- Joined
- Aug 3, 2023
- Posts
- 412
- Reaction score
- 851
- Location
- Las Vegas
- First Name
- Nick
- Truck Year
- 1987
- Truck Model
- R10
- Engine Size
- 350
Hey Bob - some of the HD and HP TH400s/475s had 6 frictions and steels in the direct clutch along with 5/5 in the forward...Post 73, they used stamped steel apply pistons with selective apply rings so it's very easy to fit an additional friction and steel by swapping out apply rings to short ones for each drum. Everything else is the same so you just need to raid your local hard parts suppler (or eBay) for the apply rings that you need to add those additional clutches to your packs and you're good to go. Most of the high performance muscle car stuff got either 5 or 6 direct clutch frictions. For aluminum pistons, you can either machine your pre-existing piston or look for one of the pistons with the letter code corresponding to a 5 or 6 clutch stack, if that's what you'd like to build.A bit off topic here Nick, but I was wondering about your knowledge of the OW trans used in the '70 W-30's, compared to other Olds & RARE Buick applications. I understand the during the GM strike of late 1970, that some OW's were installed into the GS Buicks on accident, due to unknowledgable strike scabs(haha!) I know the W-30's had specially built clutch packs, do you know in comparison if they were indeed built differently than the standard OW's that were used well into the mid-late '70's? They started using the OW's in the '68 442's also, just wondering how many versions of the OW that you know of? Appreciate your insight on this!
Here's a quick ref table that shows the various stamped steel and aluminum piston and clutch configurations over the years, as taken from my TH400 fast facts doc. Note the codes for the 6-clutch stack ups. That stuff will install into any TH400 as long as you have the right parts as shown below.
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Clutch pack clearance is still .010" per friction, per General Motor's guidelines; forwards can be a bit tighter than direct.
My TH475 Assembly PT1 video shows a factory 5 clutch fwd drum and 6-clutch direct drum for reference.