A4LD Tranny-Sluggish downshift.
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Freshman User
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A4LD Tranny-Sluggish downshift.
Happy Holidays everyone!
Very difficult to downshift while in OD or D. She'll go up the gears just fine, but she'll want to stay in OD and she'll lug in OD down to 17mph while slowing. If I need her to downshift while on a slight grade, she refuses to 4-3 shift or even 3-2 shift unlesss I stand on the gas pedal. Starts from 1 and upshifts just fine, its the downshifts that are mule-stubborn to convince to go.
Ideas?
Specs: 1991 shorty automatic with 167K miles, 2WD, changed every 50K (so
I'm 16K into this fluid). Cold not a factor.
Thanks for the input!
Merry Christmas!
Very difficult to downshift while in OD or D. She'll go up the gears just fine, but she'll want to stay in OD and she'll lug in OD down to 17mph while slowing. If I need her to downshift while on a slight grade, she refuses to 4-3 shift or even 3-2 shift unlesss I stand on the gas pedal. Starts from 1 and upshifts just fine, its the downshifts that are mule-stubborn to convince to go.
Ideas?
Specs: 1991 shorty automatic with 167K miles, 2WD, changed every 50K (so
I'm 16K into this fluid). Cold not a factor.
Thanks for the input!
Merry Christmas!
Freshman User
Joined: May 2003
Posts: 26
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From: Hawaii
Might Be This
Throttle Position Sensor check the voltage at the middle wire, key in the run position but with engine off. You should get (Closed Throttle- 0.4 Volts) (Wide Open Throttle- 5 Volts) it is critcual that you have this wide range of voltage or your Aero will act dumb "dead spots" when you give it just alittle.
My throttle response was alittle sloppy felt sluggish. Then I checked the voltage at the TPS (Closed 1 Volt, Wide Open 4.3) That was the problem for me.
Check what nighthawk said, there is a Modulator on the passenger side of the transmission with a vacuum line going to it. Pull the vac line off if fluid drops out of it, its bad replace it. Also small kine bonus on the modulator, there is a screw somewhere on it tighten it one turn this will help the tranny hold a gear a little bit longer. This is good for launching it up slight grades, keeping your MPH steady.
My throttle response was alittle sloppy felt sluggish. Then I checked the voltage at the TPS (Closed 1 Volt, Wide Open 4.3) That was the problem for me.
Check what nighthawk said, there is a Modulator on the passenger side of the transmission with a vacuum line going to it. Pull the vac line off if fluid drops out of it, its bad replace it. Also small kine bonus on the modulator, there is a screw somewhere on it tighten it one turn this will help the tranny hold a gear a little bit longer. This is good for launching it up slight grades, keeping your MPH steady.
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Freshman User
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Thanks!
Well, the best tranny shop in Akron, Ohio (Richard's Garage) checked the symptoms and he saw what I meant. Tranny is in great shape with one issue: hard to get to downshift, likes to lug around and rumble the engine.
He checkedthe replacement modulator from 90k (has 170k now) and it was fine. Only thing he could do was flush and clean out the VB at $150. He rally didn't want to do it as he felt it would come back with no real fix and possible start screwing up the seals...
Overall... no fix, so...no charge.
If the above works, I'll give him a heads up and a sawbuck for his trouble, and a GREAT BIG THANK YOU to you.
He checkedthe replacement modulator from 90k (has 170k now) and it was fine. Only thing he could do was flush and clean out the VB at $150. He rally didn't want to do it as he felt it would come back with no real fix and possible start screwing up the seals...
Overall... no fix, so...no charge.
If the above works, I'll give him a heads up and a sawbuck for his trouble, and a GREAT BIG THANK YOU to you.
Elder User
Joined: Aug 2005
Posts: 996
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It sure sounds like the modulator to me. Just because the modulator is not leaking, fluid in vacuum line doesn't mean it is in spec. I believe the problem is the modulator or its hydraulic circuit. the modulator is what tells the trans how hard you are pushing on the pedal, other than full throttle detent downshift which works.
Remember flushing is not terrible unless the filter isn't changed, then it is terrible. slightly dirty fluid is ok, plugged filter is terminal. witness honda automatics that have no filter other than a bird screen in the inlet.
modulator is cheap and easy to change, I would change this first and pass on the flush for now.
ken
Remember flushing is not terrible unless the filter isn't changed, then it is terrible. slightly dirty fluid is ok, plugged filter is terminal. witness honda automatics that have no filter other than a bird screen in the inlet.
modulator is cheap and easy to change, I would change this first and pass on the flush for now.
ken
Post Fiend
Joined: Apr 2005
Posts: 5,720
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From: Washington state
Valve body flush is safe if removed from tranny, flushed with a non solvent, ATF only, and reinstalled with new gasket
Allows for pressure and leak testing of valve body operation with proper jig.
suspect the od/3rd servo piston, neoprene diaphram hardened, worn or torn and leaking....line pressure is lower on coasting downshift and with leaky worn servo, slow low pressure band application
replace both servo piston diaphrams, both wear/age at same rate, located on passenger side of tranny, different for different A4LD models, sized by diameter and end plate marked with 2 letter code, best to take in to get correct size
leaking pump seals and/or worn pump will also cause low line pressure especially on coast
loose valve body bolts common cause of erratic shifting performance especially in V6's which are notorious for rough running...tighten valve body bolts to specs on every filter change...
Allows for pressure and leak testing of valve body operation with proper jig.
suspect the od/3rd servo piston, neoprene diaphram hardened, worn or torn and leaking....line pressure is lower on coasting downshift and with leaky worn servo, slow low pressure band application
replace both servo piston diaphrams, both wear/age at same rate, located on passenger side of tranny, different for different A4LD models, sized by diameter and end plate marked with 2 letter code, best to take in to get correct size
leaking pump seals and/or worn pump will also cause low line pressure especially on coast
loose valve body bolts common cause of erratic shifting performance especially in V6's which are notorious for rough running...tighten valve body bolts to specs on every filter change...
Last edited by 96_4wdr; Jan 11, 2006 at 11:53 AM.
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