Lotus Elan

Gearbox question

PostPost by: craig chima » Tue Sep 12, 2023 4:24 pm

Hello,

Looking for some feedback on a CR trans that I recently rebuilt. Most of my business is race-related and as such I've done way more dog box conversions but this is a synchro box that is being used in a S3 coupe street car. I rebuilt this box in the spring and unfortunately the customer didn't have much luck with it. Both the 1/2 and 4/3 shifts are now very messy indicating an issue with the synchro baulk rings (the ones I used during rebuild were supplied by my customer so I don't know the source of them). The synchro hubs are in good shape and sliders move easily and freely. I did most of the disassembly this morning and have attached pix of how both the original and replacement synchros fit on 3rd and 4th. The originals sit considerably further down on the taper as can be seen. I obviously want to get this right and as such am wondering if anyone else on the forum has experienced similar issues or has any recommendations. Thanks in advance for the follow-up. Craig Chima, CC Motorsports, Akron, OH
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PostPost by: rgh0 » Tue Sep 12, 2023 4:53 pm

These look like the early type baulk rings the box probably needs the later type ? Were you able to compare the new rings with the ones that were removed ? The baulk rings need to use the match hubs

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PostPost by: promotor » Tue Sep 12, 2023 7:14 pm

craig chima wrote:Hello,

Looking for some feedback on a CR trans that I recently rebuilt. Most of my business is race-related and as such I've done way more dog box conversions but this is a synchro box that is being used in a S3 coupe street car. I rebuilt this box in the spring and unfortunately the customer didn't have much luck with it. Both the 1/2 and 4/3 shifts are now very messy indicating an issue with the synchro baulk rings (the ones I used during rebuild were supplied by my customer so I don't know the source of them). The synchro hubs are in good shape and sliders move easily and freely. I did most of the disassembly this morning and have attached pix of how both the original and replacement synchros fit on 3rd and 4th. The originals sit considerably further down on the taper as can be seen. I obviously want to get this right and as such am wondering if anyone else on the forum has experienced similar issues or has any recommendations. Thanks in advance for the follow-up. Craig Chima, CC Motorsports, Akron, OH


What does a "very messy" shift manifest itself as?

BTW, the synchro rings match the 3rd/4th synchro unit you've got there.
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PostPost by: joe7 » Tue Sep 12, 2023 7:27 pm

Could you please post a pic of the 3/4 hub you have sitting there in the same position. Next any pictures of the 1 & 2 rings and gears would also help to see how they fit. Also measure the "gap" clearance between the rings and the gear face for each one.
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PostPost by: craig chima » Tue Sep 12, 2023 10:01 pm

Joe,

I will take additional pix and get some measurements tomorrow. By "messy" shift I mean crunched gears and lousy engagement. And I just verified with the car owner that the issues after rebuild were in the 1/2 upshift and 3/2 downshift so will focus on 2nd gear synchro in particular. Thanks for all the feedback thus far.

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PostPost by: 2cams70 » Tue Sep 12, 2023 10:58 pm

Check how the synchro hub blocker bar springs were assembled. On either side of the hub the spring ends need to be in the same blocker bar and need to be fitted in the right direction so they form a full circle - bit hard to explain without pictures but it’s all in the manual.
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PostPost by: craig chima » Wed Sep 13, 2023 5:46 pm

OK, here are a few more pictures and information. The first picture shows the 1/2 slider, synchros, and gears. All appear to be in good shape. The second picture references how 2nd gear baulk ring fits onto the tapered portion of the gear and how I measured the gap. With the original ring (pre-rebuild) the gap is approximately .030 and with the new ring it is about .048. To me this is to be expected given that the wear on the old ring(s) allow it to sit further down on the taper. This is the same on all 4 gears when comparing the new versus original rings so I don't think this has any bearing. Again, the issue is with the 1/2 upshift and 3/2 downshift so definitely something the 2nd gear synchro. The last two pictures are of either side of the 1/2 slider assembly and you can see that the internal teeth are also in good condition. My only concern relates to the previous comment about the springs needing to form a complete circle. The "tang" or end of each spring is indeed in the same blocker bar but not sure about the complete circle issue and wondering if that may be the issue or whether someone sees another area of concern. Thanks again!
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PostPost by: craig chima » Wed Sep 13, 2023 6:34 pm

And upon further inspection, I have one last thought/question. If you look at the last set of pix I just posted you will see that while the "tang" on each spring fits into the same blocker bar, if the tang is placed at a 12 o'clock position you can notice that the spring goes in a counter clockwise direction to the termination point of the spring. It is the same on each end of the hub.

I just inspected the spring orientation on the 3/4 hub (there are no problems with either 3 or 4 as mentioned previously) and both tangs are in the same blocker bar, however when the tang is positioned at 12 o'clock the spring goes in a clockwise direction to the termination point and it is the same on both sides of the hub.

I don't know if this may be the issue or not but it was a question worth posing to the forum. Thanks again.
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PostPost by: snowyelan » Wed Sep 13, 2023 6:45 pm

Cortina manual page with the relevant info.
p5.JPG and
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PostPost by: craig chima » Wed Sep 13, 2023 7:02 pm

Thank you Scott. Maybe the direction of the spring is not the cause as it seems it doesn't matter whether clockwise or anti clockwise as long as both go the same direction. Now what?
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PostPost by: Craven » Wed Sep 13, 2023 7:21 pm

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PostPost by: craig chima » Wed Sep 13, 2023 8:49 pm

Per a request via PM, here are pix of the 3/4 hub. The side with the white dot is the side that faces the front of the shaft (4th gear). Thoughts?
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PostPost by: 2cams70 » Thu Sep 14, 2023 8:23 am

I can’t see it clearly in your photos but all the synchro rings where the blocker bar engages should be the same type. If the u shaped groove is open then you have an early design synchro ring. If the u shaped groove has a backing where the ring contacts the cone on the gear you have the later type. The backing reinforces the ring and is a design improvement. Doesn’t matter which you use but the design can’t be different to the originals unless you also change the corresponding hub. Again sorry difficult to explain in words without supplying pictures. One of the gears in your photo might have a later ring compared to the others. Your photos aren’t clear enough in the critical area
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