Muncie 4 speed swap
 

Over the past few months I've been gathering everything I need to convert my 357/th350 combo over to a 4 speed muncie :) I have the Trans, bellhousing pedals and linkage but now I'm wondering about a clutch? A friend of mine has a perfection clutch new in the box never opened its a borg and beck style ceramic button clutch for these years of truck but the problem is its a 12" clutch and iI am wondering if it will work with the bellhousing? Any advise?

Re: Muncie 4 speed swap
 

I'm not sure about the 12".... I put an 11" out of an Astro Van in my '67 when I put the S-10 5 speed in it. There is a lot of reading in the thread I posted the link to below, but you may find your answer there....

http://67-72chevytrucks.com/vboard/s...d.php?t=313954

LockDoc

Re: Muncie 4 speed swap
 

Don't forget the pilot bushing..

Re: Muncie 4 speed swap
 

I haven't done it myself but I think the 12'' clutch works in the bellhousing for the SM465 Muncie. I have an 11'' clutch behind an L6 292 in a '68 C/10. And (I think 11") in a '71 GMC Jimmy [4x4] 350/SM465/NP205/3.73 Posi. The 12'' was optional [for SBCs], but can't say the whys and wherefores.
You will need a flywheel for a 12''.

Re: Muncie 4 speed swap
 

I have a 12" flywheel for it but I'll have to see if it works! The Trans I got is actually a m21 from a guy out here in Canada and have a chevelle bellhousing he told me it can fit an 11" but I'm not sure if 12 will do? Will a sm bellhousing work on a m21?

Re: Muncie 4 speed swap
 

12" clutch will fit fine as long as the bellhousing will accept it. Most trucks I have seen had the larger version of the bellhousing. The smaller clutch housings where usually on cars or I6s. They are pretty obvious as they don't look like a 1/4 of a circle. Instead they slope done quickly towards the trans mounting bolts.

Re: Muncie 4 speed swap
 

The bellhousing for the SM465 has the casting number [GM5]3925505 with a 5-1/8" I.D.
The SM420 bellhousing has casting: [GM11]3815891 w/4-9/16'' I.D.

Re: Muncie 4 speed swap
 

One thing you may also want to consider is that a borg & beck clutch is going to have a higher pedal pressure than a Diaphragm clutch. Had both styles in a 69 Camaro, back in the day, and the diaphragm clutch was much easier on my left leg in traffic than the borg & beck.