Drum has a slight lip on the inside of small bushing bore that's good for ruining the bushing when you press it in. I realize this could be a mushroomed surface from wear but in this case it appears to be mismachined at the factory. Trans was a low mileage unit that was actually pulled before they burnt it up (I know, right?!). Plastic washer looks perfect, face of drum surface doesn't appear worn down in any way. Anyone seen this? Torn between taking it back apart and cutting that lip off in the lathe or simply driving the bushing in from the opposite way and leaving it.
Found a new way to fail: Direct drum small bushing bore
- Thread starter INEEDAGN
- Start date
David Husek
Turbo Buick Performance
- Joined
- Mar 16, 2007
I have. Depending how thick the step is, you can use a half round file and file it off. It won't affect anything, just always lock the busing in this location.
It's a weird feeling to press a bushing in, and it requires more force than usual, but when it gets right to the point where it belongs, it shoots out the bottom of the bore. The lip was crushing the bushing excessively and when it was done resizing the bushing, it hit that slight taper at the end and used that to propel it out the bottom lol.
Is that drum running true in the lathe? Reason I ask is we tried to turn some drums at RC's and could not come up with a good way to mount it to run true.
It's within a couple thousandths. Which is close enough for what we have the capability to do, meaning polish the outside surface with progressing grits of sandpaper. Its a three jaw "self centering" chuck that's clamped against the original large bushing which is usually replaced later, though it does minimal bushing damage. Funny story, the first one we tried to do, we used the four jaw chuck with the drum facing the opposite direction and clamped with outward pressure by the tabs. Indicating it in manually, we couldn't put as much clamping pressure on it as we'd like because it was trying to turn the drum square where we clamped it. Turned the lathe on and it spit the drum out, hit my buddy in the chest and I broke the drum's fall with my foot and managed to not damage the drum or either of us. So that method doesn't work in case anyone is wondering. The self centering three jaw takes seconds to mount and is much quicker and safer and barely marks the bushing. Same chuck to cut the OD piston, but the low/rev support we have to use the four jaw and indicate it manually off the bushing to center it.
This lathe is too small to actually cut the band surface and even if we could, it probably wouldn't do it any justice and would likely ruin the drum. The trans shop owner in the next town over (who happens to own a GN he bought new) says he has a surface grinder to properly resurface the drum if I ever need it "but the setup time is probably cost prohibitive unless you're doing several in a row" (his words). If I ever have a drum with band surface torched I'll probably give it to Dave or Lonnie in hopes they have a use for it. I sent a couple wrecked pumps and a couple stock forward drums in to Lonnie when I shipped him the case for the nailhead trans mods because they were useless to me. I HAVE gotten the tabs welded and fixed on a couple but that was a bitch and I see why everyone cites the direct drum availability as the problem child of the whole trans.
Should note that "within a couple thousandths" was indicated off the band surface. Never tried to run an indicator in the bushing bore and probably don't want to know GMs tolerance on the drum being ground true. Ignorance is bliss lol. I've been fortunate to get decent drums I guess. We run an indicator across every drum after polishing it and they're always flat with no band groove in the middle (so far) and only seen a couple with ring wear inside
I polish them on the brake lathe at home. Bison has turned me onto resurfacing them. I know Dave sends his out to be resurfaced as well. I had some resurfaced by Bison last year when he has access to a lathe.
Teflon rings will seal on an imperfect bore inside the drum.
Teflon rings will seal on an imperfect bore inside the drum.
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