Cat 977H Traxcavator transmission problem?

[lnpirr]

Greetings all,

I have a Cat 977H (1963) that has been gradually having issues with both forward/reverse in that it seems to slip when under load - worse when machine is cold. Checked oil levels/quality, checked filter - guessing this is a 'wet clutch' setup. Oil is not burned, no fragments of clutch packs in filter ... someone told us some of these 977's have an external pump, others internal - appears this is internal. (They said it sounded like there's air being introduced somewhere into the hydraulics of the transmission). Once machine is warmed up sufficiently and can roll - it steers well; not sure if the two are related.

Thanks in advance - hope not to scrap this machine as it runs very well otherwise - does not burn oil, tracks/sprockets still have 60-70% life left - there's no way I could afford a trans rebuild - would be cheaper to scrap it and find a 955 for what I need to do - the 977's overkill for my work.

Larry

 

[dirtfan]

It's good to hear about some of the old machines that are still in use.
I'm not a mechanic but I have operated and helped work on these old machines for a long time. First of all, is this a stick/manual trans or a powershift? The early sixty's were when the first power shifts came on the market. If it is a manual trans. is the clutch in proper adjustment? If it is or if there is no adjustment left, this could be bad news, but a new clutch is not the end of the world.
If it is a powershift, Does the trans system have oil pressure, usually with these older machines you either had enough pressure to put it in gear or you didn't, there was no inbetween. Is the pump working properly (enough pressure?), it's not a lot of trouble to hook up a guage and check the pump pressure. If there is air being introduced into the internal system, sometimes you can overfill with oil and it will start working again, but when you get on a slope it can "kick" out of gear. Try maybe a 20% overfill before you go to the trouble of tearing it down. Is there an oil line internally that might be plugged up with dirt or debri? If it is the clutches that have worn out, sometimes you can tear it down and replace the worn out clutches with out a lot of expense if you are handy with a wrench.
Some of the old H models had only a 2 speed power shift with a high and low. If you have one of these I'm not sure if any of my statements would apply, as I have experience with only the 3 speed powershift.
Good luck, and I hope you can get the old gal repaired.

 

[Bob/Ont]

They are relative / two speed with high low and the three speed.
Works good untill warm usually means an oil leak.
Works good when warmed up sounds to me like too thick of oil.
Try changing it to TDTO 30 and see if it works better.
Not sure if you did this but check and clean the suction screen in the bottom of the trans with oil drained.
Look for a cover, round with square like a keyhole. If memory serves me.
Later Bob

 

[Forest]

It's good to hear about some of the old machines that are still in use.
I'm not a mechanic but I have operated and helped work on these old machines for a long time. First of all, is this a stick/manual trans or a powershift? The early sixty's were when the first power shifts came on the market. If it is a manual trans. is the clutch in proper adjustment? If it is or if there is no adjustment left, this could be bad news, but a new clutch is not the end of the world.
If it is a powershift, Does the trans system have oil pressure, usually with these older machines you either had enough pressure to put it in gear or you didn't, there was no inbetween. Is the pump working properly (enough pressure?), it's not a lot of trouble to hook up a guage and check the pump pressure. If there is air being introduced into the internal system, sometimes you can overfill with oil and it will start working again, but when you get on a slope it can "kick" out of gear. Try maybe a 20% overfill before you go to the trouble of tearing it down. Is there an oil line internally that might be plugged up with dirt or debri? If it is the clutches that have worn out, sometimes you can tear it down and replace the worn out clutches with out a lot of expense if you are handy with a wrench.
Some of the old H models had only a 2 speed power shift with a high and low. If you have one of these I'm not sure if any of my statements would apply, as I have experience with only the 3 speed powershift.
Good luck, and I hope you can get the old gal repaired.

Hi Dirtfan. I just bought an old 977H and seems most everything works pretty well. However, it will not go into HIGH. Has no trouble going into FORWARD-LOW and FORWARD REVERSE. Do you think this could be a linkage issue? The folks that sold it to me thought it probably was.