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Discussion Starter #1 (Edited)
I'd like to start this thread as more of a brainstorming session rather than a "tell me how to fix it from start to finish" thread. Well, unless one of the resident trans builders wants to tell me how to do that... :p

Basically here is what happened:

A few months ago I had a bad ISB. I pulled apart the trans and replaced all bearings and synchros while I was I there. The synchros were not bad but I figured might as well do it while it's open. I followed this guide and followed the suggested specs in that thread. One thing I found interesting during dissembly is my third, fourth, and fifth gear assembly all just slid off the shaft. I didn't have to use a press or bearing pulley. Interesting...

So I put it all back together and hooray, no more ISB noise! But wait a minute, now third and fourth gears grind. The only way I can avoid the grind is by double clutching and granny shifting at low engine load and under ~4000 RPM. I did fill my engine mounts with window weld and replaced my shift linkage bushings with polyurethane, so I'd like to believe those variables are good. I did initially have Synchromesh in the transmission and did swap the fluid in a futile attempt of troubleshooting for 10W-30 oil.

I'm on the hunt for a comprehensive service manual with tolerances for everything inside of these transmissions so I can check everything. I'm not a transmission expert so I honestly don't really know where to start with inspecting and troubleshooting. FWIW I did initially rebuild this with a garden variety rebuild kit on eBay.

Thanks for any and all input.

 

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Discussion Starter #3
I found one being hosted privately so I couldn't actually access it. I saw some advice from Bone via another site, but I just need to find out what "worn" means for shift forks or a slider because again, I'm no transmission expert.
 

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Brokedick Millionaire
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Howdy :)

As Dave Vaughn relayed to you, it appears the 3-4 fork is worn on the third gear side judging by the shiny area, the 3-4 slider might have excessive wear but the synchros can be cleaned up.

90-91 Si trans, the input shaft bearing is in backwards.

Why the Craftsman combination wrench cut in half? (LOL!)
 

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Discussion Starter #6 (Edited)
Haha, yeah I saw the conversation between you two. I read it and thought "is he God? How does he know it was third and fourth that was grinding?" But it turns out you were just being observant. Ha!

Oh the wrench? I needed a tiny wrench. What? I have extras! lol I suppose the halved wrench in the background would kind of discredit me from working on anything mechanical. Anyway, thanks for the invaluable advice. I'll get at it with a feeler gauge/mic after work now that I have a direction to go in.
 

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Discussion Starter #9
Yeah my forks ended up being fine as well. I did discover that my pilot bearing was toast but replacing it didn't completely solve the grinding issue. I can double clutch and not grind now and I can put more load on the engine when shifting without grinding but redline+shifting=third/fourth gear grinds. I can do something about the rest of my shift linkage since the stabilizer rod (whatever the thing is called) has poly and the shift arm still has plenty of free play. I'm not convinced that that's the issue though; I'm thinking janky synchros are the case here. If nothing else I may just look into purchasing a properly built trans.

Having a LSD in it would be nice too.
 

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Id just get the proper sync set since youve checked everything else.. but then again, your eyes are on it, not mine..
 

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Discussion Starter #11
Possibly, but I'm also no trans expert and could very well be overlooking a small detail somewhere. Currently trying to weigh the cost-to-benefit of getting proper synchros and tearing the trans apart a third time only to do it again later this year when I really want a LSD.
 

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Discussion Starter #13 (Edited)
I've solved my issue.

I'd like to start by saying that if you have a transmission with 250k miles on it and have developed a grind, then I do not condone this procedure. In my case I have a freshly rebuilt transmission with all components within factory spec. What I did to fix my third and fourth gear grind was burnish the synchros. I decided I needed to do this because 1.) I checked all tolerances and nothing was out of spec and 2.) The issue of synchros being out of round on the inner diameter seemed likely considering they were from an unknown factory sourced through eBay.

In December of 1999 Honda released a service bulletin for this procedure:

On an M/T vehicle with less than 2,000 miles, you
can sometimes fix a shift grind by burnishing the
offending gear’s synchronizer. Here’s how:
1. Make sure the clutch releases fully by shifting in
and out of reverse with the engine running and
with it stopped.
• If the shift effort is higher with the engine
running, the clutch is dragging. Repair it as
needed.
• If the shift effort is the same with the engine
running, go to step 2.
2. Park the vehicle outside, away from other cars,
and set the parking brake.
3. Raise the engine speed to 2,500 rpm.
4. Without pressing the clutch pedal, apply light
pressure to the shifter toward the gear that grinds.
The pressure should be the same as when you
engage the gear.
5. Hold the pressure for 5 seconds, then release the
shifter for 5 seconds. To avoid synchronizer
damage, follow these intervals exactly.
6. Repeat step 5 carefully 10 times.
7. Test-drive the vehicle. If it still grinds, you may
need to disassemble the trans, inspect it, and
replace worn or damaged parts.

I tried this and it did not work for me. What I did instead was park on a flat surface, turned the engine on, and began to "feel" the synchros engaging on their respective cone for each gear. As expected, first, second, and fifth gear had a great amount of resistance and the engine began to take on load when pushing the shift lever toward the gear without depressing the clutch, while third and fourth had little to no resistance, allowing the collar to slip towards the gear before it had a chance to decelerate.

What I did was put the shift lever in the position for third/fourth where the synchro meets the cone and revved the engine until resistance was found and the engine began to take on load. For me this was ~4500 RPM. I did this for approximately 10 seconds. Following this procedure I went for a drive and now have no grinding in third or fourth gears at any RPM or engine load.

Honda later retracted this service bulletin and it is no longer a suggested procedure. In my opinion I think this was due to people using the procedure on old transmissions that actually needed servicing. I can see the practicality of this procedure on a new transmission with synchros that just need the runout of the mating surface corrected. At any rate, this fixed my grinding issue on my freshly rebuilt transmission.
 

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ED6&7. EE4&5, MB1
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Also on the September 99 issue following is stated:

Don’t Skip Gears When
Shifting

Recently, an Internet newsgroup message reported
that it’s OK to skip gears when shifting a manual
transmission. Here’s our response:
Vehicles with manual transmissions should
be shifted through their gears in sequence.
Repeatedly shifting out of sequence, such
as going 2nd to 5th, especially when speed
shifting or power shifting, can cause
accelerated syncro wear which can lead to
gear grinding. To avoid possible problems,
tell your customers not to skip gears and
not to speed shift or power shift.
 

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1996 Civic Type DX
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Using close ratio gears (MFactory) will also decrease component wear. The less the RPM drops on upshifts, the less wear occurs.
 

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...
In December of 1999 Honda released a service bulletin for this procedure:

On an M/T vehicle with less than 2,000 miles, you
can sometimes fix a shift grind by burnishing the
offending gear’s synchronizer. Here’s how:
2. Park the vehicle outside, away from other cars,
and set the parking brake.
3. Raise the engine speed to 2,500 rpm.
4. Without pressing the clutch pedal, apply light
pressure to the shifter toward the gear that grinds.
The pressure should be the same as when you
engage the gear.
5. Hold the pressure for 5 seconds, then release the
shifter for 5 seconds. To avoid synchronizer
damage, follow these intervals exactly.
6. Repeat step 5 carefully 10 times.
7. Test-drive the vehicle. If it still grinds, you may
need to disassemble the trans, inspect it, and
replace worn or damaged parts.
Thank you so much for this! I got a rebuilt ex tranny from synchrotech about a year ago and right from the start it would grind 3rd and 5th unless you let the revs drop way down or double clutch. Just went out and did this and it's butter smooth now.
 

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Brokedick Millionaire
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40,310 Posts
Also on the September 99 issue following is stated:

Don’t Skip Gears When
Shifting

Recently, an Internet newsgroup message reported
that it’s OK to skip gears when shifting a manual
transmission. Here’s our response:
Vehicles with manual transmissions should
be shifted through their gears in sequence.
Repeatedly shifting out of sequence, such
as going 2nd to 5th, especially when speed
shifting or power shifting, can cause
accelerated syncro wear which can lead to
gear grinding. To avoid possible problems,
tell your customers not to skip gears and
not to speed shift or power shift.
I don't have any problems, but I know to let the shaft speeds be right for the shift.

I've driven my 5 speed transmission as a two speed, never bothered it. Just give time for the rpms to drop. Start out in second gear, rev to 4500 rpm, be at 2000 rpm going into 5th gear.

ZC gears are near perfect for me.
 

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I don't have any problems, but I know to let the shaft speeds be right for the shift.

I've driven my 5 speed transmission as a two speed, never bothered it. Just give time for the rpms to drop. Start out in second gear, rev to 4500 rpm, be at 2000 rpm going into 5th gear.

ZC gears are near perfect for me.
yep me too
but i rarely skip more than 1 gear.
If i space-out n realize i'm near the redline i'll skip 2.

( PS: Hi Mr Bone ! ) :)
 
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