Cat 735b rock truck , no power to move while loaded

[Kels306]

I've got a cat truck , has the c15 , engine runs good , checked intake and exhaust system , bypassed fuel system , its got around 80 psi fuel pressure , no engine related codes , drives good not loaded but when stalling it with the brakes applied it'll only rev to 850 , lifts a full load no problem so not thinking it's engine related , I was wondering if anyone has had an issue like this , I've also checked to see if I was getting pressure at the converter lock up modulating vale and I'm not getting any so it shouldn't be locked on thanks

 

[Nige]

With those symptoms my money is on a failing/failed freewheel clutch in the torque converter stator.

How many operating hours does the transmission/converter have on them.?

 

[Nige]

I've also checked to see if I was getting pressure at the converter lock up modulating vale and I'm not getting any so it shouldn't be locked on

Unless it’s commanded by the powertrain ECM you won’t get anything at the LUC valve. This would only be in 1st speed above a certain ground speed or immediately after a shift in anything from 2nd speed upwards. Have you tried measuring pressure at the LUC while running the machine around empty.? That will confirm that it is being signalled correctly.

 

[Kels306]

It's got 15,500 hours , I was just checking to see if that valve was stuck or letting some pressure in

 

[Nige]

It's got 15,500 hours ,

If the transmission/converter has never been out before then it’s probably about time it was pulled for overhaul.

I was just checking to see if that valve was stuck or letting some pressure in

If the LUC was engaging when it shouldn’t be then when you engage gear either it would stop the engine dead or the truck would take off like a scalded cat, because an engaged LUC gives you direct drive, bypassing the converter.

Do you have any info on how the freewheel stator in the converter works.? I can post something up if you like. Post a Serial Number for accurate information.

 

[Kels306]

Sure that would be great the serial number is CAT00735CB1N00779

 

[Nige]

Sure that would be great the serial number is CAT00735CB1N00779

Even though it might be wearing 735B decals that's not a 735B, it's a 1st generation 735. Built at the end of November 2006. Production of B models didn't start until almost 3 years after that.

See the attached for the operation of the stator freewheel (one-way clutch) mechanism. If the ratchet, springs, or rollers are worn/broken the stator will rotate "in reverse" when torque converter drive is required and lead to the symptoms you have.

 

[Kels306]

So it'll still drive on flat ground good with nothing holding it back but once it gets loaded or hold it back with the brakes it's not letting it spin so the engine can't rev up , the one way clutch isn't spinning freely right now

 

[Nige]

once it gets loaded or hold it back with the brakes it's not letting it spin

It's the opposite. When the machine is in torque converter drive the one-way clutch is supposed to hold the torque converter stator in a locked position so that the oil from the impeller to the turbine is diverted at the correct angle by the stator in order to provide the torque multiplication effect.

 

[Kels306]

Alright gotcha , so without that being broken or worn out it's trying to work way harder to move the truck , that being said that's why with a load it's not creating that multiplying effect causing the engine to work way harder then it can

 

[Nige]

You got it. If the stator is not firmly anchored in converter drive you loose pulling power.
Transmission out time I think. First maybe take a look at the magnets in the transnmission suction strainer to the transmission pump for any signs of lumps of metal from the one-way clutch. If you find bits of spring or rollers it's nailed on.

 

[Kels306]

I know on our other 735s the strainer is easer to get at in the suction hose but this truck is a year older and doesn't have that , sis is not much help so you know we're that screen is , I had taken the filter out the bottom and there was nothing on that magnet or in the screen , and nothing on the drain plug

 

[Nige]

Is #2 what you're looking for.?
Part of the 245-2766 Pump Drive Group.

 

[Kels306]

This transmission doesn't have that it's the older style with the filter underneath only has the steering and hoist pumps on top

 

[Nige]

Just checked the machine Serial Number. You're right, the transfer case is different to the illustration I posted above.

 

[Kels306]

It's weird with that sis it shows both styles of transmission with that serial number , this one has the pump behind the torque converter, and it shows the transmission removal with this style of trans , thanks for all your help and advice I'll let you know what I find when I get around to pulling it out

 

[Kels306]

So this is what I found , this is where the springs ride

 

[Kels306]

this will be the free wheel

 

[Nige]

Your parts list is going to be pretty long........

We always replaced everything that moved in the stator freewheel assembly. I'm looking at 233-8137 Converter Gp (TCY1-6792). Sorry can't upload an image for some reason.

The list would include items # 24, 25, 28, 30, 31, 42, 53, 54. No second-guessing, just replace them.
With 15.5k hours on the machine it's probably time to rebuild the complete converter.

 

[Nige]

this will be the free wheel

Try rotating the stator in both directions. One way it should click like a ratchet, the other way it should lock but probably won't