Allison tt series transmission issue

[zlssefi]

Hey guys,

Years ago i bought a TEREX 7231 BA wheel loader with the two speed allison tt2000 series transmission in it. It has been a good machine for many years. After this past snow storm one of my operators told me that it was very slow in 1st gear and reverse, but 2nd gear seems more normal speed wise. The only thing ive had time to check so far was to verify the complaint and to check the clutch pressure on the dash which appears to be normal in neutral, 1st, 2nd and reverse. Im going to drop the filter and fluid tomorrow to start looking into this but do these symptoms ring a bell as to what the issue might be? Just seems odd that both 1st and reverse are equally slow.

Thanks in advance!

 

[Dave Neubert]

The transmission uses the same 1st gear clutch pack for forward and reverse you have range clutches 1st and 2nd and directional clutches forward and reverse

 

[zlssefi]

A little update. Today i dumped the oil and cut open the filter. There is very minimal metal both in the sump and in the filter pleats. A stall test showed zero psi converter pressure but im thinking that gauge may have been junk. I will double check tomorrow. When i drained the oil after the test it was very aerated as well.

 

[zlssefi]

Today i also dissasembled the main pressure regulating valve in the valve body. According to the manual it says a weak or broken main spring could cause low converter out pressure. The springs look good, trimmer plug looked good. The main regulating valve did have one scuff on the side and it was a bitch to get out of the bore. Any chance this could be the issue? The book also references lube and converter pressure regulating valves. Does anybody know if those are located where they can be cleaned and checked while in the machine?

 

[zlssefi]

A few more updates. Today i got a new gauge and verified my converter pressure. It runs between 50 and 65 consistently in any gear. The loader has plenty of torque as it can get into a pile and fill the bucket while spinning the tires while digging. The big issue here is speed, everything it does is at half the speed that it used to do it. The manual states that there is a 1st and 2nd turbine in the torque converter and it shifts automatically between the two. Does anyone have any experience with these??

 

[56wrench]

Just a guess but does your parts book show if the torque convertor can be taken apart? If it is a two-stage convertor, there MAY be an overrunning( sprag) clutch on a stator that is either slipping for the high range turbine or a sprag that is locked up for the low range turbine and not releasing as it tries to switch to high range. If the convertor is a one-piece welded assembly, you may have to find another convertor or a specialized shop that can cut yours apart to fix it

 

[zlssefi]

Im going to dig into the manual today to find this info. Im 99 percent sure it shows the converter put together with a ton of bolts so i assume it can be taken apart and repaired. Im hopeful that its something like this as there is no metal in the oil like something came apart.

 

[Rustyfender]

I have been told the 2 speed sprag will either lock up in low range giving you torque and low speed, ( as your situation) or as mine is locked up in 2 nd range giving me speed and low torque.

 

[zlssefi]

Here is the breakdown of my converter. Would i be wrong to assume that the stator (Item15 ) would be the same as a sprag?

 

[Birken Vogt]

No specifics, but in the automotive world the stator is a thing with fins that redirects the oil from the impeller (driven by the engine) to the turbine (driving the rest of the transmission) in such a way as to create torque multiplication at low speeds/high loads. The stator is pushed backwards by the oil flow and it is locked in place by a one way clutch (sprag). After the vehicle begins to gain speed, the stator is just in the way, so it is allowed to rotate freely in the other direction by the same clutch.

If the sprag clutch is freewheeling, it will be hard to take off. If it is locked up, the converter will get hot when things are moving at speed.

 

[zlssefi]

No specifics, but in the automotive world the stator is a thing with fins that redirects the oil from the impeller (driven by the engine) to the turbine (driving the rest of the transmission) in such a way as to create torque multiplication at low speeds/high loads. The stator is pushed backwards by the oil flow and it is locked in place by a one way clutch (sprag). After the vehicle begins to gain speed, the stator is just in the way, so it is allowed to rotate freely in the other direction by the same clutch.

If the sprag clutch is freewheeling, it will be hard to take off. If it is locked up, the converter will get hot when things are moving at speed.

Ok, im just trying to wrap my head around this so i can go after the correct part. Im not seeing any one way clutch in this parts breakdown. Does the stator control what stage the torque converter is operating on? IE low range ( 1st turbine) vs high range (2nd Turbine)? Im guessing that all of the shaft speed is controlled by the torque converter, meaning other than manually shifting the transmission shifter to low or high gear the shaft speed can be increased or decreased by the converter depending on speed and load conditions?

 

[Nige]

If the sprag clutch is freewheeling, it will be hard to take off. If it is locked up, the converter will get hot when things are moving at speed.

If the converter is equipped with a sprag clutch and it is not locking then in my experience the machine won't move. All the loader will do when the operator tries to move it is bog the engine down. It's hard to tell from that illustration but it certainly doesn't appear as though the stator has a sprag clutch.

 

[Rustyfender]

There is a post a few years ago about Case W24B Allison transmission parts that might interest you

 

[zlssefi]

There is a post a few years ago about Case W24B Allison transmission parts that might interest you

I actually did come across that post. The slow symptom matches up for sure. Yet i dont think my transmission is slipping per se. I can spin the tires while loading the bucket with dirt. Im really torn on this one because the machine isnt worth a huge investment. The torque converter can be dissasembled in the machine as it is divorce mounted and i can access the converter housing by removing a driveshaft then all the accompanying torque converter parts. Getting the actual converter housing off of the trans housing might pose a decent challenge unless i remove the cab.

 

[Rustyfender]

That is exactly where I am at, but as of right now my engine is out so that makes it easier. And like yourself my machine is not worth the investment, but when fixed I know that part should be ok lol.

 

[zlssefi]

So ive done some more reading in my manual and the service manual lists a freewheeling clutch assembly which " locks the 1st or 2nd turbine to the output shaft based on load requirements " per the manual. Im thinking this freewheel clutch (item 14) is the issue.

 

[zlssefi]

That is exactly where I am at, but as of right now my engine is out so that makes it easier. And like yourself my machine is not worth the investment, but when fixed I know that part should be ok lol.

do you have your transmission open yet?

 

[Rustyfender]

No not until the weather gets warmer up here in Canada

 

[zlssefi]

For what its worth ive done a bunch of digging on this. I have found the parts for my application, about 950 bucks for a complete " freewheel clutch" unit. If your transmission is divorce mounted from your engine you can remove the torque converter housing and get to this part with the transmission stll in the machine. Just food for thought.

 

[Rustyfender]

Have you taken yours apart yet?