Bad synchro? - RX8Club.com



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Old 08-29-2014, 08:23 AM   #1
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Bad synchro?

Hi. I'm grinding 2nd if shift over 5K, and for what have read have a bad synchro. My question is if don't shift 2nd over 5K, I am damaging anything else in the trans? I'm planning a trans fluid change to alleviate thei. Any recommendation? Mine is a 2007 wit 42K miles in the odo. Thanks.
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Old 08-31-2014, 02:48 PM   #2
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if it doesn't grind, then it is not doing damage.

in addition to the fluid change, you might want to check the clutch freeplay, click on freeplay adjustment, takes 3 seconds if its in spec, about 90 if you actually have to adjust something.

and then shift slower

EDIT: link would help i'm sure http://foxed.ca/rx7manual/2003mazdar...041030W01.html
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Old 09-25-2014, 07:58 AM   #3
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Originally Posted by j9fd3s View Post
if it doesn't grind, then it is not doing damage.

in addition to the fluid change, you might want to check the clutch freeplay, click on freeplay adjustment, takes 3 seconds if its in spec, about 90 if you actually have to adjust something.

and then shift slower

EDIT: link would help i'm sure CLUTCH PEDAL ADJUSTMENT


Thank you. Excuse my late reply.
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Old 07-15-2017, 07:02 PM   #4
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Hi everybody. I'm reopening this short thread only to let you know that my "bad grinding 2nd shift" has gone like magic. Is this posible? 4 years with the grinding 2nd gear shift if shifting over 5K and the only thing I did was under 5k shiting to 2nd. Today I notice the problem resolve by itself. I can go all the way to 9K and shift to 2nd with no problems. How is this? Any one with the same situation? Thanks.
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Old 07-16-2017, 10:08 AM   #5
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I think I'm losing 2nd gear!!!!?

I'm having the same problems when upshifting to 2nd at 4000 or more rpm, doesn't happen during downshifts. Changed to royal purp gear oil, shifts smoother but still grinds at high rpms. Only changed fluid 60 miles ago. How long until I see a real difference? How many hours or days to replace synchros?
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Old 07-16-2017, 10:10 AM   #6
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FL I think I'm losing 2nd gear!!!!?

2nd gear grinds when upshifting at 4000 RPM or more. Doesn't grind while downshifting, just changed gear oil to Royal Purple, shifts smooth ER but still grinds. Could it be synchros? How long does it take to replace Syncro? A few hours or a day or two days?
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Old 07-16-2017, 11:20 AM   #7
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Don't use Royal Purple. You want a GL4 fluid. GL5 ruins synchros. It's possible the synchro is damaged beyond what fluid alone can fix.

Rather than replacing a synchro, I would just find a known good transmission.
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Old 07-17-2017, 01:04 AM   #8
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Originally Posted by 8Killin'It View Post
Could it be synchros? How long does it take to replace Syncro? A few hours or a day or two days?
Let's just say that I had mine repaired(5th gear synchro), and I prefer not openly discussing it. No rebuilt ones are available around me and the only used ones are also stupidly expensive.

Go for a good rebuilt one instead is a much better decision if you can source one. Shouldn't be hard in the US.
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Old 07-17-2017, 09:57 AM   #9
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My fourth gear grinds sometimes at high rpms. Usually if I let it pause before the gear it sometimes won't grind or if I double clutch it, it doesn't grind at all.


When I autoX, getting back into 1st gear can be a bitch at high rpms.
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Old 07-17-2017, 10:43 AM   #10
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When I autoX, getting back into 1st gear can be a bitch at high rpms.
You're not supposed to need 1st. 1st on these cars (all cars?) is really just a 'get rolling' gear. Shifting into it at speed is just abuse :/
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Old 07-17-2017, 11:49 AM   #11
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You're not supposed to need 1st. 1st on these cars (all cars?) is really just a 'get rolling' gear. Shifting into it at speed is just abuse :/


A lot of people use first gear, rx7's corvette's, GT3's, Miata's all shift back into first on some of the corners.


Does the rx8 have some sort of locking feature to lock us out of 1st gear when moving? Another thing I could do is run smaller diameter tires.....
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Old 07-17-2017, 12:00 PM   #12
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Originally Posted by lOOkatme View Post
A lot of people use first gear, rx7's corvette's, GT3's, Miata's all shift back into first on some of the corners.


Does the rx8 have some sort of locking feature to lock us out of 1st gear when moving? Another thing I could do is run smaller diameter tires.....
No locking feature, just the speed differential between mating gears is waaay too high for the synchros to absorb properly. You have to revmatch it perfectly.

How fast would you say these corners are? Because I somehow doubt that a GT3 or Corvette who knows what he's doing is giving up a downshift and subsequent upshift back to 2nd to pull through a corner. He's got plenty of grunt to do the whole thing in 2nd with less drama.

I did it once, I didn't like the sounds it made, and it turned out to be the slow way to do that corner.
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Old 07-17-2017, 12:20 PM   #13
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My old Corolla would grind if I try to downshift into first gear at speed. Some cheap econoboxes are said to not have synchros in first gear. That, or the synchro was shot.

I don't think downshifting into 1st is really necessary unless you need that much straight line acceleration, which our cars are not really great at anyways. I don't downshift into 1st unless I am below 16 kph/10 mph. You'd have to be pretty good at rev matching to pull it off.
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Old 07-17-2017, 01:47 PM   #14
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A properly operating RX8 trans downshifts into 1st gear no problem
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Old 07-17-2017, 03:27 PM   #15
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No locking feature, just the speed differential between mating gears is waaay too high for the synchros to absorb properly. You have to revmatch it perfectly.
I rev match and downshift into 1st, at speed, every day. It doesn't need to be absolutely perfect by any means. You just can't force it into gear. Even in my first car with the 1st and 2nd gear synchros almost completely shot there were no issues with this.

Something tells me people aren't downshifting properly.
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Old 07-17-2017, 05:54 PM   #16
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here is the corvette using 1st gear in a lot of the section. keep in mind that we are at 6K+ ft above sea level and when the revs drop to 4K rpms you need to go to first. We are talking about an rx8 with not much WHP. If an rx8 has 185WHP at sea level that power up here is only 145WHP.
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Old 07-17-2017, 06:07 PM   #17
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No locking feature, just the speed differential between mating gears is waaay too high for the synchros to absorb properly. You have to revmatch it perfectly.

How fast would you say these corners are? Because I somehow doubt that a GT3 or Corvette who knows what he's doing is giving up a downshift and subsequent upshift back to 2nd to pull through a corner. He's got plenty of grunt to do the whole thing in 2nd with less drama.

I did it once, I didn't like the sounds it made, and it turned out to be the slow way to do that corner.

These guys compete at SCCA nationals, at least some of them do. some are instructors and they use first gear. Perhaps my gearbox is trashed. I will definitely trash it around some more but the 2011 gearbox is the most robust of them all? just use a different mating plug at one spot?
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