Automatic Trans Conversion

[tcramstrek]

I have a 1979 Corvette with only a little over 4000 miles on her with a Factory TH-350 Transmission. The factory engine is not at all stock now, and it dyno tested at 350 bhp. Since I reside outside the borders of Smog checks, I removed every lick of power robbing emission equipment. What a amazing difference.My question is what would be your choice for a Genuine Quality Shop to provide me with a Turn Key Price for Removal of the T-350 and Retro-fitting the installation of a Heavy Duty Remanufactured Hi-Performance THM 700 R-4’s w\ Torque Converter, including Drive Shaft, and shifter plate Modification as required. ( I am not apposed to replacing my original Drive shaft with a unit that is available in the aftermarket as a direct bolt on for this application, if available)

The gear ratio of the rear end is 3:55 and this equates to a very high tach speed when I am traveling 75mph. The result is the fuel mileage is horrible and the wear on the newly broke in engine is tremendous. I have heard of several other vettes with this modification done, and the results were favorable. I have also seen the VETTE magazine article on converting to a manual tranny. Is there anyone who has experience with this type of conversion. If so is there a Turn Key solution ( A reputable shop with in 300 miles of SoCal )

 

[like2drive]

Keisler.com, Bow-Tie.com, Fourth Gear.com, GearVendors

I've been working on this for about a month, since my TH350C started giving me problems..again. I've never really felt like a "sports car" should have a automatic in the first place and really like swapping gears. And the current gas prices tell me one of my last earthly joys is going to soon be greatly compromised due to fuel costs.so, I felt like the idea answer is the Keisler solution which is the Tremec 5 or 6 speed manual with overdrive. Richmond Gear has this too, but I never got a answer out of them on recommendation. Also, Bow-tie and FourthGear offer 700R4 and 200R4 overdrive automatics in a "package deal" to swap out the old 350 or 400s. Then there is the alternative, Im doing which is switch to the 4speed manual and add an over drive.
The costs are really crazy: The Keisler deal for the 5 speed is $3000 for the unit, and another $1500 for the pieces to convert from a automatic...plus cost of install unless you can do.
The Bowtie or FourthGear deals are the most affordable if you have a automatic. Their "package" is around $1500 by the time you get all the components you need to do the conversion with the transmission itself, Plus Labor.
From what I've found so far, converting to the 4speed muncie (or BorgWarner) is about $1300 in parts like flywheel, clutch, another pedal w/attachments, slave cylinder, electrical pieces...plus the cost of someone who can do this conversion, plus the Muncie itself. I did find a salvage yard, Contemporary Corvette.com that quoted me $1200 for this "package w/trans" but that would be /a risk that may be hard to undo with the business in Pennslyvania.
To the Muncie, I hoping to attach an overdrive unit..$2300 (from GearVendors}which may have to wait until I've digested the conversion expense. I don't see why the 4speed w/OD wouldn't achieve the same results as the 5speed for about $1000 less. sorry got so long winded, good luck. jim

 

[Jack]

GM 6Lxx

1979 Corvette with only a little over 4000 miles on her with a Factory TH-350 Transmission. My question is what would be your choice for a Genuine Quality Shop to provide me with a Turn Key Price for Removal of the T-350 and Retro-fitting the installation of a Heavy Duty Remanufactured Hi-Performance THM 700 R-4’s w\ Torque Converter, including Drive Shaft, and shifter plate Modification as required. The gear ratio of the rear end is 3:55 .

I'm not suggesting you do this ... but if it were me ... I'd tend to wait for junkyard availability of new GM 6-speed automatics that are soon to be released. The first is a Hydra-Matic 6L80 for the 2006 rear wheel drive supercharged 440 HP V8 Northstar Cadillac STS-V sedan ... three additional 6Lxx are to follow in other GM vehicles. Only an estimate, but fair to expect 6Lxx will turn up in junkyards in about 2 years & in that time the retrofit trans vendors should become familiar with 6Lxx pros & cons.
JACK:gap
*edit* STS-V final drive ratio 3.23:1 ... more 6L80 specs here http://www.corvetteactioncenter.com/forums/showthread.php?t=59267&page=2&pp=15

 

[like2drive]

Jack, I thought about that reality too and that isn't bad advice...especially if your trans is still working. Mine really isn't. I've lucked up on a unimaginable great deal on a Muncie 4 speed and I really want to get back to manual. There's a $1500+- premium for putting in a manual if you have an automatic because of the manual stuff like pedal, shifter,clutchpac, hardware.... My thought is to get this Muncie installed to take care of the present. Then add a OD unit later, or keep an eye on the eventual "Used" 5-6 speeds that will start popping up. I don't drive the Vette but around 5000/yr. so the fuel expense is not that great YET. good luck, incidentially, just moved back from Clemson after 20 yrs. good memories in SC jim

 

[BLACKDOG]

tcramstrek - I had BowTie Overdrives (about 40 minutes south of Barstow) swap out my TH350 for a 200/4R in May of '03. I'm running 3.55's also, and having the overdrive drops the rpm's WAY DOWN ... approx 2200 @ 75mph !!! The original driveshaft was used. They build the 200/4R's in 4 different levels ... level (or stage) 2 will take up to 400HP. The Trans, 2400 stall converter plus install was $2500 back then. Glad I had it done. Good luck !!

 

[Jack]

I've lucked up on a unimaginable great deal on a Muncie 4 speed and I really want to get back to manual. There's a $1500+- premium for putting in a manual if you have an automatic because of the manual stuff like pedal, shifter,clutchpac, just moved back from Clemson after 20 yrs. good memories in SC jim

Jim: You're probably not too far from Mooresville ... lotsa parts-deals floating around there. Last season, I paid $700 for an aluminum Muncie 4 that'd just been blueprinted by Tex Racing http://www.texracing.com with Richmond cases & mostly Richmond guts ... essentially better than a new Rich super T-10 ... it's done a great job in a late model stock ... for about $200 more got a nice, like-new ex-nascar hurst shifter with brand new heim-end shift rods & aluminum tailshaft bracket. Manual clutch retrofits may find it cheaper, easier & reliable to go with hydraulic clutch (pedal,slave,ram-bearing) like quartermaster, tilton etc. Lakewood has a steel NON-sfi "clutch can" ... just like the sfi version but without a block plate (that you don't need) ... ya can find em new for under $200. There's a fellow near Ellerbe NC that does me right on trans, shifter, rear gears, blueprinting etc ... email me if you want his contact info.
JACK:gap