Help with CAT 950B transmission

Hey Folks,
Thanks to all that answer these posts and make the rest of us look smart in front of the boss. We have an old CAT 950B wheel loader that is in good shape but recently it sporatically started to lose both forward and backwards power which we believe is somewhere in the transmission. It is all of a sudden, as if a transmission valve decided to stick or not function. When cold, it move great. Every once in a while, when hot, the motor pulls fine - plenty of RPMs and it sounds like lots of power - no skipping or missing - but the machine will not go uphill or over any type of road blockage such as a hole or a rock. Anything can stop its forward or reverse movement. When it happens, we can't even get it up on the low-boy for transport.
Being an X-automotive trany guy, two things come to mind here: 1.) transmission slippage; 2.) torque converter failure. I have sort of ruled out transmission slipage because the trany oil does not smell burnt at all. Also, it has been doing this for a while and my thought is that by now, the clutch packs would have been burnt up and not work at all. (By the way, it does this in all forward and reverse gears/speeds.) But, you let it cool down and the machine goes back to working normal. So, I have been thinking about the torque converter.
Can any one tell me if the torque converter in these CAT 950Bs have the ability to fail (not multiply torque) and then start working normally? I put a pressure gauge on the converter outlet pressure (Test Point D) and I am getting 55psi which is in line with the spec. I could really use some help here before I tear this trany out. Again, thanks to all for sharing their knowledge and experience!:scool

Chris

You need to check main pressure before going after that transmission. I can't remember where the trans pump is mounted but I'm sure it is on the back of the engine. Cat usually put a plug in the top of the pump somewhere where you can hook a gauge into. Someone here will be able to tell you what pressure you should have there.

Check the gauge when you shift it into gear. Watching the gauge should tell you a little of what is going on inside the box.

Good Luck!

Jonn C., Thanks for the help here. I will do this.

Chris

Remember to always check screens and filters first!

If clean go ahead with transmission pressure check and this can be done easily at the top of the filter housing. The pressure should be approximately 400 PSI and you should run it through all four speeds in both directions while watching the gauge to see if one particular speed is dumping however this seems unlikely since you have power loss in forward and reverse and it is unlikely that you would simultaneously loose two clutches.

That torque outlet pressure seems ok but it must be done in stall condition with hot oil otherwise misleading.

Hey AmerIndependent,
Thank you for the info. it was very helpful. Filters and screens are clear. We did a service on the tranny when the problem occurred. We hooked the gauges up to the "E" and "F" test ports and the "E" (speed pressure) was only around 100 psi. It appears that we need to pull the hydraulic controls and check the modulation relief valve the the operation of the load control valve. Do you know if the valve body can come off while the tranny is still in the vehicle? We are trying to pull it out and we have some space issues. Thanks again for all the help!

Chris

We’ve pulled them before by removing the seat, tight but should be doable.

Have you checked your neutralizer? Might be wise to disconnect the line coming into the side of upper transmission case first.

These valve’s rarely go bad but there is a plastic orifice screen in there that can be clogged.

Hey A/I,
Good call! I was thinking of this because if that left side brake valave ever leaked and pressure was held in that line, the transmission would be stuck in a sort of a neutral position. So I pulled that line and found no air pressure so it seems that this area is OK. It seems the P1 (speed pressure) hovers right around the 75-80 psi range rather in neutral or in gear. I believe this is the pressure for the neutral position which is sort of interesting. I'm surprised the machine moves at all with this low pressure. Could it be that maybe we are not getting the full movement on the direction selector spool valve? I don't believe this lose of pressure is caused by an internal leak because all speed positions and both directions give the same P1 and P2 pressures. So, I'm focussing on the pressure feed end most likely some where in the valve body.

I'll keep you posted on what I find. What ever it is, it was intermittent and now it is all the time. Not sure what can cause this situation. Broken springs in valve bodies are permanent so I'm doubtful of this. I've seen checkballs do this but it is rare. So as I go through this trany, I'm really worried that it still could be a seal some where inside the trany because of the problem being intermittent at first. Again, I'll let you know what I find if I ever get lucky enough. If you think of anything else, give a shout. Thanks again for all the support. We really appreciate your time!

Chris

Well Chris, you are becoming quite the transmission expert!

Correct you are about neutral pressure and that’s what it is designed to do for example if you were to start the machine while in gear (another thing to check) as it’s supposed to maintain protective lube pressure while not allowing the machine to move. You might try playing with the shifter to make sure the cable is not stretched causing you not to find true neutral.

We have done thousands of these transmissions and valve wear is extremely rare so I’m skeptical on that theory and that spool movement is mechanically controlled by a cable so you should feel that when shifting (also doubtful) but as an experiment you could disconnect the cables and try shifting manually with vise grips.. I’m still thinking it might be that plastic orifice but I guess you’ll know soon enough. We have these valves in stock that we can offer to loan to you just to try it out if needed. Unlikely to be in the transmission as like I said before there are six separate clutches and it’s unlikely they could all have failed….there should be a common denominator somewhere.

A/I,
Great info - thanks! Just wanted to update you on something we found. We still had the magnetic screen out and inside the screen we found 2 plastic pieces that look like a broken washer of some kind. If I was to guess at the diameter of this plastic ring, I would say 1.5". Not sure if it is anything but I have a picture of it but can't figure how to attach a picture to a post.
While I have you here, can you explain the comment you made a few posts back about the plastic orifice screen that may be clogged at the neutralizer valve? If that clogs, do you think that could cause what I think is a "neutral condition" I am experiencing?
Also, thanks for the compliment. I used to do automatic transmissions back in my prime days (70s). Now, I'm a shop manager and I pretend to know what I'm doing. Thanks again for all this info and your time. I love learning this stuff and with the age of all of our equipment, you don't meet up with many people that know this older stuff.

Chris

Uh oh….that plastic piece sounds like a planetary thrust washer which can be very bad if allowed to run to destruction. We can positively identify it if we have a good photo.

The plastic orifice is located under the pressure control valve and the entire valve block must be removed in order to get to it.

As far as old stuff is concerned these transmissions really haven’t changed much over the years except for electronic shifting verses cable shift and a few speed sensors here and there so DON’T CALL ME OLD!!!

Don't call you old - got it. Thanks for the info. I'll let you know what I find. How do you attach a picture to this forum? If you give me an e-mail, I'll send a picture. It sounds like we have to pull the trany. Oh well. Thanks for the info and I'll update you on what we find. Thanks again for everything. We really appreciate all this. (Not coming to the Carolinas for anything in the next week or so, are you?)

Chris

Send pics to: sales@americanindependentinc.com

What kind of time do you have to get this machine up and running? I may be able to find an exchange transmission for you, or even better, possibly rebuild yours.

950b, looking one 950b loader to buy in case you are interested

looking one 950b loader to buy in case you are interested