Help needed with Lancer Boss forklift and Borg Warner T12 trans

[Crystal LatticeParticipant @crystallattice86401]

[Crystal LatticeParticipant @crystallattice86401]

Hi,

I'm hoping someone here could help me. We have a Lancer Boss forklift with a Borg Warner T12 transmission. The problem is that the inching valve does not seem to work as expected. With the pedal pressed in and the trans in F, the truck rocks as if the clutch is grabbing and letting go. Once you let go of the inching pedal it moves forward but then the pedal has no more effect and you have to put it in N to be able to stop.

In R, it starts going immediately regardless of the inching pedal position.

The forklift was standing for many years and we replaced the trans fluid before doing any testing.

The two theories we have is that the clutch plates are rusted and thus have too much friction and can not slip.

The other theory is that the oil is too thick or there is a restriction in the clutch piston orifice which causes the pressure to build too quickly and cause the clutch to engage fully without much control.

The last theory makes more sense because putting the trans in N, enables you to again start with the rocking motion in F with the inching pedal depressed. The pressure to the clutch is dumped back to the tank when the trans is in N, this is according to the hydraulic circuit diagram.

 

 

There are various ports on the transmission case for what we presume are to check the various pressures in the circuits. Unfortunately none are labeled so we can not use any of them. Any info on this would also be very welcome.

A service manual for this transmission or something very close would be appreciated as the only document we have is a parts breakdown we obtained from a company that rebuilds these units.

 

Thanks in advance!

 

[MonomanParticipant @monoman]

You might find you will get more information from the MadModder site. There are people on there who are solving these problems (almost) every day. **LINK**

Many members are experts at recovery old, and not so old, equipment back to use.

[I.M. OUTAHEREParticipant @i-m-outahere]

If the inching valve sort of works in forward but not at all in reverse that would indicate to me that the issue is the transmission and not the inching valve .

Forward and reverse in an auto trans is selected by directing hydraulic pressure to either of the two clutch packs or possibly a band inside the transmission and as you unit is only single speed the clutch packs / band for 2nd and 3rd may not be installed .

If the only way you can stop it once you have released the pedal is to seleect neutral it would suggest the toque converter or fluid flywheel is seized and you are trying to use the inching pedal to disconnect the drive and the fact that it goes into reverse and takes off would indicate this . The reason that putting in neutral sort of resets this is because hydraulic pressure is used to drive the clutch pistons back out releasing the pressure on the clutch pack , it also is used to move the spool valves back and forth in the metering block. If it is slamming into gear there are dampening pistons in the metering block that when the hydraulic pressure is applied to the clutch pack these pistons are forced into thier cylinder against spring pressure taking the shock loading out of the system so they could be seized . While the internals of the older transmissions are not overly complicated you have to know what you are doing especially with clearances and end float – too tight and it will bind up and the tinyest piece of dirt in the metering block where the spool valves run will at best cause them to stick – at worse it can score the valve or housing causing it to stick and this is usually throw it away time !

The last auto i rebuilt – a turbo 350 for a 4wd about 12 years ago was a learning experience ! I think i spent more time making tools to knock bushes in than i did putting the damned thing back together – after that experience i started using a reputable transmission shop .

The clutches in an auto are either engaged or free they don't operate like the clutch in a manual car so when you put an auto in drive the first gear pack will engage and the torque converter will slip and when you push the accelerator pedal the engine revs a little and causes the torque converter to apply a driving force from the motor to the transmission .

I would suggest you pull the transmission out and get it rebuilt by a transmission shop .

 

 

Edited By XD 351 on 25/07/2018 19:34:14

[Crystal LatticeParticipant @crystallattice86401]

Someone else also suggested the torque converter. But, the hydraulic diagram shows the pressure from the pump T'ing of to the inching system and the torque converter. The inching part of the diagram is:

pump->inching valve->Forward/reverse clutch valve(basically a seat interlock)->FNR selector valve-> clutch packs

In the torque converter side there are two regulator valves: Pressure regulator valve and Converter regulator valve.

So if the inching valve does not let the clutch slip, what is the purpose then? My understanding is the clutch piston has a small orifice in, thus if oil in is less than what can leak out, clutch is disengaged. Releasing the inching pedal allows more fluid in and the clutch moves forward. Doing this in a controlled manner will give "clutch control".

Unless the pressure is so high and the opening and closing so crude that it is like you say, either in or out. But how does one do fine control of the movement?

Again, without knowing the exact location to measure pressures, we can only assume the pressure regulator is not doing its thing based on what you have explained. We made a new gasket for the valve body and also cleaned it out. Nothing fancy, a few spools and springs. It is on the list of things to take apart again and check for any blockages. Unfortunately the history of the forklift is unknown, but judging by all the backyard mods and missing parts it seems it had a hard life, so anything is possible inside the torque converter. Could there be mechanical issues with the torque converter or is it mostly fluid pressure/metering issues?

I watched a youtube vid on torque converters to educate myself a bit on the inner workings and it would appear the only component whose function changes with relation to pressure is the lockup clutch. So, high pressure = lockup = no smooth pull away?

[Howard LewisParticipant @howardlewis46836]

Reading the above, it would seem that the Torque Convertor is not the problem. Otherwise, the problem would exist in Reverse as well Forward.. Lock up clutches usually operate when the output shaft reaches a certain preset speed

Possibly pistons, or valves, are sticking with gummy oil, after having stood for so long.

Is there a filter in the circuit that needs replacing?

Taking the lazy man's way out, it is just possible that repeated attempts will free things off, rather in the same way that the brake bands on an epicyclic gearbox can be adjusted by toggling in and out of gear.

Would draining and refilling with clean oil improve matters?

Edit for another thought:  Is it possible that any hoses may be breaking up internally, and acting as unwanted one way check valves?b

Just idle thoughts.

Howard

Edited By Howard Lewis on 28/07/2018 14:57:59

[Chris Evans 6Participant @chrisevans6]

As you have already changed the oil could it be worth adding an oil systems cleaner ? these are available from good industrial oil distributors. It may just free things up, if not it is a lot of work but still cheaper than a second hand truck.

[Brian Sweeting 2Participant @briansweeting2]

Just a thought on your oil change. How much oil came out first against design capacity? How much did you put in?

[Crystal LatticeParticipant @crystallattice86401]

Thanks for the thoughts guys!

To answer some questions:

The oil in the trans seemed and smelled fine but was somewhat low. we had to drain it to fix a leak and also fixed the strainer in the bottom.

No filter just a fine stainless mesh.

There is only one mark on the dipstick, no min max. We also do not know what the design capacity is.

The only external hose to the trans is a metal one. The other two to/from the cooler is hydraulic type hoses so doubt they will have issues.

We adjusted the leverage of the inching pedal (the linkages/fulcrum were all missing so had to be made up) and it seems to work now. In F the forklift just sits there with the pedal in or out. Once the revs are increased with the pedal out, it starts moving forward. Pedal in or ease up on the revs causes it to stop/slow down. Reverse is still a bit touchy. When in Reverse with pedal in it slowly crawls backwards, when the pedal is let go, it runs and with pedal in again, it slows down. It does not seem to let go completely. Could just need a bit of exercise to work better?

This was all without the brakes working properly yet. We fixed the brakes and now you can stop when going forward but reverse is still a bit unsafe as even with the brakes applied it wants to crawl back. This is with activating the inching pedal which in turn activates the brake pedal.

The "synchronization" of the two pedals with regard to the amount of travel as well as the inching valve free play and brake adjustment would appear to solve the "dead band" between activating inching and activating braking and thus eliminate the "freewheeling". The only problem is we have no documentation or experience with this and then there is also the inching pedal leverage which we made up so not sure if this is correct ratio or not.

Any comments/suggestions of the adjustments are still welcome!

Anyways, thanks again, saved us from removing the transmission, for now…

[MCGUIRE IRVINEParticipant @mcguireirvine72564]

I have a Wiggins forklift with the same BW T12 and am having similar issues with the inching pedal making zero difference in engagement. I do have a service manual for the transmission, if you're interested.The troubleshooting section doesn't have anything pertaining to the inching valve not reducing clutch engagement pressure.

I will say, it's worth taking the transmission apart just to see how the dual clutch setup works, it's pretty cool. There's a set of counter rotating shafts driving a pair of clutches attached to a double flywheel drum setup.

I have not put on gauges to verify line pressures yet, similar to your situation, I figured I'd get the brakes working before doing a whole lot else.

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