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Customs 58 GMC 100 driveline swap

Discussion in 'The Hokey Ass Message Board' started by CandD's 58, Nov 26, 2016.

  1. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    Hello, long time viewer, very few posts!

    I have a 58 GMC 100 Fleetside pickup with a 336 Pontiac 4 speed hydramatic. It runs and drives but there are multiple issues with both the engine and the tranny. I checked the numbers and fortunately / unfortunately it is not a numbers matching driveline.

    I am looking to replace at least the engine and tranny, possibly the rear end. I've been on Craigslist and found a 1984 Corvette with a 350 / 700r4 tranny and was wondering if this would be a good donor car for the driveline etc..? The car is $2200 and has 67k miles on it but the tranny slips.

    Also, would any of the suspension stuff work with the GMC?

    If not what would be a better donor car?

    Thanks all, I've really enjoyed the site!

    Carl
     
    Last edited: Nov 26, 2016
    1959rod likes this.
  2. davidh73750
    Joined: Apr 21, 2009
    Posts: 1,541

    davidh73750
    Member

    Motor and trans is good choice some may like the tpi some not you can switch to carb if it's not up to par. I believe you can run 15" wheels with the suspension to keep the look traditional. Please don't run big late model wheels


    Sent from my iPhone using The H.A.M.B. mobile app
     
    1959rod likes this.
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 45,693

    squirrel
    Member

    the suspension is probably a bit too wide, and would also be a fun challenge to install. I don't really see why you'd want to....maybe something a bit more mild would work? That's a lot of money for a crappy engine and burned up trans. The 84 model was crossfire injection, which is not very high on many peoples "dream engine" list.

    I'd sooner buy a new GM crate 350, and find another trans to rebuild. See what ratio rear the truck has in it...it's likely a Spicer 40 or something like that, it may possibly have a tag on one of the rear cover bolts with the ratio or the number of gear teeth on the gears, stamped on it.
     
    jeffd1988 and APACHE FS like this.
  4. A 350 Chevy and trans fit in there like it was made for it, because...well, it essentially was. The Chevy version came with a small block Chevy (283) as an option although you wouldn't be able to mount it the same way because the GMC front cross member is different from the Chevy. Doesn't make any difference though if you use side motor mounts (which is what you should do, in my opinion). I have a 350 in my '58 GMC with the original GMC Spicer rear diff. Everything fits great with room to spare. Not sure about all the Corvette suspension stuff. My guess is the track width is wider than your pickup.
     
    squirrel likes this.
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  5. Squirrel (see post #3) is an authority on this era of GM trucks so listen to what he says. he has a point about that particular motor and trans. If the trans is no good and needs to be rebuilt then all your getting for your project out of that Vette is a questionable motor of a not-very-desirable vintage. For $2,200 (or a little less) you could get a new crate motor.
     
    APACHE FS likes this.
  6. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    OK, thanks for the responses guys, this is exactly the advice I was looking for.

    So I'll pass on the Vette lol, and check into a 350/700r4 with trans-dapt motor mounts.

    I was looking for a car or truck so I would have all the peripheral stuff, alternator power steering pump etc..

    Carl
     
    Last edited: Nov 27, 2016
  7. I could really use the exhaust manifolds. Shame you're in Colorado and I'm in the UK ;-)
     
  8. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,094

    d2_willys
    Member
    from Kansas

    Was the 336 Pontiac a front or side mount engine in the 58 truck? If it was a front mount engine, then the frame will have bell housing aligned side mounts. You may need to build both new front and rear crossmembers for mounting newer engine/trans. Perhaps you may want to use a W engine such as a 348 and a cast iron Powerglide.
     
  9. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    The 336 is front mounted so I was hoping trans-dapt would have some motor/tranny mounts available. My main concern is if the from cross member is structural or not. If it is I may need to find one from a Chevy and do some ciphering. ;>)

    Hey Blackjack, I think shipping to the UK may be cost prohibitive! Good luck on your search.
     
  10. mopar362000
    Joined: Feb 14, 2008
    Posts: 88

    mopar362000
    Member

    you do not need trans-dapt mounts.use 1966 impala 327 motor amd trans mount.you can get trans and engine crossmember from speedway if you can not make them yourself have to weld engine to frame.I usually make my own .Your truck is an easier swap.Get crate 350,turbo 350 or 700r4 trans .Stay away from the vette.Jimmie King
     
  11. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,106

    Rusty O'Toole
    Member

    I'm thinking this is a golden opportunity to use a later Pontiac engine and trans. Or maybe rebuild the Hydramatic and replace the engine with a 389 or 421.
     
    belair likes this.
  12. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    Mopar, there are no vettes for me in the near future!
    Rusty, the Pontiac engine would have to be a pre-1961 because later engines are mounted side to side. Not to say it's not an option but....

    The more I learn, the more I'm leaning toward a 350 / 700r4.

    I'll be gathering parts through the winter and starting the work in spring. I don't have a heated garage and I'm old lol.

    Carl-
     
  13. borderboy1971
    Joined: Oct 20, 2008
    Posts: 677

    borderboy1971
    Member
    from Canada

    I'm sure you've heard the saying "the vette makes them wet", but I suspect in this case "the vette you'll regret".

    Sounds to me you made the decision not to buy it....good choice. As that 2200 can be spent more wisely elsewhere.
     
  14. I'd have to go with a '59 or '60 Pontiac 389.. It's a direct bolt-in to the truck and it bolts up against the 4 speed hydro. Parts are available.
    389-2.jpg
    AND! I'd search out a 55-56 front clip for it.
     
    Last edited: Nov 28, 2016
  15. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,094

    d2_willys
    Member
    from Kansas

    Jist remember the pilot bushing for the hydro input shaft.
     
  16. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,094

    d2_willys
    Member
    from Kansas

    IIRC: 1958 and up Pontiac 370, 389, 421, etc. are side mounted. 58-60 are the only blocks that will bolt to the existing hydro. 1961 and up use BOP pattern.
     



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  18. The 84 Corvette had unbelievably awful reliability issues. Many engine faults, fuel system issues, the worst TH 700 R4 of the entire generation, and was prone to evil handling from poor reared bushings and components. The p. Steering rack was prone to leaks and sticking as well.
    Ask me how I know.
    Run away as fast as your feet will carry you from that dog.


    Sent from my iPad using The H.A.M.B. mobile app
     
  19. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    Yea, I've been severely counseled on the vette option lol. Not going down that road.

    So a few of you recommend going with a Pontiac block and keeping the 4 speed hydromatic.

    If I do that I would have to rebuild the tranny cuz it leaks like crazy and shifts REALLY hard from 2nd into 3rd. Is it strong enough to handle the larger engines?

    Maybe a 389 is the way to go, the 336 parts are expensive, maybe not so much for the 389?

    Suspension and brakes are on the list too.

    Carl-
     
  20. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    And give up those dual headlights and all that chrome? No way ya hippie! o_O
     
    gimpyshotrods likes this.
  21. belair
    Joined: Jul 10, 2006
    Posts: 8,363

    belair
    Member

    The hydro is plenty strong.
     
  22. 73RR
    Joined: Jan 29, 2007
    Posts: 6,300

    73RR
    Member

  23. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 24,796

    Jalopy Joker
    Member

    do not throw away the current 336 w/ 4spd hydramatic - this combination is very hard to find - put in a good dry place and place some ads
     
  24. carryallman
    Joined: Jan 5, 2009
    Posts: 399

    carryallman
    Member

    dont want to step on this post BUT IVE STILL GOT MY 58 GMC 337 MOTOR AND 4 SPEED TRUCK THAT IM PARTING OUT motor runs good -does have a bad water pump ,this is a complete drive line truck with exh manifolds clutch trans starter driveshaft and rear axle -3/4 ton thanks mike
     
  25. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,094

    d2_willys
    Member
    from Kansas

    Use the hydro! Easily sealed up when the engine is removed. Pull the torus and it's members off the transmission and replace the front seal. Re-install the torus and members. While out, change the rear seal too. Easier outside of the vehicle. When re-installing the hydro use PLIOBOND 30 to seal the flywheel to the new engine's crankshaft flange. Also use this on the flywheel bolt threads. Coat the 30 bolt gasket with gasket sealer. The 18 bolt o-ring just gets some vaseline to hold into place in flywheel groove. (You have either the gasket or the oring.)
    Remember to install a pilot bearing if the 389 does not have one before mating the engine to transmission.

    Finally change both side and bottom pan cover gaskets. The side cover will also get linkage seals.
    This should seal the transmission up really well.
     
  26. Torkwrench
    Joined: Jan 28, 2005
    Posts: 2,448

    Torkwrench
    Member

    The 4 speed Hydros are VERY TOUGH transmissions. Just check out what many of the early 60's gas class drag cars used for transmissions.......4 speed Hydros. By the way, they naturally shift hard. Even when they were new.
     
  27. Any photos of the truck ?
     
  28. CandD's 58
    Joined: May 4, 2014
    Posts: 15

    CandD's 58
    Member
    from Colorado

    Excellent replies folks, and I am excited to fix / keep the hydro. So now I have a plan.

    I am going to find a 389 4bbl and rebuild it, redo the suspension with posies super slider springs, and convert the brakes to a dual master cylinder and front disks. Should keep me busy next spring!

    Couple pics...
     

    Attached Files:

    73RR and swade41 like this.
  29. Nice looking truck and sounds like a good plan, good luck with the new go and whoa departments.
     

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