Can't Shift Into First

[john walker's workshop]

check out the diff housing, in a drilling right between the holes where the shift rods were, and see if the detent is still sitting there. if the housing was jostled or plunked on the bench after the gears were removed, the detent may have relocated itself. this is a very important detent and has to be in the right place when you reinstall the shift shafts. it often slides up into the top of the bore and is forgotten until the trans goes into two gears at once farther on down the road. there is another one in the end of the intermediate housing.

[rcecale]

I'll take a look.

I had it standing on the bell housing when I removed the shift rods. It was sitting on the floor with my feet holding it in place while I pulled the rods. I don't think I jostled it around, but I'll definitely take a look.

Getting anxious to get this thing apart so I can get the parts on order. I'll probably need some help identifying all the parts. I'll post pics of the pieces and will leave it up to you experts.

Randy

[rcecale]

John, here's a pic of the diff and the holes where the shift rods were. There is a bored hole that goes somewhat at an angle between the two shift rod holes. My guess is this is what you'rre talking about.

I can see the detent. Looking at this pic, the detent is in a recessed area that runs to the left of the hole on the left, if that makes sense...


If I'm correct, the shift rod on the left is for 1-2, and the one on the right is 3-4. There is another drilling in 1-2 that runs away from 3-4. That is where the detent is.

Anyway, thanks for this piece of knowledge. I wouldn't have noticed that on my own.

Randy

[rcecale]

Here's a better shot of the detent.


Randy

edit: John were you saying that this detent should be in the drilled hole BETWEEN the two shift rod holes?

[john walker's workshop]

the detent lives in between the two shift rod holes, cross-ways. it is loaded into the bore originally by removing that steel cap on the outside of the case. there's a like steel cap in the intermediate cover for another detent.
how is the condition of the big flat shims that were under the retainer plates? they often get killed by the bearing lip. measure with a micrometer and replace any that are chewed.
how are the cast iron retainer plates? the lip of each bearing should stand just a tad proud of the face of the retainer when you pull them snug with your fingers. the lip should not be below the surface of the retainer, or the shaft(s) will have end play, which makes for a noisy trans.
remove the side cover and remove the ring gear assembly, and get all the metal bits out of there.

[rcecale]

this is a pic from the 3-4 setup. The dog teeth seem to be in decent shape (IMHO). You can also see the hub and the thruster block. (Look at me, sounding off like I know what I'm talking about... )


Here is a pic of 1st gear (I believe). You can see the broken parts of the hub and the missing dog teeth which allowed the ring (Not sure the correct nomenclature) to release and drop the thruster block, allowing it to roam free around the transmission.
The reason I could not shift into first!!!


Another pic of first gear, showing the broken hub, the ring which was released by the failed hub and dog teeth and the thruster block which was floaring around the case.


A closer shot of the above pic showing the broken ub and the ring.


Fixing to tear into dis assembly of this thing in just a bit.

Randy

[bigchillcar]

Go Randy go!!
Ryan

[ischmitz]

Randy,

The "ring" is a syncho band or synchro mesh. It is the part that provides the friction surface to match the RPMs of the operating sleeve and the gear with its dog teeth before they mate and lock. It rubs against the inside of the operating sleeve. The whole setup acts very much like a drum brake: Once the operating sleeve (drum) gets pushed towards the synchro bands (brake pads) by the shift fork the anchor block and the thrust block push the synchro bands apart and eliminate the RPM difference between the two before they mate.

If you shift too hard the synchro's don't have time to complete their work and the dog teeth on the gear grind against the teeth of the operating sleeve. If the synchro band's friction surface is worn out the breaking effect lessens and the tranny grinds more.

Trust me, after you have put everything back together you will take each shift with a deep appreciation knowing exactly what's going on in the tranny. Ask me how I know.

Go Randy go, this one cool thread,
Ingo

[Jim Sims]

915 brake bands and synchronizer (synchro) rings are distinct and separate parts. The brake bands are inside the synchro rings and do not contact the operating or sliding sleeve. They instead, bear against the inside of the synchro ring.

See:

Please help me create a tranny rebuild list.

[ischmitz]

Ooops Jim,

you are right, it's been some time since my 915 was apart and I just looked at PET this time to get the names right. Totally forgot about the brake bands. PET diagrams are borderline. I should have taken the time to look at the factory WSM.

Ingo

[rcecale]

Just a reference shot before I beat up my garage floor...


Randy

[rcecale]

And another...


Randy

[rcecale]

"The Usual Suspects"

First Gear...You can see the missing dog teeth.


First Gear and the Synchro Band. My guees is that the Band should NOT be out-of-round like this one is.


The Toothless Hub


I'll continue dissassembly of the shaft and see if anything else looks damaged. I'm sure there will be more pics to come.

Randy

edit: By the way, is there a technique or a special tool I should use to get that C-Clip off of First Gear?

[rcecale]

This bearing came from Second Gear.


Everything else seemed to look okay. How far should I tear Second Gear down to inspect it. Here are a few shots of Second.



As far as I could tell, I wasn't having any problems with Third or Fourth, so I think I'm going to leave them alone for now.

Randy

[ischmitz]

Randy,

I would replace the synchro's on 1 to 4 while you have the tranny appart. If you are really cheap you can at least flip them over. They mostly wear on the side facing the operating sleeve. Take a look at the synchro rings, if you see dark spots on their outer surface near the gap the friction material is about to go. From what I understand new synchro rings have better material and wear less. But that could also be a rumor. The last photo shows the circlip in all its beauty and the dog teeth. But again, take a look at the outside of the synchro rings.

I don't know for sure but I think you can reuse the needle bearing. If I remember I had one cage cracked like that and reused it. No biggy.

Ingo

[Grady Clay]

Randy,

There is a major disparity between the 1st gear dogs (worn and broken) and the 1st gear side of the sliding sleeve (not terrible). Had the sliding sleeve been replaced recently and not the 1st gear dogs? Is there something else going on here?

It seems to me that when things started to fail, attempting to force it into first may have caused this extensive damage. The important diagnostic is what precipitated the first problem.

Best wishes,
Grady

[rcecale]

Ingo!

Are you back from Taiwan?

Yeah, I am trying to fix this as cheaply as possible. From what I can see so far, and following your recommendation on the Synchro Bands, this is what I'm looking at:

Synchro Bands: 1st through 5th
Synchro Hub: 1st
Synchro Hub Tool: 1st Gear
Tranny Gasket Kit
Shift Shaft Seal
Needle Bearing: 2nd Gear

From what my inexperienced eye can see, the rest looks okay.


Grady,

I'll get a pic of the sliding sleeve so you can compare. Took me a bit of playing with the parts to figure out what you meant, but I've got it now. Anyway, there has been no work done in this area for at least 5 years....let's say, maybe 5,000 to 10,000 miles.

As far as symptoms preceding this, there were a few. First, there was the other thread I linked to at the beginning of this thread. I was stuck out of First AND Second gears, but jostling the shifter "freed" it up.

Prior to that, I had occasionally experienced a symptom I've seen recently posted here. Basically, it was an extreme difficulty in shifting to Second. It was extremely intermittent and was difficult to duplicate. It happened whenever it wanted to, no matter how it was being driven. Double-clutching seemed to "free" up second.

When I had her in the shop for her 90K service, I mentioned this to my mech. He said he would check it out but was unable to duplicate it. I suppose I should have torn into this at that time, but.....here I am

Randy

[rcecale]

Here's a pic of the Synchro Band showing just how much it was torn up.

[rcecale]

Here's the sliding sleeve.


One thing I noticed was that the points on these gear teeth are offset on one side and centered on the other.

And here is Second Gear with the Dog Gear. The Dog Gear actually has a little play, in that it can actually come 'out" almost 1/16th of an inch. I can pull it out this far and then press it all the way flush as well You can see that in this image.


Randy

[Beethoven]

Randy,
I don't know how you do it, but everyone of your photos is beautiful, almost lyrical. Great lighting and composition, lovely colors. Someone who can't read might well think this is a thread about the beauty of engineering.
Keep 'em coming!