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  #1  
Old 12-09-2011, 06:35 AM
subaru subaru is offline
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hesitation shifting 3rd-4th at low rpm

Hello

Lately the transmission is hesitating between 3rd and 4th in low rpm (2000-2500) This means driving up to 50-55 mph. When adding gas rpm rise very quickly up to 3000 without shifting back. When pullling harder 3000-4000 rpm no problem shifting at all

As I read a lot here, could it be the brakeband?

Thanks for your input

Rinus Slippens
The Netherlands
1992 251000 km blue
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  #2  
Old 12-09-2011, 09:23 PM
oab_au oab_au is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by subaru View Post
Hello

Lately the transmission is hesitating between 3rd and 4th in low rpm (2000-2500) This means driving up to 50-55 mph. When adding gas rpm rise very quickly up to 3000 without shifting back. When pullling harder 3000-4000 rpm no problem shifting at all

As I read a lot here, could it be the brakeband?

Thanks for your input

Rinus Slippens
The Netherlands
1992 251000 km blue
It could be the band.
If it slips going into 2nd it is.
If it does not slip in 2nd, then it is probably low line pressure that is causing it to slip in 3rd/4th, so that it goes back to 3rd, and then back to 4th, that is low line pressure.
4th gear is 3rd gear + the band, when it slips, your back in 3rd.
At the higher rpms the line pressure is high enough to hold.

Harvey.
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  #3  
Old 12-10-2011, 11:54 PM
THE NEW GUY THE NEW GUY is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by oab_au View Post
It could be the band.
If it slips going into 2nd it is.
If it does not slip in 2nd, then it is probably low line pressure that is causing it to slip in 3rd/4th, so that it goes back to 3rd, and then back to 4th, that is low line pressure.
4th gear is 3rd gear + the band, when it slips, your back in 3rd.
At the higher rpms the line pressure is high enough to hold.

Harvey.
Dear Harvey: would you please explain to me how does this gearbox works? specially the part of the brakeband.
how can I determine if my car slips in second? Is it possible to increase line pressure? (line pressure= hydraulic pressure?)
thanks.
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  #4  
Old 12-11-2011, 01:03 AM
Tapani Tapani is offline
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Re: hesitation shifting 3rd-4th at low rpm

Dig into the manuals

http://phantomotaku.com/SVX/

Br,

Tapani
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  #5  
Old 12-11-2011, 08:54 PM
oab_au oab_au is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by THE NEW GUY View Post
Dear Harvey: would you please explain to me how does this gearbox works? specially the part of the brakeband.
how can I determine if my car slips in second? Is it possible to increase line pressure? (line pressure= hydraulic pressure?)
thanks.
Well without straying too far from Rinus's post, I'll expand a bit more.

The band is used to hold the front sun gear still in 1st and 4th. In 1st the forward clutch is on, for 2nd the band comes on also.
If the band is worn, and is slipping, you will find that it will change into 2nd at a higher rpm. The same thing happens for 4th.

When it goes from 2nd to 3rd, the band has to be released, and the high clutch has to be applied, at the same time. If the band is worn, it will release before the high clutch comes on, so the box goes back to 1st and revs till the high clutch grips, this is called “flaring”. This is when adjusting the band can help.

The 3rd to 4th change has the high clutch on for 3rd, and the band is applied also to raise the gearing for 4th. This is when the band can loose pressure and slip, and the box goes back to 3rd.

This usually happens when you are driving slow in 4th with the engine reving about 1500 to, 2500. The low engine rpms that drive the pump is too slow, and the pumps flow will be too low, to provide good line pressure, so the band slips, it goes back to 3rd, this lets the engine rev higher, the line pressure comes back up, and the band grips to goes back to 4th.
I believe this is Rinus’s problem.

This is really a case of a box that is draining too much oil due to wear, and will burn the band up if it continues. It is better to drive in 3rd at low speeds to keep the line pressure up and the load on the box low.

Harvey.
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  #6  
Old 12-13-2011, 07:12 AM
subaru subaru is offline
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Re: hesitation shifting 3rd-4th at low rpm

Thanks a lot everyone, could adjustment of the brakeband be a solution?

Rinus
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  #7  
Old 12-13-2011, 03:10 PM
oab_au oab_au is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by subaru View Post
Thanks a lot everyone, could adjustment of the brakeband be a solution?

Rinus
For the problem that you describe, I don't think it will.
If you unplug the dropping resistor, behind the battery, it will raise the line pressure to max, if this stops the random changing, then it is the low line pressure that is the cause.

You might check the setting of the Throttle Position Sensor, to ensure it is set to 0.5V, and its readings are smooth through the sensor movement.
If it has some worn spots, it will cause the box to change when it gets to a bad spot.

And drive in 3rd around town.

Harvey.
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  #8  
Old 12-14-2011, 08:14 PM
THE NEW GUY THE NEW GUY is offline
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Re: hesitation shifting 3rd-4th at low rpm

put a 100K ohms (1/4Watt) resistor in parallel with a 22 micro farads (16VDC) capacitor (polarized). Then connect this in parallel with the throttle sensor: the positive of the capacitor goes to the most positive wire on the throttle connector (5vdc comming from the ECU).
The negative of the capacitor goes to the output signal wire of the throttle sensor connector. (please confirm the voltage and colors on the wires in the throttle connector. One of them should be ground, other will be 5vdc, the third will change voltage with the throttle position; this is the output to the ecu. with the engine in iddle, the output signal will be around 1.2vdc. The wiring schematic in Phantomaku for this chapter is unaccurate: http://www.phantomotaku.com/SVX/MSA5..._injection.pdf. but it's a reference)

Last edited by THE NEW GUY; 12-16-2011 at 06:52 AM.
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  #9  
Old 12-20-2011, 05:56 AM
subaru subaru is offline
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Re: hesitation shifting 3rd-4th at low rpm

in plain english, do I need a new trans???

Rinus
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  #10  
Old 12-20-2011, 07:45 AM
THE NEW GUY THE NEW GUY is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by subaru View Post
in plain english, do I need a new trans???

Rinus
jajaja.... Test the throtltle sensor. DO NOT REMOVE IT. If it's ok, then add the electronic components I just describe bellow. they're very common and cheap. if the problem continues, then go deeper in tranny stuffs... Did you try unpluging the dropping resistor as Oab au said?

Last edited by THE NEW GUY; 12-20-2011 at 07:49 AM.
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  #11  
Old 12-21-2011, 12:55 AM
subaru subaru is offline
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Re: hesitation shifting 3rd-4th at low rpm

Sorry,

I unplugged the resistor but it seems no difference while driving , except when putting in gear (D or R) it shifts really hard when cold.

The trans is not randomly shifting, only in 4th at 55 mph and adding gas for overtaking it would rev up without speeding but not shift back, only with more gas it would shift back to 3rd
If i work very smoothly with the gas its ok
If I really press the gas it goes like a tornado (still a lovely fast car)
If necessary on highways it shifts from 3rd to 4th at 170 km/h (105 mph)

Is there any pic where the TPS is located? (Found it)

I will measure it


Thanks
Rinus

Last edited by subaru; 12-21-2011 at 01:15 AM.
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  #12  
Old 12-22-2011, 12:36 PM
THE NEW GUY THE NEW GUY is offline
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Re: hesitation shifting 3rd-4th at low rpm

good new: your tranny is OK. replug the dropping resistor.
When was the last time you change tranny oil?
This problem bothers me some time ago.
Cleaning the MAF sensor with a "no residues" cleaner helps a few, but, if problem continues, then do the electronic thing for the TPS.
TPS is located behind the throttle body plastic cover, oposite side of the gas steel ropes.
Do you have the "forced power switch"?
Basically this problem is typical of a bad TPS. Is not the position of the TPS but the linearization of the signal. If you can, change this sensor and problem solved. If you would like to save some money, try the electronic ad I told you before.
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  #13  
Old 12-23-2011, 12:24 AM
subaru subaru is offline
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Re: hesitation shifting 3rd-4th at low rpm

Thanks

All fluids are yearly replaced, I take no risk about that
I use the car only in wintertime, in summer it is garaged as I use my NSU Ro80
The MAF was replaced a few years ago
I will replug the resistor and check the TPS like you said

I can only look into the car in the weekends as is is dark when I leave for work and it is dark when I return home

Rinus

Last edited by subaru; 12-23-2011 at 12:29 AM.
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  #14  
Old 12-23-2011, 11:31 AM
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by oab_au View Post
Well without straying too far from Rinus's post, I'll expand a bit more.

The band is used to hold the front sun gear still in 1st and 4th. In 1st the forward clutch is on, for 2nd the band comes on also.
If the band is worn, and is slipping, you will find that it will change into 2nd at a higher rpm. The same thing happens for 4th.

When it goes from 2nd to 3rd, the band has to be released, and the high clutch has to be applied, at the same time. If the band is worn, it will release before the high clutch comes on, so the box goes back to 1st and revs till the high clutch grips, this is called “flaring”. This is when adjusting the band can help.

The 3rd to 4th change has the high clutch on for 3rd, and the band is applied also to raise the gearing for 4th. This is when the band can loose pressure and slip, and the box goes back to 3rd.

This usually happens when you are driving slow in 4th with the engine reving about 1500 to, 2500. The low engine rpms that drive the pump is too slow, and the pumps flow will be too low, to provide good line pressure, so the band slips, it goes back to 3rd, this lets the engine rev higher, the line pressure comes back up, and the band grips to goes back to 4th.
I believe this is Rinus’s problem.

This is really a case of a box that is draining too much oil due to wear, and will burn the band up if it continues. It is better to drive in 3rd at low speeds to keep the line pressure up and the load on the box low.


Harvey.
part of this sounds like what is happening to me now between 35-43mph the car seems to be confused about weather it wants to be in 3rd or 4th so it goes back and forth until i speed up or slow down...lately i have been leaving it in 3rd until i hit 45mph...
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  #15  
Old 12-23-2011, 08:10 PM
oab_au oab_au is offline
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Re: hesitation shifting 3rd-4th at low rpm

Quote:
Originally Posted by LastSVXintheChi View Post
part of this sounds like what is happening to me now between 35-43mph the car seems to be confused about weather it wants to be in 3rd or 4th so it goes back and forth until i speed up or slow down...lately i have been leaving it in 3rd until i hit 45mph...
I think it is very common, with the high ratio.
The car is designed to do 150 mph in 4th, so asking it to do 35-40mph is asking a lot.
It's not that the car can't do it, the low speed torque is strong enough to do it, but due to the load on the band, and low line pressure, it will eventually die.
I make a point of 3rd till I am running 100kph/62mph, then 4th.

Harvey.
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97 Liberty GX Auto sedan. 320,000Kls.
04 Liberty 30R Auto Premium. 92.000kls.
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