Hello everybody, I have a 61 GMC 1500, 305 V6 and a 4 speed even though its really a three because 1st isn't useful unless towing haha. I have a 283 I am building to put in but had a few ?'s First what are the older pistons made from? I see most of the rebuild kits are cast aluminum and I am not sure if the originals were forged or cast as well bc if there forged I'll reuse them if I can. and secondly does anybody know were to get motor mounts for the swap? I've checked speedway, jegs, summit etc but have not found a set. and if anybody knows the gearing in the rear on these itd be appreciated. I'll post pics this weekend before anybody asks haha thanks for the help ahead of time
I drove a 66 4x4 GMC once, and it needed to start off in first gear, which surprized me. I mentioned that before on here, and thought the trans First/Second gear was geared differently, and squirrel said it can't be. It turned out that it had a rear ratio around 3.4 ish to 3.5-ish. So, if you can't use first, I would bet your ratio is 3.9-ish to 4.1. Jack up one wheel, put a mark on the tire, the floor, and the driveshaft. Now turn that one tire two exact turns while counting driveshaft turns on it's mark. If it is not quite 4 turns, it is around 3.9. If 3 and 3/4 turns, it's around a 3.70. A hair over 4 turns would be around 4.10. The 283 and your gas budget won't like any of those gears.......VIDEO LINK for posi and also non-posi ratio testing: Cheapest way out is to look for a later 70s to mid 80s Chevy/GMC 4x4 rear end complete. These 4x4's will have same 6 lugs and in those years, they had many different ratios, and you can pick a ratio for your speed requirements....hiway or city, etc There were ratios available like 3.07 2.76 to around 2.5 in the 1980s.. Earlier 70s rears will fit, but the ratios are not quite as good...many were 3.07 and higher numbers Mounts; you may need the steel mounting towers from a Chevy truck of those years...I am not sure if GMC had towers like chevy trucks or not. Then bolt on the new chevy V8 rubber mounts to those. 1958 or later 283 has the side holes on block for those mounts. 57 does not
here's one way to build mounts for a Chevy V8 using the welder....and some steel strap, etc. This is a solid mount, but you can use a normal rubber mount for a 1960s car instead.
Practically all factory pistons are cast. They may have used forged pistons in a handful of super performance muscle cars (not recommended for street use) in the sixties but, cast pistons in everything else.
K thanks guys, I gotta check to see if there is a front mount motor mount or if I have to weld one on, and I will check the conditions of the pistons this weekend and go from there, I will put pics up this weekend, thanks again
I will see if I have a motor mount tower for a 63-72 GM truck, and will post a pic if I can find one. I know I used these towers on a 61 C10 many years ago, but that one had a 72 front suspension crossmember. I can't recall how I bolted the top part to the boxed frame on the 61. I am sure I bolted them, not welded. The top outer edge of the tower fits on top of the frame rail, and the bottom inner leg of it, bolts to the top of that crossmember. The towers are steel, and then the 63-72 truck rubber mount bolts to the tower with a single larger bolt.
I found one tower. The top flange with 2 bolts sits on to of the frame. The lower one bolt leg sits on the large front suspension crossmember. Then the truck rubber mount pad bolts to that single side hole. 63-72 uses these types of towers on straight 6, V6 and SBC and BBC...but I don't know if they were all exactly the same identical bends. Someone might have a parts book to look that up if you need to start looking for some. anyways, I would think this type of tower should be able to work, but may need a spacer somewhere, maybe on top of the rail? I kind of recall that, but maybe I am thinking of another build. It was so long ago, when I used these on the 61 C10; 350 V8/AT swap.
I did that swap years ago. What I recall was that in spite of many people telling me that Chevy parts would fit in a GMC, nothing did. The GMC frame is different (wider) this required us to make the engine mounts. I used the Chevy bell housing. I found that the transmission bolt holes in the Chevy bell housing were in the right place but that both the transmission's mounting holes and the bell housing's holes were threaded. I had to drill out the holes in the transmission in order to get the bolts into the bell housing. The radiator hoses did not line up and that required a trip to the parts store with a tape measure. The GMC had a hydraulic clutch and the slave cylinder was on the passenger side while the Chevy clutch fork is on the drivers side. I made the bracket needed to move the slave cylinder. The only thing that actually fit without modification were the headers that I picked up at a garage sale; I have no idea what they were originally for. In spite of what you may have heard a Chevy small block is not a "bolt in" in a GMC. I did the swap over thirty years ago and still remember the frustration involved. That said; the truck ran well after the transplant.
Norm, What was the year of your GMC swap? The reason for my question on years, is that Chevy trucks in that 60-66 body style DID use a hydraulic clutch on the 60-62 versions. The Chevy trucks in those years DID use a "V8 pattern-truck bell" that had the passenger side fork/slave, and it too, had 2 trans bolts theaded and the other two were drilled out. The lower two holes in the bell, you put those bolts in through the inspection cover, and threaded into the truck trans. It's just a matter of getting the correct parts for the swap, and finding out how GM did it and what parts were used. and the "wider frame" you mentioned was also on 60-62 Chevys due to the "torsion bar front ends" and the "boxed X frame" on those 60-62 Chevys. That is also why a bed from a 60-62 won't be a direct bolt-on to a 63-66 without changing the locations of the underside cross rail bolting brackets. Thanks for bringing up the bell housing info, as I completely overlooked that on the OP's original swap question.
I don't see the fascination with turning a somewhat unique powertrain, ie a 305 v6 powered GMC truck into a common as dirt small block Chevy drone. If you want a Chevy truck, why not buy one and avoid the aggravation of tearing up a GMC. A grill swap makes more sense. It's your truck, but that's my take on this
Well, gas prices are "down" for the moment, but they will return. Those GMC motors are not as fuel friendly by any means. They are low revving, low horsepower gashogs. Lots of torque, but very heavy and thirsty. Just not a good "vintage" combination for todays high speeds on even secondary roads, let alone highway speeds. I have a nice 66 chev camper special 4x4 350/TH400 with 3.20 gears and I honestly have not driven it since last November. It sits in the storage building, still registered and insured. We used to do all our towing with it, until my son completely spoiled me with his Cummins 12 valve stick/OD truck. It runs circles around my Chevy, and is extremely fuel friendly, so he does 100% of my towing now. If my Chevy was more fuel efficient, I would be using it, so that is why modifications are sometimes more important than "unique" or "stock". I still like my Chevy, but I can't justify using it. (I might look into a 4BT as I doubt a 6BT will fit.)
You are making an argument for buying a Prius and / or a new truck rather than an old GMC. Fuel economy improvement by going to a 283 makes little sense unless you are going to drive 20000 miles per year. Again, it's your truck. My '60 Ford came to me with a small block Ford, but I'd just as soon have a "traditional" Y block. Good luck.
F & J, I'm pretty sure the problem that we ran into was due to using a car bell housing, etc. The truck was a '62 four wheel drive originaly with the V6. If I remember correctly it was a 350 or so. I always though that bolting two of them together to get a monster V12 would be cool; practical not so much. I am also fuzzy on the details since we did the swap so long ago. There was a lot of screaming and hair tearing; that I can assure you.
Norm, GMC already covered the "two V6's tied together" . The GMC big rigs had an optional V12 that was basically twin 305's upper halves, but a V12 block. Four heads, two intakes. 700-something Cu In. Talk about gas hog I worked for DOT years ago and half of our districts fleet were aging 66 and 68 GMC dump trucks with 478 V6 gas 5 speed/2 sp rears. They pushed snow good, but anything over an 8" wet snow storm, one would blow an engine. It was the over-revving on certain big hills, and not getting a road speed to keep it lower. As I recall, ONE point FIVE MPG pushing, with a sander on the back.
Well, we don't know how many miles the OP will drive. But I do see where he lives; Long Island, NY. That is a low, long and flat sand spit, left behind from melting glaciers. He won't be pulling big hills, as there are none like where I am. So, a lower torque 283 will do just fine when he gets his final drive ratio changed out. Then MPG will go up quite a bit. I like the idea of the smaller 283, rather than a 350...I am sure there is a potential gain in MPGs with less CI Some old truck owners actually use them as daily drivers. I did. I drove a 63 Suburban with 400 sbc, TH400, and a 2.76 rear. I drove it as my only daily driver from 1995 till around 2004-5, when gas went so high, it was killing my budget. If I knew what I know now, I probably would have kept it and went with a diesel, as I liked that truck. My stuff needs to "earn it's keep" if I am forced to drive them on a regular basis. My hobby "cars" are all multiple carb V8's.. 340 sixpack, early Olds Rockets; two tri-powers and one 2x2. My newest vehicle I own is 44 years old, so a Prius is not in my future.
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