I have been discussing a project with a buddy o mine, who is building a '59 Vette. He asked me about using a NP-A833 trans, which is really a 3spd w/OD. In the process of trying to locate one of these units, I found out about a kit that is available that would convert a regular Muncie 4spd to an O/D unit. What it involves is changing the Input shaft, cluster gear, and I believe 1st gear on the mainshaft. It makes "4th" into an O/D with a .78 ratio. So you would have basically a 3spd O/D. Is that cool or what? You can keep your car looking completely original, and no-one but you would know it was an O/D trans. The kit was quoted to me for $485,( my cost), which is REALLY reasonable, considering I'v seen some cluster gears sell for that!! I got this info from one of my std. trans parts suppliers, but the guy didn't have all of the info handy when I talked to him this afternoon. I'm gonna try to get more specific info tommorrow, and update as I can. I think this would be the way to go if you don't want to spend $2000 on a 5spd, but would just like to bring the rpms down a little on those road trips. Unfortunately, the kit is only avail. for the Muncie, and not the BW T-10/Super T-10. What do youse guys think? Stock trans,clutch, shifter,etc. Nothing to cut or modify externally.Adams' Apple38483.831099537

I wish there was a cheap quality overdrive for a THM 400.

I know cheap quality is an oxymoron.

I am interested.  Let us know what you find out.  See if he can let you talk to someone who actually has this setup to find out about any driveability or reliability issues.

Thanks

Neil

Ken, it's not cheep but what do you think of the overdrive unit in the new yearone catalog...page 381.  This is for the TH400..

Actually, I just got my catalog yesterday.  I haven't had a chance to look at it as of yet.  The good news, yesterday was my last late class until the end of August.  Now I have some time to work on my beast.

I'll take a look and let you know.

Okay, I just looked.  Gear Vendors has a good rep for applications I have seen in the past.  Other than the price, it looks like a good unit.  I do wonder about the stated clearance problems in some applications.  What about our C3s?   As far as splitting the gear ratios to emulate a close ratio, that can work.  But it too much trouble and really does not give an advantage unless the engine has a very narrow power band.  Some very wide ratio manuals could benefit.  For the most part you would just shift normally, the go for overdrive.

I would like to have one of these, but the cost kills it for the time being.  ( Probably for a couple of years at least.  Too much else to do.)

Man..I did'nt have time to check on this deal today, but I will definitely get the scoop tommorrow. I'm really curious to see what this set-up is like. I'll see if they have someone I can ask who has used it. I tried to get more info when I talked to the guy yesterday, but he said he did'nt have the stuff in front of him at the time.
Ken, it seems like I might have some info on changing the ratios in a 400, but nothing on O/D except for the bolt-on units, such as the 'Gear Vendors' unit. They are really proud of them, but they've been around forever. I doubt you could get one bolted in a Shark without some MAJOR surgery!! If I was gonna go that route, I'd just go ahead and use a 4L80-E with a stand-alone 'puter. I think it would take less hacksaw blades to use it than the O/D unit!!

OK, folks! Here it is. The place that makes this kit is in N.Y. What it does is, you have to flip the 3-4 shift arm upside down on the trans, effectively making '3rd' gear direct drive. Then the parts in the kit turn what was 3rd gear in the trans into the O/D gear. It makes sense to me the way it was explained, but I don't know if I can relay the info to ya'll to where it's understandable. Anyway, they told me they had sold quite a few of these conversions at the Super Chevy shows and such, but none here locally, so I can't talk to anyone to see how they like it. It would seem to be a big jump from 2nd to 4th, but I shift like that a lot anyway. The O/D ratio is actually .87, not .78 like they told me to start with. Still, if you have a 3.73 diff., this would make it drive like you had 3.24 in O/D. I found their web-site, but it doesn't have a lot of info, just some ratio spreads. I'm looking hard at this set-up. I think it's a good deal for someone who wants to 'keep it stock'. You would still have the power on take-off of the 2.20/2.52 trans, but a better rpm speed while you're cruizin' Here's a link to the mfg.

http://www.autogear.net/hiperform.htm#

Just click on the 'Details' box Adams' Apple38485.8022222222

I looked at their website.  Think I will give them a call Monday.  I have M20 tranny and bottom line I want to know what will my cruising RPM be at 70 mph if I convert with their kit.  Still think it is a must to talk to someone who has one.  This is one case where I don't want to be the first one to try it.

Let us know if you come up with any more info and I will do the same.

Rgds

I was afraid the bolt on would take up too much room under the car.  And for the price, the trans swap will make more sense. 

I know there are different gears for the 400, but I really don't think I'm going to go that route.  Granted more launch, but that's not my concern at this time.  At full torque multiplication at launch Chevy says between the converter and 1st gear it's an effective 5.2:1 ratio.  Gotta love torque multiplication.   Although I like it, that's about the last thing on my list at this time.  Someday the Trans swap and perhaps some 3.55s.  In the mean time, I got a lot of work to do!

Update.....Finally got a call back from my local supplier today. Not much more info, but he did fax me a flyer(sort of ) Any-who....it is available for both close/wide ratio units, has .87:1 O/D ratio (13%). You have to do some reconfiguring of 3-4 shift linkage, as you have to flip the 3-4 arm over on the trans. (I think this means the shift linkage rod probably has to be made longer). He assured me that no cutting or modification to the body or chassis is required.
The kit includes:
1-input shaft
1-cluster gear assy
1-new gear to replace 3rd (on the mainshaft)
Price is $413.85 (retail)
It will NOT work on the earlier Muncies with the small cluster shaft, only on the ones with the 1" cluster shaft.
I still have not heard back from AutoGear in N.Y.
I'll keep tring to get more info, and I'm looking for a guinnie(?)pig locally to try one out on. If they had them for the BW units, I'd be puttin' one in my '74 NOW! Adams' Apple38492.822974537