The gear thread got me thinking about something I talked about a number of years ago and I think the conversation was that it could be done but I cant remember the particulars. I'm hoping a tranny guy can fill in the blanks and share the reality with me. I know the small block is easy just use a later model lock up trans but what about a BB can you convert it? I think this would help tremendously since no BB OD unit was factory available. Do they make a lock up convertor that will handle significant torque and power?

Thanks in advance, Kevin

no, you cannot convert a non lockup 727 to lock up.

But they did make some lock up BB 727's in the late 70's.

Interesting do you know the application and the strength of the convertors? My guess is there would be an issue unless you were running something pretty serious. It could inprove the highway situation buy 2-300 RPM I would think.

i thought there was a lockup 904 in the late 80,s also-----my torque converter guy tells me one of the most common fails is the lockup--that is why the market is hot for the billet units now---and yes it only saves you 300 rpm.....

Yea but 300 rpm would drop your effective gear (if that's the right term to use here) .50, essentially taking a 3.91 to a 3.42 and a 3.55 to a 3.08.

I have a NOS BB 727 lockup trans for sale in the transmissions forum if anyone is interested.

I think I found it, doesn't say lock up in the ad if it the one I was looking at. What is the application?

You can turn a non-lockup trans in to a lock up - need the valve body, input shaft and corresponding rear clutch retainer, pump support (reaction shaft support). There are two basic valve bodies - hydraulic control only for lockup then electronic control lockup. Early lockup control with electronics was called PTU (part throttle unlock), was one wire to actuate the lockup solenoid. You just need to be careful that you identify and get all the correct parts to do the swap.

When talking about lockup converter failures - a lockup and non-lockup converter are almost identical inside except the lockup piston, seal and friction material. Any 727 or overdrive 46 trans with the 10-3/4" converter built before 2002 has the potential to fail if used behind high torque high load applications. Think 360 van or truck hauling a enclosed trailer while lockup - worse if in 4th/OD. We made a change to the lockup piston around 2002-2003 that eliminated this condition. The other condition is high throttle low speed use in any gear when the lockup is not applied - you will likely balloon the converter enough to fail the unit. Most guys never check for this. The heavy duty converters have thicker front covers that help prevent the front cover from deflecting - and if you add an anti-ballon plate to the impeller - then you are in good shape. And don't compare FWD to RWD lockup failures - two different animals. When Chrysler launched lockup - the lockup disc was a floating disc design - that in itself caused failures.
We have been bonding discs for over 20 years now.

Application is 1978 400 I believe B or C body

There was only one lockup big block 727 and it was such a dismal failure the factory recommended that it be replaced with a non-lockup. Part number of that trans is 4028824, it was used behind the '78 400-2 in B and C-body wagons.

You can't convert a non-lockup to lockup because the lockup case casting was changed to clear the lockup valve assembly on the valve body.

Ah, no.

Case is different for lockup vs non-lockup as well.

Wrong - you can convert a non-lockup to lockup all day long. Case was never an issue. Nothing in the case is different. There was a slight "machining" clearance cut - but the casting is no different from previous years. And i believe this slight machining change was needed only for the early valve bodies that used the lockup module - the later electric lockups with the electric solenoid don't need that cut. As for dismal failures of the 78 lockup in big block applications - i am not aware of any mechanical failures - they were customer unacceptable because of the drone noise due to low vehicle speed lockup at low engine speed - causing a drone noise.

AMC 727s were also available with a lockup in the mid 80's, I have one in my cj

To quote the factory literature on the lockup changes, "the case was revised to provide clearance with lockup valve body." So the case was (is) an issue. The pic below shows the point of major interference between the lockup VB and the non-lockup case.

Your initial reply to the OP stated "You can turn a non-lockup trans in to a lock up - need the valve body, input shaft and corresponding rear clutch retainer, pump support (reaction shaft support)." which implies that the case is OK as is. Whether the revision is in the casting or "machining" it's obvious from the pic and the factory literature that it is an issue.

Yep - if you want to split hairs. But read my post again and the one later on - no one would likely use that old valve body with the module - when it is antiquated - when you can use the electronic version - which does not need the machining/relieving.

And you said "cannot convert" which is more incorrect - and leads people on this website to believe it cannot be done - I bet everyone on this website has a die grinder. That is all it takes John. And Supercuda is misleading in his statements as well. But that is ok - we have it cleared up for most everyone reading this so that is the desired end - good info.

Sure, you can put a Hemi in an Isetta with "a little grinding".

I'll drop it after this post - both of you said "you cannot convert a non-lockup to a lockup".

That is false. And if you do not use the early model valve body with the lockup module - NO grinding is needed. And yes - just a little grinding, not near the amount needed to install a Hemi in an Isetta. People come to this site hopefully to get good useful info - your two posts were glaringly wrong when you both said "you cannot convert a non-lockup to a lockup".

To the op.
Why don't you round up the parts, and do it yourself, and see if it works or not, and then write the book?

What's misleading is your original response said nothing about case mods. You came back and mentioned it later.