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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2006

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700R4 Transmission

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arbee - 05 Nov 2006 17:50 GMT
I'm going to be rebuilding my transmission this winter and am studying
the working process of this particular one.  Noone as yet has been able
to explain this to me.  Why does the lo-reverse clutch apply in manual
lo but not in o-drive range?  Why does the apply of the overrun
clutches in manual lo make a difference?  What would happen in manual
lo if the lo-reverse clutch didn't apply?  Would not the lo roller
clutch do the job as it does in o-drive range?
John Kunkel - 05 Nov 2006 18:57 GMT
> I'm going to be rebuilding my transmission this winter and am studying
> the working process of this particular one.  Noone as yet has been able
[quoted text clipped - 3 lines]
> lo if the lo-reverse clutch didn't apply?  Would not the lo roller
> clutch do the job as it does in o-drive range?

The l-r clutch applies in manual lo to provide engine braking on
deceleration. It doesn't apply in the normal automatic range in order to
prevent the objectionable lurch that would accompany the downshift to 1st
when coming to a stop.
arbee - 05 Nov 2006 20:27 GMT
> > I'm going to be rebuilding my transmission this winter and am studying
> > the working process of this particular one.  Noone as yet has been able
[quoted text clipped - 8 lines]
> prevent the objectionable lurch that would accompany the downshift to 1st
> when coming to a stop.

Correct me if I'm wrong but I think that it is the overrun clutches
that supply the engine braking as this clutch is also applied in 2nd.
and 3rd.(manual)  This clutch locks up the forward sprag.
Comboverfish - 06 Nov 2006 03:53 GMT
> I'm going to be rebuilding my transmission this winter and am studying
> the working process of this particular one.  Noone as yet has been able
[quoted text clipped - 3 lines]
> lo if the lo-reverse clutch didn't apply?  Would not the lo roller
> clutch do the job as it does in o-drive range?

The low reverse clutch pack is hydraulically engaged by the manual
valve to operate only in manual low and reverse positions.  There is no
other way for fluid pressure to reach it than in those two positions.

It is used in manual low to hold the "low one-way clutch" from
freewheeling, thus providing engine braking.  If L-R wasn't engaged,
manual low would act just like drive low.

In any other speed range, the low one-way clutch is physically spinning
but no torque is transfered through it.  It is considered to be
"overrunning" anytime that it is not transfering torque.  There would
be mass internal friction if L-R was engaged outside of 1rst speed
range (forward).

Toyota MDT in MO
 
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