4th Gear Grinds while downshifting

[muthkw25]

Hi Everyone,

I am trying to diagnose the concern with my transmission and wondered if someone can help shed light on the matter.

When I am shifting up through the gears from 1st through 5th, there is no grinding. Very smooth. But if I am in 5th gear and want to downshift to 4th, there is some massive grinding. But it only occurs within certain parameters.

For example, if I am on a level road and I am in high or low, if I want to downshift to 4th gear, if I am going more than 15 mph or the rpms are above 1500, it grinds hard into 4th. I always make sure there is enough time to downshift and I have even tried double clutching and it still does it. If I am on flat ground and I am going below 1500 rpms and or 15mph, it does not grind.

If I am on a hill with the truck and I get to about 1600 to 1700 rpms, I can downshift to 4th and will not get any grinding whatsoever. It almost feels if there is more of a load, it won't grind, but on flat terrain it will. My problem with waiting that long to downshift is, when I am on steep grades, I have to immediately go to 3rd gear or the truck will come to a hault. I am wondering if its my driving, if the speedometer is off and is why its grinding (because I am going faster than what 4th states) or if its fourth gear. Like I said, it happens only in this gear for both high and low range. I guess if I am on flat ground and I am only going 10 mph, I really don't need to downshift to 4th, but if I am at the crest of a steep hill and I want to downshift to help ease the speed of the truck, I should be able to do so without the grinding that occurs.

Anyone else have this issue? Any help on this matter would be greatly appreciated.

 

[gungearz]

Are you power shifting or using the clutch...? Have you adjusted your clutch to the TM's...? Do you split shift or have it in high range all the time...? It could be that your not waiting long enough to downshift and your rpm range is still to high.... You do know the gauges in these trucks are all not accurate... Right...? I'm a driver of a split shift 10 speed on a day to day basis.... I don't use the clutch, just to stop and go. On the other hand, my deuce don't like to be power shifted into gear (although I still can do it)... With my deuce, I almost have to wait for the rpm's to drop down to idle before I can downshift... I leave it in high and don't split shift cause I'm never loaded... No problems upshifting...

 

[sandcobra164]

I'm in somewhat the same boat. When mine's cold and the oil is thick, it can go into 4th without issue. When warm, it won't go into 4th unless you wait about 4 seconds and then it won't grind. I normally shift around 2,200 to 2,300. I know that my truck needs a new synchro on the 4th gear. While I'm in there, I replace the bearings and other synchros. I now drive my truck like the OTR or over the road truckers do. I use the clutch when coming to a stop and getting underway. When getting underway and ready to shift into 4th, I ease off the throttle slightly to make it easy for the truck to come out of gear, ease off the throttle even more to drop the engines rpms in neutral and pull the shifter into 4th without a sound. For downshifting, I ease off the throttle so i can pull easily out of 5th, increase throttle slightly and pull the shifter into 4th. It's an old technique called "rev matching". Alot of older folks perfected it as alot of cars came with non-synchronized transmissions back in the day. Heavy Trucks as in Class 8 rigs took alot longer to get synchronized transmissions and that's why alot of truckers to this day only use a clutch when stopping and starting their rigs. It'll take a little getting used to but I can do it without even really thinking in my Deuce now. Perhaps I got some practice when I drove a Commercial Rig for a few months for a Forestry Service. That rig was beat to heck and didn't have a synchro left after 800,000 miles of abuse on dirt roads and tight trails by previous drivers. I got to where I could shift that truck like it was a new tight rig. I do the same with my Deuce with worn out synchros.

 

[mobileauto2000]

When I first got my truck I had problems with grinding gears on down shifts. Also had problems shifting into seconded gear all the time. Drained out the GL5 and went to 40w motor oil and over a few weeks all these problems went away. I think the GL5 is just two slick for the synchros in some transmissions. The synchros work like clutch's to slow down or speed up the gears so they mesh. The friction modifiers in the GL5 can cause to much slip for them to work. Not all transmissions are effected by it. But the trans was designed to be filled with motor oil not GL5 so I would try a fluid change before any major repair. Also a miss adjusted clutch will almost always affect lower gears first. So if its only 4th it most likely won't be the clutch.

 

[muthkw25]

It was my driving. I figured it out. I was going to slow between 4th and 5th and if you let the truck slow to 1500 rpms on its own, then you engage the clutch and pull back to 4th and no grinding occurs. I also blip the throttle in between shifts to match the rpms to keep from the sudden jerking motion. Thanks everyone for the help.

 

[Diecorpse]

I am starting to have issues with mine, never did before. Doesn't matter what gear I'm in, but if I have been driving a while, I here a lot of grinding noises. I'm pretty sure it's the clutch slipping because I feel it when it does or does not engage properly. I also noticed that I leak oil from the bell housing plug. Is this my rear main going out, and the oil making the clutch slip? I plan on checking my clutch out tomorrow. How is it taking the tranny out, removing the clutch and pressure plate and replacing the rear main seal? Any tips that I can do for the time being until I fix the problem to aid in better function of the clutch? Thanks in advance.