bobb

Does anyone know what specifically is different about the OW code TH400 in the 1970 W30 as compared to any other TH400? I'm asking because if I take the trans to be rebuilt I want to make sure the OW specific parts aren't replaced with generic TH400 parts.....but I need to know what parts those are. I know a good TH400 rebuilder but I haven't talked to him to see if he knows anything specific about the OW trans or if he'd rebuild like it's an everyday Chevy TH400. And maybe it is like a Chevy TH400.....I just don't know. Any insight would be greatly appreciated.

thanks,
bob

rcorrigan5

My answer is fairly generic; I don't have the specifics. But, from what the ads said back in the day, the biggest differences between the OG and OW THM 400s are that the OW transmission had a "high[er] performance torque converter, high[er] RPM shift points, and firmed-up shifts".

Randy C.

507OLDS

There's not really anything specific inside,as far as rare pieces go.Just have it rebuilt with good parts,and it will be just as good,or better than it ever was.I don't know where you are located,but I have Dennon Behel,in Killen,Alabama,rebuild all of my TH400's for myself,as well as all of my customers,and he can rebuild the torque converters too.He could get more scientific about what is different inside of the OW trans.I had him do a few of those for me as well.If I remember correctly,the inside of the case is machined differently for extra clutch.

joe_padavano

Not sure about the OW, but the TH400 in my 69 H/O had an extra clutch disk in the intermediate clutch pack (6 instead of the normal 5). I'm pretty sure the valve body spacer plate is programmed differently and the governor is different also.

Olds64

I don't know if the inside of the OW transmission was different, but when rebuilding a TH 400 an easy upgrade is to get the high quality sprag.

http://www.summitracing.com/parts/TCI-227900/

MX442

The matching VIN!

Wish mine still had it's #'s OW TH400. Other than that, like others said, shift firmness, and clutch packs.

You need the older drum to run the 34 element sprag. IIRC, prior to 1970 or 1969. I can't remember what year they changed.

BlackGold

What Joe said. Also, no wavy plates were used in the clutch pack.

But, all of this is somewhat irrelevant. The shop which rebuilds your transmission, if they are going to warranty it, will likely want to build it "their" way. Tell them the shift characteristics you want, and they will program the shift kit to do it. Tell them your usage, and they will select the proper clutch packs, sprag, etc. Of course, the higher quality stuff will cost you more. They will also probably insist on a new torque converter so that metal particles in the old one won't ruin their rebuild.

If originality and provenance is important to you, make sure they understand the importance of the VIN stamp, OW tag, and OW paint stencil on the bell housing. I emphasized this to my shop, and they still took a wire brush and spray bomb to it. Grrrrr.

jensenracing77

i do know that the piston in the drive clutch pack (i think all clutch packs but know for sure the drive pack) on OW transmissions have an extra check ball in them. i know this because i broke one. they seem to be made of "unobtainium". we had to modify a standard one to be like the OW. i rebuilt an OW and forgot to put in a snap ring on the drive clutch pack and broke the piston. my dad was not happy with me. i think the entire valve body is differant but can't remember that far back.

507OLDS

I know when Dennon rebuilds anything for me,he does the needed work to put the extra clutch in,and the sprag/drum,if it is not in there already.I like to have things built once.

ziff396

When I rebuilt my 71 OG 400 out of a 442, the intermdiate clutch pack had 6 instead of 5. I also upgraded to the 34 element sprag and used a new 4l80E drum. The drum is the same.

cdoering

What does an OG trans go for?

MDchanic

Sort-of-on-topic:

Would the additional 6th clutch plate apply also to the OB trans of 1968 (used with the high-comp. 455 in the big cars)?
I was under the impression that it does, but figured I'd ask while the subject was up for discussion.
Obviously, it's set up for smoother shifts at lower RPMs in the big cars.

"Oldsmobile type G"
The first letter signifies the GM Division.
The second-letter assignments stayed similar, but not necessarily identical, from year to year, and signified the specific trans. version for the assembly line, for instance, "OB" seems to have been the "big car / big engine" trans. most of the time.

- Eric

cdoering

What are they selling for

jensenracing77

Just a note to the old OP post. the apply pistons in an OW have 2 check valves compared to one in other TH400s. We broke one in the mid 90s and could never find one. we ended up making one from a standard 400 clutch apply piston. If i remember right, it allows the ATF to empty one clutch pack faster because of the faster upshift to the next clutch pack.

matt69olds

The OW trans has a specially calibrated valve body and specific spacer plate, a governor calibrated for higher upshifts and a special direct drum that has a extra clutch plate. The special direct drum has a smooth sprag race (just like every direct drum made prior to 71) and has the snap ring groove located a little higher up in the drum to allow the extra disc. It also does not use the wave plate that cushions the direct clutch apply. The special drum is easy to visually identify by a chamfer machined into the inner diameter at the top of the drum. I have found these drums used in 1 ton 4X4 trucks, the heavy duty TH475 trans (basically a extreme duty 400 trans with straight cut gears) and early TH425 trans (the Toronado) with a 425 and 455 engine built before 69. They made have used that in later models, the latest one I have dissasembled was a 69 and it had it. If you use a drum from a Toronado trans you need to flip the sprag upside down so it locks and freewheels correctly for a rear wheel drive application (ask me how I know!).

As for the checkball location, you can have a check ball in the piston, one in the drum or both. The checkball was originally located in the aluminum piston, it was moved to the drum when they went to steel apply pistons in the later years. It doesn't matter where the checkball is, as long as the assembly has at least one.

stevengerard

The cost of obtaining one :-)

cman442

I know this is a really old thread, but in case anyone is still wondering, according to the GM TH400 information I have there was lots of differences between an OW and other 400's not just the number of clutches in the direct drum. The thickness of the steels, number and type of springs used in the intermediate and direct drum pistons. No wav's except in the forward drum as pointed out earlier. This would all have an effect on shift timing. I'm not sure on the valve bodies or case, but I can verify with an ow and std case when I have some time.

Our W30's really were special!

And if you have one waiting to be rebuilt, be careful who you take it to.