Ok guys - lets see if we can figure this one out (please). I’m trying to get a healthy/ functional gearbox in the ‘73 1.7 car.
This is the car that had the bearing whine but otherwise shifted well. The whine was loud and getting worse so I pulled the box. Other than the whine the gearbox shifted well and would hold each gear properly. Let’s call this gearbox A.
I replaced that gearbox with one that I bought from a local member that was known to be good except for popping out of first gear. The first gear dog teeth on this one were nearly totally gone. The box looked good otherwise. I ended up re-using the same first gear shift fork as was in this gearbox which may have been a mistake). Let’s call this one gearbox B.
When I removed gearbox A from the car I opened it up and harvested the complete first gear cluster but not the shifter fork. I then installed the first gear cluster into gearbox B and then put gearbox B back into the car.
The car is still popping out of first gear - which is a bummer. It will go into first gear but as soon as the clutch is gently released it pops out. You can see the shift lever actually move forward when the clutch is let out.
Shift linkage cone screws are tight. I’ve adjusted the shifter and can get reverse and 2-3-4-5 cleanly. It holds all the other gears properly.
What I am wondering is if I have a bad shirt fork would cause this behavior. I am also wondering if I may have mis-positioned the shifter fork on the shaft. OR do you think I just have an incorrectly aligned shifter? I suppose I can disconnect the linkage and manually put it in first and see what happens.
Any ideas for me? Should I open it back up and swap in the fork that was in gearbox A?
Picture; Not my gearbox but this is the depth question I have - how far down on he rod should the fork go? Mine is slightly lower on the shaft than this.
Thanks!Click to view attachment
Full Version: First gear woes
Paging @Dr Evil
Anyone have some ideas here - don't think the shifter fork location is a unique question to my car so would be good to document this for the forum.
Thanks!
Anyone have some ideas here - don't think the shifter fork location is a unique question to my car so would be good to document this for the forum.
Thanks!
Was that picture taken with a potato?
http://www.914world.com/bbs2/index.php?showtopic=152051
QUOTE
In short there is a recess that is machined within the syncro hub (that is mounted to the gear) and the associated slider (that moves when you shift gears). That positive feel of engagement you get when you shift into gear is when the hub and slider are becoming 100% engaged. The two recesses are now merged into one single recess and the synchro ring was compressed during the shifting motion has now popped into the merged recess. The force of the syncro ring living in that recess is what keeps the slider and hub engaged (car in gear). To shift out of that gear you get another positive feel of disengagement as you compress the ring to get it out of the recess and then the slider disengages from the hub and you are back into neutral.
So what causes it to pop out of gear? Ultimately there is not enough force keeping the slider and hub engaged. Typical causes would be...
1. Worn hub, slider and/or synchro (items associated with the ring in the recess are worn out an no longer provide the required force to keep engaged).
2. Incorrect adjustment on the shift fork (not able to fully engage 1st so it pops out before it is 100% engaged).
3. Incorrect adjustment on the shift linkage (not able to fully engage 1st so it pops out before it is 100% engaged).
Any are possible. As you say you have problems only with 1st, I tend to think it is most likely #1 and not #2 or #3. If you said you had a problem with 1st, 3rd and 5th, then it would be more likely to be a shift lever adjustment problem.
Depending upon how mechanically inclined you are, you can (as Jim suggested above) shift into first via your lever. Then detach the shift linkage and then double check directly at the linkage on the transmission that it is in first gear and fully engaged. This should remove any questions as to linkage issues. Then see if it pops out of 1st gear when you apply power (drive the car).
If you have narrowed it down to being inside the transmission then I would not use 1st gear until you can get it fixed. The first/reverse slider is a particular costly item and any 1st gear "grinding" is an indication that you are damaging the slider and synchro hub. They may already be worn beyond reuse at this point.
Lastly you mention that reverse work fine. If you had said you also grinding when shifting into reverse, I would say that your clutch is not fully disengaging. But that does not sound like the case.
Sorry about your problems. Let me know if there is anything else I can do to help.
Richard
So what causes it to pop out of gear? Ultimately there is not enough force keeping the slider and hub engaged. Typical causes would be...
1. Worn hub, slider and/or synchro (items associated with the ring in the recess are worn out an no longer provide the required force to keep engaged).
2. Incorrect adjustment on the shift fork (not able to fully engage 1st so it pops out before it is 100% engaged).
3. Incorrect adjustment on the shift linkage (not able to fully engage 1st so it pops out before it is 100% engaged).
Any are possible. As you say you have problems only with 1st, I tend to think it is most likely #1 and not #2 or #3. If you said you had a problem with 1st, 3rd and 5th, then it would be more likely to be a shift lever adjustment problem.
Depending upon how mechanically inclined you are, you can (as Jim suggested above) shift into first via your lever. Then detach the shift linkage and then double check directly at the linkage on the transmission that it is in first gear and fully engaged. This should remove any questions as to linkage issues. Then see if it pops out of 1st gear when you apply power (drive the car).
If you have narrowed it down to being inside the transmission then I would not use 1st gear until you can get it fixed. The first/reverse slider is a particular costly item and any 1st gear "grinding" is an indication that you are damaging the slider and synchro hub. They may already be worn beyond reuse at this point.
Lastly you mention that reverse work fine. If you had said you also grinding when shifting into reverse, I would say that your clutch is not fully disengaging. But that does not sound like the case.
Sorry about your problems. Let me know if there is anything else I can do to help.
Richard
From your description it sounds as if the 1st/R shift fork is miss adjusted.
I would be inclined to drop the back of the trans enough to pull the rear cover and then support it back in place and have someone operate the shiftier in and out of 1st & rev.
Does the shift fork move the slider far enough onto 1st gear?
Of course this is easier done in a shop with a lift and supports and such but that is my past and now I have to work on the floor with jack stands.
The fork could be worn or damaged but your symptoms seem extreme for a worn fork.
You can do a complete 1st gear replacement with the trans in the car and the rear cover removed.
Jim
I would be inclined to drop the back of the trans enough to pull the rear cover and then support it back in place and have someone operate the shiftier in and out of 1st & rev.
Does the shift fork move the slider far enough onto 1st gear?
Of course this is easier done in a shop with a lift and supports and such but that is my past and now I have to work on the floor with jack stands.
The fork could be worn or damaged but your symptoms seem extreme for a worn fork.
You can do a complete 1st gear replacement with the trans in the car and the rear cover removed.
Jim
Thanks gentlemen.
It does sound like the fork - since the first gear cluster worked fine in the gearbox it was removed from.
I'll open the rear cover up and pull the fork that is in it and then swap in the known good one from the donor gearbox.
Hopefully between that and check the spacing of the fork on the selector rod I'll be back in business.
I appreciate the links and responses.
It does sound like the fork - since the first gear cluster worked fine in the gearbox it was removed from.
I'll open the rear cover up and pull the fork that is in it and then swap in the known good one from the donor gearbox.
Hopefully between that and check the spacing of the fork on the selector rod I'll be back in business.
I appreciate the links and responses.
"Known good" is a meaningless term, you have to visually inspect the dog and slider teeth and the brake band. Easy to check the 1st at this point.
Check the dog teeth, brake band and the teeth on the 1st/rev slider, you can do an inspection by removing the 1st/rev slider. The teeth should look like perfect little house roof peaks, not what I call shark toothed.
The peaks of the slider can be slightly rounded and still OK, but not totally rounded over.
The band should be a rough finish, no shiny/smooth sections or lines.
1st and 2nd teeth, sliders and bands take the most abuse, 3rd to a bit lesser extent.
How you can make one good trans out of two cores is because these parts above are usually perfect on 4th/5th and 3rd is often good enough to use on 5th.
2nd to 5th dog teeth, sliders and bands are all the same part.
The dog teeth are different on 1st, but the kit from 2nd-5th can be used, just come to a full stop before shifting to 1st.
Check the dog teeth, brake band and the teeth on the 1st/rev slider, you can do an inspection by removing the 1st/rev slider. The teeth should look like perfect little house roof peaks, not what I call shark toothed.
The peaks of the slider can be slightly rounded and still OK, but not totally rounded over.
The band should be a rough finish, no shiny/smooth sections or lines.
1st and 2nd teeth, sliders and bands take the most abuse, 3rd to a bit lesser extent.
How you can make one good trans out of two cores is because these parts above are usually perfect on 4th/5th and 3rd is often good enough to use on 5th.
2nd to 5th dog teeth, sliders and bands are all the same part.
The dog teeth are different on 1st, but the kit from 2nd-5th can be used, just come to a full stop before shifting to 1st.
There is a proper way to set those and it is shown in the Dr's video. That being said; look at the shift rod very carefully. If it is off you will see where the fork was previously clamped. It leaves a mark. Reposition it. If it hasn't moved you will need to realign the shift fork(s). If you don't have his video you can watch mine and reset it here. I won't loan it out as I'm still patiently waiting for MM (a long time member) to return another video I lent him. 
OK - just to close this out and pass along two lessons learned. I pulled the exhaust and pulled the rear cover with the transmission in place.
1) I swapped the fork over from the known good first gear box, and one doing this should make sure to swap over all the know good bits.
2) I made sure the bolt that locates the shift fork was properly tight this time. When I went to remove it from the installed box that was still popping out it was on my finger tight, make sure that is tight!
Not sure if it was the fork,or the bolt, or both but I’ve got a nice clean action on first now and it holds all of the gears properly.
Thanks for the help and support gentlemen!
1) I swapped the fork over from the known good first gear box, and one doing this should make sure to swap over all the know good bits.
2) I made sure the bolt that locates the shift fork was properly tight this time. When I went to remove it from the installed box that was still popping out it was on my finger tight, make sure that is tight!
Not sure if it was the fork,or the bolt, or both but I’ve got a nice clean action on first now and it holds all of the gears properly.
Thanks for the help and support gentlemen!
QUOTE(sixnotfour @ Jun 23 2019, 08:18 PM) 
Yep - dope move on the locating bolt. I was rushing in hindsight, not my finest hour.
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