From: leif@tde.lth.se (Leif Olsson)
Subject: Re: Braking techniques
Organization: Applied Electronics, Lund University, Lund, Sweden
Date: Fri, 8 Jan 1993 10:10:16 GMT

In article <4338.88.uupcb@chaos.lrk.ar.us> dave.williams@chaos.lrk.ar.us (Dave Williams)  writes:

->-> I'd much rather wear out my brake pads which are designed to be
->-> regularly rep my clutch which isn`t.  Can someone please explain to
->-> me why so many people i using their transmissions as brakes?

[ text deleted]

-> Vehicles that were driven hard - heavy trucks and race cars - often
->used downshifting and engine braking to assist the rear wheels when
->slowing.  Of course, the engine isn't much of a brake anyway - in some
->cars, it will hardly make a difference - but it was a necessary skill
->when you were trying to stop a wire-wheeled Alfa at the end of the
->Mulsanne Straight at LeMans.  So engine braking became associated with
->racing, and became stylish.

-> Using the engine as a brake is VERY hard on the differential and
->transmission, which are spirally or helically geared and designed to
->accept load in the other direction.  I've broken one rear and two manual
->transmissions by letting off hard at the end of a long straight; I
->guarantee this is maximally exciting as you do a smoking 360 off onto
->the side of the road with the rear wheels locked.  That's why, when I
->drive nowadays, the clutch pedal goes down FIRST, THEN the brake.
->Driving the engine instead of v. versa also reverses the film loads on
->the crank (usually not that bad) and causes very high intake vacuum,
->which can suck oil past the rings and valve guides, and past the seals
->on some turbo installations.

I almost always use the engine as a brake when driving a car with
manual transmission. In contrast to US > 90% of the cars here in
Sweden has manual transmissions, drivers license tests are done in
cars with manual transmissions, hence driving schools use cars with
manual transmissions, and they all teach you to use the engine as a
brake.

The reasons are simple. You still have the right foot on the gas pedal
so you can accelerate in shorter time if you need to, and you do not
have to use the brakes that hard to get maximum braking force. An
other reason is that if the engine stops during the braking you can
move the car with the starter if you already are in low gears. 

You should however not use the engine as a brake in the winter (if
there is snow on the roads) if the car is a rear wheel drive. You
should not use this technique if you have a two stroke engine
(motorbike) since the fuel supplies the oil to the engine.

-> During the 1950s and 1960s, race car braking technology improved
->tremendously.  By the 1980s most passenger cars had practically
->fade-proof discs, at least in front.  There's no reason to use the
->engine to slow, or to open the door and drag your foot, which is about
->as effective.

Your engine needs a rebuiling ;-). The only thing that is not
effective when braking with the engine is that you do not turn your
brake light on unless you use the brakes simultaneously.

-> These minor technical difficulties are meaningless to those who think
->their mufflerless Toyota sounds like Fangio at the Monte Carlo, and it's
->probably mommy's car anyway.

->=======================================================================
->can you help me...help me get out of this place?...slow sedation...
->ain't my style, ain't my pace...giving me a number...NINE, SEVEN, EIGHT
->(Nazareth)               XJ900 TURBO at 15psi          DoD# 978  KotFAQ
->=======================================================================


Leif
--
===============================================================================

Leif Olsson 
Department of Applied Electronics         email: leif@tde.lth.se
Box 118
S-221 00 LUND
SWEDEN
Newsgroups: rec.autos.tech