XLTByAccident
Member
- Joined
- January 11, 2010
- Messages
- 37
- Reaction score
- 0
- City, State
- PTown, California
- Year, Model & Trim Level
- '92 XLT
I recently rebuilt a '92 A4LD. The donor came out of the wrecking yard, so previous operation history is unknown. I replaced all the bearings, clutches/steel, bands and the OD planet assembly due to some minor bearing damage to the mating surface. Servo's have been replaced, valve body rebuilt with an A4LD junior shift kit as well as the sonnex booster valve upgrade and installed an end plug kit. I replaced the torque converter (rebuilt one). Pretty much everything you would expect in a good rebuild. I did not replace the 3-4 shift or overdrive solenoids in the VB. They tested fine, so I re-used them. I did not replace the vacuum modulator either. It is holding vacuum and does not appear to leak. Transmission shifts normally under all loading conditions. Kick down works.
Everything seems perfect...except when I am on the freeway cruising at a constant speed. About every 3 or 4 seconds, the RPM will jump 200 to 300 RPM (goes from 2000 to 2200/2300) as if the torque converter is unlocking or it is downshifting. It immediately locks up or up-shifts again and the RPM returns to normal. 3 or 4 seconds later, it does it again.
What I am trying to determine, is the torque converter unlocking momentarily or is it doing a 4-3 shift and what would cause this? Putting the shift selector in D forces a shift to 3rd and the RPM is higher (2500 RPM) than the momentary jump. So, I don’t thing it is doing a 4-3 shift. However, it happens so fast, that it could be a 4-3 shift. The only testing that I've done so far, is a pressure test. Pressure is good in all gears under light and heavy loading (to spec). When the jump in RPM occurs, pressure is running at about 90 psi. The pressure fluctuates by about 10 psi when the jump in RPM occurs. I figure this is normal as the engine RPM is changing.
A couple of questions. How do I determine for sure if this is the torque converter unlocking or the transmission doing a 4-3 downshift momentarily and then how I can narrow down the culprit? None of the diagnostics that I've read about seem to cover this one.
Everything seems perfect...except when I am on the freeway cruising at a constant speed. About every 3 or 4 seconds, the RPM will jump 200 to 300 RPM (goes from 2000 to 2200/2300) as if the torque converter is unlocking or it is downshifting. It immediately locks up or up-shifts again and the RPM returns to normal. 3 or 4 seconds later, it does it again.
What I am trying to determine, is the torque converter unlocking momentarily or is it doing a 4-3 shift and what would cause this? Putting the shift selector in D forces a shift to 3rd and the RPM is higher (2500 RPM) than the momentary jump. So, I don’t thing it is doing a 4-3 shift. However, it happens so fast, that it could be a 4-3 shift. The only testing that I've done so far, is a pressure test. Pressure is good in all gears under light and heavy loading (to spec). When the jump in RPM occurs, pressure is running at about 90 psi. The pressure fluctuates by about 10 psi when the jump in RPM occurs. I figure this is normal as the engine RPM is changing.
A couple of questions. How do I determine for sure if this is the torque converter unlocking or the transmission doing a 4-3 downshift momentarily and then how I can narrow down the culprit? None of the diagnostics that I've read about seem to cover this one.