Sudden Gear Slipping After Fluid Change (Emergency?)

[WarrenBoostit]

Hi all,
I'll cut to the chase. A few weeks ago in my SHO, the RDU was replaced (a whole nightmare in itself, took 2 RDUs and this one still sings slightly as 70 mph). I did a break in period of about 500 miles on the new RDU, driving very gently. I then brought it over to a Lincoln dealership to get the fluid drained out, and swapped with Redline Lightweight Shock Proof fluid that everyone recommends. While I was there, since I had extra Redline, and I was told it could be used in the PTU, I asked them to swap the fluid in the PTU as well.

Today was the first day driving again, and slowly I began to lay into it a bit more. It was great the entire morning commute, driving around at lunch, and for about 25 minutes of the 30 min commute back home. Drove it a bit more aggressively on the commute home, but still no WOT. Suddenly, the car felt like the clutch was slipping in nearly every gear, where a gear change would normally happen, from 4th to 5th, the car would suddenly freely rev, and if it even let me into the next gear, it was with a sudden jolt. This was occurring in all gears, it kinda seemed like it could only bite the next gear at low rpms. This also seemed to occur once the transmission was warmed up to about 190-200 degrees.

I'm at the end of my wits, I've barely driven this car for two months now due to all the troubleshooting and repair work being done, and am out about $4k just to get to the point of driving again. What could have caused this? Should I have not used Redline in the PTU? Did the dealership put enough fluid in? Could the RDU be bad? I have noticed (I think even pre-new RDU) that deaccelerating in gears 1-2 has a subtle almost brake dragging like sound, except no brakes are being applied, though I'm not sure if that's at all related. I should also add this isn't the first time the PTU fluid has been swapped, it was swapped like 10k miles ago with OEM fluid, and fluid changes in general have been pretty diligent.

Any help or troubleshooting will be greatly appreciated, I'm getting close to the point where I might just sell the damn thing because every month is something new to stress about. I suppose my next step is to let everything cool off and see if it still occurs, but I really am at a loss.

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Black 2018 SHO Non-PP | GH e30/AO Tune | PPE Catted Downpipes | DG2 Trans Mount | M-12405-35T plugs at .026 | 170 Tstat | 3 bar | H&R Springs | XDI-35 | Badges removed | Chrome delete | Fuel-it Bluetooth ethanol analyzer | GH IC | EPP Gen2 CAI | Noisemaker delete | MSD coils | Ceramic coating | Window Tint | EPP Hot Pipes | Black AR924 w/ General GMAX AS 05 255/45r20 | MRT axle back w/black tips

 

[Texas Marauder]

Not likely the PTU or RDU. PTU is only a gear box. RDU is only a gear box with an electronic clutch. Sounds like transmission trouble. Check the transmission fluid. Check for any DTCs.

 

[WarrenBoostit]

Not likely the PTU or RDU. PTU is only a gear box. RDU is only a gear box with an electronic clutch. Sounds like transmission trouble. Check the transmission fluid. Check for any DTCs.

No DTCs, checked transmission fluid, and it was above the hot/max line, even after multiple checks. The car had been sitting for about 30 minutes, so I'm not sure if it's accurate. Maybe it's time to get the transmission fluid swapped? It was swapped a year ago, but to be honest I wasn't watching over the mechanic as I assumed he would be putting the standard Mercon LV in. Transmission does seem to get hotter than I'd expect for 30 minute drive, was pushing 205 degrees at the end of it.

I know this shouldn't be the PTU or RDU at all. It's just, these were the only things touched recently. I wasn't getting into higher revs prior to the fluid change, so I can't say for sure that the issue didn't exist prior, but this is sudden and extremely out of character for the car. It's never shown any symptoms of transmission issues. I was wondering if maybe incorrect fluid in the PTU could translate to bad shift logic in the trans? Or the car had learned my shift patterns during the break in, and glitched out once I started leaning into it? Seems all very unlikely but I am going to be crushed if immediately after buying a new diff, I'm out for a transmission.



IMPORTANT EDIT: I am now increasingly concerned. I drove it around for a bit, noticing particularly that it was fine 1st - 2nd, then really jumping hard in 3rd. While idling, I checked the fluid again. Trans Temps around 180. No matter how many times I checked, fluid always seemed below the minline. I don't see anything dripping, is it possible I popped a leak after it was so lightly used for the few months? Am extremely confused now and even more worried.

 

[6500rpm]

Add a transmission friction modifier and top off your fluid to the proper level to slightly above and see how it does.

 

[Joshw0000]

Make sure the trans fluid is within the min/max while hot. I wouldn't think that being slightly low or overfilled would cause that much of an issue, but let's scratch that off the list of possibilities.

Honestly, if sounds sorta like a torque converter issue. It's very common with this car. I've replaced mine.

Do you notice the RPM's jumping slightly as you drive? You can try putting 1 or 2 tubes of Shudder Fixx in the transmission. If the issue goes away almost instantly but comes back after a while, it's time for a new torque converter.

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[WarrenBoostit]

Make sure the trans fluid is within the min/max while hot. I wouldn't think that being slightly low or overfilled would cause that much of an issue, but let's scratch that off the list of possibilities.

Honestly, if sounds sorta like a torque converter issue. It's very common with this car. I've replaced mine.

Do you notice the RPM's jumping slightly as you drive? You can try putting 1 or 2 tubes of Shudder Fixx in the transmission. If the issue goes away almost instantly but comes back after a while, it's time for a new torque converter.

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I've been on the lookout for torque converter issues since I've heard the issue is common, but honestly, I genuinely never noticed any RPM/TC issues, outside of an occasional slightly rough shift when decelerating 3rd to 2nd, and some questionable RPM shudders at idle. Though if I put my memory to it, some vibration symptoms might've occurred that I just chalked up to exhaust loudness vibration. I'll definitely keep this in mind and bring it up tomorrow, I'm bringing it back to the Lincoln Stealership just to see if they have any ideas or perhaps have a "Oh sh*t" moment that makes them realize they drained the transmission instead of the PTU (though I sincerely doubt that).

 

[Joshw0000]

I've been on the lookout for torque converter issues since I've heard the issue is common, but honestly, I genuinely never noticed any RPM/TC issues, outside of an occasional slightly rough shift when decelerating 3rd to 2nd, and some questionable RPM shudders at idle. Though if I put my memory to it, some vibration symptoms might've occurred that I just chalked up to exhaust loudness vibration. I'll definitely keep this in mind and bring it up tomorrow, I'm bringing it back to the Lincoln Stealership just to see if they have any ideas or perhaps have a "Oh sh*t" moment that makes them realize they drained the transmission instead of the PTU (though I sincerely doubt that).

Ok, the Red Line fluid. Where did that go? And what weight did you use? PTU and RDU take different weights.

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[WarrenBoostit]

Ok, the Red Line fluid. Where did that go? And what weight did you use? PTU and RDU take different weights.

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In all honesty I just provided the fluid to the dealership, under the assumption that they knew proper installation. Also, I didn't know the Redline Lightweight Shockproof came in different weights, I think its similar to 75w-140, but I swear I've seen folks here say it can go into both.

 

[WarrenBoostit]

Make sure the trans fluid is within the min/max while hot. I wouldn't think that being slightly low or overfilled would cause that much of an issue, but let's scratch that off the list of possibilities.

Honestly, if sounds sorta like a torque converter issue. It's very common with this car. I've replaced mine.

Do you notice the RPM's jumping slightly as you drive? You can try putting 1 or 2 tubes of Shudder Fixx in the transmission. If the issue goes away almost instantly but comes back after a while, it's time for a new torque converter.

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When you replaced your TC, did you only replace that, or was it an entire rebuild?

 

[Joshw0000]

In all honesty I just provided the fluid to the dealership, under the assumption that they knew proper installation. Also, I didn't know the Redline Lightweight Shockproof came in different weights, I think its similar to 75w-140, but I swear I've seen folks here say it can go into both.

No sir. There's a big difference. If you put the same in both, you should change one ASAP.

RDU = 75w90
PTU = 75w140

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[Joshw0000]

When you replaced your TC, did you only replace that, or was it an entire rebuild?

It was just the TC.

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[SM105K]

In all honesty I just provided the fluid to the dealership, under the assumption that they knew proper installation. Also, I didn't know the Redline Lightweight Shockproof came in different weights, I think its similar to 75w-140, but I swear I've seen folks here say it can go into both.

Redline LWSP doesnt not come in different weights.

You 100% CAN RUN it both in your RDU and PTU. Numerous people including myself have with zero issues.

This is 100% transmission related, and I would venture to say TC.

 

[Joshw0000]

Redline LWSP doesnt not come in different weights.

You 100% CAN RUN it both in your RDU and PTU. Numerous people including myself have with zero issues.

This is 100% transmission related, and I would venture to say TC.

Well, I learned something new. I guess it's a one-size-fits all. The manufacturer says it's fine and so do others but I'm old fashioned and use the specified weights (Royal Purple).

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[WarrenBoostit]

I know typically by time you need to replace the TC in a car, it's failure probably infected the rest of the trans, so the whole thing needs rebuilt, but since these failures are common in the SHO, and assuming the fluid isn't glittery or burnt, is it more common just to replace the TC?

Also, what are the odds this ended up having downstream effects on my RDU?

 

[Joshw0000]

I know typically by time you need to replace the TC in a car, it's failure probably infected the rest of the trans, so the whole thing needs rebuilt, but since these failures are common in the SHO, and assuming the fluid isn't glittery or burnt, is it more common just to replace the TC?

Also, what are the odds this ended up having downstream effects on my RDU?

I've put nearly 70K miles on my car so I realized immediately when my TC started acting up. It sounds like you may not know the history of this car, so your situation may be different.

The TC can damage the transmission if it's gone unchecked for extended periods but as you mentioned, I think you'd be fine to replace it if the tranny fluid looks good and no glitters. I don't see how the TC could affect the PTU or RDU.

My suggestion is to put a couple tubes of Shudder Fixx in the transmission fluid. It's cheap and can be bought off Amazon or most auto part stores. You'll know relatively quickly if it helped or not. If it doesn't, you've lost $15 and that stuff definitely won't hurt the tranny. If it does, then start making preparations for a new T/C.

Oh, and don't go to the stealership unless your brother is a mechanic there or your family is good friends with the owner. Take it to a local transmission shop. They'll probably do a better job for half the price.

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[WarrenBoostit]

I've put nearly 70K miles on my car so I realized immediately when my TC started acting up. It sounds like you may not know the history of this car, so your situation may be different.

The TC can damage the transmission if it's gone unchecked for extended periods but as you mentioned, I think you'd be fine to replace it if the tranny fluid looks good and no glitters. I don't see how the TC could affect the PTU or RDU.

My suggestion is to put a couple tubes of Shudder Fixx in the transmission fluid. It's cheap and can be bought off Amazon or most auto part stores. You'll know relatively quickly if it helped or not. If it doesn't, you've lost $15 and that stuff definitely won't hurt the tranny. If it does, then start making preparations for a new T/C.

Oh, and don't go to the stealership unless your brother is a mechanic there or your family is good friends with the owner. Take it to a local transmission shop. They'll probably do a better job for half the price.

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Thank you for the advice, agree on the point of not having the stealership do anything transmission related, I luckily have a shop my family members have been going to for a while that is reliable. It's definitely seeming more and more TC failure, and I'll definitely make sure to try some ShudderFixx. I'm just kinda shocked the TC was capable of seemingly sudden failure, unless I just really wasn't picking up on it for the 13k miles I've owned it for.

 

[Paramedic Terry]

Before you go any further, rule out the possibility that some kid in the dealership garage put that heavy weight gear oil in the transmission. Just like in most other industries, skilled mechanics are scarce. Lack of experience and a communication breakdown could easily lead to a mistake like that. It's a cheap & easy first step.

 

[skyshadow07]

As for the weight concern, Redline Lightweight Shock Proof behaves like 75W90

 

[Joshw0000]

As for the weight concern, Redline Lightweight Shock Proof behaves like 75W90

I googled it after it was mentioned earlier and apparently it can behave like a thicker oil as well. That doesn't seem feasible to me, but they're making that claim and people seem to be doing fine using it.

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[WarrenBoostit]

I regretfully initially brought the car back to the Lincoln dealership, just to make sure they washed their hands of any fault. Fully intending on bringing it to my desired transmission shop anyway unless the issue was insanely minor, I am still in disbelief that after roughly a morning of looking at it, the receptionist relayed that the tech said it'd be $10k total, with only $1700 in labor. When I asked what went wrong the receptionist didn't know, but said something related to flushing coolant lines. I asked what exactly was diagnosed as failing, and she said she'd have an answer for me once he got back from lunch...it's been two hours...
Obviously there is no universe where I'll be paying that much for a new transmission. My first instinct is to take that price as a "screw you, I don't want to work on it" price, but paired with how the transmission went literally the day after a supposed PTU fluid change, I'm starting to get really nervous that something funny is going on at this dealership, and I can't help but think maybe something is at play that I'm not being told here...regardless, I'm getting my car out of that stealership as soon as possible.