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MN12 Grinding third gear?

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Old 05-29-2006, 11:06 AM
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Default MN12 Grinding third gear?

I took the car to the track yesterday. I was spinning pretty bad through first and second. I short shifted to third cleanly and then fourth. When I got back on the return road I noticed that the car didn't want to shift into third with out a horrible grind. None of the other gears grind and the grinding goes away once the car is stopped. It did this the whole way home. So I just went from 2nd to 4th. Did I ruin a syncro or something? I would geuss the 3/4 shift fork but it doesn't grind 4th and shifts fine at idle. It has been hard to get into reverse since I got home from Iraq. What do you guys think is wrong?

Brett
Old 05-29-2006, 11:28 AM
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Originally Posted by Pray
I took the car to the track yesterday. I was spinning pretty bad through first and second. I short shifted to third cleanly and then fourth. When I got back on the return road I noticed that the car didn't want to shift into third with out a horrible grind. None of the other gears grind and the grinding goes away once the car is stopped. It did this the whole way home. So I just went from 2nd to 4th. Did I ruin a syncro or something? I would geuss the 3/4 shift fork but it doesn't grind 4th and shifts fine at idle. It has been hard to get into reverse since I got home from Iraq. What do you guys think is wrong?

Brett
Sounds like you either bent a shift fork or bad 3rd gear synchro. It seems like a shift fork problem to me, being that it didn't grind while you were going down the track, and you say you didn't miss any shifts. So you most likely bent the shift fork when you grabbed 3rd, caising it to grind into 3rd afterwards (since it wouldn't be all the way in gear).

If it is in fact a bent shift fork, I'd invest in an aftermarket shifter, something like a Pro 5.0 with stop bolts. That will ensure you don't ever bend another shift fork
Old 05-29-2006, 11:46 AM
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To replace a shift fork you have to compleatly tear into the trans correct? No easy fixes on that one?
Old 05-29-2006, 01:12 PM
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Could be the blocker rings. I had mine go out on my transmission because they do not have the best friction material on them. Either way when it is apart make upgrades like the shift fork.
Old 05-30-2006, 10:16 AM
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its a blocker ring... REPLACE IT AND GET IT FIXED NOW lol..

i just had mine replaced... i drove it with it grinding but just RPM matched and didnt force stuff..


i ended up with a 1500 dollar rebuild rather than a 700 dollar rebuild ... t56 rebuilds.com just got done with mine. it drives and shifts AMAZING !
Old 05-30-2006, 10:28 AM
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Shifting with the wheels spinning is a real bad idea. It will burn the friction material up ( what I suspect you did). You will need a teardown and I suggest a fork upgrade. It still will not survive spinning shifts long.
Old 05-30-2006, 09:02 PM
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So you guys think I am looking at a blocker ring. I tried calling T56rebuilds today but I didn't make it before they closed. I am going to talk to them tomorrow and see what they think. I will order the parts then and do the rebuild if there are no special machines needed. I am also going to change the shift forks while I am in there. They seem like cheap insurance. I have rebuilt three or four autos with pretty good success. I also used to run a machine shop where we had to do large gear boxes so I should be alright. I just can't afford a whole new tranny right now. I will definately up grade later considering I am putting out well over 600rwhp with out the restrictor plate. I have been avoiding third like the plague. I just run 2nd up to 3,500 and shift into fourth. It is working so far. But not the best solution. Thanks for the input guys.

Brett



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