D6N transmission problem

[jrobb]

i'm having problems with my d6n. second gear works fine, forward and reverse. but first gear doesn't. it gets really bad when you are in the 2r/1f option. when you're in 2r, and go to switch back to 1f, the machine acts like you're pushing on the brake. the mechanic calibrated the transmission, and thought he fixed it. he then changed a modulating valve, and said it was fixed. the dozer is acting the same. any other ideas as to what the real problem is?

 

[Bob/Ont]

Get an oil sample done and look for fine metal. I have a feeling there might be a short in your wiring between two different clutch wires. I have seen this before and after the third trans rebuild for the same clutch wearing out the harness was checked and short found. Manually shift through the speeds and directions and note the speeds that drag and the speeds that run free. If you have a slope to run on helps, when you are not using the clutch with a shorted wire the mach might not run down a slope, shift and use the clutch it might run free. Your trans needs one speed and one dir clutch engaged to drive, if a third clutch drags it will wear out or lock the drive up.
Later Bob

 

[D6 Merv]

Hi Bob; always take a lot of intrest in your replys to peoples problems, you have a wealth of knowledge. When did cat go away from the old bulletproof manuel over hydraulic engagement of its trans clutch packs; and go to this electronic bull for powershift transmissions. ? Would like to know what dozer models were the last to use the non electronic controls. D4 thru to D8 if you don,t mind sharing.
Thanks and cheers from almost the bottom of the world :drinkup Merv

 

[Bob/Ont]

It was during the High Drive tractors. You can tell sitting in the seat, the cable/linkage shift have a lever that you can feel shifting through the detents. The new ones have buttons and switches. New stuff shifts nicer(can be adjusted to) but it also shifts money nicely out of your pocket if you need to hire a guy with a computer to set it up much.
Later Bob

 

[D6 Merv]

Thanks Bob. At a guess did this change around the D6R-2 and D7R-2 ?? Around the same time as the 3306 got replaced by later engines ?
reason I ask is may have to look at a later bigger machine sometime and it will still have the bulletproof 3306 in it for me. but would also like the non electronic trans. So this will probably be a D7H-2 or early D6R. Don,t know enough about the D7R ??
To me out in the real/remote world, the combination of dust/moisture/electronics is just a recipe for trouble.
Thanks for your help

 

[jrobb]

Thanks Bob. I sent your insights to the mechanic. He was as baffled as I was

 

[Bob/Ont]

What happens if you select manually? Get on a hard surface for easy running and try 1&3, F&R avoid second from start up and see how it runs. If it runs free try 2 F&R If it runs free try F 1&2 shift up and down a few times. Then F 2&3 shift up and down a few times. Then try R 1&2 and R 2&3. Comeon back with what you find.
Later Bob

 

[John C.]

I'm kind of wondering if there are pressure taps for each range? A cross shorted harness will allow pressure on three packs at once which is very easy to see on pressure gauges. That would eliminate all the guess work of traveling the machine looking for freewheel or dragging.

I believe the last manual units I have worked on were H model machines. As I recall the "M", "N" and "R" machines all have the electronics.

 

[tctractors]

The leccy gear selection starts with D6R (the 1 sporting the 3306) D6m's early use rods like D5H gear control, there is some benifit in that you can strip out the transmission (gear box) and leave the diff steer and bevel gear etc still in the tractor.

 

[jrobb]

Tried manual and auto, tried all gears. First is the only problem. It seems to get worse when auto 2r/1f is selected

 

[Bob/Ont]

Tried manual and auto, tried all gears. First is the only problem. It seems to get worse when auto 2r/1f is selected

Am I correct in thinking you experianced some drag in first forward and reverse and it gets worse when you use auto mode?

 

[jrobb]

The drag, per se, doesn't get worse, but the frequency does in auto. I'm hauling it to CAT because the mechanic couldn't get any psi on the first gear...

 

[Bob/Ont]

Good Idea, From what you say I can't condemn any clutch as dragging but am sure there is one.
Later Bob

 

[jrobb]

Thanks Bob. I'm sure I'll be picking your brain again in the future

 

[tctractors]

I have not done a transmission in a D6N but if its like the D6M unit with a few bits of electrical tack on the control your problem is easy fixed as all your drama is in the front of the transmission, the plates wear out fast on 1st gear, giving to much travel on the piston (No oil pressure) plus the Belville Washers break up or wear on the edges, I would fix this chariot on site not a problem.

 

[Chisumtrail]

Did you get the dozer fixed I have one doing the same thing.

 

[overworked]

Yes, you need to check pressures.

 

[overworked]

Just looked at the date, how did you make out?

 

[tctractors]

Some transmissions on the small CAT's dont use oil pressure on 1st speed to activate the clutch, the oil pressure holds the clutch free, the belville spring pack loads the plates to drive if I recall, all the other clutch activation is via oil pressure working on slave pistons, so this point might need checking, I am near sure the D6M transmission is like this, so finding no pressure when selecting 1st speed is a good thing?
I think.
tctractors

 

[overworked]

I see, it would be nice if people would update there posts, I have seen modulating valves (6r) with the Allen screw back out and let pressure to packs.