Cat 988A - 3rd gear slipping

[Double N Hay]

I bought an old scrap Cat 988 87A machine and found a used D343 to bring the beast back to life. Should be a good machine for me loading some gravel, and occasional dirt around the farm. Now I am afraid I am losing 3rd gear forward. It is slipping, or seems to be. Is this going to take out 1st and 2nd gear? I can honestly live with out the 3rd gear, it won't be fun moving it, but I can live with it. Is this like other powershift transmissions, where it shares pressure with another clutch pack? Any help is appreciated? Blaine

 

[Nige]

The clutch for 3rd gear doesn't share anything with any of the other gears, it just does third gear both forward and reverse. If the 3rd gear clutch had a bad enough leak in it then it could affect the direction clutch by starving it of oil. If you can live without 3rd gear then don't use it.

It would also be an idea to remove the transmission suction screen and check it for the presence of burned-up clutch material. That would give you an indication if you have a clutch starting to fail. If the screen is clean then the problem with your transmission could well lie in the control valve or the cables that control it. Have you tried removing the speed control cable and shifting the speed spool manually..?

 

[kshansen]

The clutch for 3rd gear doesn't share anything with any of the other gears, it just does third gear both forward and reverse. If the 3rd gear clutch had a bad enough leak in it then it could affect the direction clutch by starving it of oil. If you can live without 3rd gear then don't use it.

It would also be an idea to remove the transmission suction screen and check it for the presence of burned-up clutch material. That would give you an indication if you have a clutch starting to fail. If the screen is clean then the problem with your transmission could well lie in the control valve or the cables that control it. Have you tried removing the speed control cable and shifting the speed spool manually..?

As I recall the 87A models do not have cable shifts but solid rods. Older version had a range shift by lifting up or down on shift lever, newer versions had the rotating handle to shift 1-2-3 with lever forward and back for direction.

That being said I would agree to making sure the linkage is all adjusted right and that when in 3rd gear it is 100% in position. Also that there is not any excessive slop in the linkage.

As I recall there is a "centering" adjustment that is done by adjusting the yokes on the ends of the spools inside the top of transmission. Not exactly easy to get to the top of transmission to access the cover as first you need to remove the seat and then depending on the vintage probably remove batteries and battery box floor. Then work with head between your knees to get the cover off.

But would have to agree one of the first and easiest things to check would be the magnetic filter/suction strainer. If it is half full of clutch facing material adjusting linkage may not be worth the effort!

 

[Double N Hay]

Ok thanks. For the record I do have the older one with the up for forward and down for reverse. I will check the suction screen. Do I have to drain the trans to do that? We just got it filled. Thanks again

 

[lantraxco]

I'm not familiar with the A model, does it have the disconnect/inching pedal on the left brake like the newer ones? If it does make sure that the heel of the pedal is clear of mud and debris, the pedal moves freely and there's absolutely no residual air pressure being held. Bit of a reach but I have seen it happen, chisel some hard mud out from under the pedal, solve a transmission slip/brake drag problem.

 

[kshansen]

I'm not familiar with the A model, does it have the disconnect/inching pedal on the left brake like the newer ones? If it does make sure that the heel of the pedal is clear of mud and debris, the pedal moves freely and there's absolutely no residual air pressure being held. Bit of a reach but I have seen it happen, chisel some hard mud out from under the pedal, solve a transmission slip/brake drag problem.

Not to be a wise a$$, but never saw a 988A(87A) with air brakes! That being said mud under the brake pedal could still mess with the transmission function. Been too many years since I work on an 87A vintage machine, to be sure how the suction strainer is positioned but most Cats you can pull them without loosing much oil. I know it has to be located on the right side of the machine near the say 3 inch suction line that goes to the pump by the motor mount on that same side.

Found a picture, not very good but it does show the magnetic strainer #32 by the red arrow. That would be on the right side of the transfer case at the front, suction line #10 comes off the back of the case. By the way that suction line #10 has been known to have holes rubbed in it from a hydraulic hose in that area!

 

[Bob/Ont]

Yes the 88 and 92's had hyd brakes from a pump, the 769 trucks used an air over hyd system, similar but used air chambers to pump the hyd piston. Straight air brakes stopped with the 980 back then. Anyway the power shift barrel can be removed for clutch repairs fairly easily, leaving the transfer case in place.
Later Bob

 

[lantraxco]

Right, 980 B's and C's with air over hydraulic? were what I was thinking of I guess, only ever worked on a couple of the 88's...

 

[kshansen]

Right, 980 B's and C's with air over hydraulic? were what I was thinking of I guess, only ever worked on a couple of the 88's...

Can't say the same here the 988's 87A's were our main pit loaders for many years. Ten when the 988B's can out the 988A's were held on to as the ones that loaded out of the stock piles for customer trucks. Can't think of any part of the 87A's I have not had the pleasure of knowing first hand!

 

[lantraxco]

Can't say the same here the 988's 87A's were our main pit loaders for many years. Ten when the 988B's can out the 988A's were held on to as the ones that loaded out of the stock piles for customer trucks. Can't think of any part of the 87A's I have not had the pleasure of knowing first hand!

Ah, there's just something about the familiarity of an old lover you've been intimate with so many times

 

[kshansen]

Ah, there's just something about the familiarity of an old lover you've been intimate with so many times

Just glad those old Cats can't talk because I probably used a few not so nice words at times while being intimate with them!