Chris & Ann Green <mggreen@awinc.com> write:
> I recently purchased a 68 Spit a wonderful roller skate, but there is
> a transmission problem. Under deceleration in third gear the gearshift
> jumps to neutral.
> Is this a common problem with these stanpart cars?
> Could it be a problem with.
> 1. The selector shaft and plungers
> 2. Selector fork
> 3. Synchronizer springs and balls
> 4. Third gear locating circlip on mainshaft
There are two primary causes of jumping out of gear: worn/weak
selector pungers/springs/shafts, and wear to the 'dogs' on the gear or the
sleeve. Given that yours only jumps out when in overrun, I expect it's the
dogs (though you might have some of both).
Basically, the dogs are what lock the mainshaft to the gear when that
gear is selected, and they're what you hear grind if you have weak synchros -
though that's the points of the dogs; your problem is wear on the 'flat'
portion. Diagram from above:
^
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The straight sides are what engage with the sleeve to select the
gear, and the torque acts through them. One side takes the torque under
power, the other under overrun. If they get worn at a slight angle towards
the point (perhaps by not having the clutch fully disengaged when shifting),
when you apply torque it will want to force the dog and the sleeve engaged
with it apart, back towards the point, at which point it pops out of gear.
This wear can be on the dogs of the gear or on the equivalent part of the
sleeve, but most likely is on both.
The selector-fork plungers and springs oppose this, but only to a
degree. They're cheaper than the gears/sleeves, but replacing either
requires pulling the trans. Perhaps once it's disassembled you'll be able
to tell exactly what part is worn, but unless you're sure I'd advise
replacing the springs, gear and sleeve. If you don't mind pulling the trans
again, try the springs (and perhaps shim them for extra force) if the
gears/sleeve don't look too bad.
It could be other things (like bearings), but I'd guess 9/10 times
jumping gears are caused by the above.
jstovall@earthlink.net (J. Stovall) writes:
>Subject: '66 GT6 stuff
> Ok. So we recently got the car back from the garage here, who
>charged us $90 to adjust the float level. But at least they made the car
>drivable.
Given the rest of the story, I suspect they don't really know what
they're doing.
> Now, about twenty minutes ago I went out and looked at the carbs
>and the damper oil. The garage had put the stuff you order from the catalog
>in there and I had a hunch that was too light. I drained it out and put in
>some 10W-40 and the darn thing started with the first turn of the key.
Probably no connection. 10W40 can be used; it's perhaps a bit heavy
but shouldn't be a problem. The "correct" lighter oil will work too. All
the oil does is damp movement of the piston when you suddenly open (or close)
the throttle, providing a pseudo-accelerator-pump (enriching the mixture).
>Extremely hesitant when I revved it, but it was running.
Important fact.
> Here's what was happening right after we got it back from the
>garage: extremely hard to start, it would take 10-20 tries to get it
>running. Absolutely no power when cold, but fairly improved when warm. You
>had to have the choke out until it warmed up, and when idling you had to
>rev it some to keep it from dying. And there was just a feeling that
>something wasn't right about how it was driving, you know? Maybe a
>combination of all this.
Also important. From this I'd guess there are one, perhaps two major
problems: I'm guessing that the ignition is probably set incorrectly, and the
mixture is probably too lean. If they adjusted the float levels they should
have checked/set the mixture, since the mixture is directly affected by the
float levels. On ZS carbs, this requires a special tool. Other possible
problems: torn diaphragm in the carb (common, trivial to fix, might well
cause problems like this, though not hard-starting), major air leak in
carb/manifold/vacuum hose.
> And here's what happened when I drove it about twenty minutes ago:
>stalled once, mostly my fault, but it started back up on the second try.
>Hiccuped a good bit.
Ignition off, mixture may be off.
> Still got a pretty big loss of torque. I parked it in
>the drivaways once and turned it off, but it ran on for about 7 seconds.
Really sounds like the ignition timing is off. Could be a bad cap/
rotor/wires, but it really sounds like timing. Probably too retarded.
> I started it up agian right off. After I pulled into the driveway for the
>last time and turned it off, it immeditly blew a backfire that sounded like
>a shotgun.
The last nail. Set the timing correctly, then work on the carb
tuning. I always prefer setting the timing statically (non-running) and
perhaps making small adjustments from there (removes some annoying
variables). The TR6 (similar engine, longer stroke) likes ~12-16 degrees of
static advance (12 is stock).
>My point? If something else major goes wrong, even not that
>major, me and Dad have lost out. Mom will sell it in a minute. Yickes!
It's an old (british) car; other things will go wrong. Get ahead of
the game by replacing all the common wear items (and keep the old ones as
spares in the trunk): Cap/rotor/points/wires/water hoses/belts/etc. Carry a
flashlight, a bunch of correct fuses, wire, spade connectors (for the wire)
jack, basic tools, common bulbs (1054, etc), oil, antifreeze/water. Look for
things that appear to be marginal (cracked vacuum hoses, etc) and plan to
replace/repair them. Get the TRF and Moss catalogs (perhaps some others too).
Perhaps get and carry rebuild kits for the hydraulics (both masters,
clutch slave and a rear drum slave). The rebuild kits are cheap (just some
seals), but it's handy to have them with you if you break down in east
nowhere - or even at home, since you don't have to wait 2-5 days, and that
assumes they aren't backordered.
On ANY 15+ year-old car, you'll have occasional breakdowns - 80 Camry,
76 Toyota pickup, or GT6. Make sure your mother knows this. The advantage
of an old British car is that the engineering is so "50's" that you don't need
anything more than a few tools and basic mechanical understanding to fix it.
My insurance company (State Farm) has roadside assistance coverage
for about $4/year. Get something like that or AAA.
--
Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
Randell.Jesup@scala.com
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