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Unable To Shift Gears

micchev99

By micchev99
in Ask A GM Technician

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micchev99 Enthusiast

micchev99

Posted
Posted

I am wondering how to troubleshoot this without actually removing the transmission to inspect the clutch. I am not sure if it is a clutch component or the transmission itself. When the truck is moving, I cannot shift in/out of gear. With the engine off, I am able to shift in/out of any gear. Sometimes when I come to a stop, I can change gears, but sometimes I have to turn off the engine. This started all of a sudden when pulling up to a stop sign. There are also metal-on-metal rubbing noises when I press in on the clutch pedal. Since this began, I have driven it about 4 miles in 3rd gear. The clutch fluid resevoir was full when I checked it at the stop sign.

 

1999 silverado 1500 ext cab, 4.3L, 5 speed, 2WD, 127k miles, with original clutch, trans and fluid.

micchev99 Enthusiast

micchev99

Posted
  • Author
Posted

Also, is there a way to use the VIN to find out which 5 speed transmission it has? There seem to be a dozen RPO codes for 5 speed manuals, the repair book says it is either NV 3500 or NV 4500, and the truck is in the parking lot at work, 45 miles away

Nytemare Senior Enthusiast

Nytemare

Posted
Posted

its 90% chance a 3500...the NV4500 usually came in the HD trucks...its a upgraded version of the old rock crusher (SM465).

 

But yeah...with the VIN a dealership can tell you in like 30 seconds what trans is in it.

 

Chances are if you cannot change gears its hydraulic related...or the pilot bearing is gone...that one would be a 10 dollar part at most...the slave and master...may as well change both isn't really expensive either...125 for the slave cylinder...master is usually around 50 or less.

micchev99 Enthusiast

micchev99

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Nytemare -- thanks for the input. Where would the clutch hydraulic fluid be leaking to? the ground? I guess if there is a clutch fluid leak, then pumping the pedal a number of times would cause a drop in the resevoir level as well. I can check that tomorrow when I go into town. The repair manual calls for DOT3 for the clutch hydraulics and different fluids for transmission itself:

 

NV 3500 -- Syncromesh transmission fluid

NV 4500 -- Syn-torq synthetic transmission fluid

 

Any recommendations on a brand of replacement bearings, etc ... ? I was thinking if it comes to that, I would just get an AC Delco clutch kit for about $350. All the components are original, which means they have 127K on them.

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Nytemare -- thanks for the input. Where would the clutch hydraulic fluid be leaking to? the ground? I guess if there is a clutch fluid leak, then pumping the pedal a number of times would cause a drop in the resevoir level as well. I can check that tomorrow when I go into town. The repair manual calls for DOT3 for the clutch hydraulics and different fluids for transmission itself:

 

NV 3500 -- Syncromesh transmission fluid

NV 4500 -- Syn-torq synthetic transmission fluid

 

Any recommendations on a brand of replacement bearings, etc ... ? I was thinking if it comes to that, I would just get an AC Delco clutch kit for about $350. All the components are original, which means they have 127K on them.

AC Delco is probably the best way to go man. Check Rockauto.com for pricing...I've found them the best.

 

The leak may be an internal leak too. The pressure may just be passing through the slave cylinder and right back into the reservoir. If you can pump the clutch a few times than change gears easily...thats whats going on.

 

This could also be your synchros...but you can usually change gears with the synchros gone, they just grind a little...and they usually don't all go at once.

micchev99 Enthusiast

micchev99

Posted
  • Author
Posted

Nytemare -- I have a bit more information now as I was able to get into town to check on it. Also, I came across a VIN-to-RPO website, which says the trans is

 

MG5 TRANSMISSION,MANUAL 5-SPEED(GETRAG) GETRAG 5-SPD M/TRANS(MG5)

 

which the owners manual says is the one without the "low gear" and requires

the syncromesh transmission fluid. There are no signs of fluid leaks from the flywheel to the drive shaft, its all dry as a bone and there is a bit of rust on the flywheel.

The clutch resevoir is full (the diaphragm under the reservoir cap just touches the fluid), but there seems to be two liquids in the reservoir. I took a couple photos which I can post when I get home. In all of the following scenarios, pumping the clutch pedal multiple times (as one might do with a slow brake fluid leak) has no effect.

 

I drove the truck about 5 miles this afternoon and spent a total of about an hour investigating the clutch/transmission behavior.

 

When driving, I found I could shift in and out of gears 1,2,3,4 without using the clutch. When doing so, no noise is heard and everything runs smooth. I am wondering if this means that transmission is ok, and that the problem is in the clutch system.

 

If I come to a full stop, then there may or may not be problems getting underway again. Sometimes it will shift into any gear using the clutch without having to stop the engine. Other times it will not shift into any gear at all, regardless of how far down I press the clutch pedal, and then I need to turn off the engine. With the engine off, I can shift in and out of any gear without using the clutch. This gives me two options -- restart the engine in neutral or in gear.

 

When I restart in neutral, sometimes I can shift into gear, other times not. When I am able, there is usually screeching / rubbing noises when I then shift from neutral to 2nd gear. The noise continues and changes as I let out the clutch pedal. But sometimes a restart in neutral will still not let me shift into gear. In this case, I turn off the engine yet again, shift into 2nd gear, and restart the engine.

 

Starting the engine in gear works only some of the times, because sometimes the truck just lurches because the transmission presumably is still engaged despite the clutch pedal being fully (or partially) depressed.

 

When I can get the engine restarted in gear, there is only a faint noise which would not be heard if the heater or radio was on. Other times, it causes the same screeching / rubbing noise that continues and changes pitch as I release the pedal.

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Nytemare -- I have a bit more information now as I was able to get into town to check on it. Also, I came across a VIN-to-RPO website, which says the trans is

 

MG5 TRANSMISSION,MANUAL 5-SPEED(GETRAG) GETRAG 5-SPD M/TRANS(MG5)

 

which the owners manual says is the one without the "low gear" and requires

the syncromesh transmission fluid. There are no signs of fluid leaks from the flywheel to the drive shaft, its all dry as a bone and there is a bit of rust on the flywheel.

The clutch resevoir is full (the diaphragm under the reservoir cap just touches the fluid), but there seems to be two liquids in the reservoir. I took a couple photos which I can post when I get home. In all of the following scenarios, pumping the clutch pedal multiple times (as one might do with a slow brake fluid leak) has no effect.

 

I drove the truck about 5 miles this afternoon and spent a total of about an hour investigating the clutch/transmission behavior.

 

When driving, I found I could shift in and out of gears 1,2,3,4 without using the clutch. When doing so, no noise is heard and everything runs smooth. I am wondering if this means that transmission is ok, and that the problem is in the clutch system.

 

If I come to a full stop, then there may or may not be problems getting underway again. Sometimes it will shift into any gear using the clutch without having to stop the engine. Other times it will not shift into any gear at all, regardless of how far down I press the clutch pedal, and then I need to turn off the engine. With the engine off, I can shift in and out of any gear without using the clutch. This gives me two options -- restart the engine in neutral or in gear.

 

When I restart in neutral, sometimes I can shift into gear, other times not. When I am able, there is usually screeching / rubbing noises when I then shift from neutral to 2nd gear. The noise continues and changes as I let out the clutch pedal. But sometimes a restart in neutral will still not let me shift into gear. In this case, I turn off the engine yet again, shift into 2nd gear, and restart the engine.

 

Starting the engine in gear works only some of the times, because sometimes the truck just lurches because the transmission presumably is still engaged despite the clutch pedal being fully (or partially) depressed.

 

When I can get the engine restarted in gear, there is only a faint noise which would not be heard if the heater or radio was on. Other times, it causes the same screeching / rubbing noise that continues and changes pitch as I release the pedal.

 

That all sounds like a busted slave cylinder/throwout bearing/or pilot bearing. My money is on the Slave though...I would bet the slave has an internal leak and is bleeding across, and back into the res. That would explain the different looking color.

 

Either way...you are going to have to pull the trans out to fix either one of them.

 

Pilot bearing...10 bucks....ACDELCO Part # CT1082

Slave and throwout bearing....90 buck...ACDELCO Part # 386433

Master and reservoir....80 buck...ACDELCO Part # 385533

Clutck kit.....340 buck....ACDELCO Part # 381472

 

All parts are available from other manufacturers at lower prices too. I tossed the Clutch in there as it may be on its last legs too...but if its good I would leave it alone.

micchev99 Enthusiast

micchev99

Posted
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Posted

Thanks again, Nytemare. Here is a photo of the clutch fluid reservoir. I though the main fluid was essentially black, maybe the flash causes it to appear grey. I'll look at the resevoir tomorrow.

 

If there is an internal leak, will one see some turbulence in the resevoir while another person presses the clutch pedal? Is it ok to operate the clutch when resevoir cap is off?

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post-61238-1263184621_thumb.jpg

micchev99 Enthusiast

micchev99

Posted
  • Author
Posted

And here is a shot of what I think is the clutch plate, and i'm guessing that the green circle points out a bit groove that is still left on the friction surface. The oil is from the engine.

post-61238-1263185460_thumb.jpg

post-61238-1263185460_thumb.jpg

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Nytemare Senior Enthusiast

Nytemare

Posted
Posted

Yeah man...there looks to be quite a bit of friction material left....your pretty easy on a clutch aren't you.

 

You may or may not see turbulence happen...be warned though...it may spray at you. And its fine to operate it with the cap off...the cap just keeps the fluid in the reservoir, and dirt out.

micchev99 Enthusiast

micchev99

Posted
  • Author
Posted

Any comments about the two fluids in reservoir, one appears grey, the other clear/yellow/green? or the grey sludge on the interior wall of the reservoir?

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
Any comments about the two fluids in reservoir, one appears grey, the other clear/yellow/green? or the grey sludge on the interior wall of the reservoir?

Could be water in the fluid, could be grease from the internals of the slave cylinder. Its definitely not supposed to be grey. The yellow is what color its supposed to be...a yellow or a brownish color.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

my brain hurts ,change the gd clutch m/cyl and pull the tranny and replace the hydraulic slave cyl already ,holy smokes,

 

the going down the road pressure is 100% mechanical (pressure plate spring pressure),if it slips in gear driving the truck then it is ....the clutch disc,

 

if the tranny cant shift under stress......slave or m/cyl or leak

 

rant off

 

sry,couldn't stand it anymore lol

Nytemare Senior Enthusiast

Nytemare

Posted
Posted
my brain hurts ,change the gd clutch m/cyl and pull the tranny and replace the hydraulic slave cyl already ,holy smokes,

 

the going down the road pressure is 100% mechanical (pressure plate spring pressure),if it slips in gear driving the truck then it is ....the clutch disc,

 

if the tranny cant shift under stress......slave or m/cyl or leak

 

rant off

 

sry,couldn't stand it anymore lol

LOL Rob....

 

I thought your new year resolution was to not go off on stuff like this...LOL

:cool::D:lol::lol:

LeoS41280 Enthusiast

LeoS41280

Posted
Posted
Any comments about the two fluids in reservoir, one appears grey, the other clear/yellow/green? or the grey sludge on the interior wall of the reservoir?

 

 

Looks like oil to me. There is no grease in the slave cyl. The spot on the disk you've circled is normal. Do you see a spot like that on the other side of the disk? Looks kinda thin to me. I belive it will have a pilot bushing instead of a bearing.

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