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?
700R4 Transmission
Nov 05, 2006
3 Replies
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.
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.
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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