armye7

I think I got it......hope it drives...lol

Dougs951S

Sorry to drag this up from the dead, but I'm curious how far I'd need to dig into the trans to replace 2nd and 4th gear synchros? I would just need to take the diff out, and then take off gears 5-2? If I didn't replace any bearings (the trans is quiet in all gears, just grinds going into 2nd and 4th) would I still need to mess with setting the diff preload, ect?

Also, what could keep the car from going into Reverse easily? It's not synchronized, so I'm not sure what could be the issue. It usually takes a few tries to get the box into reverse; I usually have to go into 1st first and it grinds going into reverse half the time.

Box is an LSD 951 box, so worth it to me to rebuild as I can't afford to replace it.

Alan 91 C2

The pro's may have other comments. No need to open up the differential section. And there is a synchro for reverse, but mine is like you discuss, but should not grind. Grinding would indicate the clutch is not fully disengaged. Make sure no additional carpet under the clutch pedal, from floor mats. Also, you may have some remaining air in the clutch hydraulics, as these are a pain to bleed.

I have replaced the synchros in 3 of my 944 transmissions. Not overly difficult, but you will need access to a press, and gear puller. And lay out all the parts in order removed. Go through the pictorial teardown a few times.

JET951

Alan's could be spot on there. by the sounds of it the clutch may not be completely disengaging. Unless of course you have some very worn synchros. Reverse does not have a synchro and in saying that we have seen some very worn reverse gear engagement teeth. Almost to the point they are square instead of pointy which can cause the symptoms you are having. As Alan said there is no need to remove the diff side plate just undo the gear section of the box and slide it out.
Regards
Sean

Dougs951S

OK. Leave diff in place. Check.

I'm crystal clear on the procedure until step 22.

To replace 2nd gear synchro I'll have to disassemble the pinion shaft with a press. Ok, no problem.

After that, on step 23 is states you must then set pinion depth and preload. Is that strictly necessary if new bearings were not installed and just synchros were replaced? Also were is Reverse located on the main shaft? I'd like to examine the teeth and replace if required Any idea where I'd find a reverse gear if I needed one?

2nd, 3rd, and 4th gear synchros are available from vertex auto fro ~140 bucks, or I can do 1-4 for ~190.

That's chump change compared to ~3k for a used box or ~2k for a professional rebuild. I just need the box to run for a few more years till I'm done with school.

JET951

no need to re shim the box if your using the same bearings as nothing is changing and it should be fine.
The actual reverse gear is offset in the box, photo attached. you can see that the teeth have a pointed edge to them, if its squared off then this may be the issue. Usually we do 2nd and above synchro as 1st hardly get punished like the rest.
regards
Sean

Dougs951S

Thanks Sean! I'm assuming the removal of reverse will be obvious with the pinion shaft out? I think I'm going to give this a shot. My only fear is I don't have the tool to hold the shaft while I remove the rear triple square tool that's behind the rear seal. Is that required; I don't see why a stout impact won't work?

The issues with reverse might be an alignment issue stemming from a previous, poorly done repair that I believe may be locating the shifter support/fulcrum lever improperly.





Talking about this bit here. The issues with reverse started cropping up after this repair. Let me go grab the trans and put it on my bench and take some pictures of it so you all can get a better understanding of how it originally failed, how it was repaired, and what the hell I'm talking about.

Alan 91 C2

There is a synchro for reverse, not in the usual sense, but the PET 6 does call the device a synchro, as it provides a synchronizing function. See part 52 in the attached. The reverse synchro does stop the free wheeling gear for shifting. A draging clutch will overpower the synchro. The way the trans is designed, with the requirement for each shift rod to be in neutral (home) position, before any shift, make the exterior shift linkage not part of any shifting issue. My normal approach for shifting to reverse is to cycle through 3rd to stop the main shaft spin, and then into reverse. As Sean said, often the reverse gears are pretty beat up so the gear faces do not help to align the gears. When new, these have nice sharp angles so the gears glide past each other. In Sean's picture, you can see some dulling of the sharp edge. Still serviceable. The device just to the right of the shinny teeth is the reverse synchro, on the reverse gear hub.

To hold the main shaft for assemby and disassemby, I took an old clutch, and bolted a 3 foot long piece of metal through the clutch media, to make a long lever. Works fine.

Sean your work is very helpful for all of us.

Dougs951S

This is what I was talking about. The trans case actually cracked, and I had it TIG welded and redrilled. I'm wondering if it's a little off center/mislocated and that is contributing to my issues with the box.

Alan 91 C2

The external pivot has no role in how the gears shift. The pivot point is a driver (you) feel variation for how the shifter feels.

Take Sean's advice and replace synchros 2-4. You can verify the others are good per the factory minimum distance measurement from the synchro face to the gear.
.

Dougs951S

Cool, thanks!

First things first, I'm going to give the trans a quick wash with dilute lye; yes I know it attacks aluminum but it works great to clean 30 years of grime off if you only let it sit for 5 minutes and then rinse with a hose.

JET951

Your right Alan, never looked at it that way.

Dougs951S

After a 5 minute soak with dilute lye: Much cleaner!

nimblemotors

Thanks for the great writeup, all the pics really make a difference.

I am resplining the input shaft so the trans will mate directly to an Audi v8.
If I understand the pics properly, it appears I don't need to remove fifth gear? Just undo the shift shaft, then
I can just unbolt the gear section from the housing and slide back the gears, exposing the front of the input shaft?
This should be enough to machine the new splines. Thanks.

JET951

You could do that but i would be very careful that no metal filings make there way into the gearset. Is the Audi V8 significantly different spine count and size? i take it the shaft is smaller for the Audi?
Regards
Sean