Julian wrote:
> The gearbox is an A727 behind a 440 motor in a 1973 Jensen Interceptor.
>
> My box has developed an annoying problem. When the box is cold I can't
get
> any forward gears although reverse works perfectly. If I hold it on the
> brakes and give it a few revs in reverse for a minute to warm the oil up
it
> suddenly starts working normally, whereupon it then works perfectly for
the
> rest of the day.
>
> The fluid is new, (and clean) the filter is new and the oil level is OK.
> When the gearbox is working normally it behaves perfectly without a hint
of
> any problem.
>
> I've studied the schematic and 'elements in use table' in the Chrysler
> workshop manual and have decided that the problem must be connected with
the
> rear clutch, probably sticking. I can't see any problems with the valve
> block, because in drive and stationary, oil is ****ted straight through
the
> manual valve (which can't stick because it connected to the selector
lever)
> through to the rear clutch. Oil pressure must be fine because it drops
into
> reverse perfectly.
>
> Would anyone care to comment on my diagnosis, is there anything that can
be
> done without removing the box and has anyone rebuilt the gearbox
themselves?
>
> Thanks Julian.
>
How old is the unit since last overhaul? I have the same transmission in
several vehicles, and the only time I experienced the same problem was
when my 1966 727 was about 35 years old and had not yet been overhauled.
The colder the weather, the longer it would take to decide to engage in
a forward gear, and I even got into the habit of dropping it into
reverse and gently revving the engine against locked brakes in order to
heat the fluid more quickly. Once it finally dropped into gear, it would
work flawlessly all day long.
Cut to the chase- I finally opened it up and found that the piston lip
seals on the rear (direct) clutch were as hard and brittle as un-cooked
pasta. Once heated above room temp, they would soften and seal to the
cylinder, but when cold enough fluid bled past to prevent the direct
clutch from engaging.
The problem can be aggravated by other internal hydraulic leaks in that
transmission as it ages so that the pump output just isn't sufficient to
overcome the clutch leakage. A common spot that you have to watch is the
thrust washer between the input and output shafts- make sure you set the
end-play (and therefore the fluid loss at that junction) correctly on
rebuild.
Good luck!
-Steve
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