Changeover from 305V6 to 283 - need help!

[IamBrian]

First time writing on here so bear with me please. I have a 67 GMC 1/2 ton with a 305 V6 and full synchro 3-speed transmission. My V6 is burning oil and since I had a Chevy 283 V8 sitting around, thought no big deal to switch engines. I replaced the motor mount stands to V8 and bought new motor mounts for them. Of course my issue is with the bellhousing, clutch, shift linkage and driveshaft. The Chevy bellhousings are about 6 3/8 inches (shorter than the GMC I removed) and of course this moves the tranny up.
This pickup had the V8 available, so what do I need to do? I'd like to keep the three-on-the-tree shifting. Were the shift levers shorter for a V8? Any help or advice would be helpful.

[ETsC10]

HEY! Welcome to the board!

Not really sure on the 3 speed linkage for a V-8 vs V-6,
but I tend to think they were different.

Maybe someone can chime in with more info for you.

I sold this so I can't measure it; but here's a picture.

[IamBrian]

Thanks for the welcome. I thought I did enough research before I started this change - even looked up a few threads here concerning the engine stands, etc. Guess I was wrong. Wish I had a donor V8 pickup or even one to study, but...
Anyway, I placed the V8 in the V8 position so that is correct. I don't have a correct bellhousing so can't use the mount on the bellhousing, but intended to support the rear tranny instead. But, until I got the engine in the bay I couldn't see where I stood as far as lengths went - of the clutch linkage and shift rods, or even the driveshaft.
Looks like the driveshaft will be around 3 inches too short. Shift rods seem very long - maybe 6 inches (tough to tell for sure). I would cut and weld, but don't really want to for many reasons.
How long is the stock bellhousing? - I can't believe it would be longer or the tranny wouldn't work. Is my tranny made special for the V6? - how long is a V8 3-speed?
Hey, still having fun though!

[Livrat]

Hello Brian, Welcome to the board!!

Unfortunately I do not have answers to all your questions but here is what I do know.
V6 stick transmissions do sit farther back than a V8, I do not know know if the V6 trans input shaft length it self is different (Can not imagine GM doing it that way) But in 67 the trucks normally did not have a full syncro 3 spd (The Saginaw didn't become standard until 68) Could you post a picture or two of the transmission? Maybe some one else could chime in here??

I do know V6 clutch linkage is totally different, the rod comes through the firewall much lower than a V8, and the Z bar pivot mount on the frame is different.
I personally would locate stock V8 clutch linkage and the correct shift linkage,
(there were several different sets of shift linkages, 67 6cyl with GM 3spd, 67 V8 with GM 3spd, 68-72 6cyl with Saginaw 3spd, 68-72 V8 with Saginaw 3spd)

Since I do not have one to measure I am not able to answer your question about the length of a stock belhousing or the overall length of a V8 3spd.

Can anyone else help out??

[IamBrian]

Hello, thanks for info. Boy, I really didn't do enough research! But, to tell you the truth, until I opened the hood the first time - I didn't even know GMC made a V6! Crazy...
After I bought the pickup, I read this thread from Vintage Windmills dated 3-28-2011, 1157am and laughed! But had some good info, that's how I found out about the full synchro tranny.
Ok lets see if I can figure out how to add pics...
guess not.

[IamBrian]

Think I managed to load the pics but now have to figure out how to write on them. Well, the first is obviously the V6 I yanked out. The next is a view of the V8 sitting inside and the distance from engine to the firewall (if you can tell) and finally the SPID list on the glove box.

[Livrat]

The SM326 is The Saginaw, So you can use any shift linkage from 68-72 V8 that had a 3spd. (still not an easy one to find) personally I would just cut and weld the ones you have

[Danny Bost]

I may have the shift and clutch linkages that you need, I will have to look. Unfortunately my spare parts are 200 miles away. I won't be back down there for 2 weeks, but I will look for the parts then. If I still have them I will give them to you.

[IamBrian]

Oh wow, I would really appreciate that - I hate to cut mine because I hope to return the V6 to the pickup someday. If I ever figure out how to get it rebuilt without spending a fortune. I think its a neat engine - and different. But I gotta tell you, this hasn't been an easy swap like I figured it would be.
Thinking today I'll slide the engine back to the I6 mount holes to see if that'll give me better placement of the V8 (looks too far forward) in respect to the firewall. And in turn that'll be better for my driveshaft - I should be able to use it. Think I'll go with the stock bellhousing for mounting to crossmember - provided my sliding it back doesn't cause problems. Really wish I could see a stock V8 setup and ck measurements. Like I said, mine seems too far forward of the firewall.
Gotta keep smiling though - just amazed at how much can be done with these pickups and all the help there is available. Thanks

[Danny Bost]

On my truck it is 6 1/2 inches from the back of the intake (behind the dist) straight back to the firewall. Mine is a stock 350 71. Hopefully that will help some.

[IamBrian]

Hmmm, slid the engine back like I said to the rearward mount holes and it seems to look better within the engine bay. About 3 1/2 inches from intake to firewall - so guess I should leave it at the stock V8 mount. I managed to get the shift rods hooked up though (temporarily only) and the clutch z bar is somewhat closer???!!! I probably should find a stock bellhousing to see if it fits the crossmember.
Still tinkering...

[IamBrian]

By the way, while the 305V6 was sitting in my driveway I wired up a battery to do the compression test. After taking off the exhaust manifolds during engine removal I noticed the number 5 cyl. showed oil in the port while all others were dry. Read 6066GMCguy website and saw 125 psi was normal. I showed 120 - 125 on four cylinders, 110 on number 6 and barely 100 on number 5. Are pistons rings even available for these engines? Think I've read where oversize pistons aren't. Is there hope for this engine?
Well, still researching the bellhousing and linkage issues with the V8 swap.

[IamBrian]

Guess i should do a followup: finally mounted the v8 in the bay and have been driving it all winter. ended up redrilling frame to move the v8 engine mounts rearward three inches, afterward installed a chevy bellhousing and clutch to the original three speed. sliding the engine back those three inches allowed me to use the stock driveshaft. however, i couldn't use the bellhousing mounts so installed a rear tranny mount between the frame. the shift linkage was the trickiest thing though and had to modify the z-bar.
Would still love to get the 305v6 running properly and reinstall it in the 67 cuz it was pretty cool! boy, what a smoker though....
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[MrSchaeferPants]

Sweet deal. Now that you have the V8 as a runner, you have all the time in the world to research parts and rebuild it. And when you're done, post all the part numbers and where you got it from on here so it'll be easy when I do mine.

[Bob B.]

Be patient, you will find the parts to rebuild that V-6. Parts for those show up on E-Bay often. Start collecting!