1984 4 speed muncie questions (Page 1/1)
fierobro59 FEB 01, 10:25 PM
I am planning on swapping a 4.3L even fire engine chevy into my 84. I know that the 84 4 speed muncie has a weak case and is likely to break with an engine swap. My question is, is there anyway to “beef up” or possibly build extra supports or something of the sort to make it stronger because i’m having a hard time finding a 85-86 4 speed to buy. This 4.3 is built with gm aluminum heads, forged stock style pistons 10.5:1 comp, .500 lift comp cam ,aluminum performance intake, roller rockers etc… That should be pushing 300 hp to the flywheel just wondering if anyone has tried any way to make the 84 trans work. Thanks
pmbrunelle FEB 01, 11:28 PM
Well the LH side case seems to want to separate in tension:
https://www.fiero.nl/forum/...L/140469-6.html#p200

(maybe also look at other pics to see how 84 Muncie cases break)

You might be able to weld ribs cut from aluminium sheet onto the case. The ribs can be oriented in a way as to bridge the cracks that would typically occur. Also look at photos to see how the M17 was done.

For sure weld distortion will be a concern, not sure if the case would still be serviceable after. I would definately re-verify the bearing shimming after doing a bunch of welding to the case.

A nearby tuning shop did a weld repair to my transmission case, and he said that welding cast aluminium like that is a major PITA, since the cast aluminium is porous and absorbs all kinds of junk. So the surface to be welded should be ground down to expose clean metal below, and then the case should be baked to drive out contaminants. Even then, it wasn't perfectly smooth sailing.
Pyrthian FEB 02, 04:27 PM
the insides of the 4cyl and 6cyl 4-speed muncies is the same. I did this on mine. took the 4.10 gearset and installed it into a v6 case. and, yes, finding a v6 4-speed was a tough find. my whole car is for sale in the mall. it has blown head gasket/cracked head/cracked block, not sure which, but, due to injury, cant work tools like I used to, so, will not fix. great suspension, borla stainless exhaust.

edit: and, yes, that 4 cyl case is weak. I blew mine wide open dumping the clutch at the drag strip.

[This message has been edited by Pyrthian (edited 02-02-2022).]