3rd gear syncro out- grinding


#1

A 2000 Chevy s10 p/u, 5spd, 2wd with 53000 miles. Is this typical Do the other gears start to gring so replace all syncros at the same time


#2

It’s definitely premature to have trans issues with that low of miles. If you’re going through the trouble of tearing apart the trans you might as well replace all damaged and possibly damaged parts.


#3

Or you could just learn how to double clutch.


#4

While the odds of a possible factory defect at least exists, the likely cause of a grinding gear due to a synchronizer problem is more than likely due to driving habits.
Wear due to shifting into 3rd gear a lot, half-clutching while shifting to 3rd, or driving around as many people do with their hand resting on the gearshift lever can all contribute to a problem like this.

Any high miles or aged transmission that is gone into should be gone over completely; replacing all seals, gaskets, bearings, and anything needed in regards to gearsets and/or synchronizer assemblies.


#5

My last car, the 3rd synchro was bad for years

When shifting from 2nd to 3rd, I just waited a second for the speeds to match, before shifting into 3rd

Wasn’t a big deal


#6

Hi OK:
I’m just curious.
While I don’t endorse driving with a hand resting on the gearshift lever, how does that wear the syncros? Specifically, if one is already in a gear, how will the additional pressure of the gearshift lever cause wear on a syncro?


#7

It won’t unless perhaps you’re applying pressure toward the next gear in preparation to shift.
What generally kills the synchros prematurely is speed shifting, especially when downshifting and especially if the driver makes no attempt to match the speeds of the gears during the shifting process. Slamming the shifter from 5th to 3rd to slow down without touching the gas pedal gives your eyeballs that nice pulled-pork feeling, but it comes with a cost.

Synchros are systems, one for each gear, that have conical surfaces that engage in the beginning of the shifting process and through friction cause the gear being engaged to spin at the same speed as they will be once engaged, but just prior to tooth engagement. That eases tooth engagement and prevents tooth damage. But forcing the system means excess wear on the conical friction surfaces of the synchros and they stop matching the speeds of the gears before engagement, causing grinding. They can also develop a raspy sound when they’re freewheeling.

Bottom line: they wear out due to poor shifting habits. And once they do, you can either resort to having them replaced or learning to doubleclutch, which is just a manual form of rev-matching the gears being engaged. Or you could keep driving as you do until the gears get too torn up to engage or stay engaged.


#8

Maybe you downshift from 4th to 3rd a little quickly? Or bang off 2nd to 3rd shifts? Both will prematurely wear out the syncro rings. If you do a rebuild, replace them all and the bearings, too. Last time I bought a B-W T5 rebuild kit it was about $250. The labor just to rebuild it will be quite a bit more. Once it is apart, you might as well do the full rebuild, there isn’t really any more time involved sine the 3rd gear syncro is the more difficult one to get to. A rebuilt exchange unit may be about the same cost and a better way to go. Techs that can rebuild 5 speeds are rare these days.


#9

For what it’s worth, most of these small truck (and car) 5-speeds were made by Mitsubishi…5th gear was the weak point, not 3rd…Can you shift into reverse without any gear grinding?


#10

Synchronizers are for wimps. Learn to double clutch. I drove an old Dodge–I think it was a 1937 that didn’t have a synchronized transmission. Once you get the hang of double clutching, you will see that there is no need for synchronizers.


#11

@Joe Mario, my reasoning behind the weight of the hand on the lever cause is that when metal contacts metal under pressure there is no oil film and vibrations are transmitted which lead to wear. As this goes on the shift fork and synchronizer sleeve wear which allows more vibration and wear to develop as the synchronizer rings and gears jitterbug around a bit so to speak.

I’ve done a lot of Subaru manual transmision work for gear gnash and/or jumping out of gear complaints and when talking to the car owners the common deonominator seemed to be hand on the shifter; especially on cars driven in traffic and using predominantly 3rd and 4th gears. Most were not aware they were guilty of this habit and I’ve even caught myself doing it on manual transmission cars.

To provide a clearer example, consider Subarus that were manufactured in Japan and shipped to the U.S. by boat. The cars were backed into stalls on the freighter and chained down. Policy was that the car was to be left in neutral but a number were left in reverse.

The rocking of the car due to ocean swells would cause the reverse gear set teeth to wallow around on themselves. This led to varying degrees (some very loud) of whining or growling when backing up. Often this was not noticed until a customer bought a new car and discovered on a higher speed reverse maneuver. This led to a warranty transmission teardown and replacement of the reverse drive, driven, and idler gears.
The point being that those gears were all immersed in oil the entire time on a non-running vehicle and would get absolutely eaten up due to an action that could be compared to rubbing the thumb and forefinger tips together.


#12

@Triedaq‌
But that was back when men were men and women were glad of it. Things have changed and many of us are wearing everything from earrings to bling all over our hands and shifting with our delicate little pinkies while trying to double clutch in our elevated shoes is the last thing on our mind. Getting the hang of double clutching ? Some of us just don’t want to be good at it. We want to be good at matching our slacks to our shirts. Synchronizers ? We can barely “shift” and automatic.


#13

@ok4450‌
Thank you for taking the time to write your explanation. It does make sense


#14

Our 3rd synchro went out around 30k miles. Warranty fixed it. Was the only issue we ever had with that car.