The Stovebolt Site Forums The Shop Area Paint and Body Shop Convert 58 GMC to Chev Cab

Hi folks.
My 58 small window Chev cab is in fairly bad condition in the bottom door hinge / air vent / fender mount area. Also the floor is pretty much gone. Door steps are partly gone. Doors are also real bad. Dash is in perfect condition. Not butchered in any way.

I local fellow has a replacement GMC big back window cab in central US that has very little rust. Just some light dings, and maybe some mild pin holes in the back cab corners.

Cost would be $1500 for a replacement cab with doors and glass.

Any one have experience swaping the GMC dash out for a Chev dash?

I can also get a small back window Chev cab in very good condition for $2000.

Any recommendations ? Anyone else ever swapped out a dash panel ?

Thanks.

Does anyone have a picture of a 55 GMC big back window cab? I presume both Chev and GMC had a 2nd series in 55.

I found a picture that seems to show a 3 piece big back window on a GMC cab.

I've put a deposit on a 'clean' 55 GMC cab, that is supposed to match my 58 chev cab.

I know I'll have to swap out the dash. That doesn't worry me too much. But I sure don't want a surprise that the 55 GMC rear big window is not like the big one piece Cheve big back window cab.

Thanks.

John - that "3 window" GMC cab was a factory modification of the usual big window cab used only on the largest trucks, they're scarce but otherwise same as any other 5-9 cab, and other than the dash all 5-9 GMC and Chev cabs are interchangeable, big or small window .... changing the dash isn't a cakewalk tho, involves drilling out many pinch welds right on the windshield flange, good luck w/ that!

Bill

Thanks Bill.
Are you saying that I should stay away from that kind of a change? My cab is pretty rotten. I know a place that has a very clean chev cab complete with original doors, but for $500 more, but a small rear window.

Unless you are after originality, it sure would be easier to use the GMC dash. If by chance the GMC was a fleet option model, it would have a Chev dash to begin with. The cab shells on GMC and Chev started out the same, but they used lots of welds putting the dash in to make either GMC or Chev.

Thanks crenwelge.
My plans are to restore to original, if possible.

My Chev truck is complete, and original so far. The 235 seems to have a stuck valve, with a bent pushrod. Seems to run OK on 5 cylinders. If the 235 isn't damaged and can be used, I think I'll restore to original. If the engine is junk, then I have other plans to put in a v8 and auto trans from my Dad's old Impala wagon.

I figure I should weld in some braces to hold the cab structure together. Remove the windshield. Cut the spot welds at the bottom of the dash. Then cut the top of the dash out leaving 1" or so. Then I remove my chev dash from my cab leaving as much material as I can up to window chanel. Then mig in the Chev dash into the GMC cab.

Alternatively, If someone could swap me a GMC instrument Panel for a Chev instrument panel, I guess I could save a lot of work

From what I've been told, the GMC cab was on a tow truck. It might have holes in the roof for lights that I might have to plug. It was a 55, so I don't know if it will have GMC or Chev dash.

if you're comfortable with the metal work the dash swap can be done, and takin both out isn't the hard part, just tedious, drill the welds, don't cut - you'll find the structure solid with the dash out, cab deforming won't be a problem

myself, I'd look a bit longer and maybe come up with a 58/9 Chev cab even if it needs a bit of work, note that the firewall is slightly different on a 58 from the 55, making for issues with hood hinge mounting - can be overcome but .... 1500 is pretty top dollar [just OK with the doors], 2000 would be too spendy for my taste

Bill

John,
I replaced the small window cab on my 59 chevy with a big window cab from a 58 GMC. I also did the dash swap and it wasn't that bad. Like everyone is saying there is a lot of pinch welds to drill out. I would also make sure that it is on a flat surface when doing the swap. The cab remains ridgid but im sure there is a chance it could twist a little.
The cab i purchased was from a 1 1/2 ton GMC so there were a few more holes in the firewall that my body man plugged and welded for me before he painted it. At 40.00 per hour I think i should have waited for the right 59 cab to come along. Fortunately the hood hinge holes were the same. You will need to change them if youre using the 58 front clip. One other small thing was the transmission cover plate. The hole for the four speed on the GMC is a little off from the Chevy.
Good luck.
Brian M

Thanks BrianM.
My Chev is a 3spd column shift.
The GMC is probably a 4 speed, so I probably have to do something with the transmission cover as well.

Maybe I should wait for a 'perfect' cab, but they are getting hard to find.

I kinda prefer the big back window cab. That's why I'm going for this one. The other Chev cabs in Ontario are all small back windows. I suppose I could wait a while longer, as I have lots to do with the chasis, engine etc.

Anyway, I've got enough space in my garage for the cab, and I can get something done over the winter, then get on to the chasis when the snow is gone.

Thanks again folks.

Other than the hood hinge bolts, is the front of the GMC and CHEV cabs the same?

Will the hood and fenders (inner and outer) bolt up OK?

Any other surprises I should know about?

the hood hinge bolt position difference is 55-7 vs 58/9 for either make, otherwise no other problems mixing sheet metal, including doors

Bill

The dash has nothing to do with the structural parts of the cab. It appears that GM built cabs without a dash and then installed either a Chev or GM dash with spot welds. I use these kind of bits to drill spot welds. http://www.dentfix.com/viewItem.asp..._Weld_Drill_Bit_for_High_Strength_Steels I have the Spitznagel drill, but if you are going to just do one project, you can use any drill. The bits appear on eBay ever so often. They are also sold under the name of Würth. They are all made in Germany and make other spot weld bits seem like toys.

Thanks Guys.
Looks like it's easily within my abilities.
That drill bit is cool.
Great web site for auto body tools.

Thanks again.