trans issues

jjanak79 · #1 10-02-2010, 07:51 AM

so i have been driving my car a lot lately on the interstate. (brand new certified tranny with mobil 1 fluid in it) It seems like on the interestate when i'm steady at 75 it will slip and then go back into 4th and then overdrive. what would cause this? it doesnt do it around the city at all! i can go 55 and nothing will happen. but around 75 to 85 it will. it seems like its getting confused.

dcarrb · #2 10-02-2010, 08:20 AM

My silver SVX used to "gear hunt" badly at a particular speed/RPM range. Replacing the throttle position sensor solved the problem.

dcb

Huskymaniac · #3 10-02-2010, 08:41 AM

Quote:

Originally Posted by dcarrb

My silver SVX used to "gear hunt" badly at a particular speed/RPM range. Replacing the throttle position sensor solved the problem.

dcb

Listen to this man jj. I have found him to be very accurate and helpful!

1986nate · #4 10-02-2010, 09:26 AM

Quote:

Originally Posted by dcarrb

My silver SVX used to "gear hunt" badly at a particular speed/RPM range. Replacing the throttle position sensor solved the problem.

dcb

yep, one of the typical symptoms of a bad TPS.

My laguna on occasion does the same thing.

Hocrest · #5 10-02-2010, 10:14 AM

Yes, check the adjustment of the TPS.

When you had the trans installed did you have an external cooler added? If the ATF gets too cool it will unlock the torque converter.

jjanak79 · #6 10-02-2010, 10:20 AM

i do not have a external cooler installed yet on it. i have one that i'm gna put on it with a filter kit and i'm gna run a gauge. but a tps sensor is 254 bucks at my parts store in my town!

Hocrest · #7 10-02-2010, 10:23 AM

Checking the adjustment is free

http://www.subaru-svx.net/forum/showthread.php?t=53959

jjanak79 · #8 10-02-2010, 10:32 AM

and this will solve the problem? and thank you btw

Hocrest · #9 10-02-2010, 11:12 AM

Possibly?? If the TPS is adjusted out of spec it will shift odd...

If the TPS is bad it will shift odd...

If your ATF gets too cool the TC will unlock...

You're description is a little vague, 4th and OD is the same. There are a few possible causes. Personally, when troubleshooting I try for the cheap/easy fixes before I go for more expensive fixes.

No matter what happens, an ATF temp gauge should be one of your next moves.

1986nate · #10 10-02-2010, 12:00 PM

Quote:

Originally Posted by Hocrest

You're description is a little vague, 4th and OD is the same.

Dave, 4th and OD are not the same. OD is 4th gear with the torque converter locked up. There is a big difference in how the car performs when it is in 4th and in 4th with the TC locked up. TC locking and unlocking is a symptom of failing TPS on almost any vehicle that has one. Often times a TPS won't throw a code or like on my 94, it will once in a great while, or flicker for just a second. On OBDII cars, it is made that if it ever gets a TPS code, it will lock it in until a hard reset.

I just replaced one in my parent's Durango that I thought had issues with the TC slightly for months (with the TC still engaged, RPMs rising about 100 or so, not the usual 3-400 when it is not engaged). When it finally threw a SEL, it would hold 1st gear until 3500 RPM before shifting and shifted very hard under very light throttle and would not hold the TC locked under any amount of throttle.

Hocrest · #11 10-02-2010, 12:35 PM

I thought that OD was the 4th gear, signifying any gearing that is below 1:1. The gearing in 4th and 4th w/ TC Lock is exactly the same.

I know the difference between 4th and 4th with TC Lock. When driving on the highway in the winter I can watch my trans gauge and tell you exactly when my TC will unlock. But I fixed the issue on Melis's car by adjusting the TPS into spec.

1986nate · #12 10-02-2010, 01:40 PM

Quote:

Originally Posted by Hocrest

I thought that OD was the 4th gear, signifying any gearing that is below 1:1. The gearing in 4th and 4th w/ TC Lock is exactly the same.

Huh?
Just watch the tach. When your TC locks up, the RPMs drop about 300 or so. Also, when accelerating, the RPMs don't rise much at all compared to when it is unlocked. The gear ratio remains the same as far as the gear, but when the TC locks, it essentially holds the transmission at the same speed as the engine.
That is what overdrive is. Overdrive is controlled by the TC ultimately, not the transmission. Back in the 80's, you had many 3 speeds and 3 speeds with overdrive depending on what car company you look at. The OD is simply caused by the Torque converter locking up.

I hope I explained that halfway decently. I can never put thoughts to paper and don't have the technical terminology.
Also not trying to argue, or clog up this thread.

And in response, yes, adjusting the TPS can help it. I've adjusted mine on my laguna some and it fixed some issues but a few others have creeped up. The SEL stays off more often now but I've still got to check it out some more.

kwren · #13 10-02-2010, 02:04 PM

your information is always appreciated, Nate!

Keith

jjanak79 · #14 10-02-2010, 03:10 PM

what its doing is . i'm going 75 miles an hour. I'm running under 2500 rpms. all of a sudden it shifts up and (it feels like its slipping.) goes into 4th like over 2500 rpms. and then settles down under 2500rpms. is that better?

Mike621 · #15 10-02-2010, 03:18 PM

Quote:

Originally Posted by jjanak79

(brand new certified tranny with mobil 1 fluid in it)

Can you bring it back to whoever "certified" it?