Guys , I’m confused here . Can someone please set me straight on this . I’m swapping a Tremec TKX transmission into my 86 IROC . The engine is a 383 with the one piece rear main seal. American Power Train sells this kit with the 168 tooth flywheel with an 11 inch clutch, Hawks sells the same kit but it has the 153 tooth flywheel. I had purchased a LT 1 Flywheel and had it balanced with my assembly. I understand I can’t use the with the TKX application? Please let me know how to proceed. Thanks in advance.

 

The bell housing they recommended will accept either clutch/flywheel configuration. Assuming you have a 153 tooth now, if you stick w that size you can use the same starter you have now. A larger flywheel will take a larger clutch. A larger clutch has more surface area and this equals better grip potential and better heat dissipation. The engine/trans and release system don't care what size clutch and flywheel you have.

 

As per your other post on this matter, the LT1 flywheel is NOT compatible with a traditional push-type clutch. It ONLY works with the 93-97 F-body pull clutch. Which ONLY works with a stock (or stock-like, if there are any such) 93-97 LT1 bell housing. NOT with any other. ONE LOOK at the 2 types of system side by side will make it clear and obvious to you. If you can't do that for whyever such as if one isn't available, take my word for it.

Posting the same tale of woe and grief however many times won't increase the chances of the metal suddenly changing dimensions and allowing it to work.

However, there is one convenient relief on the other side. And that is, the transmission DOES NOT CARE whether the clutch & flywheel is 14" (168 teeth) or 12.8" (153 teeth), as long as the flywheel is the right thickness, and the right throwout bearing height for the clutch diaphragm (there are 3) is used, and the spline count on the disc is right. Meaning, you COULD use either a REGULAR 12.8" flywheel such as for T-5, OR a REGULAR 14" one such as for older muscle cars, with a transmission designed for the typical push-style clutch, BUTT NOT one for LT1. So there is that consolation. The LT1 flywheel IS NOT the right thickness (among other differences) and therefore CANNOT be used with ANY OTHER clutch system. Doesn't matter how much money you sunk into it or how fervently you wish that it would, it's NOT GOING TO WORK unless you can somehow figure out a way to use the LT1 clutch setup, which NO bell housing other than a LT1 one, will support; and a BH like that, WILL NOT support a push type clutch, that the TKX is set up for. At that level the FW and trans are fundamentally incompatible. Square peg and round hole type stuff.

This is why I told you in your other post pleading your unfortunate hopeless case, NOT to build an externally balanced 383 if you hadn't already; and ABOVE ALL, NOT TO allow any "custom" balancing. You now have a rotating assembly with some random unknown "custom" balance, that the ONLY flywheel that you can bolt to it is (maybe? do you trust the shop?), the ONE and ONLY THE ONE in the entire known universe - however incompatible with everything else you have that it may be - that was "custom" balanced to it. If you're lucky, somebody will be able to take your LT1 flywheel, and "custom" unbalance a "normal" one to match it, so that it will work on your motor. I'm not holding my breath butt it IS possible even though most machine shops won't touch it for fear of comebacks and bad reviews and a blamestorm. If you can't find someone willing to shoulder that risk FOR YOU, it'll be time to tear the motor back down and ... deal with it somehow. Which my advice in that case would be, take the rot assy BUTT NOT THE FLYWHEEL to the shop and have it set up to the STOCK 400 spec, so that you can use flywheels and whatnot that are STOCK 400 stuff, and not end up right back in the hell you are now in. Then later on, take your FW in and have it set up likewise to the STOCK 400 spec. Don't let em tell you they "have to have" all the parts together: a STOCK 400 motor will bolt right up to a STOCK 400 damper and a STOCK 400 flywheel (well, flex plate; 400s only came with auto trans from the factory, butt the weight is the same) WITHOUT any "custom" ANYTHING. Which in turn means, DO NOT UNDER ANY CIRCUMSTANCES allow your flywheel and your rot assy to exist in the same shop at the same time: tell them you want your rot assy set up to match the STOCK 400 specs, and when you pick it up and it's safely OUT OF there, hand them your flywheel and tell them you want the flywheel set up the same way. Otherwise they will SURELY do to you what's already been done, which is, take a rot assy of completely random balance, and HACK your flywheel to match it, because that's EEEEEEZZZZZZYEST for them even though fatal to you. As you've already experienced. And if those people won't do what you tell them you want, pack up your pile o poop and WALK. Go find somebody else that will. I'd suggest going to a circle track in your area - NOT a drag strip - and hanging out in the pits, and getting to know the guys THAT WIN, and find out who does their machine work, and go there. Might cost more, might be a wait since you're not a regular customer and they're busy with their regulars that need their motors for next Saturday night, butt you'll at least have a chance of finding somebody that won't try to just take your money and hope you shut up and go away.

Posting on here repeatedly will not somehow either make the LT1 flywheel work with a push type clutch, or overcome the balancing issue. You have evidently already gone down the road I would have told you NOT to go down had you asked BEFORE you did it instead of AFTER, and now you'll just have to deal with cleaning up the mess. I've written over and over and over again on this forum why NOT to do what you've done, or rather, allowed somebody to do to you at your expense and to their profit; and you just found out why, the hard way. I feel sorry for you, butt my sorrow, however genuine, won't change the dimensions or the mass of the metal. I'm even sorry my sorrow is so useless and ineffective. I've seen your pain more times than I care to recount, and tried to tell people why NOT to put their butt into the crack yours is now in, butt nobody listens to me, because (I guess... ?) I don't tell them what they want to hear. It's my fate on this miserable cosmic cinder I suppose for as long as I'm stuck on it.

 

Using a a hydraulic release system like the American powertrain hydramax uses numerous shims between the trans front bearing retainer and the actual release bearing body. These shims allow for different clutch/flywheel combos. If you measure your engine block to bell mounting surface to flywheel face and then take the depth of the bell housing to trans depth you can figure out how much room you have for a clutch and release bearing, calculated distance will tell you what will fit. I don't know anything about LT1 flywheels. That said, if you're questioning what people are saying will work or won't work, do the math and figure it out. A while ago you asked about T56 swaps. There are ways to use your flywheel w them.

I'll tell you that you don't want to half *** piece together a clutch and release system and get it together and realize it won't shift/release or it just sucks. American powertrain and numerous other companies know what works. It doesn't mean they and we know every combo that will work. It's time to do the math and figure it out or move on to a known combo.

 

Does your engine block have 3 starter holes or two?
2 diagonally - proceed with the 168 tooth flywheel, probably.
3 in a triangle - determine if your 93-97(?) LT1 flywheel is custom balanced.

If no, replace with 86-92 Camaro V8 flywheel. It is balanced the same as the LT1. Now you have a 153 tooth flywheel. Clutches for it can be had in 10.75" disc size (88 Vette) if you are obsessed with clutch size. Or lots of 10.5 options exist.

If yes, reconsider using that shop ever again. Being able to use replacement parts that bolt on and work is a major awesome factor of the industrial revolution.

 

Problem here is, since the motor in question is EXTERNALLY balanced if the OP is properly informed about it, it requires a COMPLETE OTHER balance than the LT1 flywheel would have started out life as, or that the 86-92 one would, which is, the last tiny little rearmost bit of INTERNAL balance weight attached to the flywheel instead of the crank flange. Those motors are still INTERNALLY balanced, even though the weight looks to the eye like it's "external"; even the mfrs have given up trying to name it correctly because the confusion in street-stroke world at large is so pervasive.

That would definitely be the right part to start out with though. All that would have to be done then, would be to figure out somehow, how the motor is balanced; and unbalance the INTERNAL balance flywheel to match what the motor requires. Maybe there's a record somewhere of what that is; that would save a great deal of guessing. And while that's possible enough in principle even if there isn't, finding somebody willing to do it and GUARANTEE it, would be tough; not least because (a) they'd have to be sure enough of their technique for doing it, to be willing to take it on, and (b) willing to take the risk that the unusable LT1 one is correct enough to begin with, that there would be no problems if its balance was duplicated on another part. Personally, if I owned a machine shop, I wouldn't do it, without requiring at the very least (a) a signed statement to the effect that there is no warranty on the result, and (b) full payment up front before any work begins. Maybe the shop at the center of this whole botch could be pressured into doing it butt at this point it's hard to trust them at all.

A typical EXTERNALLY balanced 383 rot assy requires approximately the same unbalance as the stock 400, since the same factors that apply to a 400, apply identically to a 383. No guarantees on how close to this the end product of such a build will actually be, butt at least should be somewhere near that. Which is, about 24.5 in-oz, either with the weight directly opposite the #7 & #8 rod throw on the crank, or with holes drilled directly in line with that throw. Takes about 20 ½" holes about ½" deep around the edge of the flywheel to do that. Alternatively a "pork chop" weight can be used butt I'm personally not a fan of those. I'd alter the flywheel if it was mine, like I've done in the past.

I don't know if there are any stock 14" flywheels with the 86-up bolt pattern. If there are they'd be for trucks. Butt there very well may be aftermarket ones.





A stock GM block with 3 starter bolt holes can be used with a 12.8" wheel as long as the inner one closer to the crank matches the one I drilled in this photo, which is a 73 400 block (509 casting) that I put into my 83 L69/T-5 car back in the 80s. The 3rd hole that some older blocks already had cannot be used with the starter for the small wheel, because a bolt that installs in that hole, would have to go RIGHT DIRECTLY THROUGH THE SHAFT of that starter. Therefore there is no starter for the small wheel that will work with that bolt pattern. It's not physically possible. Sure, there are plenty of aftermarket starters that will work with either wheel size; butt that's IF AND ONLY IF the block has that particular inner bolt hole in it. Since the ring gear on the smaller wheel is about 5/8" closer to the crank, the starter innards need to also be 5/8" closer to the crank, and thus the inboard bolt along with its hole also has to be 5/8" closer to the crank, to clear the starter drive.

Older blocks with 3 holes (of which there aren't many) had their 3rd in the place where the 2 cyan lines meet. The old heavy-duty 3560 starter, with the cast-iron nosepiece, could use those 3 holes. The 3510 starter for PG, T-350, most 4-speed & T-400 cars, and 86-up trucks with 14" flex plates, with the aluminum nosepiece, would use only the 2 that aren't in line, and those are all that most 70s blocks have. The one that's circled in magenta is the one needed for the starter for the small flywheel, which I drilled myself by hand in this block. AFAIK any block w 1-pc RMS SHOULD have that hole, butt I'm far from willing to guarantee that it DOES. That would need to be verified by the engine builder. And if the block needs that hole drilled, it'll be ALOT wiser to go ahead and do it BEFORE putting the motor in the car, even if you are using a solution that doesn't require it, as it would be NO FUN AT ALL trying to do that with the motor in the car laying on your back and still get it accurate enough. No point in remaining in denial about needing it until it's too late, like what led to this whole flywheel fiasco. Just do it and get it over with and don't argue about it. Note that it needs to include that lead-in section before the threads start, to allow for the special shank that starter bolts have on them, which makes the bolts act like dowel pins to securely lock the starter into the exact place on the block. Clutch bolts incidentally are "special", being made the same way, and need the holes in the flywheel to have the same feature.