700R4 went out while towing. Culprit?

[OuchMyToe]

I'd like some help identifying three likely culprit (besides myself) to my transmission going out. I need more information before I make decisions about fixing/upgrading it. Here are the circumstances:

It's an '85 C10 into which I've put a 400 SBC. I believe it was a stock 700R4. I was towing a light-weight unloaded trailer up and down hills at 60 to 70 mph at night.

First, ATF blew out the dip stick and covered everything. Then I lost power. Since I was blocking a lane on a rural highway at night, I needed to move it as quickly as possible. I added ATF and got first gear back for about 120 seconds. Added more and got first gear again for 2 more minutes. Added a bunch this way until it seemed full (?). After that, I didn't add more but let the truck sit for a couple minutes after which I got about 30 to 45 more seconds of first gear. I did this until I reached a pullout and then finally got the truck towed home.

It will still go in first for about 45 seconds. It never shifted into 2nd and there's absolutely no response (no noise at all) when shifting into reverse—not even after letting it sit.

I should mention that this episode was the first indication ever that the trans was at all unhappy. So...

1st, has anyone experienced this before and if so, what was the prognosis?

2nd, I've always suspected that pairing the 400 sbc with a 700r4 might be asking for trouble; is this true? (I did put on the externally balanced flexplate). I originally intended to stick a turbo 400 in the truck but was always hesitant to lose overdrive (as a 2wd, this is mostly a highway truck). I also believe that modding the driveshaft to fit the th400's extra length is beyond my ability to do at home. So, should I keep it with a 700r4 or pay someone to put in a turbo 400?

 

[Big Chip]

If you were in OD that's going to be most of your issue I think. I would get it rebuilt and roll with it and remember to use 3rd when hauling anything besides your lunchbox.

 

[Termite_Delight]

Did you use the the 700r4 cable bracket?
Did you have the cable adjusted properly?
Did you use the '85 carburetor or the one with the 400ci ?
There are many different variations of brackets for accelerator and detent cables for small blocks.

 

[OuchMyToe]

Did you use the the 700r4 cable bracket?
Did you have the cable adjusted properly?
Did you use the '85 carburetor or the one with the 400ci ?
There are many different variations of brackets for accelerator and detent cables for small blocks.

I'm using the q-jet, bracket, etc. I believe it was all adjusted "correctly" but if this failure is indicative of an incorrectly installed cable then please let me know. That being said, it is a franken-truck so...yeah. And while the carb is kind-of stock (the stock carb was that weird m4med q-jet), because of money and transportation requirements I had to mess with a bunch of stuff to get it running. However, it's run without a problem for 2 years now.

 

[Matt69olds]

The TV cable needs to be right, close enough won’t get it done. Ideally the cable needs to be adjusted with a pressure gauge connected.

Unless you have a really stout 400 engine (500-600 hp) a 700 is just fine.

Drop the pan, I bet you find a bunch of crud in the pan. That’s the remains of the clutches and band.

When you rebuild the trans, install the raybestos Z pac, wide band, upgrades drive shell, updated input sprag, hardened pump rings, and a decent shift kit.

Once all that is done, make absolutely sure the TV cable is adjusted right. The line pressure needs to increase as soon as the throttle is increased.

BTW, the linkage on a old school carb for the kickdown linkage won’t work for a 700.
Read this, even though it says 2004R, the process is the same.

https://www.ckperformance.com/Files/112573/ThrottleArmTVarticle.pdf

 

[Dave M]

Are you running a Transmission Cooler? You've cooked the trans.

 

[shiftpro]

What size tires and what is the final gear ratio?

 

[yevgenievich]

+1 on what Matt69olds posted. And trans cooler. Generally should tow in 3rd if it shifts alot when in od. Probably overheated, then burned some clutches and then clogged filter causing only being able to drive for a minute or so.

 

[Nasty-LSX]

I build stock and performance transmissions. For my 2 cents, if you towed in overdrive that fast you cooked the TC. If you have no external cooler you cooked the trans to. I bet you fluid is black. Get it rebuilt with upgraded parts and put a big cooler if front if you going to be towing.

 

[Itali83]

Don’t forget about making sure converter lock up is working. If that isn’t working, which I bet it isn’t since that’s the first thing everyone does when the monkey with these trucks is throw away all the digical “garbage” under the hood in the trash which includes the vacuum switch for lockup. A non functioning lock up converter is the biggest maker of heat there is.

Ben

 

[oldretiredafguy]

Did mine the same way several years ago: towing in OD as opposed to dropping it down into 3rd. Expensive life lesson you will never forget!

 

[Matt69olds]

As long as the trans isn’t constantly shifting/downshifting between 3-4, the converter doesn’t slip or chatter, and the engine doesn’t lug, you can tow in overdrive. The “don’t tow in overdrive” rule of thumb came about because the weezing engines of the early 80s barely had the power to pull the truck unloaded, put any weight behind the truck and the nonstop shuttle shift overheated the trans.

The 3-4 clutch has been a issue with the 700 since day one. The trans originally had 5 clutches, then later in its production run they made engineering changes to fit 6, when the 4L70 came out they upgraded to 7. The problem with adding more frictions in the same space requires thinner clutches/steels. The thinner parts don’t handle heat nearly as well. They warp, burn, glaze, once that happens it’s all downhill

The ultimate fix is the Raybestos Z Pak, it uses 12 single sided frictions. The 12 thick single sides frictions offer more surface area, and radiate heat better than thinner clutches

 

[M00SE]

My bet is the lockup was never plugged in or converted. Need a rebuild but like others say... Use all the upgrades and you will get plenty out of the 700. Big cooler! There is a small "breather" tube on top the trans. Run that down away from exhaust to prevent a fire if it ever over heats again.

 

[sirweesarunch]

https://www.bowtieoverdrives.com/. Talk to these people , they are 700 r 4 experts


Sent from my iPhone using Tapatalk

 

[OuchMyToe]

Are you running a Transmission Cooler? You've cooked the trans.

LOL! Yes. Yes I have. There's the stock transmission lines running to and from the radiator. Because of the all the tweaks I had to make, it's got a somewhat upgraded cooling system (4-core rad, upgraded fan, etc.). I was planning to add an aftermarket trans cooler though.