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Ditching the 4spd for a TH350

Discussion in 'The Garage' started by pitviper, Apr 18, 2005.

  1. pitviper

    pitviper Newbie

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    78' SWB that has a mildly built 350 in it, on 35s with 4.10s and a 205. I have the SM465 right now but I would like to get an auto in there. Am I going to have a power loss, and if so how bad will it be? I already have another 205 with the adapter so all I'll need to do is make a new crossmember and make sure the driveshaft will be the right lenght.
     
  2. nerraw117

    nerraw117 1/2 ton status

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    sometimes i wish i had a 4 speed instead of my th350
     
  3. 1979jimmy350

    1979jimmy350 1/2 ton status

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    you will also have to put a tranny cooler in get a flexplate, get the brackes for the kick down cable, new steering column, tranny shift linkage
     
  4. stizkidz

    stizkidz 1/2 ton status

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    Grab that automatic starter as well. Don;t want to ruin your brand new flexplate... Ask me how I know.
     
  5. 350350

    350350 1/2 ton status

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    Ditto that. Seriously, not slamming you here, but why would you want to give up the control of a manual, plus go from 4 gears to 3, by choice? I want to buy all of your 4-speed components so I can go from a TH350 to an SM465. Seriously, shoot me a price for the whole kit.

    You will definitely have a power loss, as automatics take more power to operate than manuals, plus stretching your gear range over 3 gears instead of 4 will give you a power loss as well. You can't keep the motor in its 'sweet spot' for as long with 3 gears as you can with 4. I have a 6 speed in my Camaro and can't imagine going back to a 4 speed due to the ability to keep the motor in its sweet spot nearly constantly.

    To each his own though, and going from a manual to an auto is way easier than the other way around!
     
  6. big_truxx

    big_truxx 1/2 ton status

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    what's the diff between auto and manual starters? I always thought they were the same...
     
  7. pvfjr

    pvfjr 1/2 ton status

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    Never changed my starter when I converted... :dunno:
     
  8. mr_beer

    mr_beer 1/2 ton status

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    Same here, I've been running for 5 months with no problems. I start it several times a today also.
     
  9. zeroz400

    zeroz400 1/2 ton status

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    Ive got a th400 i wish i could throw in my truck. Its not so much that i hate the 4speed, its that my clutch linkage is all messed and mechanical linkage sucks...But i like having control so the manual will stay. I dont think the power loss will be to significant with a good motor and your gears.


    Later
     
  10. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I have a th350/205 in my truck and i just picked up a sm465/205 i'm thinking about freshening up and putting in there with a hydro clutch setup.
    When i put a tranny temp gauge on my th350. then i put a B&M stacked plate 29,000 gvw cooler the biggest one, my temps dropped significantly, but the tranny still gets warm when pulling hills in 2wd.
    When i put it in 4low locked up front and rear it creates a lot more heat in my tranny. Like sometimes 230 or 250 if i'm in the crawling in the rocks on a hot day.
    So i want a 465 just so i know i won't be cooking my tranny, and it should be fun with a granny low... for sand hill climbing and racing theres nothing like my th350 though, i would miss that.
     
  11. big_truxx

    big_truxx 1/2 ton status

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    I would preffer an auto :waytogo: :D and this is after driving 1000+ miles w/o clutch in a 465 setup :D I just have been driving my 82 dd lately and realized how much I had missed its auto :D
     
  12. captaininsano

    captaininsano 1/2 ton status

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    I just swapped out the TH350 slush box for a stout SM465, I want my rig to drive like a dump truck! My 350 slipped so bad when wheelin it was pathetic. Gear boxes are sweet. I have 350 core anyone can have for free, only been used as a jack stand once! :D

    [​IMG]
     
  13. stizkidz

    stizkidz 1/2 ton status

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    An sm465 may technically be a 4 spd, but let me assure you... Driving it around town, you only have use of 3 speeds (2,3,4). 1st is low and is not used unless you need to crawl.
     
  14. Z3PR

    Z3PR Banned

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    Personally I'd stay with the sm465. My 72 had the sm465, and my 76 had a TH350. In all honesty, the 72 was more enjoyable too drive.
     
  15. big_truxx

    big_truxx 1/2 ton status

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    I think it all is up to your personal prefference. You can still break/damage 465 gearbox's. They will break a tooth on a gear and then pop out of gear @ inoportune times, lose the clutch(as I know all too well :D) So I believe that "slush" and gear oxes are equal. They both have their ups and downs. :)
     
  16. captaininsano

    captaininsano 1/2 ton status

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    True true, most of my hatred for the automatic transmission is cost, and that nasty ATF fluid, so happy to be rid of that stuff. I will say this, I drove my TH350 for 6 months while it was going bad, it would not shift on its own, so I put a ratchet shifter on it. When it was vibrating like it was ready to pass on to the happy shifting grounds in the sky I was in Fresno,CA. I drove it all the way back to San Jose,CA(about 150 miles) over Pacheco pass (2000 feet and a steep grade). Made it... However the next day I could barely get into the garage. :D
     
  17. big_truxx

    big_truxx 1/2 ton status

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    I also like the comfot and ease of just the skinny pedal and the fat pedal :waytogo: just throw 'er in D and away ya go. Traffic bugs me w/ a stick cuz I think everyone should just get out of my way so my standard can roll along w/o so much usage :haha: But that's a driver prefference as I despise heavy traffic anyway (read I am 200% country boy :D) Also more room for a female companion to sit in the middle w/o that big stick in the way :D :waytogo:
     
  18. diesel4me

    diesel4me 1 ton status Premium Member

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    I changed from TH350 to SM465..once..

    My 72 K5 I had years ago with a Th350 would not go into any forward gears for at least 5 minites,longer in cold weather!--once it shifted in when the motor got up to temp,I could drive it all day,and it worked fine until the next "cold start" after sitting all night..this led to me being late for work a good many times--finally,the poop hit the fan,and my boss told me if I didnt start getting to work on time--I could look for work elsewhere!-- :blush:

    So out went the TH350 in favor of an SM465 setup out of a wrecked K5 like mine that WAS mint,until the owner slid it broadside into a fire hydrant.drunk out of his mind on easter sunday--I used to drool over his truck every morning,it was always parked at a "Firestone" tire place next to mcdonalds where I ate breakfast often..now it was totalled!--but I got a lot of good parts for 300 bucks,like the entire 4 speed setup,everything to convert it,power brake booster,peadls,etc...

    But after a week of 6pm to midnite work sessions,I finally got it all in and driveable--first thing I noticed was the "growling" noise coming from the coupler that joins the tranny and transfer case--I drove it several months,and eventually pulled the T-case out,and found the coupler,and the splines on the tranny's output shaft were worn pretty bad--had no cash to waste,so I threw in a brand new coupler with a ton of green "locktite" bearing and sleeve retainer compound in it,and hoped for the best....

    I drove it about another year,it was starting to get noisy again--I kicked myself for not just having the TH350 rebuilt and re-installing it...the 4 speeds gear ratio spread sucked--1st gear is for climbing walls or pulling a heavy trailer at a crawl,useless in city driving..2nd gear is like first in most "normal" tranny's,a bit on the "low" side..the jump to 3rd was a big one!--you had better redline it in 2nd gear before shifting into 3rd,or it will bog and fall flat on its face--you could wind it up to 65 in 3rd though,good for "passing gear" on the highway--4th was like overdrive,the K5 had 3.08 gears,too high for a manual tranny in most cases...

    I wasn't real happy with the manual tranny,especially when driving in city traffic--the 12 inch 3 finger clutch was murder on my left leg,and it wasn;t long before 2 of them had been installed,due too defective pressure plates,and I eventually put a "centerforce" 11 inch clutch(diaphram style) in its place--then the issues with the "coupler sleeve" started in.. :angry1: :doah:

    I've had fairly good luck with TH350's,only the on in my 74 K20 had finally lost reverse after 15 years of beatings with a 454 and a 400SB and lots of abuse snowplowing with it...other than the one in my K5 that had the "delay" in forward gears,all the others I've had held up good,even behind 454's...I had a few TH400's in cars that were pretty rugged too,but they all can suck in one way or another I guess...I prefer the automatics until they fail,then I wish it was a standard!--at least when you let the clutch out on a manual,you can be 99% sure its going to move!--and putting a new clutch in is easy compared to tearing down an automatic--I doubt I could ever rebuild one successfully...

    I wished my K5 had a tranny like a close ratio Muncie 4 speed like the vette's and camaro's used--Advance Adapters made an adapter to put them in a 4x4,I think that would be a good tranny,because the gears arent so far apart in ratios..

    .I still dont know why GM hasn't made a beefy,yet streetable multi-speed streetable tranny with close ratios--maybe the newer trucks 5 speeds and 6 speeds are better,I have no experience with them--but the SM465 tranny is a good one for a dump truck or bus,but not exactly street friendly--many other friends had troubles with them popping out of gear due to broken snap rings,and the tailshaft splines wearing out...seems like no matter WHAT tranny you have,they all have their downfalls... :frown1:
     
  19. pitviper

    pitviper Newbie

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    My deal is that I have never owned an auto personaly and I wanted an auto in my play toy just because of how easy it is to tear the damn thing apart and rebuild it. TH350s are cake for rebuilding, then again I have done a couple of them. Like it was said before the 4spd has too big of a step between 2nd and 3rd gear, if you don't have the tach in the red it's gonna fall on it's face in 3rd.

    When I swap motors is when the trans is getting swapped, so when I do that I will have tons of stuff for sale. Right now I'm rebuilding my spare 205 that I bought for the th350 adapter. I will have a SM465, 205, linkages and everything up for sale.
     
  20. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Each gear on a 465 cuts your RPMs in half... so get to 4000 in 2nd to go to 3rd, and you'll be good to go. Get to about 3500 in 3rd to go to 4th... I've never had any "falling on it's face" problems, but then again, I learned the 465 on a 82 C30 farm rig that was used to pull heavy equipment around. In my K5, it's like a dream shifter compared to that C30... It only ever pops out of gear when its in 3rd (up) because the stick is heavy... not because of any teeth missing...
     

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