wrote:

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I can't claim to be a expert but the only way I know to allow TC lockup is by using the TCC solenoid. A very simple way to control lockup is by running +v through your brake switch and then into the 4 prong connector in your tranny. You don't need any ECM input this way but you still have 1 wire going to the plug.All other switches such as temp and downshift switches are available as case grounded single prong switches that are wired in series with the TCC solenoid. You have to have your brake switch in series to prevent the TC from being locked while you have the brake on, would be like braking a standard with the clutch engaged. It is common practice to disable the TCC solenoid and replace the TC with one designed for a nonlockup 700, basically making it a THM 400. If you have nothing plugged into the 4 wire connector on the drivers side of the case, just above the pan, I doubt you have any TC lockup. At least I don't know how to make it work like that. If anyone else does please let me know. I would guess that it is very unlikely for your in radiator cooler to transfer enough heat from the tranny to overheat the vehicle. If the tranny was getting that hot you would have surely fried it by now. There is a line pressure check port directly above where the shift linkage enters the case. I believe it is 1/4 npt. This is a check port for diagnosing the tranny, very helpful to use a pressure guage with a long hose and watch it during driving. You can also screw in a temp sender here to check your tranny temp

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Thanks for the good info David... I will look into the electronic lockup thing as soon as I'm able to work on the truck again.
The overheating issue really has me scratching my head. It never overheated before the engine fire that took it off the road. After I got it running, I couldn't drive it due to the TV cable being toast. The tranny shop (of course) stated that the 700R4 was in need of a rebuild anyway, and then when it turned out that the case was damaged, it was just replaced with a used tranny rebuilt by them.
Unfortunately, this means that several changes were made before the truck was on the road again, (wiring harness, tranny swapped and with a different lockup configuration, carb changes, plus sitting for almost 6 months) so I can't simply point to any single change as the likely culprit.
I definitely want a tranny temp gauge in the cab. I'll probably follow your suggestion and install one ASAP. I'd been planning that anyway.
Thanks again,
~jp
David Johnson wrote:

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Mine never overheated. One failure was blamed on a defective (and too small) TConverter. Apparantly there's two models which are different diameters and have different bolt holes in the flex plate. I installed everything myself and can vouch for the fact that the only hookup is with the throttle cable which has some very fine adjustment positions (for shift points). I seem to recall that I was told the shifting is controlled only by the valve body and pressure in this modification. I definitely have 4 "gears". The TC locks up around 40mph. I was told that a "little" off on the throttle cable adjustment can cause slippage (and maybe overheating). LD

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Warning, THE TV CABLE IS NOT INTENDED TO ADJUST SHIFT POINTS. DO NOT USE IT FOR THIS PURPOSE.

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As I understand it, there is a position that is optimal. A click in or out from this point is still OK and WILL change the shift points. Too much deviation from the optimal can damage the transmission. As I recall, the "starting point is to adjust tight and maybe with some help, mash the pedal to the floor, causing the adjustment to "slip" into the correct position. this may work only with the modified valve body for the non-electric shift. LD

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wrote:

It means that basically 6 5 of power is being lost to pumping loss and heat at cruise or more simply for every 100 RPM's the engine develops, the inputshaft to transmisson does 94. ALso I might mention that early 700R4 did have tranny cooling isues that were partaily resolved in 84 and fully resolved by 87 models. I seem that from 81 to 83, GM mostly bypassed the tranny cooler in OD (not completely but the majority of the flow to it was bypassed) and this caused a lot of heating problems. Not quick sure what their logic was for doing this at first either. ----------------- TheSnoMan.com
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