4 vs 5 frictions in a 904

Is there a difference in performance between using 4 clutches and 5 clutches in a front drum on a 904?

My original trans builder managed to fit 5 but used 4 thick frictions(Borgwarner)and 1 thin (Alto) with a machined pressure plate to get it to fit.I have 5 thick which only gets me .035 in clearance. After looking at the original frictions it explains why one looks different in colour its .062 instead of all the others. If 4 clutches will be enough handle a 450hp 360 I'll just use a stock pressure plate i have lying around and put it together with 4 clutches.

You always get more holding power by adding surface area, more clutches. Different manufacturers make different thickness clutches and steels. Many make specialty clutch steel combinations to increase holding power in drums. Many rebuilders have lots of different clutches laying around, as long as the clearances are correct stack as many as you can get in the drum. If you bought a stock trans kit, you will most likely only get 4 clutches in the pack. If you want more you will have to buy a different clutch and steel.

It is good to see you are doing the rebuild yourself. It's not that difficult and you'll know what you have when you're done.

Since you're in there I'd go for 5. I've had good luck with Alto Red fibers and Kolene steels. Like jbw123 noted - you can get different thickness fibers and steels to make room.

I'd also check all tolerances since you didn't originally set this one up. Set everything on the tighter end of the specs.

I'd purchase Carl Munroe's book: https://www.amazon.com/Torqueflite-727-Transmission-Handbook-HP1399/dp/1557883998. There's still lot's relevant information in there.

If you're interested, I'll send you my 904 build notes for reference.

Rear clutch frictions are .063, and other than being thin, are interchangeable with the thicker front clutch plates. Steels are also available in .068 and .080. Snap rings also came in different thicknesses if you have an assortment of those. Cutting the pressure plate like that makes it a PIA to measure clearance and weakens it.. Use an uncut pressure plate or on the outside chance that you have to trim it some, trim the entire width. Use good hi-energy or blue rear clutch plates (12760), along with a mix of thick and thin steels to dial the clearance in. Measure and adjust clearances before oiling everything for assembly. At .012 per disc, that's .060 total clearance. You should be able to get very close to that just adjusting part thicknesses.

This was recently discussed; rear clutches are not intended to apply under power and are, therefore, different.

That was true of the OEM stuff. Not so much the present aftermarket pieces. We aren't worried about Grandma complaining about a harsh shift.

Thanks Humpty. I have both Munroe's and Tom Hand's book for reference as well as the ATSG manual. It certainly has taken the mystery out of transmissions and the reason to pay some one else to build them for me again.

Yeah the machined pressure plate is a PITA to check clearances but i can understand why it was done that way. I'll have to see if i can 5 thins for the front clutch and correct clearance with a different pressure plate. Otherwise ill just throw the original thin clutch back in as it looks good.

Thanks again guys.

the better fibers are grooved (not waffled) and can be used in either clutch pack.

You can check the clearance with a dial indicator easy enough.

That's how i measured it.