#371
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Transaxle Update
I’m moving away from bodywork to the transaxle for this post. In summary, I’ve run into an issue with a space conflict between #4 exhaust port and the positioning of the current shifter. As a reminder, this custom transaxle uses a Tremec TKO 5 speed transmission sandwiched between billet aluminum transfer, tail shaft and final drive cases. Here are some pictures for context:
And here is the trouble area. I had to remove the studs from #4 exhaust port just to make clearance to fit up the transmission: The main constraint for this application is no available space above the transmission as the header needs to run there and thus all components used in the shift mechanism also need to be able to operate in a high radiant heat environment. It’s a long story for how we got to this point but the short version is that we built the transaxle using a “core” Tremec main case and didn’t have the shifter mechanism you see in the pictures to use for reference. Tremec TKOs have 3 basic positions where shifters can be located (tail shaft housing rear, tail shaft front, main case) and we chose the main case location as it seemed to have the best chance at avoiding a space conflict with the exhaust ports and thus exhaust header. Well after having the transmission built and converted to the front shift location, it’s obvious this just won’t work. The mid-shift position with a standard TKO shifter also won’t work for the same space conflict with #3 exhaust port. There is no rear shift option as we built custom billet, shortened tail shaft housing. My transmission guy, Bob Hanlon of Hanlon Motorsports, came up with an idea that we are trying to prove out now. The idea is to adapt a shift mechanism from the TR6060 transmission (6 speed that was used OEM in high end Cameros, Mustang GT500, etc.) and locate it on top of the custom tail housing. Here’s a picture of them from a Camero (upper) and Mustang (lower) along with a shift finger from a TKO trans. The idea is to rotate the shift lugs 180 degrees so they are engaged from above instead of below and replace the arm on the TR6060 shift mechanism with the TKO shift finger. Here’s a mockup in a “core” TKO tail shaft housing showing what the shift lugs look like once rotated for engagement from the top. We’re guessing the shift finger will need to be modified in length as part of the alteration. The main challenge with this approach is to minimize the height added above the tail housing. The TR6060 shift mechanism is not a bolt on to that opening so will need an adapter plate. By eyeballing various tubing U bends on the exhaust port, it looks like anything more than 1 ½” added height is a non-starter. Obviously, less than 1 ½”added height is better or the primary tube may have zero clearance which equates to direct heat transfer into the transmission.
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Joel Heinke Be original; don't be afraid of being bold! |
#372
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Sounds like you have some great connections to help you through this.
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Marcus aka. Gojeep Victoria, Australia http://willyshotrod.com Invention is a combination of brains and materials. The more brains you use, the less materials you need. |
#373
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Any chance you can clock just the transmission counterclockwise to 10 or so o'clock to pull it away from the head? May have to re-drill or make new adapter plates to mount it on both ends.
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Ira Scratch Building Bugatti Atlantic 57SC with BMW S65 |
#374
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Quote:
It's no mystery to me now why the original Miura engine and transaxle were cast as 1 piece. By integrating the transaxle into the engine block they were able to minimize the distance between crankshaft and transmission main shaft.
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Joel Heinke Be original; don't be afraid of being bold! |
#375
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It's a fantastic job you are doing there Joel, hope you get a solution without too much head/heart ache.
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David Hamer |
#376
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Joel, what occurs to me is to move the selector mechanism to the tunnel and controlling each fork shaft with a dedicated push/pull cable. Some of the higher performance control cable has very little compression or elongation so it should not make the shift mushy. It's possible a billet plate less than an inch thick could mount three shafts that engaged with the fork shafts. It is hard to tell, but even more clearance might be possible if the cable could enter the tailshaft front cavity and be below the top of the main transmission cavity. That might give you over and inch of clearance to the exhaust depending on the thickness of the cover plate.
I'm with everyone else on what a fantastic project you have going.
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Eugene Last edited by Reno; 04-26-2021 at 09:53 PM. |
#377
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Transaxle Progress
Working through the lack of space for a shifter mechanism issue, I’m trying to adapt a shift mechanism from a Tremec TR6060 transmission to the TKO. It’s a different size and bolt pattern so an adapter plate is required. The TKO needs 3/8” movement on each shift rail to engage a gear, there’s 2 gears per shift rail, so the shift mechanism needs to give ¾” overall movement to work. The TR6060 shift mechanism provides only ¾” movement so it will need very precise positioning if it is to work.
In addition, I need to swap in the shift finger from the TKO and it’s not quite long enough once an adapter plate is in place. I’m thinking a ¼” thick adapter plate is needed for rigidity. I machined out 1/16” from the plate where the TR6060 mechanism mounts on it and .100 off the bottom of the TR6060 mechanism. The shift finger is getting close to being long enough now but I probably need to find another 3/16” inch somewhere. If it comes down to it, I’m told that people weld and reshape these shift fingers to fine tune them so I could lengthen via welding. Here’s what it looks like in situ: So while the exhaust ports are still close, this is looking promising. The 1 ¼” thick plate with the red duct tape on it is no longer needed with the different shift mechanism and gets replaced with a thin metal plate. So that frees up space for #4 exhaust port leaving #3 with main space consideration. To check potential clearance, I taped on 3/8” bar stock to simulate the header flange and here’s how it looks with a 90 degree, 2” CLR bend of 1 ½” tube. It clears but just barely. The header primary tubes are 1 5/8” but if the shift mechanism gets lowered down another 1/16” then it should work. As part of mocking this up, I built out a mount to attach the transaxle to the engine block. I was able to use the bolt holes normally used for the motor mount on the side of the block so this bracket is held very solidly. So now the transaxle is bolted to the engine through the bellhousing and now secondarily with this bracket. So I’ve got the adaption of the TR6060 shift mechanism close enough that it’s time to re-do the transmission shift fork and shift rail internals so I can have that in place to nail down the final details; like how much lower the shift finger needs to go and positioning for adapter plate. My mockup unit uses wood and aluminum tube so I want to have the real parts in place for final fitting and positioning.
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Joel Heinke Be original; don't be afraid of being bold! |
#378
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Quote:
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Joel Heinke Be original; don't be afraid of being bold! |
#379
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The elbow doesn't need to be exactly square to the header flange. A 1/16"off the top to zero will greatly increase clearance and it will be virtually undetectable. You could do all the same to look even.
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#380
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Joel, glad to help. I'm going with your tag.
Another thought is that I tend to think that almost everything can be solved with a casting. In your neck of the woods, there is someone with the 3D print capability of making a plastic pattern of that shifter mechanism housing with a larger base and reduced height. It appears to be a simple draft casting with minimal machining. Modification of the finger to reduce the thickness of the collar above the shaft would allow lowering the bulge on top and provide the clearance you are after. I really like your mockups, and believe you have a solution with what you are showing.
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Eugene |
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