I finally broke down and decided to put a 4-speed in my profusely-tranny-fluid-leaking, low-mileage, numbers-matching weezer 300HP '70. I've never attempted such an expedition on a Vette before.....bought an M20 on ebay a couple weeks ago form one guy along with pedals, bellhousing, flywheel, pedal assy, Z-Bar and some other small items from another guy. Think I got lucky....everything looks in pretty good shape so far but I'd REALLY appreciate any advice from y'all about the various pitfalls and tragedies to avoid. I'm already 48 yrs. old and I'd really like to try and get this right on the first attempt. I've pretty successfully rebuilt the rest of the car but in an attempt to replace the front tranny seal I smarshed it on the tork converterizer so here's my excuse to put the four speed in it that I always wanted....

 

Tackle the pedals first and fore most. It is absolutly the worst part of the job. Take the steering collum out right off the bat and on mine I pulled the instument cluster, as well as the seat (The seat has to come out when you cut the hump anyhow). The rest is all down hill from there.

Scott..

 

Scott, I purchased a Hurst Comp. Plus shifter from Summit- they sez no tunnel mods req'd....do you know if that's correct?? thanks greatly mucho for the info...

 

Well, if your car is an Auto...........No shifter hole yet.

Scott..

 

Scott, I pulled the console out today; under the [auto] shifter there is a molded rubber cover that was attached with 10 hex-head sheetmetal screws through a steel retainer. The hole in the tunnel underneath it had some rather ragged-looking saw cut marks in it (typical early C3 workmanship). The Hurst shifter has a bracket that bolts directly to the tailshaft; seems to put it in about the same spot as the stock shifter goes but until I actually get the tranny in I won't know... probably next week sometime.

 

...changed my '75 over last year. I did not remove my column, just disconnected it at the rag joint, put a towel on the driver's seat, pulled it away from the firewall and let it rest on the seat. Then dropped the left dash pod. Replace ALL the bulbs while you're at it. You'll have to re-wire & by-pass your safety neutral switch when you pull your automatic shifter. I remember it being pretty simple-all the safety neutral switch really is just a break in the starter circuit. The automatic crossmember can be easily used, but you'll have to buy or get if you haven't already that crossmember extension piece. It bolts to the crossmember, then forward to the tranny as a 4spd trans is shorter than an automatic. On my '75, I used a "correct & correct dated"(that was just dumb luck )Borg-Warner Super T10. On going from my automatic to the 4spd T10, the same tranny yoke for the front u-joint is the same-don't know if your Turbo 400 yoke will work in a Muncie though. On my '75, the hole for the 4spd shifter was already there. Just had a metal ring with a rubber block piece. I just neatly cut a hole for the shifter and it works great. Guess I coulda got the "factory lower 4spd boot", but I just made my existing one work. You'll also have to have the frame Z-bar support welded to your frame or I believe you can use the '80/'81 bolt on Z-bar frame support piece.

Good luck-keep us up to date-I love my '75 being a 4spd now-damn near cruise it EVERY chance I get. I don't intentionally take it out in the rain or snow, but I've been caught in it before and the car's NOT going to melt.

 

Thanks Paul- I like your ideas better.....I've already got the crossmember bracket so all I need to do there is weld a couple little attach tabs onto the crossmember. As far as the cross shaft bracket goes I ordered the weld-on piece from Zip but I may go ahead and pick up the bolt-on piece just to see if I can use it. Any and all advice is GREATLY appreciated!!

 

If your 70 had a 400TH tranny as it should, you will need to get another yoke. One from a 350TH/4speed. They are the same, but the 400 yoke will not work in the 4 speed.

 

I recieved a slip yoke with the pile o' parts (from a guy in AZ) that I got a couple weeks ago- it fits the output shaft of my M20 but I haven't gotten my other one out yet so I don't yet know if'n it'll work...should know in the next couple daze unless I really get motorvated today and pull the old trans out-thanks folks

 

HMM, that makes it alot easier. Not sure about the early years as far as workmanship goes, but it doesn't seem out of the question for it to be a little rough. Also I assume your car has a removeable cross member? They are alot nicer for doing tranny work of any kind. And your hurst shifter will fit fine.

Scott...

 

Thanks again Scott. Actually as far as build quality goes I'd like to believe that it gets a little better every time I work on this thing!! Should have the TH400 out tomorrow;big box o' parts coming from Zip any day now (still looking for that !!&*%??!** slip yoke though) and then the putting-back-together stage can begin....

 

Just an update (in case anybody wants to chime in and share in the misery)...got the ol' TH400 out Thursday nite, drained it, set it aside, then spent this morning cleaning car bottom. Foil shield was pretty well shredded under the tunnel- think I'll try the Bubbapatch method rather than spring for a new one (Heavy-duty Reynolds Wrap glued on w/ Hi-Temp RTV maybe??). Replaced the vacuum switch under my center console also, pulled a couple wrong screws out and one of my AC switches exploded and fell in little pieces thru the shifter hole- DANG! That took about 1 1/2 hrs. of fiddling to put back together. Undid the rag joint and spent the next two hours ripping the whole dash apart to get the left side panel out-ooohhh....REEAALLLL scary. Many tube and wire now hanging everywhere, but it's out and so far I haven't broken anything and I took enough pics. that I think I know how to put everything back. Tomorrow I'll work on getting the column the rest of the way down and maybe even get the old pedal hanger out. Bye for now

 

Sounds like you got it going pretty good. Good luck with the transformation. If you decide you want to part with the TH400 and other parts please email me.

Good luck!

 

I haven't decided just yet...once I get this thing dialed in and wifey complains about the greasy lump I may just take you up on your offer!

 

OK, Now I need some advice.......got the whole dash ripped out, dropped the column, unhooked and marked all the connectors, pulled out that big clanky iron bracket that bolts onto the cowl, took four nuts off of the pedal hanger that attach it thru the firewall to the brake booster, and what I now have is the pedal hanger and booster in coitus- what's the trick to separating these two pieces???

 

there is a pin in the brake pedal lever that has a jesus clip on the end of it, remove the clip and the pin and the booster should seperate

 

Since I didn't get any immediate answers, that's how I eventually got the booster out....I undid the clevis from the pedal and took out the booster with the plunger still attached. NOW for the fun part- can anybody provide for me the correct locating dimensions for the weld-on cross shaft bracket or nice clear fotos of the installed bracket?? I've got the vent grate removed from the left side of the body, the brake booster is now out of the way, so there's room to weld in there. This is obviously the trickiest part of the project so I'd like to get it right...