Automatic Overdrive Caution !!!

[dq409]

There has been severals posts on the use of the automactic overdrives and I though I would throw in this caution that hasn`t been mentioned.

NEVER drive the car in overdrive (4th) without the converter locked !!!

This will cause extreme heat and burn up your trans in short time !!!

,,dq

 

[DIV1RACER-2]

Lockup

That is an old wives tale!!! Voice of experiance !!

 

[Bungy]

So what prompted this alert?
Sounds like a bad experience talking.

 

[tripowerguy]

My 200-4R has servos to lockup in 3rd and 4th gear after 45mph. I clipped the wire going to the 3rd gear servo so it will only lockup in 4th gear. One of my friends has a Studebaker with a Cadillac engine and a 200-4R. He had a trans shop build his trans and the shop said he didn't need a lockup converter. He blew up the trans on the Hot Rod Tour. SOOOOO I still think I will always use the lockup on the road. Roy

 

[dq409]

I`ve was told this by several trans techs.

When I bought my Astro van the converter would not lock up.
The seller told me this when I bought it.
He was having computer problems with the van and unpluged the trans from it at the trans.
I think the converter would not un-lock at stop lights.

He just had the trans rebuilt just before I bought it and the computer quit working all together shortly after that.
He replaced the computer but never plugged it back into the trans.
I bought the van and on the way home put 2 & 2 together, pulled over and plugged the computer back in to the trans.
The converter would now locked up !!

The old owners used the van to commute to work about 20 some miles each way.

I mentioned this to a trans tech shortly after that and he told me the burn up theory.
Several other trans shops I asked also agreed.

All agreed that the trans would die a slow death on short trips but on a long trip at highway speeds it could burn up in several hundred miles.

I`m just passing along what I`ve been told.

The trans in my van gave up the next year after I bought it. ,,,dq

 

[rwagon57]

I have 45,000 miles on a non-lockup F%$# AOD with Zero issues, fluid is clean, red, and smells new.

I have 15,000 miles on a non-lockup 700R4 in a '66 Buick Skylark with the exact same outcome.

Both transmissions were purpose built for their respective applications as non-lockup transmissions.

BTW the AOD is in a 4,000 pound station wagon with ~ 420 HP at the crank.

 

[models916]

Cool Man!

Fluid temp is the key answer here, lockup or not.

 

[rarerodder]

It's all in the fluid

Models is correct, the ultimate answer is fluid temp. Now I don't profess to be an expert on the subject but I just happened to be talking with my uncle on the phone when I read this. His credentials are: he has been buiding hot rods for about 40 years, he raced stock cars for a good while in the 70's, and-he's owned a AAMCO transmission shop for over 30 years. He explained how the overdrive does generate alot more heat from the inefficiency of the higher gear which is, of course, the purpose of the lock up mechanism-to eliminate the inefficiency of the fluid against the turbines in the converter. So, the lock up is definitely a good idea but not mandatory if you have a good or heavy duty trans cooler. His advice-be safe, buy the lock up aftermarket kits or use the computer and keep a good cooling system at the same time.

 

[MileHiSS]

Why would you not want the convertor to lock up?

 

[348NUT]

My 2 cents

I agree that it is certainly best to lock the converter, but I have put many thousands of miles on two used 700r4s with non locking setups with no issues. Not only did I drive the 55 to the convention 500 miles one way but drove my 56 from MN to Spokane, WA a few years ago driving straight for 24 hrs only stopping for gas! That car has 2:46 gears (no that's not a typo) so I haven't been in too big of a hurry to pull the pan and do the lockup wiring. The 56 has a standard in radiator cooler and the engine tends to run hot too. Something to keep in mind though. Thanks for the warning dq. NUT

 

[dq409]

Both transmissions were purpose built for their respective applications as non-lockup transmissions.

seems you did it right !!

I don`t know why I have been told this by several unrelated shops??

Thought I just pass it along,,,,dq

BTW,,, Anyone know the best rear gear ratio for a 700R ?
The gears in the Blazer are to high IMO and at freeway cruzining sometimes it seems the ratio is right in the middle between high and lockup. If driveing around town it seems best to drive it in third other wise it shifts back and forth,,,dq

 

[rwagon57]

What I didn't say earlier was that the F%$# wagon cools the AOD with a stand alone 24,000 GVW cooler mounted in front of the radiator. I actually use a thermostatic control valve to keep it from running cold in the winter.

As for gear ratios with an OD trans, select a ratio based on tire diameter and OD ratio that will put your desired cruise RPM at your desired Highway cruise speed. You will need to determine at what speed/rpm the convertor locks and factor that in also.

Again my wagon runs 235/60-15 tires (~25 inches in a diameter) with a 3.54 ratio. With the 0.7:1 OD I cruise at 75mph at 2300 rpm.