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Changing synchros (an account from experience)
I can help you. My brother and I just replaced
the synchros in his '88 80q, about 2 months ago. It went off mostly without a
hitch, largely because we were able to avoid most of the aspects of the change
that need special tools, or are simply a real pain.
We only did 1st, 2nd, and reverse.
First of all, you must have the Bentley manual.
All I can do is help you interpret what it says (which takes som
Second, here's a problem that we ran into that the manual
doesn't mention: Audi change the 3rd/4th sychro rings, springs, hub and sleeve,
in around 1990, and they stopped making the synchros that go on the old style
hub/sleeve. So, if you have an old style 3/4 hub & sleeve, you'll need to
buy new ones. They were expensive, either $150 each, or $150 for the set, i'm
not sure. The rings will be approx $45 each. I can't tell you how to determine
exaclty which you have. We didn't need to change 3/4 synchros, so we avoided
this whole problem, for reasons I'll get to in a minute...
On one hand, people will tell you that if you do this
operation, you'd be silly not to change them all, or at least change 1st &
2nd while you're at it, because they're the ones that are most likely to wear
out. However, with this tranmission, the 3rd & 4th synchros are on a
different shaft than the 1st/2nd and 5th/rev synchros. 3/4 are on the input
shaft, and 1/2&5/r are on the drive shaft. If this confuses you, read on...
Suffice it to say, the hard part (i.e. need special tools) of rebuilding a
tranny is the presses you need to pull the gears off the shafts, and to press
them back on. We just took the whole internal drive shaft, bearings, gears and
all, to a tranmissions shop. We handed them the shaft, the new synchro rings,
and the Bentley manual, and gave them some specific pointers on details
particular to this transmission that they had to do a certain way. The pulled it
apart, put the new rings on, and put it back together for $90. I believe that
was 1.5 hours labor. It probably would have cost the same amount again to get
them to do the input shaft with 3/4 on it, so we just blew 3/4 off
Ok, know for how a tranny works. For those of you who don't
know, every "gear" (e.g. 1st) is actually 2 gears, one that gets
turned by the engine, and one that turns the driveshaft. Furthermore, all 12
gears (1-5 + r) are in *constant* contact (i.e. mesh). When you shift gears, you
might visualize toothed rings pulling apart and going together (I did). Not so.
The way it works is that of the 2 gears in each pair, one is fixed to the shaft
that it's on, and the other spins freely on the shaft that it's on. When you
shift into say 2nd, the 2nd gear synchro sleeve locks the spinning 2nd gear onto
the shaft it's spinning on. The synchro sleeve has teeth that meet up with teeth
inside 2nd gear. The syncho ring & sleeve slides back & forth on a hub,
which also has teeth. 2nd's teeth meet the sleeve's teeth, which are already on
the hub's teeth. The hub is fixed to the shaft, and presto, you're in 2nd gear.
The acutal synchro ring just sits in the middle of this whole process, and rubs
up against the inside of 2nd harder and harder while you're shifting into 2nd,
until the freewheeling 2nd gear is going the same speed as the synchro ring.
Somehow (I don't exactly understand how), the synchro ring is
shaped such that it's very hard to make it spin & slide at the same time.
This is why you can't shift into gear when the gear isn't synchronized. I think
it's just that there's a lot more friction for you to overcome. Once the gear is
synchronized, you just have to overcome the sliding. This is just a guess, it's
hard to see inside these things when they're on the shaft. When they're off,
there's nothing to look at. Just rings & teeth. There may be more to it than
this at the physics level.
So, what it boils down to, is the fixed gears for 1/2, 5/r are
on the input shaft (the one that goes into the clutch), and the free gears for
3/4 are between them. Conversely, the free gears for 1/2, 5/r are on the drive
shaft (the one that goes to the front & rear differentials), with the fixed
gears for 3/4 in between them. Also, for those who wondered, the synchros are in
pairs. One sleeve sits between 1st and 2nd, actuates the syncrhos for both,
depending on which direction you push it. Likewise for 3/4, and 5/r. And yes,
there's an extra gear for r. It's actually not on any shaft at all - it's betwen
the input and output shafts, mounted on the back of the housing. It links up
between the fixed r gear on the in put shaft and the free r gear on the
driveshaft only when you actually put all the shafts back into the housing. This
is how the tranny manages to make the drive shaft go the opposite direction when
you use *that* gear.
There's a lot more I could tell you, but it's
better if you just ask questions. Getting the trans out of the car took us 7
hours. We could have done it in 6, but we were moving pretty slowly b/c it was
hard to understand the manual. Getting it back in took 4 hours, not including
the time we wasted trying to bleed the clutch not knowing that it's supposed to
be pressure bled. You don't have to bleed the clutch at all to do this job, but
my brother *wanted* to.
Incidentally, I'm in the Air Force Reserves, so
we had the benefit of the Auto Hobby shop on base, which had real hydraulic
lifts, and a transmission lift for carefully pulling the trans out instead of
letting it drop to the floor. A transmission lift is like a floor jack with a
big pole on it going straight up, and a table at the end of the pole. It's good
for getting the trans at just the right angle to pull it out. This took a lot of
fiddling, and I don't know how we would have done it otherwise. You'll need a
makeshift trans lift if you don't have a real one.
Here's a tip - if you get to steps in the manual
that seem irrelevant, or seem like it would be easier to do them later, you're
wrong. Trust me.