Symptom diagnosis

[oregondave]

Ok so just had low mileage used tranny installed.

Shifts fine as far as i can tell especially under power.

However, when i'm cruising at low speed in town in 3rd, after accelerating and letting off the gas I get a light "thud". I want to say it's the car shifting back into 2nd or 1st?!

Definitely shifts better than previous trans. No delay going in to reverse, crisp downshift at highspeed.

Thoughts?

[TomsSVX]

Originally Posted by oregondave

Ok so just had low mileage used tranny installed.

Shifts fine as far as i can tell especially under power.

However, when i'm cruising at low speed in town in 3rd, after accelerating and letting off the gas I get a light "thud". I want to say it's the car shifting back into 2nd or 1st?!

Definitely shifts better than previous trans. No delay going in to reverse, crisp downshift at highspeed.

Thoughts?

Is the transmission actually downshifting? First thing to do would be check that your TPS is adjusted properly and that it have a smooth increase in voltage with no drops or spikes as you open the throttle

Tom

[oregondave]

I'm not sure, I don't even know how trannys work when slowing to a stop or idling. I understand the concept of going through the gears as you accelerate and downshifting for power when you hit the throttle, but not so much when you do the reverse.

TPS?

[oab_au]

Originally Posted by oregondave

However, when i'm cruising at low speed in town in 3rd, after accelerating and letting off the gas I get a light "thud". I want to say it's the car shifting back into 2nd or 1st?!


Thoughts?

Not out of the woods yet Dave,
I take it that you have the stick in 3rd, and when you lift the foot, it thuds.
If you watch the taco when this is happening, it may tell what is going on. In 3rd when you lift the foot off, the over-run clutch should come on to give engine braking.

The revs should only drop slightly, if you see the revs drop way down, then jump back up with the thud, it is more that likely to be the Throttle position sensor as Tom says.
The TCU looks for the closed throttle position before the over run clutch is applied.

If the revs just suddenly drop 800 rpm or so, and stay there when you lift off, it has changed back in 2nd.

If you then pull the stick back to 2nd, nothing will happen, as it is there already.
If it does changes back then, it was in 3 rd waiting for the closed throttle position signal.

Harvey.

[oregondave]

Originally Posted by oab_au

Not out of the woods yet Dave,
I take it that you have the stick in 3rd, and when you lift the foot, it thuds.
If you watch the taco when this is happening, it may tell what is going on. In 3rd when you lift the foot off, the over-run clutch should come on to give engine braking.

The revs should only drop slightly, if you see the revs drop way down, then jump back up with the thud, it is more that likely to be the Throttle position sensor as Tom says.
The TCU looks for the closed throttle position before the over run clutch is applied.

If the revs just suddenly drop 800 rpm or so, and stay there when you lift off, it has changed back in 2nd.

If you then pull the stick back to 2nd, nothing will happen, as it is there already.
If it does changes back then, it was in 3 rd waiting for the closed throttle position signal.

Harvey.

OK thanks Harvey. Well explained.

I went to a well respected tranny shop today and went for a drive with an experienced tech there. He described the over run clutch and how it works. He thought the transmission shifted fine and said I shouldn't worry. Perhaps the TPS does need to be adjusted though just to be safe?

If the TPS needs to be adjusted should I take it to them? Does the TPS sometimes need to be replaced? How costly is that?

Thanks guys. Never thought i'd know so much about a transmission (not that I know jack)

[oab_au]

Originally Posted by oregondave

OK thanks Harvey. Well explained.

I went to a well respected tranny shop today and went for a drive with an experienced tech there. He described the over run clutch and how it works. He thought the transmission shifted fine and said I shouldn't worry. Perhaps the TPS does need to be adjusted though just to be safe?

If the TPS needs to be adjusted should I take it to them? Does the TPS sometimes need to be replaced? How costly is that?

Thanks guys. Never thought i'd know so much about a transmission (not that I know jack)

Thats good, do the TPS adjustment, I think there is a 'How to ' on it.

Harvey.

[oregondave]

Just went for a drive to test it out. Couldn't get it to thud. When I get to 3rd and let off the throttle the rpms drop about 800 and slowly drops from there. However, when I drop the lever into 2nd it then downshifts. I have to drop to like 10-15 mph (from 3rd) before I can drop the lever and not have it shift (meaning it already shifted).
What do you think?

[oab_au]

Originally Posted by oregondave

Just went for a drive to test it out. Couldn't get it to thud. When I get to 3rd and let off the throttle the rpms drop about 800 and slowly drops from there. However, when I drop the lever into 2nd it then downshifts. I have to drop to like 10-15 mph (from 3rd) before I can drop the lever and not have it shift (meaning it already shifted).
What do you think?

I would still do the throttle position sensor adjustment. You have nothing to lose.

Harvey.

[oregondave]

OK, will do. Will any harm result if i don't do it right away?

Tom what do you think about my road test results?