G56 jumps out of gear coasting downhill with engine brake on...

[truckmen]

And then, we have the transmission "issue".

Popping out of gear while coasting downhill in 6th particularly with the engine brake on.

This only happens when I am coasting down a hill and only in 6th gear.
I can coast down in 5th and never have this. I also accelerate easy or hard in all gears and it does not pop out of gear.
Could this be indicative of a bad synchro for 6th only?

 

[RVTRKN]

Is your truck new, and how many miles do you have on it? Read this thread and maybe there’s a trend on the newer trucks. https://www.turbodieselregister.com...-2017-Manual-Transmission-popping-out-of-gear

 

[NIsaacs]

And then, we have the transmission "issue".

Popping out of gear while coasting downhill in 6th particularly with the engine brake on.

This only happens when I am coasting down a hill and only in 6th gear.
I can coast down in 5th and never have this. I also accelerate easy or hard in all gears and it does not pop out of gear.
Could this be indicative of a bad synchro for 6th only?

This could be a number of things. How often do you change oil and what do you use? When you change the oil do you see any metal contamination? Bearings play a big part in jumping out of gear, especially the pocket bearing. It is in the joint where the input shaft and main shaft couple together, it is also right next to 6th gear. Due to the angle cut of the gears, coast will push them apart, power will pull them together, thats why coast pops out, pulling don't.

It could also be a bad shift fork pad or a bad shift fork. They are not one piece like most shift forks. They are actually 2 piece stamped steel, spot welded together. The weld can break. When you change the clutch the transmission needs rebuilt or an exchage unit if time is a factor, and it usually is when the truck is for busness hauling.

Here is a link to some good info on the G-56: http://r.search.yahoo.com/_ylt=AwrTHQYxfOxZxHsABg5XNyoA;_ylu=X3oDMTEya244MGdiBGNvbG8DZ3ExBHBvcwMyBHZ0aWQDVUkyQzNfMQRzZWMDc3I-/RV=2/RE=1508699313/RO=10/RU=http%3a%2f%2fblog.genosgarage.com%2fwordpress1%2fwp-content%2fuploads%2f2012%2f05%2fTDR71_RebuildingTheG56.pdf/RK=1/RS=.WYo_rr2QJ.5_U7sqA5m4LnDLzs-

Nick

 

[truckmen]

Is your truck new, and how many miles do you have on it? Read this thread and maybe there’s a trend on the newer trucks. https://www.turbodieselregister.com...-2017-Manual-Transmission-popping-out-of-gear

Hello RVTRKN,

Mine is a 2014 with 192,000 miles on it.

 

[RVTRKN]

Hello RVTRKN,

Mine is a 2014 with 192,000 miles on it.

What oil do you use, with ATF you’ll never see the gold color from the bronze syncro’s wearing. The honey looking Mobil trans fluid I use will show that bronze color easily, if the syncro’s are wearing.

With the miles your reporting, I would probably replace it. Set it up with a proper cooling system as well. I believe the aluminum case G56 gets softs when hot, causing improper gear meshing.

 

[truckmen]

What oil do you use, with ATF you’ll never see the gold color from the bronze syncro’s wearing. The honey looking Mobil trans fluid I use will show that bronze color easily, if the syncro’s are wearing.

With the miles your reporting, I would probably replace it. Set it up with a proper cooling system as well. I believe the aluminum case G56 gets softs when hot, causing improper gear meshing.

Hey RVTRKN,

I changed the oil only once at 80,000 and went with gear oil.
I can also tell you exactly when an what caused the popping out of 6th...I loaded a 4th car in Bishop, CA about 2 Months ago and stupidly chose to run across Death Valley during the day. The transmission got very hot expanding the aluminum case. An expensive lesson as I could have just run the long way round via Barstow.

 

[NIsaacs]

Hauling the loads you do and getting 192K miles out of the oem clutch shows driving skill/care. I really doubt Death Valley was the cause, trucks run the desert southwest daily in hot temps. One oil change in 192k miles is more likely the cause.

Nick

 

[truckmen]

Hauling the loads you do and getting 192K miles out of the oem clutch shows driving skill/care. I really doubt Death Valley was the cause, trucks run the desert southwest daily in hot temps. One oil change in 192k miles is more likely the cause.

Nick

No, no ... one oil change in 80,000 (which is bad enough, I know) ... oh wait, that's right ... holy cow! 110,000 miles since. Miles sure fly when your having fun.

 

[RVTRKN]

I just noticed gear oil, that is to heavy a oil.

 

[Too Tall]

I had that once years ago. It was a bad bearing.

 

[Hoefler]

Most likely a broken detent spring on that shift rail.

 

[Mariner2010]

Had this issue on my 2014 g56. I found that adding a weighted shift knob helped it stay in gear much better. I went with Uinta Diesel's option. Amazing quality!