Sudden Acceleration in Reverse

[HBarlow]

That's bad news. If it occurs more than a time or two without input by the owner/driver the news will soon spread to the parasite class and the lowlife ambulance chaser industry and billion dollar phony lawsuits will start cropping up. Then we'll be hearing of class action lawsuits because little old ladies backed over their grandchildren and on and on.

 

[SPucillo]

HBarlow,
All true and Chrysler knows this so why not cover their butts by fixing this. All they need to do is look at what Toyota went through with surging vehicles! They were taken to the legal cleaners!
Is is so hard to not allow the trans to shift if there is low pressure in the TC?

 

[CTufte]

I have a 2012 2500 work truck with the 68RFE that has did three times and it is used every day. I have put 3300 miles on it in less than a month. So it will do it driving
every day. The first 2 times I push on the brake hard and it killed the engine. The third time I have plenty of room to so I let go and it released in about 20 to 25 feet
The truck is park and attached insulated garage not heated. As it has been warmer it hasn't happen.

 

[SPucillo]

I have a 2012 2500 work truck with the 68RFE that has did three times and it is used every day. I have put 3300 miles on it in less than a month. So it will do it driving
every day. The first 2 times I push on the brake hard and it killed the engine. The third time I have plenty of room to so I let go and it released in about 20 to 25 feet
The truck is park and attached insulated garage not heated. As it has been warmer it hasn't happen.

I'll see if I can get some input here from the factory trans guy.

Edit: Here he is, see below.
Thanks TransEngineer for sharing your expertise!

 

[transe]

If you experience "must mash the brake pedal to hold the truck," only after a cold startup, then the problem is likely a bad cooler return (spin-on) filter, which is inside the trans pan. This filter contains an anti-drainback diaphragm, to prevent oil in the torque converter from draining out into the trans sump when the engine is shut off. If this diaphragm is too weak, or isn't sealing correctly, then you can get converter drainback, which leaves the converter up to half full of air instead of oil.



Converter drainback has two main symptoms:

(1) Slow engagement (or what feels like slow engagement) into gear. Actually, the trans engages normally, but since the converter is half full of air (and air doesn't transmit torque very well), you get very little input torque to the transmission. The input torque slowly rises as the converter refills with oil. This makes it feel like the trans is "oozing" into gear (that's the best way I can describe it). Once the converter is full again, truck will drive normally (except for symptom 2 below), so the "oozing" into gear happens only on a cold start, not on warm restarts.

(2) Momentary Torque Converter Clutch (TCC) drag. As the converter refills with oil, the air that's expelled travels through the cooling system, and then returns to the trans pump. When this slug of air reaches the pump inlet, it can cause a momentary dip in line pressure. This in turn causes a momentary drop in converter feed pressure. This drop in feed pressure allows the TCC to drag, which tries to pull down the engine speed. The PCM increases engine fueling (to maintain the proper idle speed), which increases the engine's output torque, which forces you to apply more brake pressure in order to hold the truck stationary. As with symptom 1 above, this will happen only after a cold startup. If you experience this symptom on a warm trans, then you have some other issue (such as a failed TCC, sticky TCC control valve in the pump, etc. )



The fix is to replace the spin-on cooler return filter (P/N 05179267AC) inside the trans. For 2012 trucks, hopefully you can still get this done under warranty. If doing it yourself, use only a Mopar filter, since we have seen inadequate diaphragms on some aftermarket filters. Until you get your filter replaced, allow the truck to idle in Park for a minute or so (after a cold start) before taking off. This will allow any air to be purged before you start driving.



If you have this problem and are getting your filter replaced at a dealer (under warranty), please PM me (or post here if PM doesn't work) BEFORE you take your truck in. I will contact your dealer and arrange to get the bad filter returned to us so we can analyze it. I need to contact the dealer in advance because otherwise they will simply scrap the old filter and by the time I call them it will be too late. Please include the following info in your PM/post:

• VIN (last 8 digits)

• Dealer name

• Dealer location (city and state)

• Your name

• When you plan to take the truck in for filter replacement

 

[bigblock_doc]

Not to be a smart *****, but how big are your feet? Sometimes while applying the brake your foot hangs out and touches the gas pedal.

The harder you push the brake the more it wants to go. Just a thought. It has happened to me, mostly with smaller cars.

 

[CTufte]

I been letting it run for a few seconds before putting it in reverse and it hasn't did it. I think your right TransEngineer I have the dealer take a look as soon I can
get the truck in.

 

[cerberusiam]

(2) Momentary Torque Converter Clutch (TCC) drag. As the converter refills with oil, the air that's expelled travels through the cooling system, and then returns to the trans pump. When this slug of air reaches the pump inlet, it can cause a momentary dip in line pressure. This in turn causes a momentary drop in converter feed pressure. This drop in feed pressure allows the TCC to drag, which tries to pull down the engine speed.

If any of this is really true then that truly some POS engineering. Allowing any chance of air bubbles getting to the pump just doesn't make sense. TCC clutch should normally be in an off position. No line pressure drop of any kind should allow that clutch to apply. The apply circuit should be solenoid controlled and if there is a situation that pressure is allowed in it has to be a parts failure.



The TC, spin on filter, and mounting base are a POS in stock form, that is a given. The explanation defines the results of a foreseeable condition that I doubt was over looked. It just doesn't track.

 

[HBarlow]

If you experience "must mash the brake pedal to hold the truck," only after a cold startup, then the problem is likely a bad cooler return (spin-on) filter, which is inside the trans pan. This filter contains an anti-drainback diaphragm, to prevent oil in the torque converter from draining out into the trans sump when the engine is shut off. If this diaphragm is too weak, or isn't sealing correctly, then you can get converter drainback, which leaves the converter up to half full of air instead of oil.

Converter drainback has two main symptoms:
(1) Slow engagement (or what feels like slow engagement) into gear. Actually, the trans engages normally, but since the converter is half full of air (and air doesn't transmit torque very well), you get very little input torque to the transmission. The input torque slowly rises as the converter refills with oil. This makes it feel like the trans is "oozing" into gear (that's the best way I can describe it). Once the converter is full again, truck will drive normally (except for symptom 2 below), so the "oozing" into gear happens only on a cold start, not on warm restarts.
(2) Momentary Torque Converter Clutch (TCC) drag. As the converter refills with oil, the air that's expelled travels through the cooling system, and then returns to the trans pump. When this slug of air reaches the pump inlet, it can cause a momentary dip in line pressure. This in turn causes a momentary drop in converter feed pressure. This drop in feed pressure allows the TCC to drag, which tries to pull down the engine speed. The PCM increases engine fueling (to maintain the proper idle speed), which increases the engine's output torque, which forces you to apply more brake pressure in order to hold the truck stationary. As with symptom 1 above, this will happen only after a cold startup. If you experience this symptom on a warm trans, then you have some other issue (such as a failed TCC, sticky TCC control valve in the pump, etc. )

The fix is to replace the spin-on cooler return filter (P/N 05179267AC) inside the trans. For 2012 trucks, hopefully you can still get this done under warranty. If doing it yourself, use only a Mopar filter, since we have seen inadequate diaphragms on some aftermarket filters. Until you get your filter replaced, allow the truck to idle in Park for a minute or so (after a cold start) before taking off. This will allow any air to be purged before you start driving.

If you have this problem and are getting your filter replaced at a dealer (under warranty), please PM me (or post here if PM doesn't work) BEFORE you take your truck in. I will contact your dealer and arrange to get the bad filter returned to us so we can analyze it. I need to contact the dealer in advance because otherwise they will simply scrap the old filter and by the time I call them it will be too late. Please include the following info in your PM/post:
• VIN (last 8 digits)
• Dealer name
• Dealer location (city and state)
• Your name
• When you plan to take the truck in for filter replacement

This a great post!!! Welcome to TDR. My truck has an Aisin not the MOPAR transmission so I don't have a personal interest in this issue but I sincerely appreciate genuine education-based knowledge which you appear to possess.

We have thousands of members with some level of knowledge gained through experience and lots of us have opinions (right and wrong) which are generously shared here but if you are a transmission engineer, which you appear to be, I consider you a valuable resource to TDR. The entire TDR membership can benefit from your knowledge and I for one encourage you to hang around and participate. Sadly, not everyone will appreciate your comments, but please don't be deterred. Many will appreciate your participation.

 

[PC12Driver]

If any of this is really true then that truly some POS engineering. Allowing any chance of air bubbles getting to the pump just doesn't make sense. TCC clutch should normally be in an off position. No line pressure drop of any kind should allow that clutch to apply. The apply circuit should be solenoid controlled and if there is a situation that pressure is allowed in it has to be a parts failure.

The TC, spin on filter, and mounting base are a POS in stock form, that is a given. The explanation defines the results of a foreseeable condition that I doubt was over looked. It just doesn't track.

Remember the rule of thumb that said to keep the 47s and 48s around 2,000 rpm to provide adequate hydraulic pressure in the trans to keep the TC clutch locked? Now there's no chance of the new setup slipping due to low rpm/high temp pressure loss. Less chance of partial engagement under load and the resulting TC clutch destruction. More of a fail-safe design, not, as you say, "POS engineering. "

If the problem is a simple failed anti-drainback valve in the filter, then this really isn't a case of poor engineering, is it? If you had a stuck thermostat in any liquid-cooled engine and the engine seized as a result, is that poor engineering?

 

[orhusky]

Remember the rule of thumb that said to keep the 47s and 48s around 2,000 rpm to provide adequate hydraulic pressure in the trans to keep the TC clutch locked? Now there's no chance of the new setup slipping due to low rpm/high temp pressure loss. Less chance of partial engagement under load and the resulting TC clutch destruction. More of a fail-safe design, not, as you say, "POS engineering. "

If the problem is a simple failed anti-drainback valve in the filter, then this really isn't a case of poor engineering, is it? If you had a stuck thermostat in any liquid-cooled engine and the engine seized as a result, is that poor engineering?

My thoughts also!!

 

[PC12Driver]

Something else I just thought of - the factory exhaust brake will hold down to about 1,200 rpm. Gotta have a guaranteed positive lockup that low.

 

[cerberusiam]

Remember the rule of thumb that said to keep the 47s and 48s around 2,000 rpm to provide adequate hydraulic pressure in the trans to keep the TC clutch locked? Now there's no chance of the new setup slipping due to low rpm/high temp pressure loss.

Your mixing up engine requirements with transmissions speculation and missing the whole point. You might have deluded yourself into thinking a 47 or 48 needed 2000 rpms to hold the clutch but that's all. If you ever put a gauge on them you would see the bulk of pressure developed in the apply circuits is controlled by TV and is pretty much all in as it goes thru 1600 rpms. The reason the clutches don't hold well under 2000 is not pertinent to this discussion.

If the problem is a simple failed anti-drainback valve in the filter, then this really isn't a case of poor engineering, is it? If you had a stuck thermostat in any liquid-cooled engine and the engine seized as a result, is that poor engineering?

It is in fact poor engineering if the sticking of said piece introduces a large air pocket that cause the engine to destroy the piston and cylinder. That doesn't and can't happen if the process is performed correctly and the coolant is not leaking. If you had bothered to read the whole thread you would have deduced there are no external leaks or problems detected and no failures that can be traced. Example is totally invalid in the discussion.



If you had bothered to read the theory of why the TC seems to lockup, it would have become obvious why it has holes and where the questionable theorization occurred. The whole theory revolves around the TC draining down and the air in it being pushed back into the pressure pump. That in itself should have raised enough of a question. That cannot happen in any of the previous designs and while it may be able to happen in this one it would qualify as bad engineering to allow such a situation to develop. Air being pushed into a gear pump that needs to generate pressure with a liquid is a bad thing.



Further more, said air bubble is claimed to drop apply pressure which cause the TC clutch to drag. If low line pressure causes TC clutch drag this would imply the clutch takes pressure to disengage and keep it so. That would naturally dictate that every time the engine is fired the clutch is going to drag causing wear and friction and scuffing off material. The obvious question then becomes WHY would such a screwy design be implemented with the potential for problems that is obvious?



The whole theory seems to be designed to explain the symptoms not the source of the problem. That is where the logic starts to illuminate. That and every instance of failures like this I have ever seen gets solved with a TC replacement. The conclusions seem to be a reach, that is relatively easy to deduce. Not that they are wrong, but, if they are correct then the observation of questionable engineering is warranted.

 

[PC12Driver]

It is in fact poor engineering if the sticking of said piece introduces a large air pocket that cause the engine to destroy the piston and cylinder. That doesn't and can't happen if the process is performed correctly and the coolant is not leaking. If you had bothered to read the whole thread you would have deduced there are no external leaks or problems detected and no failures that can be traced. Example is totally invalid in the discussion.

So a stuck thermostat can't cause an engine to overheat and destroy itself, as long as the system is 100% full of coolant? Really?



Other auto trannys have torque converter anti-drainback valves. Every so often you'll get in a vehicle that has one that leaks slightly and allows the fluid to drain from the converter, resulting in no motion until it gets filled back up after being put in gear. Air is getting pushed through that system. Not a problem unique to the 68.



I did a bunch of reading on this site and others before I bought my truck, and the general consensus is that the 68 is a great transmission that is trouble-free, as long as the engine is stock and the truck is used as intended. Except in your posts. For a guy who doesn't even own one, or as far as we can tell, doesn't even have any first hand experience with one, you sure are quite prolific with your anti-68 (mis)information.

 

[cerberusiam]

Every so often you'll get in a vehicle that has one that leaks slightly and allows the fluid to drain from the converter, resulting in no motion until it gets filled back up after being put in gear.

As usual, you are not reading the problem description. The truck doesn't NOT move, IT RUNS AWAY WHEN PUT IN GEAR, even standing on the brakes.



As to your assertion I said there was anything wrong with the engineering of the 68RFE, its as bogus as the rest of your drivel.

 

[PC12Driver]

As usual, you are not reading the problem description. The truck doesn't NOT move, IT RUNS AWAY WHEN PUT IN GEAR, even standing on the brakes.



As to your assertion I said there was anything wrong with the engineering of the 68RFE, its as bogus as the rest of your drivel.

You know, the last time you told me I didn't read something, you in fact misread the information in the very link you posted. Somebody else called you on it. Your use of "as usual" doesn't really carry much weight.



So let's see what I missed. Put truck in reverse, at idle, rear tires spun in gravel even with foot on brake (I take this as normal braking), put it in neutral. Second post, same thing but tried heavy braking.



I don't know where you're getting the "IT RUNS AWAY WHEN PUT IN GEAR" part. Sounds sort of dramatic. To me, it sounds more like the time I showed a friend that I could power brake my truck (the '01 manual) with no throttle, and still spin the rear tires without killing the engine. Sort of like having an auto in gear and not having any slippage in the TC.



And, as usual, when you can't come up with anything to support your argument, out come the personal attacks and the cutsie emocons.



On the bright side, it does look like the OP is on the right track and did get some valid info and actual help from the TransEngineer (welcome aboard, btw!).

 

[cerberusiam]

So let's see what I missed. Put truck in reverse, at idle, rear tires spun in gravel even with foot on brake (I take this as normal braking), put it in neutral. Second post, same thing but tried heavy braking.

What do you suppose would happen if it were on pavement when it was put in gear, the converter hooked, and the rpms jumped? It is pretty clear from the description that without the gravel to reduce the friction the truck is going to jump forward, attempt to pull thru the brakes. I have seen 2 instances of similar behavior. One I got to ride in and shown how when randomly stopping at a stop sign\light the truck goes up on the tire about 5 seconds after a complete stop and tries to pull thru the brakes. The other was a call about the same type of behavior. In both cases a new TC solved the problem.

What exactly would you call random behavior that causes the truck to take off and drive thru intersections, parking lots, etc, despite hard braking? Runaway is a pretty apt description.

Since you obviously stayed at a Super 8 last night and know everything, then you should be able to follow the discussion about WHY and HOW air returned thru the cooling system will get into the pump, cause the line pressure to drop, and apply the TC clutch (which is off in these conditions), and, why this would be a engineering screw up were it true. As far as that goes, maybe you would like to explain how a TC that is partially drained causes the truck to go up on the tire, rev the engine, and take off, spin the tires on gravel, etc, when it finally charges also?

 

[PC12Driver]

There was never an increase in RPMs. You tell me I need to read, but you're fabricating symptoms. Let's stick to the case at hand, mmmkay? It's a simple problem with what sounds like a simple fix.

Your train is derailing. Maybe it's time to throttle back?

 

[transe]

Actually, when the TCC is released (as it should be in Reverse and in 1st gear), pump pressure is feeding the TCC release circuit, not the apply circuit. Pressure is fed into the front side of the converter (in front of the TCC piston, which pushes it away from the front cover and keeps the TCC released). This oil then flows past the outside edge of the TCC piston, into the rear half of the converter, and then flows out to the cooling system. Because the pressure on the front (release) side of the piston is greater than the pressure in the rear (apply) side, the TCC is released.



If there is a defective (weak, under-spec) anti-drainback diaphragm in the cooler return filter, it may allow fluid to drain from the converter while the engine is off. This can cause a slug of air to be pushed through the cooling system and back into the pump suction. When this slug of air goes through the pump, it can cause a momentary drop in line pressure, which can drop the pressure on the front (release) side of the TCC piston to be less than the residual pressure on the apply side. This is what can allow TCC drag. The engine speed does not increase. The PCM merely increases fueling to maintain the correct idle speed, which produces more driveline torque and requires the driver to apply more brake pressure to hold the truck.



I certainly agree that this is not a desirable situation. That's why we have a specification for minimum blocking pressure of the anti-drainback diaphragm in the cooler return filter. Apparently our supplier must have shipped us some filters which did not meet this specification. That's why I'd like to get some of these parts back, so we can verify what the problem is and hopefully prevent it in the future.

 

[cerberusiam]

There was never an increase in RPMs.

Pay attention, you might learn something. You haven't been around CR engines long enough to understand their operation if you believe that.

This can cause a slug of air to be pushed through the cooling system and back into the pump suction.

Just to clarify, how does any air pocket get to the pump suction side? This cannot happen in any of the previous models due to the fact the return fluid is used in the lube circuit. The 68 is different in this respect and the only way I can see this being possible is all or part of the return fluid is routed directly to the pump intake without going back to the sump. Air returned to the sump is never going to hit the pump intake at the filter so there must be some provision for routing return fluid directly to the pump, given this scenario is possible.



This begs the next question, how is sump fluid cooled if return fluid is not being constantly mixed back into it? Is the fluid path after the filter controlled by a shuttle valve that splits the flow to sump and pump intake? Thanks for the follow up and any more insight into the above question.



My whole point is this seems to be a bit of a engineering glitch. To allow an outsourced non-integral part of the transmission to generate this type of failure is not what I would expect as quality design. I have to think that air in the cooler return would have some bleed path that would not allow it into the pump inlet. That is too easy to ignore implementation of.

The engine speed does not increase. The PCM merely increases fueling to maintain the correct idle speed, which produces more driveline torque and requires the driver to apply more brake pressure to hold the truck.

I beg to differ, there is frequently an rpm surge. I can't say always because of course I have not seen every possible failure, but, a 150-200 rpm surge is normal. When it jumps 500-600 rpms it is bit more disconcerting. As you pointed out, warm this never happen and if it does there are other issues. However, it is interesting to note that this condition is only possible after the engine has been off for a period of time.