Coasting w/ Nissan FS5W71X Transmission

[moose60]

--Disclaimer---
I know all the common reasons that a person should not take a vehicle out of gear (safety etc.) I'm looking for the mechanical implications of this action.


When a person takes a MT out of gear while on a downslope and leaves the engine running is the trans harmed? I know that these trannies have weak input shaft bearings; does putting the trans into and out of 5th load these little guys in some strange way? Does having the output shaft spinning at road speed cause the input shaft to thrash around more than ususal?

I rev match all shifts every time (I used to drive un-synchroed class B commercial trucks) and use the clutch, so I don't think that the additional shifts would cause much additional wear to the syncros.

Thoughts?

[asavage]

When a person takes a MT out of gear while on a downslope and leaves the engine running is the trans harmed?

MT: no. Everything in the FS5W71 is splash lubed, and it's all going to be splashed just as much in neutral as if it was in any gear.

With ATs, maybe: it depends on the particular transmission. Some parts of ATs are pressure lubricated and the lube to some areas is cut off when in N and/or P.

I used to be a coaster; I've dropped out of the habit, since I trained myself to drive the speed limit about 19 yrs ago, and I now use the cruise control constantly to aid in that. So I know where you're coming from.

How, when to shift and at what engine RPM, or when to operate the clutch is something of a religion with some people here, so be prepared for some opinions. I'm going to be a role model here and show restraint -- I tried to answer only the Q you asked

[moose60]

Thanks Al,

I have my own "belief system" of how to shift my vehicles but also do not try to force it on others. Check on the splash-lube, that's what I figured.

I'm now trying to drive below the speed limit AND coast when possible.

About the when to use the clutch; I used to float gears all the time on the bigger trucks, but his is MY transmission and the clutch action is very light. There is no reason not to use the clutch. I probably should have been using the clutch on the bigger trucks, but since I didn't grind 'em I just figured I could play 18 wheeler (even though I only had 10.)

Shootin' for 44!

[asavage]

While I can drive clutchless, I find it takes too much concentration -- or maybe attention -- to do it well. I've gone to ATs and CC, and I'm sure I'll be driving a Buick any day now

[davehoos]

At idle/no load in neutral the gearbox may chatter often refered as rollover rattle adding marks and tooth wear.[minor]..

diesel gearboxes often have a springloaded constant mech gear on the lower shaft to dampen this.

towing a manual is not good as the main shaft needs the splash oil feed.

auto trans needs the oil flow inside for cooling.some bearings inside are plastic thrust washes.

petrol engines rarely idle.once the cars mobile it may stay as high as 15/1800 RPM-turning off fuel at closed trhottle coast.

[asavage]

towing a manual is not good as the main shaft needs the splash oil feed.

The layshaft and the rear of the mainshaft will turn (and splash) when being towed. Only the input shaft (front half of mainshaft) will not turn, but two gears on it will. There is no difference in lubrication with the engine running and not.

[philip]

--SNIP- I rev match all shifts every time (I used to drive un-synchroed class B commercial trucks) and use the clutch, so I don't think that the additional shifts would cause.

Thoughts?

As one matches up each next gear (on "non-synchro) you are supposed to single clutch. But when one matches down each next gear, you have to double clutch.

Any MT having synchronized using "float-gearing" ... abuses both synchrons and gear teeths. Also, during synchroniz MT you -can- "double clutch" downshifts.

[davehoos]

The layshaft and the rear of the mainshaft will turn

in neutral with the clutch engaged only the output shaft[mainshaft] turns.
the imput and layshaft are permenantly contected with the constant mech gears.the other gears are are in constant mech with the layshaft[cluster shaft]only the reverse gear idler is not conected. most nissan boxes dont have bearings with each gear.they are metal to metal with clearance splash fed arangement.the rear gears 5/rev use splash oil draining down a guide from 1/2 gears.

for a long trip you can overfill the trans.you need to get oil into the bearing between the input/output shafts.you fill it through the oil breather or the later TYPE C models in the gear stick..

front wheel drive nissans its normally only the imput and 2 other gears that wont turn when towed.these also use splash fed guides the feed oil into the shaft centers and bearings.

[davehoos]

the original post was coasting in neutral with the engine idling.i just drifted of the obvious.

if the drive shaft is good,suspension is good-then it should not whip and damage the shaft and the small bearing in the front of the mainshaft.

PS
i forgot to put oil in a suzuki cino manual gear box during a service.
after a few days of suburban driving the owner attempted a 300km trip.aprox 200 into the trip he stopped at a garage as the car did not drive when engaged in 5th gear.no other noise just an extra neutral..the owner given a rental and the car trucked back to the dealer.
the both the 5th gears had turned to sparks coating the metal casing.I replaced them both and the melted alloy fork.the 2 bearings next to them replaced as a precaution.filled it up with oil and it still in service with many km travelled.

[asavage]

Something I saw today reminded me . . .

Millions (?) of RVs tow MT-equipped vehicles thousands of miles each year.