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Author Topic: Synchro death
JD Morris Verified Driver Made Donation to Website
A slower JD...

Region: SF
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My 3rd gear synchros started making lots of noise on the 4-3 shift (and occasionally the 2-3 shift) at my last race weekend. However, the car still went into gear just fine during 2 qualifiers and 2 races, and because of the racket the synchros are making I'm learning how to make a much friendlier 4-3 shift. I'm considering doing 3 races over the next couple weeks before replacing / rebuilding the tranny - will it survive? Does the Miata tranny have a 'stuck in gear' failure mode? I'd like to finish off the season before starting a plethora of engine and tranny work.

Dusty Bottoms Verified Driver Made Donation to Website
99 all the way!

Region: Lone Star
Year : 1990
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John, I did a half season with the 4-3 problem (eventually showed up at 2-3, and 3-4) as well. I think there is another thread where someone warns that this means the tranny could quickly fail.

This crunching actually helped me do smoother shifts and now I do double clutching on all downshifts. Slower upshifts largely prevent the crunch as does the double clutching on downshifts.

I had another tranny that I was rebuilding (waiting on a shim for a couple of months):
http://www.nitrodyno.com/miata/tranny/index.html and as soon as the part came in and I finished the assembly I put it in the car. I have not taken the old one apart to check for wear. I'm assuming it was the original 106k mile transmission.

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"Your victory is tainted! Asterisk! Asterisk!!!"--Lisa Simpson

DaveC Verified Driver Made Donation to Website
...

Region: Milwaukee/Midwestern Council
Car #: 23
Year : 1999
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John,

We started to notice it was a little notchy or crunchy about 3 hours into a 10 hour race over labor day. We finished that race, I did 2 30 sprint races and 2 80 minute sprint races since and other than being a little more deliberate on the shifts in the 80 minute races I had no problems and I set a new personal best towards the end of the last session. YMMV, but I was able to go quite a while and I think the car could still go, but the season is over [Frown] .

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Dave Cox

fastoldman Verified Driver
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Region: NE Region
Car #: #51
Year : 1992
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John, Captain Crunch here, and that old turd gear synchro is,was, and has always been a problem. Ran my last two races , finished well, and still have the old grinderoo. I went about 4 races last year before I redid the tranny, and it looks like I will redo again over the Winter - even though I am sure it would make more races. My problem seems to always start at one track that is extremely bumpy and then the problem progresses from there. Hang in there and join the club, and you will in all likelyhood finish out the Season okay.

fastoldman Verified Driver
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Region: NE Region
Car #: #51
Year : 1992
Posts: 264
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PS - found out about two years ago when the clutch seemed weak and consequently I was the Grinder Man, that the clutch fluid looked like the La Brea tarpits. Changed the fluid ( good DOT 4 brakefluid like Brakeman xtreme 6 ) and the clutch was ressurected, and the grinding became a thing of the past - and still have that same clutch.

davew Verified Driver Made Donation to Website
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Region: chicago
Car #: 72 and ?
Year : 90 and 90
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You have proably broken the 3rd gear syncro. If the syncro cocks to one side it will lock in third gear. I have seen lots of broken syncros but only one that was locked in gear.

The syncro is retained by a round metal ring about the same diameter as a paper clip. At the end of the ring is a 90 degree bend. The tab created by the bend locates the ring. When the tab breaks the retaing ring is allowed to rotate. When it rotates far enough the syncro ring is not held square and it breaks (usually into 3 pieces). As long as all the pieces stay put it is only inconvenient and noisy. If one of the pieces shifts it will lock.

How long will it last is impossible to say. But eventually you will need the trans rebuilt.

I have rebuild LOTS of these transmissions. Even a 40,000 mile trans will shift better after it has been freshened. And the worst offending gears are the ones we use most, 3rd and 4th. When everything is new the chance of missing a shift is almost eliminated. Especially the 2-3 shift or selecting 5th when you wanted to downshift from 4-3.

Dave

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