Drive train binding & TPS
 

Replaced faulty transmission in my SVX with a 4.44 from another SVX (originally from a Legacy). Later swapped the rear diff to solve shuddering problem. We didn't know the trans was from a Legacy until after it was fitted.

That all runs sweet.
But, it binds up when turning on concrete. Typically Subaru AWD problem which I understood was fixed by replacing a solenoid in the transmission.
The transmission shop who swapped my trans tell me they replaced the solenoid when they swapped the trans. They looked at the car again and told me the TPS required adjustment, which they did.

Adjusting the TPS seemed to improved (but not solved) the problem for a few weeks, but it seems to have got worse over time.

Was the trans shop dreaming or is there really a relationship between TPS and the transmission ?

Thanks

Re: Drive train binding & TPS
 

I'm not an expert on what car has which numbers, but it sounds like your front and rear differentials have different ratios. If that is the case, then as well as binding when turning, you are also putting a great deal of stress on the center differential even when going in a straight line.

Re: Drive train binding & TPS
 

If you don't have a serious mismatch problem, such as mentioned above, I would suggest putting some Lubegard ATF protectant in with your tranny fluid. The stuff has worked miracles for many people with a binding center diff, including myself on my old legacy outback. It is not only great for the tranny but it tends to loosen up sticky valves. Unlikke what some people say, not every additive is snake oil. This stuff is the real deal as are all of their products.

Re: Drive train binding & TPS
 

I see you are in New Zealand; should I take that to mean the transmissions you are talking about are either Australian market or JDM?

The gear ratio is programmed into the TCU. When you swap in a transmisison with a different gear ratio and don't reprogram the TCU to match the TCU miscalculates the speed reading used for all the most important calculations and table look ups it does. It shifts at the wrong speeds, it looks up the line pressure from the wrong table cells, and it miscalculates and looks up wrong values for the all wheel drive function.

In the US where the transmissions use a multi-plate transfer clutch for the all wheel drive binding isn't as much of a problem as the shifing at the wrong speeds and running the wrong line pressure; as a result, a fair # of people drive around without reprogramming their TCU and without knowing any better. (100% of people who go from that state to getting their TCU properly programmed can't believe they were foolish enough to drive their cars without the propperly programmed TCU after they see the difference.)

I've had a couple of European customers who installed European VTD transmissions with 4.44 gear ratios. They both had binding and shifting issues and came to me. In both cases a custom ROM programmed to match the 4.44 gear ratio solved their problems. I've done both the earlier models built on the UK market FF firmware and the latter models built on the UK MS firmware. So if you have an Australian market transmission and car with the same speed sensors as the European market I have firmware ready to go for you. I haven't modified the gear ratio in a JDM firmware before so if your car and tranmission are JDM I don't have firmware sitting here ready to go but it shouldn't be a problem to make.

Re: Drive train binding & TPS
 

It's JDM. The trans came out of another SVX, so they did the conversion on it. First thing I'll try is to swap the TCU from the donor car.
I'd be surprised if that solves it as I doubt anyone here would have been aware of the problem when that original conversion was done 5 years ago.
So quite likely I'll get back to you for a firmware upgrade.
How does that work ?
Do you send a ROM to me and I find a talented soldering iron operating to swap it out ?

Re: Drive train binding & TPS
 

I've sent an email to ecutune.com. I guess that's going to end up with you anyway. Look forward to hearing back from you.

Re: Drive train binding & TPS
 

Dealership adjusted TPS (they commented that it was very badly adjusted) and now binding fault is solved.
I'll still put new ECU in, but good to know that TPS is a possible cause.

Re: Drive train binding & TPS
 

Excellent, good to know for sure.

Re: Drive train binding & TPS
 

Shane - good to hear that you might have fixed your issues with the binding.