LS Engine - 1968 4-speed?

[Hey Dude]

My search didn't produce what I wanted... Has anyone here mated an LS engine to their original manual tranny? I have a 1968 C20 with the heavy duty 3-speed+ granny low transmission. Is this possible? My donor vehicle is a 2003 silverado 4x4 5.3LS1 My initial plan would be to convert the LS to a carburetor.

The C20 has only 35K original miles. Bought new by my great uncle but, the motor has sat too long in storage and needs valve work and a new carb. To turn this into a parts chaser and cruiser would be the goal. I came across the 03 silverado cheap...

[damnyankee36]

Did a quick online search, "ls1 4 speed". Didn't read it, but try this:

https://www.motortrend.com/how-to/ma...eed-ls-engine/

[MARKDTN]

https://67-72chevytrucks.com/vboard/...d.php?t=853223

See this one also.

[Hey Dude]

Thanks, I've read a bunch of that now and have a better understanding in general.

I was hoping someone here had done this on a C20 specifically and kept the existing manual trans. I'll check back each day for updates.

[57taskforce]

It’s not that hard. Early 2000’s 3/4 and 1 tons came with a manual transmission. If memory serves me right, You use the flywheel and pilot from one of them. A factory style clutch from your truck should bolt to that flywheel. On the transmission you will omit one bellhousing bolt hole that doesn’t line up. Doesn’t matter if it’s in a c/10, or a c40. The process for mounting the engine to the trans is the same. The easiest thing is to mount the engine to the frame where it lands once it’s attached to the transmission, as the transmission is the fixed point of everything. The 4 speed in your ‘68 should most likely be an SM465. It’s been a while since I looked into doing this with my 6.0 but this thread should help you out better than my years old recollection.
Rather than the pivot ball linkage I’d suggest a hydraulic clutch. That’s the one of the best things I’ve done to my 72.
Heres a little more reading…
http://67-72chevytrucks.com/vboard/s...d.php?t=421258

[PbFut]

I did a LS to Jerico (Think 1970s Muncie Case)
I used a Quicktime Bell housing about 15 yrs ago. The new number is RM-6036. Lots of options as far as TO bearings as it has drilled mount holes or you can float on the input shaft.
It was for road racing. This is a SFI certified part so a bit pricey. Likely softer material versions out there. Took a bit of messing with to get the right pilot bearing and flywheel/clutch I wanted. But they were only 7 inches and spun up and down nearly instantly. Clutchless shifting was instant but if you flubbed the rev match it sure went bang.

[57taskforce]

Originally Posted by PbFut

I did a LS to Jerico (Think 1970s Muncie Case)
I used a Quicktime Bell housing about 15 yrs ago. The new number is RM-6036. Lots of options as far as TO bearings as it has drilled mount holes or you can float on the input shaft.
It was for road racing. This is a SFI certified part so a bit pricey. Likely softer material versions out there. Took a bit of messing with to get the right pilot bearing and flywheel/clutch I wanted. But they were only 7 inches and spun up and down nearly instantly. Clutchless shifting was instant but if you flubbed the rev match it sure went bang.

I’m gonna build something with a Jerico one of these days. I’d love to do a LS or R07 powered street legal stock car with one.

[PbFut]

Originally Posted by 57taskforce

I’m gonna build something with a Jerico one of these days. I’d love to do a LS or R07 powered street legal stock car with one.

Jerico will not play well on the street. Synchros are replaced with a very large ring with 6 tabs about the size of your thumb. Shifting is done by lifting the go pedal while applying pressure on the shift handle in the direction of next up gear. The release of engine torque on the dog rings unhooks the rings and just that fast you are in the next gear and back on the throttle. Ok for track but on the street you can't drive aggressive enough all the time to correctly shift. If you are a master at rev match maybe. Try driving with out using your clutch. If you can do it full time on the street only clutching at a stop, then you may be able to make a Jerico work driving around town. These in the photo are nicked up and in the junk pile. They don't look bad but it doesn't take much for them to act up.

[biketopia]

As mentioned you'll need to sort out how your clutch will operate as the LS engine won't have provisions for the clutch linkage. I think there are companies that make adapters to work around this, but I would upgrade to a hydraulic clutch. Everything else is "straightforward"

[Hey Dude]

Originally Posted by 57taskforce

It’s not that hard. Early 2000’s 3/4 and 1 tons came with a manual transmission. If memory serves me right, You use the flywheel and pilot from one of them. A factory style clutch from your truck should bolt to that flywheel. On the transmission you will omit one bellhousing bolt hole that doesn’t line up. Doesn’t matter if it’s in a c/10, or a c40. The process for mounting the engine to the trans is the same. The easiest thing is to mount the engine to the frame where it lands once it’s attached to the transmission, as the transmission is the fixed point of everything. The 4 speed in your ‘68 should most likely be an SM465. It’s been a while since I looked into doing this with my 6.0 but this thread should help you out better than my years old recollection.
Rather than the pivot ball linkage I’d suggest a hydraulic clutch. That’s the one of the best things I’ve done to my 72.
Heres a little more reading…
http://67-72chevytrucks.com/vboard/s...d.php?t=421258

Thank you! Another great read.

[57taskforce]

Originally Posted by PbFut

Jerico will not play well on the street. Synchros are replaced with a very large ring with 6 tabs about the size of your thumb. Shifting is done by lifting the go pedal while applying pressure on the shift handle in the direction of next up gear. The release of engine torque on the dog rings unhooks the rings and just that fast you are in the next gear and back on the throttle. Ok for track but on the street you can't drive aggressive enough all the time to correctly shift. If you are a master at rev match maybe. Try driving with out using your clutch. If you can do it full time on the street only clutching at a stop, then you may be able to make a Jerico work driving around town. These in the photo are nicked up and in the junk pile. They don't look bad but it doesn't take much for them to act up.

I used to drive a 10 speed Eaton regularly when I still used my CDL. Rev matching isn’t a concern. I don’t really use the clutch in my 4 speed trucks much at all once I’m moving. This one wouldn’t be for daily use by any means, more of a get out on a wide open desert road and let it eat kinda thing, with some track days mixed in of course.

[57taskforce]

Originally Posted by Hey Dude

Thank you! Another great read.

No problem. I’ll look thru my bookmarks when I have some more time, I bet I have a few more similar threads.

[LS short box]

Don't know if this helps but I fabbed the mechanical linkage for my 73 Camaro with a LS/TKO 600 swap. Used 3/8" rod ends and tubing. Had about $50 in parts.
See pic.