I tried the go from 3rd down in reverse in one motion trick - it worked the second time I tried it last night. aren't you locked out of reverse going straight from 5th, though? i'll have to give it a try, but I though that's what the reverse lock-out is for?

I was kind of wondering if its not just something in the linkage between my hand and reverse gear that is worn and not getting into gear fully. maybe i'll pop the ball out of the socket again and look closer for wear on 'reverse spot' on the ball/socket. certainly easier/faster than a rebuild!

that was my thinking as well, Nate. it doesn't grind at all going into other gears, but the action of the whole tranny is noticeably stiffer than the smallblock ZF5 in my gasser - which would almost tell me that the synchros are in better shape in this tranny than the gasser one. but that could be way off.

 

that certainly makes sense, but its kind of a different feel than popping out of gear. its not like the truck starts to move, then it pops out. its like it hasn't even gone into gear in the first place.

with other old manual transmissions that I've had, worn bearings seem to cause gears to pop out under heavier load, or when you get the RPMs up.

with this tranny, once I get it into gear, it stays put. its the getting it into gear that's the problem.

but, yes, you're probably right - I've got a rebuild in my future, almost certainly.

 

Should of been more specific in your original post. Check and make sure your slave cyl is getting enough throw(13-15mm) also check your pedal box for worn bushings.

 

so, I think I've gotten this issue to a point that I can live it - for a while anyway - which is good as I have too many other projects to get to work on instead of rebuilding a tranny at this very moment. ...namely a railing to go around my wood-stove to prevent my wanting-to-climb-on-anything-he-can-find son from burning himself. ...with the weather here in PA, it looks like I have about a week or two to [start, then] finish that project - but I digress.

so, I bled the clutch out - mine has a bleed screw, but apparently not all do - and got a small amount of air out. the pedal feels a little better - likes it gets stiff higher, is stiffest in the middle and gets softer just before the floor. previously, it would still be stiff at the floor. (yes, lots of innuendo there, but I don't care :-) )

also, I've found that if I time the gear slide into reverse just right, I can get it to go in just about every time. by which, I mean, if I go into reverse nice and smooth - not too fast and not too slow, just (and I mean, JUST) before the truck comes to a complete stop from going forward, or JUST as it starts rolling backward on its own (if I was lucky enough to get the nose pointed up hill before needing reverse), it seems to go into reverse clean and stick every time.

if i'm just sitting there dead still on level ground, I still have problems - but with proper planning, it seems I can always avoid that - unless i'm just starting up, at which point I put it into reverse before starting the truck and that seems to help.

going from 4th, over and down into reverse quickly works pretty well, too.

anyway - with this sort of description, would you all agree that its almost definitely bad synchros that are my problem?

...and if so, for future reference, what driving habits would cause that? i'm thinking the previous owner of this trans had a habit of jamming it into reverse with the truck still moving forward at a decent speed?

 

You described what my '95 did exactly when I had that truck 6 or 7 years ago.
I have nothing important to add other than you are not alone.
I figured out how to get it into reverse just about every time and I lived with it, had no funds to have it rebuilt.
And mine was way worse when it was hot. Stone cold it worked fine.

 

interesting - thanks for the info, Jim. I haven't been on too many long drives with the new tranny in there, so not sure how it behaves hot vs. cold but hopefully its not way worse for me when hot, as its already not great when cold.

last time I buy a used tranny without being able to drive it beforehand...

live and learn, huh?

 

Cold for me was within 15 to 20 minutes. If I drove to the mall or something 30 - 45 minutes away I'd have to pay attention, or watch people walking by stare at me with the annoying "GGGGGRRRRRRRRRR" from the truck...

 

OK, well I've definitely driven that far. and yep - that's exactly how I feel. I got stuck in a Wawa (don't ask, its a Philly area thing) parking lot at lunch the other day and finally just gave up, left the truck parked diagonally across 3 spots, shut her down, went in and grabbed my lunch and came back out, started in reverse and was OK.

lots of funny looks from people though - both for the grinding and the horrible park job.

 

Might be worth trying double-clutching, or even revving it up and trying to slide it in as it revs down.

You did put synthetic ATF in it, right? (Sorry for the "duh, of course" question, but just covering all the bases....)

 

yep - Mobil 1 ATF. not a stupid question, always good to try to simple fixes first, right?

and the revving the engine makes sense if its worn sychros. i'll have to give it a try.

a question on that though, as I've been thinking about this more and more - and maybe my understanding of synchros in a tranny is bad, but check me on this:

as far as I understand, the idea of synchros are to match (or better match) the speed of the 'counter-shaft' to that of the output shaft (which is being driven only by the rear wheels with the clutch released) through the counter-shaft-to-output-shaft synchro, and match the speed of the input shaft to that of the countershaft through the counter-shaft-to-input-shaft synchro. this way, when you're shifting at speed, you don't have to get the engine speed JUST right to change gears - like you do with an unsynchronized tranny.

however, in the case of first and reverse gear with the truck at a full stop, with a stationary rear end and fully released clutch, what role to synchros play? with everything stationary, and assuming proper chamfer on the aligning edges of the gears, every gear should go in every time if the clutch forks and shift linkages are all good, right?

if my logic is correct (which i'm completely not convinced it is), it would be a bad fork or shift linkage causing the reverse gear to just barely engage sometimes and grind the edges of the gears against each other when the clutch is let out. but, if, under the right conditions, there is enough engagement of the gears, upon application of load, the spline (angled teeth) of the gears will actually draw them together and they'll stay put. is this right?

sorry for being stupid here, i'm just trying to understand the logic behind my problem.

 

I still say that there is something worn in the shift linkage (worn ball or socket in the shift lever, or a worn shift fork busing or something). A worn synchronizer shouldn't keep you from engaging a gear altogether.

Here's a link to the manual for the S42 if it will help anyone:
https://www.ford-trucks.com/forums/1...for-a-zf5.html

By my quick scan through there it does appear as though reverse has a synchro, but first does not (you would synchronize 1-2, but there is nothing to synchronize before 1st). I'm guessing the reverse synchro is there to help you shift into reverse before the truck comes to a complete stop? I don't know for sure I guess.

 

...exactly - but strangely enough that is the only time mine does work consistently. when everything is motionless is when I have trouble.

which I agree, leads me back to faulty linkage somewhere...

also - I just remembered, I bought one of those fiber-optic inspection cameras from Harbor Freight a while back for something around the house - maybe i'll try sticking it in through the top of the tranny, or the level check hole and see if I can see anything obviously wrong with the forks or anything. it'll probably be impossible to see if anything's bent, what with that fisheye lens, but maybe badly worn forks would be visible...

 

Your exactly on the right track with the the exception of your understanding of how the gears are locked to the mainshaft. These transmission have constant mesh gears. This means that each mainshaft gear is constantly meshed to its respective countershaft gear. What allows only one gear to be locked to the mainshaft (and therefore transferring power) is the shift rails and syncronizers. For example, when you are in first gear all the other gears are also meshed and turning, however they are just freewheeling on the mainshaft "roller bearings" and not transferring power. First gear is the only gear that is locked to the mainshaft in that shifter position.

So, when you shift into reverse (or any gear) you are not actually moving the gear and meshing the teeth between the mainshaft and countershafts, what you are doing is moving the syncronizer sliding collar (which is locked to syncronizer body, which is splined to the mainshaft) which slides over the "dog teeth" on each gear. Maybe a picture will help understand.


Look at the first shift collar (top of the picture). See how there are little teeth on a ring between it and the gear and then there are little pointy teeth on the back of the gear. When you pull the shifter to 4th (in this case) you are sliding that collar up over those pointy teeth and locking that gear (4th in this case) to the mainshaft for power transfer.

When you try to shift into reverse and it pops out, it is because you were not able to get the sliding collar far enough to properly engage the dog teeth on the back of the gear. In my opinion, you should investigate two things. One, check for excessive wear in the shift tower mechanism. Did you replace the plastic bushings in the shift tower?


Second, I would investigate the shift forks for wear. These basically just ride on the sliding collars with the only lubrication coming from the transmission fluid. They can wear if the transmission is consistently forced into gear where it takes alot of pressure on the shifter to achieve gear engagement. The transmission that I rebuilt had all the shift forks worn badly. The more these wear, the less throw you will be able to achieve to slide the sliding collar over the teeth of the gears. See pictures below for how much mine were worn.




I agree that the problem is in something with the shift mechanism or shift forks.

All gears in the ZF transmissions are syncronized. You don't necessarily think about syncronization as 1-2 or 2-3. You think about syncronization of the gears as each individual gear has a syncronizer cone that will help to match gear speed to main shaft speed (which is the same as driveshaft speed). You could (try to) go from 5th-1st and the syncronizer cone for first gear would try to speed 1st gear up at the first gear ratio to match the mainshaft speed. You probably wouldn't be able to get it in gear though and would burn the 1st gear syncronizer ring up.

There has been floating around a power transfer diagram for the ZF that shows for each gear. I can't find it currently though.

 

wow - that info is awesome. i'm going to have to read it over a few more times and stare at the pictures and manual for a while, but I do get how the gears are always meshing and that its just the dog teeth engaging the sliding color that cause a particular gear to be 'selected.'

I didn't use new plastic bushings, but I did check them for play and they didn't seem too bad. maybe another check is in order.

seriously - thanks for uploading all those pics - I know that takes time and I appreciate the explanation. not to start investigating what I can before I write-off the issues as internal and eventually bite the bullet and drop the tranny ...again...

 

Happy to help in diagnosing. I know how frustrating it can be to finish and job and have a new problem pop up.

Found the powerflow diagrams. Drill down to transmission then transmission, manual. In there you select the power flow.
1996 Bronco/F-Series Workshop Manual

When you are sitting in the truck, how much freeplay is there in the shifter at the ****? You might not think the bushings are that bad, but a very small amount of play at the pivot point translates to a large movement at the shift ****. Those plastic bushings are cheap and can't hurt to replace. Also, the ball can be worn on the shift stub. Many little things can add up to a big problem...