marknessmonster : Clutch or transmission diagnosis: FIXED!

Clutch or transmission diagnosis: FIXED!
Post by marknessmonster on Aug 5, 2006, 7:13pm

UPDATED:
Couldn't find the 715 Mods board, so I hope this fits here...

Specs: GM350 crate, Advance Adaptor bellhousing, Centerforce hydro clutch, and NV4500 tranny (all newer installation).

Problem: Tranny doesn't want to shift into 1st or reverse when not slightly rolling (i.e. 2nd gear nudge forward).

Notes: clutch feels a little soft SOMETIMES; shifts worse when truck has been run awhile on short town trips on a hot day; just started on the last two drives (2 weeks between drives) and was a problem even when first started after short idle time (warm, not hot). This is very sporatic, at least yesterday.

Fix: I would appreciate any insight or diagnostic ideas from you educated guys out there.

Re: Clutch or transmission diagnosis
Post by luckypabst on Aug 5, 2006, 10:22pm

Buy American Guy: you realize that first and reverse are NOT synchronized? Meaning that many times you need the vehicle to move a bit or a quick double clutch to get the gear in alignment for smooth shifting?

Don't swap from forward (any gear) to reverse until the truck is fully at a standstill. It ain't no Toyota.

Chris

Re: Clutch or transmission diagnosis
Post by mikel on Aug 6, 2006, 7:59am

Are you able to shift smoothly when the engine is off? Non synchronized gears are a bit trickier to shift into, as the rotating mass inside the transmission needs time to lose its inertia when you step on the clutch.

Try hinting a shift into a synchronized gear (2, 3 or 4th) and then shifting into 1st or reverse.

Re: Clutch or transmission diagnosis
Post by marknessmonster on Aug 6, 2006, 8:33am

I am able to shift smoothly when the engine is off...after I double-clutch initially.
Typically, when I can't get into 1st or reverse, I have hinted to 2nd with no success. If go 2nd and let off clutch and bump forward it will generally solve the problem into 1st, but reverse is trickier. I may need to experiment more.
The throws in 1st, 5th and reverse are not real smooth with engine off either. Does 5th in NV4500 have a short throw?
I'm beginning to think that the clutch is not fully disengaging. Could it be bottoming-out against the firewall prematurely?

Re: Clutch or transmission diagnosis
Post by mikel on Aug 6, 2006, 10:54am

If you shift from one gear to 1st or reverse (at a stop), the rotating mass inside the transmission should have been at a stop, allowing you to shift smoothly. The fact that when you try this, it still grinds going into those two gears makes me vote for a clutch not disengaging completely.

I would play with the linkage adjustment until you get full disengagement.


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">I am able to shift smoothly when the engine is off...after I double-clutch initially.
Typically, when I can't get into 1st or reverse, I have hinted to 2nd with no success. If go 2nd and let off clutch and bump forward it will generally solve the problem into 1st, but reverse is trickier. I may need to experiment more.
The throws in 1st, 5th and reverse are not real smooth with engine off either. Does 5th in NV4500 have a short throw?
I'm beginning to think that the clutch is not fully disengaging. Could it be bottoming-out against the firewall prematurely?</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

Re: Clutch or transmission diagnosis
Post by marknessmonster on Aug 6, 2006, 11:15am


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">The fact that when you try this, it still grinds...</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

Mikel, thanks for the replies, as you've helped me consider a few things. I should have specified that I am not getting a grind, rather it just will not shift into 1st or reverse on certain occasions. I may isolate this problem to the transmission soon with more help from you and the others folks. Much obliged for everyones help.

Oh, keep it coming if there are more ideas.

Re: Clutch or transmission diagnosis
Post by marknessmonster on Aug 6, 2006, 11:20am

Also, I don't know the exact model year of the NV4500, but isn't 1st gear syncronized? I guess that I can easily go find out. I always thought that only reverse was non-sync in pre-'99(?) NV4500 trannys.

Re: Clutch or transmission diagnosis
Post by barrman on Aug 7, 2006, 8:04am

Did you put in a new pilot bearing? Was the input shaft clean and smooth where it goes into the pilot bearing?

It reads like your clutch just isn't adjusted right. When you do get it in gear, how far off the floor is the pedal before you start to get vehicle movement? If you are just barely clearing the floor before the clutch starts to engage, you are out of adjustment. The same is true for the clutch engaging at the top of the travel, but you don't have the slip problem.

If the clutch is adjusted right, I would lean toward pilot bearing issues.

Re: Clutch or transmission diagnosis
Post by marknessmonster on Aug 12, 2006, 11:25am


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">It reads like your clutch just isn't adjusted right. When you do get it in gear, how far off the floor is the pedal before you start to get vehicle movement? If you are just barely clearing the floor before the clutch starts to engage, you are out of adjustment. The same is true for the clutch engaging at the top of the travel, but you don't have the slip problem.</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

This post by Barrman was right on the money! I spent a half hour this morning adjusting the rod linkage and another half hour testing. The NV4500 tranny now shifts like a truck tranny should...with longer throws and a good click when it FULLY engages, which was previously not occurring. Also, 1st and reverse engagement is now PERFECT.

You're my best friend today Barrman, and I should mention Mikel too, since you were also on the right track. Thanks guys, you saved me from being in a bad mood about my truck's performance.

Also, my donation to the Zone is on its way...money well spent for good advice.