JDM-97CX

Have you ever been sitting at a stop light, holding your shifter and wondering what exactly is going on in your transmission? If so then this is for you.

The basic goal of a transmission is to connect the engine to the drive wheels through a series of gears, hubs, sleeves, and blocker rings.

The reason for the transmission in todays automobiles is the gasoline engine has a redline and a specific RPM at which it makes it best power and torque. The transmission allows the engine to propel the vehicle to high speeds without damaging the motor and alowing the engine to stay in its ideal RPM range.

Now lets start by explaining some of the more well known parts in the transmission.


<U>SYNCHRO</U>

The synchro performs a number of jobs vital the to operation of the tranmission. Its main job is to bring components that are rotating at different speeds to one synchronized speed. It ensures that the pinion shaft and the speed gear are rotating at the same speed. Its second job is to actually lock these components together. The end result is a clash-free ****.

In todays transmissions all forward gears are synchronized. One synchro is placed between 1st and 2nd, 3rd and 4th, and if applicable there is an addition synchro for 5th and 6th gear.

The synchro sleeve has a large external groove where the shift fork rests, it also has a small internal groove. The sleeve meshes with what is known as a clutch, or synchro hub. There are three slots cut into the hub in which three inserts fit that can move freely back and fourth. These inserts are often refered to as keys and then have a ridge cut into them. There are springs that hold this ridge in contact with the the synchro sleeve's internal groove.

The sleeve and hub are machined so the sleeve may slide over the hub smoothly. There are often alignment marks on the two pieces to be used during assembly.

Brass or bronze blocker rings are placed on either side of the synchro hub. Some assemblies have a friction material on the ring to reduce slippage. Each ring has three notches cut into it so it can fit around the keys in the synchro hub. Around the outside of each blocker ring are beveled clutching teeth, which help with alignment during shifting. The inside of the ring is cone shaped and is lined with many sharp grooves.

The cone of the blocker ring makes up half of what is called a cone clutch. The second half is part of the speed gear. The shoulder of the gear is cone shaped to match the blocker ring. The shoulder also contains a ring of beveled clutching teeth designed to line up with the teeth on the blocker ring.


<U>GEARS</U>

The purpose of the gear is to transmit rotating motion. They are normally mounted on a shaft and they transmit motion from one parallel shaft to another.

The shaft and gear can interact in one of three ways. The shaft can drive the gear, the gear can drive the shaft, or the gear can rotate freely on the shaft in which case it would act as an idler gear.

Sets of gears can be used to increase speed and decrease torque (overdrive gear), increase torque and decrease speed (underdrive gear), or transfer torque and not change speed (direct drive).

SPUR GEARS (Straight cut)

Spur gears are the simplest gears used in a transmission. They have teeth that are cut straight across the gear. During operation, spur gears only contact with one tooth at a time.

The straight cut design minimizes the chance of popping out of gear, something important to consider when accelerating, decelerating or in reverse. For this reason, reverse is normaly a spur gear.

The main drawback of these gears is a clicking noise that is created when the gears contact one another. At higher speeds this clicking becomes a loud whine (think of the sound of reverse). For this reason helical gears are used.

Helical Gears

Helical gears have teeth cut at an angle, or in a sort of spiral to the gear's axis of rotation. This allows more teeth to contact at the same time which distributes load and makes for a very strong gear. Helical gears are also much quiter than a spur cut gear because they make a wiping action when engaging and disengaging teeth. One drawback to these gears is that they have a tendency to cause an axial thrust on the shaft. This thrust must be absorbed by thrust washers, shafts, other gears, or the transmission case.

Helical gears are cut left and righthanded. When two gears mesh one must be left and the other right.

Idler Gears

An idler gear is placed between a drive gear and a driven gear so that both gears may spin in the same direction. This is how reverse is created.

Transaxle or Transmission?

The difference between these is not that one is for FWD and the other for everything else. The transaxle has the differential mounted inside the case. A transmission uses an external differential.


I hope this helps some of you that did not quite understand a transmission before.


EDIT: There will be more to come on the actual operation of the manual tranmission/transaxle.

Stoich EG2

hahahaha, classic introduction

litterbox

Great explanation though I think some pics would help us visualize all this better. Just a thought.

Aphelion

good writeup, but it would be easier to just link to HSW. You can start from the beginning of the article, but I linked to the animation for a graphic description of how a transmission works: LINK

nocturnaldragon

I have some pics from my last transmission disaster, there pics of the gears and syncro's closeups and some of them all sitting on there respective shafts in the housing and not in the housing. Pm me if interested.

menkio

anyone know where i can get tranny parts, like syncro's and streight cut gears

litterbox

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by menkio &raquo;</TD></TR><TR><TD CLASS="quote">anyone know where i can get tranny parts, like syncro's and streight cut gears</TD></TR></TABLE>I don't know, but aren't straight cut gears extremly loud? You're that hardcore?

menkio

there not that loud, and shrug.. as long as your not crusing aroudn town at 10krpm... i doubt it would be a problem. It's for my weekend race car anyways

Pioneer162

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDM-97CX &raquo;</TD></TR><TR><TD CLASS="quote">The end result is a clash-free ****.</TD></TR></TABLE>

IHateJDM

straight cut gears would be annoying on a DD, but as a second car, it would sound tight. That's not a noise you usually hear from a honda.

Marauder

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by menkio &raquo;</TD></TR><TR><TD CLASS="quote">there not that loud, and shrug.. as long as your not crusing aroudn town at 10krpm... i doubt it would be a problem. It's for my weekend race car anyways</TD></TR></TABLE>

Reverse gear is straight cut.

expect to pay about $5-8k for a set of straight cut gears.

alleyezonme

Is the loud whine the only reason tranny's don't have the straight cut gears stock? Are there any cars that do have them stock? Do tractor trailers use them??

Nice info though. Everyone is all about the engine, and the tranny is overlooked.

rukawa1one

good info