65 gmc build help

[andyjust4today]

Hello, I'm new to this site and am looking for some general advice. I have followed some past threads on doing a 1965 gmc 305v6 conversion to a sb 350. I have started my build with the short block off of a 93 tbi 350 and bored it 30 over with double roller timing, stage 3 cam and lifters, hv oil pump, holley dominator intake, and edelbrock carb with the bear can ports... the heads came off of a 81 I believe. Ok now for the dirty. Everything went together fine engine is pristine and all but once I got into the build Ive started to watch as the budget disappeared. The perches and mounts I bought private party I was told would fit the 65. Not the case they were off of a 73 with the clam shell mounts. First off engine sat way too high in the front and the hei would have never fit next to the firewall. Also the block huggers wouldn't fit because th clam shells where in the way, go figure right. after some research I went and purchased a set of 65 c20 v8 perches and mounts and with a little maneuvering and some new holes drilled in the frame engine sits perfect and block huggers fit. Now for the dilemma, I have a sm 420 granny low that came with the truck and due to the outstanding hauling performance I would like to keep it. The bell housing I purchased for this build was off of a 65 L6 which I have been told should work. Not only is the transmission now a pain to get lined up (had it in and out of the 305v6 in 30 minutes before), now when I get it slotted and start to tighten the 4 bolts it doesn't want to meet properly. I figured we maybe its just a tight fit on the bell housing's center hole so slowly but surely got it to mate..... Bam flywheel will no longer turn with the stater on otherwise. Pulled the transmission back out and the flywheel turns. ok... I purchase a the correct clutch set for 65 c20 v8 along with pinion bearing etc. because at the time I was using the clutch set from the 305 v6. With the new clutch installed go to put sm420 back in and am having the same problem. What went wrong?

[Palf70Step]

Sorry to hear about your rough start. I am not sure about the difference between the GMC V6 and V8 mounting. Hopefully some knowleadgeable folks will ring in for ya.

[64shortbed]

My 64 GMC had the inline 6 in it not sure what the difference in the mounts where between the inline 6 and the big v6. The inline 6 ones worked with my 350. (the mounts for the 292 inline 6 WILL NOT WORK. driver side will but pass is different) They are not the clam shell mounts they are the ones with 3 bolt in the block and 1 in the mount. As far as trans go i have no input on that. I put a th350 in mine. As far as header room again i run stock ram horns. You may have to look at making your own or buying some aftermarket ones to fit your needs.

[andyjust4today]

Thank you for the reply. I'm going to try marking the input shaft on my sm420 and sliding it back in place to check for clearance. I am wondering if the pilot shaft is too long for the application with the 95 crankshaft.

[Vinceg]

Sorry to hear about your troubles. I had my old sm420 in and out of my truck after converting from 230 to 283. I never had a problem like your experiencing. It was an older motor so you might me on the right track with the input shaft. Once your lined up before you start pulling the tranny into the bell housing with the bolts can you rotate the motor? How far can you slide it in by hand? Just wondering if there is a certain point in which it binds up while bolting it up. I'll keep tabs on your post I'm very curious to hear what you find.

[andyjust4today]

So the current conclusion I've come to is the bellhousing on the 305 v6 is 1 inch deeper from block to where the transmission meets than the chevy bellhousing. I'm going to attempt to fabricate a 1" shim between the bellhousing and the block to make up the difference which means I have to move the motor forward as well in order for the bellhousing to bolt to the mounts.

[kchampagne]

Yeah, bummer to hear the issues you are having. I recently bought a 65 GMC Suburban with a 305 that was supposedly rebuilt. Needless to say, I quickly found out that the 305 was jacked. I waffled between finding a running 305 or doing the conversion you are doing with a SBC 350. I ended up deciding to keep it as original as possible, so I am staying with the 305. During my research, I book marked this thread that may be useful for you: http://67-72chevytrucks.com/vboard/s...d.php?t=367487

Good luck, it will get better!!!

[padresag]

Originally Posted by andyjust4today

So the current conclusion I've come to is the bellhousing on the 305 v6 is 1 inch deeper from block to where the transmission meets than the chevy bellhousing. I'm going to attempt to fabricate a 1" shim between the bellhousing and the block to make up the difference which means I have to move the motor forward as well in order for the bellhousing to bolt to the mounts.

I don't think that you have to do that . should be the same trans. how close does the trans go in before it stops?
the chev bell housing should be able to sit where it mounts to that crossmember. the sbc should mount up to the b/housing and that should dictate where your frt side mounts should go. it is the later c20/30 eng perches that you need as they are about 1" shorter that the later c10 one were. what flywheel are you using.
ron

[andyjust4today]

I've finally started getting somewhere I happened to pick up a 3 speed on the floor that mates perfect without any binding. Now I just need to find out what driveline will work . Went ahead and did my test fire and that baby's sweet.

[andyjust4today]

Ultimately they were correct in saying the sm 420 will fit. With some finesse and replacing the pilot berring I managed to get it to mate fine. The problem was the pilot had a frey on it which was holding it up.haven't figured out how to post pics on here yet but as soon as I do I'll show pics of the entire build. Was getting a little ahead of myself with frustration and making mistakes because I was staring at it for too long. The 3 speed I obtained would have been more work and money to modify the floor in the cab and finding a driveline. I'll use that in my next build which is a 1969 302 z28 engine. Not sure what I'm putting it in yet. Thanks fellas

[Palf70Step]

Glad you got it. I had issues with my 3 speed, same reason. I am probably the one who nicked/frayed the bushing thrying to manhandle the tranny in my skinny arms and not using the tranny jack.

[andyjust4today]

So the truck ran great for a few days and then........ there was a zing and a pop coming from under the cab which indicated something with the transmission. I took a look and the front berring retainer shaft completely severed off and was spinning freely over the input shaft. First off I have no idea what could have caused this, maybe all the wrestling it took to get this beast back in. I don't know. I pulled it and managed to find one fairly cheap and did the swap. I also had to replace the clutch release berring because it got toasted as well. Got it back in and first thing when I started it there was a loud screech only when I push in the clutch. Adjusted it out and the screech went away but now the damn thing won't go into gear. Did I manage to cook the tranny or could it be something else??????

[padresag]

the reason the throw out bearing was toasted is more than likely it was running against he pressure plate. it heated and seized on the bearing collar which expanded and siezed on the input gearing retainer and pop. your pressure plate is more than likely toasted..are you running the long throw out when you should have the short one in. is it possible that you have the clutch disc in the right way. a chevy clutch disc goes in the other way that a V6 GMC clutch disc goes in. the reason that I say this is; is if you put the new one in the same way the old was then you would be in trouble. the disc in backwards would cause the p/plate fingers to move out closer to the t/out brg.
either that or you have the clutch adjusted up to high
ron

[andyjust4today]

I'm using the short style release berring and a new disc with the shaft guide facing the flywheel. I am however using the lever three finger style pressure plate that was from the old motor.

[padresag]

originally you said that you purchased the correct clutch set for a 65 c20 v8. so you are only using the disc? is this the orig t/out brg that you are using.? what do you mean by the shaft guide
I cannot remeber why the clutch discs are different between the 2, but I do not think that the chev disc works with the GM pressure plate. perhaps someone else can clarify that
ron

[andyjust4today]

The shaft guide on the clutch disc is opposite on the gmc where it slides on the input shaft the guide faces the transmission and on chevy it faces the flywheel. I'm going to pull it all back apart today and inspect the clutch pack for damage and possibly change the whole thing again. Is there a better way to check the transmission before I put it all back together.

[padresag]

what do you mean check it. what do you want to check it for.
simplest way is to drain the oil and check for cuttings. take off the cover and have a look inside. check for play in the bearings. odds are that it has never been touched, so after 50 years of service it should be taken apart and cleaned and new bearings and seals
ron

[padresag]

another item is what "z" bar are you using the GM v6 one or one for a sbc. there is a difference berween them
ron