Transmission noise when downshifting/ Kick down.

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97 FZJ80 with 360k miles, rebuilt engine 6 months ago. Slowly working through all the issues on the truck. Getting a terrible noise at highway speeds when it kicks down a gear when I get on the throttle. Anyone experience this before? If I baby it and dont force it to kick down it never makes the noise. It sounds like an exhaust shield or something rattling (or bearing inside the transmission?) and it only happens during/ right before the transmission downshifts. In the videos I am sort of working the throttle to make the noise last longer so that I could record it, during normal operation the noise happens quickly and stops once the transmission gets into the lower gear.

So to any automatic transmission experts, what does this sound like to you? Should I start shopping for another transmission?
Thanks




 
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I didn't think of that, makes sense. My check engine light is on for the rear knock sensor right now. I busted the wire when replacing the sensor. Once the pigtail comes in and I repair it, I'll double check my timing and run a tank of premium in it. I rebuilt the engine about 6 months ago and had the head and block resurfaced. Not sure how much they took off but could have bumped the CR up too high.
 
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I didn't think of that, makes sense. My check engine light is on for the rear knock sensor right now. I busted the wire when replacing the sensor. Once the pigtail comes in and I repair it, I'll double check my timing and run a tank of premium in it. I rebuilt the engine about 6 months ago and had the head and block resurfaced. Not sure how much they took off but could have bumped the CR up too high.


Without a knock sensor the ecu can't retard timing when it detects knock. That's a pretty sketchy setup
 
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Without a knock sensor the ecu can't retard timing when it detects knock.

I think it prevents the ECU from advancing the timing. I don't think the ECU retards the timing any further than the baseline setting, but I'm very much open to being proven wrong.

I drove without knock sensors for a couple of days and it was truly gutless. No pinging, though. That was probably with stock timing (3 degrees?), or maybe a *little* advanced.
 
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I think it prevents the ECU from advancing the timing. I don't think the ECU retards the timing any further than the baseline setting, but I'm very much open to being proven wrong.

I drove without knock sensors for a couple of days and it was truly gutless. No pinging, though. That was probably with stock timing (3 degrees?), or maybe a *little* advanced.

I doubt it retards it beyond base. But shouldn't it be capable of retarding it from it's advanced state while accelerating?


Ie: based on load, airflow, and rpm the ecu calculates timing needed is 21*. The knock sensor is detecting knock at 21 so the ecu retards until knock disappears.
 
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I doubt it retards it beyond base. But shouldn't it be capable of retarding it from it's advanced state while accelerating?

I'm not sure what you're saying. I *think* that if you set your timing to, say, 3 degrees following the FSM, that if you unplug your knock sensors then it will just stay at 3 degrees. The ECU wants to advance the timing until it detects knocking, but if it's unplugged then it just assumes knocking all the time.

I don't know how the knock sensors work. I know that they're simple "acoustic" devices. I assume that when a sufficiently hard percussion occurs, it opens the circuit, hence unplugging the sensors looks like constant knocking. That's pure speculation on my part, though.
 
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Well, thought I found the smoking gun today. Only had an hour before I had to leave for work so I checked the timing (with the diagnostic jumper per the FSM) and found my timing was set to 10* BTDC! So I brought it back to 3* and took it for a spin. Noise is still there on the down shift on the freeway. I'll have to wait until Monday when the pigtail arrives for the knock sensor. I'll try running premium too to see if that helps. I'll update this Monday or Tuesday once the sensor is fixed and my check engine stays off.
 
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I'm not sure what you're saying. I *think* that if you set your timing to, say, 3 degrees following the FSM, that if you unplug your knock sensors then it will just stay at 3 degrees. The ECU wants to advance the timing until it detects knocking, but if it's unplugged then it just assumes knocking all the time.

I don't know how the knock sensors work. I know that they're simple "acoustic" devices. I assume that when a sufficiently hard percussion occurs, it opens the circuit, hence unplugging the sensors looks like constant knocking. That's pure speculation on my part, though.


No. That's not what I am saying at all.


The ecu has timing tables based off base timing. It will advance or retard timing based on load and rpm. During this advance it will retard timing based on detected knock.

So without the knock sensor it won't retard the timing when knock is detected.

It doesn't simply open a circuit. It can detect levels of knock. Th ecu should retard timing just until knock goes away. It's not a simple on off situation.
 
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It certainly sounds like a tinny rattling noise to me, too. Have you tried hitting various sections of your exhaust system with a rubber mallet—especially the catalytic converters?
 
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Sounds more like a rattle in the exhaust or heat shields to me.
I agree, but it's hard to hear on the recording. It sounds too tinny to be ping to me. Ping (detonation) is usually slightly lower frequency (IMO)

It sounds like it's more during a certain RPM range. Can it be duplicated by holding the engine in 2nd gear (or whatever gear it's downshifting to) and running up through the range or RPM and back down again?

Check to make sure you don't have a cable or something laying on the exhaust, or a heat shield (such as around an O2 sensor) or even something possibly touching the driveshaft.
 
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Using headphones, it doesn't sound anything like detonation to me.

I had good results tracking down a noise using a LAV microphone off eBay and an extension cable. Used a spring clip to clamp it somewhere under the vehicle, then drove while recording with Audacity on my laptop. Any audio recording application will work, but Audacity allows you to record and label a bunch of tracks so you can easily compare them and figure out which is closest to the source. If you use this method, you'll definitely want a mic with a substantial foam wind block or add a "dead cat" to it, since your noise is only happening at relatively high speeds.
 
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Update:

I fixed knock sensor cable no more check engine light. While checking everything that could cause pinging I found no issues so I started looking back at the transmission. Adjusted the transmission pressure cable and noise changed slightly less of a pinging sound and more of a grind sound. After studying up on the transmission I found that when you press the brake pedal the ecu deactivates the torque converter lock up.

I’ve determined the sound Only occurs when the torque converter unlocks. I tried swapping the TCC solenoid with a cheap aftermarket one and sound is still there So now I’m assuming the torque converter is bad. At this point I might just disable the lockup by de-pinning the connector while looking into getting a new/ used or rebuilt torque converter. I may just replace the entire transmission with a lower mileage unit as this one has over 360k on it.

Looks like the torque converter is a discontinued part from Toyota. Anyone have any advise for what they would do/ buy if they were replacing a bad torque converter?

And one more question, I can’t seem to find anyone having a similar issue specifically with a grind at TC unlock, most noises people have associated with the TC are either noises all the time/ when in gear or when it locks up. Is there any chance that removing and cleaning out the valve body might fix this issue? If it would have any chance at fixing it I may give that a shot before I pull the transmission. Working by myself without a lift I’m afraid I’ll have to yank everything (engine, trans, t-case) out again like when I’ve done head gaskets/ engine rebuilds as I don’t see how I can lift the auto in place during reinstall.

Thanks!
 
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