How would you guys pursue a THM400 restoration?

[nuch_ss396]

Hi everyone !

I'm faced with a dilemna and I need some assistance from
you guys.

About 8 months ago, I purchased an original CX coded THM400
for my 69 L/78 Camaro. It is one of those Holy Grail items.

http://www.yenko.net/ubbthreads/images/graemlins/worship.gif http://www.yenko.net/ubbthreads/images/graemlins/worship.gif
The transmission was a low mile take-out ( about 18,000 )
and had been sitting with no fluid in it for about 30 years.
I have to expect that the internals are in need of attention
at this point in time. I don't want to install this THM400
and then find out I have problems. What do you think? http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif

In any event, I want to get this THM400 restored to it's
original specifications. I was given the name of a shop in
the mid-west to perform the restoration through a member
here. Here essentially is my problem. I really don't know
much at all about the internals of the CX, but I do know
that they are special ( extra clutches, special governor,
etc. ). How can I be sure that I get my real CX internals
back from the restoration shop? I don't want to be overly
paranoid, but it took me many years to get this one and I
just want to be as cautious as is prudent.

How do you guys think I should proceed? BTW, I don't want
to question the integrity of the shop I am considering, so
I won't mention their name.

Steve

[Hotrodpaul]

Buy an instruction manual and do it yourself. I have rebuilt several automatics including a late model 4R70W Ford overdrive and they are not that difficult. You will need a large clean bench, torque wrench, retainer ring expanders, a good large vise, and possible a couple of special compressor tools for the clutch packs, which you can make yourself. If you have the special 6 lug higher stall converter and it was in good shape, I would have a transmission shop flush and clean it to remove any contaminates. They can also cut it open and install new bearings and such, but I would not go tht route unles it needed it.

If you know a technician at a local transmission shop and you trust him, have the shop do it. Take photos and document the trans so it can be verified when you get it back, and don't end up with an "exchange" TH400. If fact, I will be rebuilding a CW coded Turbo 400 from my 70 Z28 here in a few months and will probably do a story on it.

I prefer to do it myself becuase of the question of "how does it work" and the satisfaction of accomplishment. Good luck with the trans!

Paul

[Pantera]

I have to agree with you, do it yourself. I did the one in my 69 Motion vette and they are not that hard. Worse thing is putting them back in the car.

Pantera

[John Brown]

As soon as you get your new clutch fibers, put them to soaking in a tupperware pan with ATF covering them. Snap a lid on the pan and the clutches will be ready when you're ready to assemble the trans. http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[mockingbird812]

Steve,

Just in case, if you want a reputable expert to do the job and ensure that it is done right and returned with all of the rare goodies intact I have a friend down the street who is retired from the GM Proving grounds and spent his career as an auto tranny engineer. He currently races a '68 Hemi Dart. His father had a hand in on developing the original TH-400.

[nuch_ss396]

Guys,

Let me elaborate a little more on this. As this CX has
been sitting for many - many years, I really don't know
if it was ever touched inside or not. The previous owner
seemed to remember a shift kit or something in 1971.... http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif

That scared me just a little. So, I really need someone
that has experience with these special THM400's to go over
it top to bottom and be sure it is all that is should be.
Can you see my dilemna now? I have no real working
knowledge with the CX or THM400's in general. I wouldn't
know how to recognize if something was wrong or not. Once
I pull it apart and find issues, I'm then faced with the
need to deliver a pile of parts to someone. Not a promising thought! http://www.yenko.net/ubbthreads/images/graemlins/hmmm.gif

If I do it myself, I know what I have. If someone else
does it, I end up hoping they were honest. Questions, questions......... http://www.yenko.net/ubbthreads/images/graemlins/headbang.gif

This reminds me of a situation I had many years ago when I
was getting my 69 Camaro restored ( 1980 ). Shortly after
I brought my car to the shop, another guy with a 69 RS
showed up with his car for a restoration at the same shop.
He was friends with the shop owner and I got paranoid that
all of my NOS GM parts were going to end up on this guys
RS instead of my car. So I made very frequent trips to the
shop to check on his progress. I hated that situation
because I felt like I lost control. When you spend a lot
of money finding special parts, the thought of getting
ripped-off is a bit scarry. http://www.yenko.net/ubbthreads/images/graemlins/no.gif

Steve

[TexasTon]

I think if I weren't going to do one myself, and you surenuf didn't have a shop you could trust, I would do some asking around and find someone that is currently running a 400 in a drag car---and either find out a source from him or if he does his own work, get him to do it if he will.

I wouldn't put back one of those factory "high stall speed" convertors though.

[nuch_ss396]

Why the negatory on the 6-lug converter? http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif
Steve

[TexasTon]

I've had two, both wouldn't come close to locking up. Back in the day (1970) a THM400 in an L78 with that convertor was considered a minimum of .50 slower than a stick car, if not more and the MPH was down a bunch. Took many years to figure out it was the convertor, a stock convertor made a horse out of them.

If you want to retain the six bolt convertor, I think I would send it to a good convertor company and have them tune it----I suppose that is possible, I am still a stick guy myself.

[nuch_ss396]

Steve,

This is an interesting topic. Do you have any specs on the
converter modifications? Also, do any other members here
concur with this converter issue? Not wanting to doubt
anyone here, just doing research. http://www.yenko.net/ubbthreads/images/graemlins/hmmm.gif

Steve

[TexasTon]

I don't know, sorry, I do know I would never have one again----at least like those I have had, which by the way were the only autos I ever saw. Supposedly only the L-78's and LS6's had them???

I bet a convertor place would know what they could do with one, they have certainly got that process down today. Probably childs play to them, the only difference being they have a much larger case to work with than their current 8-9" jobs. Again, going by mine, they couldn't make it worse http://www.yenko.net/ubbthreads/images/graemlins/crazy.gif

I think alot of their wizardry regards the small case with less mass, and a firm lockup regardless of stall, but I really have no idea http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif Surely they could adapt that stuff into a large case and only lose the different relationship to volume/mass?