Manual Transmission Reverse Gear: Does it usually have a synchronizer?


#1

On this week’s show a caller said his manual transmission car made grinding noises when trying to put it in “reverse”. Ray said the problem was likely the reverse-gear synchronizer was worn out. I was surprised to hear that reverse gear would even use a synchronizer, since you are almost always at a complete stop and the engine at idle rpm before shifting into reverse. Is that a common thing w/manual transmissions, reverse gears using a synchronizer? Or was it just that particular car, a Ferrari I think it was. Aren’t some manual transmissions on older cars configured so that the reverse gears aren’t even inside the lubricated gearbox with the rest of the gears, b/c presumably of so few miles driven in reverse?


#2

On the three manual trans cars I had before, I would have to engage a forward gear to stop the clutch disc before engaging reverse. I would imagine that some manuals still have an un-syncronized reverse, but my six-speed Nissan Versa seems to have a synchronized reverse, as I do not have to take any steps to stop the clutch to engage reverse in this car. I don’t know why anyone would design a trans with reverse outside the lubricated part of the case…That would seem to be asking for trouble.


#3

I’m unaware of any modern manual trannys without synchronized reverse gears.

The days of reverse gears being in a separate case go way, way back. I’d forgotten that ever existed at all until you mentioned it. I recall reading about it existing in the early days of automobilia, but I can’t recall ever actually seeing one.


#4

The manuals I drove (up through '83 GTI) did not have a synchronized reverse.


#5
I would have to engage a forward gear to stop the clutch disc before engaging reverse.

I had to do that on my late 70’s VW Rabbit too as I recall. It seems like if I owned that reverse-gear-grinding Ferrari, and the alternative was either rebuilding the transmission to replace a reverse synchronizer, or just putting the transmission into first before selecting reverse, that would be an easy call.

The days of reverse gears being in a separate case go way, way back.

For some reason I think some years of the old air cooled VW’s were configured like that, but I did a quick search and can’t find any links to confirm it. Might just be a case of my geezer-brain-itus … lol …


#6

Manual transmissions I’ve been into do not have reverse synchronizers as they’re not really needed due to straight cut gears and the fact that going into reverse is usually done at a dead stop.

If a transmission grinds going into reverse that’s generally caused by an iffy clutch or a faulty pilot bearing in the flywheel or crankshaft as the case may be.
As to the air-cooled VWs the reverse gearset is internal to the transaxle case just like everything else.


#7

My 2002 Miata does not have a synchronized reverse. Why would any transmission have that?


#8

Well, I guess then that I’ve learned something today!


#9

In manual transmissions the synchronizer is the part that slides along the hub on the output shaft to engage the selected gear. Except for very old transmissions from the '60s and earlier that actually moved the low/reverse gear itself EVERY manual transmission I’ve ever seen used synchronizers.

Most people here are confusing this with the synchronizer blocking ring, which is the part of the synchronizer assembly that helps reduce / eliminate the grinding and clashing of gears during shifts. Commonly called “Synchromesh” this part would be useless on reverse.


#10

Well, then we have a difference of naming - what you call the ‘blocking ring’ is what does the synchronizing. Without it that gear would not be synchronized, like reverse, and first gear in older transmissions.


#11

Well, then we have a difference of naming - what you call the ‘blocking ring’ is what does the synchronizing.

No, not really. “Synchronize” means “to cause to occur at the same time or rate”. The synchronizer engages both the hub attached to the mainshaft and also the selected gear, forcing them to operate at the same speed. The blocking ring simply blocks the synchronizer from engaging until the synchronizer and the gear are at the same speed.

Not what “i’m calling it”, by the way. My term come from the GM manual for the Muncie 4 speeds.


#12

So is reverse ‘synchronized’ in recent transmissions? I say it isn’t, like you say 'this part would be useless on reverse".


#13

“Synchronized”? Depends very much on your use of the word. If you’re asking can you select that gear without clashing the answer is “no”. If you’re asking if it has a synchronizer the answer is “maybe”. Some manual transmissions use a sliding idler gear to engage reverse, some use a synchronizer.

To say that modern transmissions do not have a synchronizer on the reverse gear is incorrect, and that is what the original post was about. To say that reverse gear is “synchronized” is also incorrect, because of what “synchronized” is defined as.


#14

On the three speed, column shift manual transmissions on the cars I owned that were made in the late 1940s through the mid 1960s didn’t have synchronized first gear, let alone a synchronizer on reverse. I remember learning how to double clutch so I could shift into low gear when the car was moving. What I found ironic is that the 3_speed transmission on the Ford Falcon was not synchronized in first gear in 1964,_yet the full sized Ford with the three speed did have a synchrnized low gear.


#15

So I will disagree @JayWB - it sounds like you’re saying most/all transmissions can ‘clash’ when going into reverse. That is my definition of a non-synchronized gear. I don’t care what the parts list calls it, really. A synchronized gear won’t clash, a non-synchronized gear will. So T&R’s answer to the caller was wrong - the reverse gear was clashing because of something else, not a worn/bad synchronizer.


#16

You are, of course, free to disagree if you like. You can call it a potato if you like. The fact of the matter is that you are disagreeing with the manufacturer as to the name of the part, not with me. T & R were referring to the manufacturer’s name of the part.


#17

No, they were stating the clashing was caused by a worn synchronizer. No ‘synchronizing’ takes place with the reverse gear, therefore their diagnosis was wrong.


#18

I was surprised to hear that reverse gear would even use a synchronizer, since you are almost always at a complete stop and the engine at idle rpm before shifting into reverse. Is that a common thing w/manual transmissions, reverse gears using a synchronizer?

George’s original post asked if reverse used a synchronizer, as shown above.
The answer is that some do and some don’t.


#19

OK - what one use a synchronizer? Are you saying they have a synchronized reverse (no clashing)? If it clashes, it’s not synchronized, regardless of what the part list says.


#20

This is an exploded view of a Borg-Warner 3 speed, unfortunately without names for the parts:
http://www.amccf.com/tech/new/tranny_six_T-14.jpg

6.080-2 is the synchronizer sliding clutch and hub
6.090 is the blocking ring
6.144-2 is first speed gear
6.144-3 is reverse gear

The description I found for this transmission refers to 6.080-2 as a sliding clutch collar.

This

is a not particularly good image of an exploded view of another manual transmission, and illustrates the fact that in some cases the sliding clutch and hub, etc. is called a synchronizer.

Combine the two and you have the fact that the sliding clutch and hub assembly used on low / reverse (and in fact on any speed / gear) can in some cases be known as a “synchronizer”.

You appear to be hung up on the use of the word “synchronized”. I’m saying that the transmission uses synchronizers. That’s all I’m saying.