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Discussion Starter #1
No Reverse in 2004 4x4 SC
Transmission: RE4R01a
Engine: VG33ER

I'm going to be very detailed to help others who may experience this. If you have input, of course I'd like to hear it.


Symptoms:
Last weekend, I started my vehicle from cold, shifted into reverse to back out of the driveway and noticed a 2 second delay. The vehicle drove fine for 20 minutes where I parked and shopped for about 1 hour. When I got back out to the car, it wouldn't engage in reverse. Everything else was normal including a soft clank that I had always heard when shifting into reverse. Since then, I've noticed that the Xterra will usually shift into reverse when cold and rarely when warm. When it does engage, sometimes it is immediate, sometimes there is a slow buildup. I haven't noticed any other problem with the transmission.


History:
I've owned the vehicle for about 7 years and have put 50K miles on it. It has 190K miles. The oil has 40K miles since replacement. I pulled a heavy trailer about 5 months ago for 1000 miles including some mountain passes that were very taxing; no problems or over heating were seen. Rarely, I'll notice a clunk from the transmission when I accelerate but for some reason have to abruptly (traffic stops or misjudged oncoming car) stop accelerating and apply the brakes; I think this is normal.


Current Findings:

Codes:
No "service engine soon" light nor ECM or TCM codes were found. The procedure for getting the TCM codes was wrong in my Chilton manual and on one page I found in this forum (a sticky). The service manual procedure accessed them correctly.

Oil:
It was a little low, I topped it off. It is a rust color and smells similar to new oil.

Stall test:
RPMs were a little low but consistent in all forward gears.
RPMs raced in reverse gear.

Oil pressure:
I've purchased a test kit which will arrive this week.

Cruise Control:
Normal

Transmission Specialist:
Looked at the oil and symptoms and told me there is some friction material in the oil and the reverse band is slipping. I need to replace/rebuild. Didn't do a pressure test. (BTW, The brake band doesn't engage in reverse.)


Considerations:
I knew almost nothing about automatic transmissions before last weekend. I've researched by watching videos, reading websites and reading the official service manual which has been the most helpful.

Before dropping $3000 on a repair, I want to make sure this isn't something that can be fixed otherwise. When a gear doesn't engage, one thinks that either the clutches are slipping or there isn't enough hydraulic pressure to push the clutches together hard enough for them to grip. If the clutches are slipping under normal hydraulic pressure, then you would need to rebuild that transmission -very difficult/expensive. If there isn't enough hydraulic pressure getting to the clutches, you might be able to resolve this through the oil pan -relatively easy/cheap.

Pump Problem:
User Ignotus posted a very similar issue here (2002 2WD XE V6 - No Reverse) 4 years ago. His issue seems exactly like mine. He attempted a valve body cleaning and solenoid replacement which did not resolve the problem. Eventually, during a rebuild, his mechanic told him that the problem was the stator which "related to the pump" and was replaced along with the rebuild. He was also told there was some wear on his reverse clutch. His problem resolved.

I really don't see how the stator would have been the problem. As I understand it, the stator allows torque multiplication and sits in the torque converter. In the automatic transmission service manual, "stator" is listed once. Maybe there is something inside the oil pump called a stator as a stator can be any stationary part of a rotary system. Someone mentioned that the pump could be providing decreased pressure that is not enough for the R clutch (needs 210 psi) but is enough for the forward gears (need 150 psi). I don't think this correlates with how it works when cold but not when warm. If the pump is the problem, this is a replace/rebuild fix because you have to remove the transmission to get to it.

Slipping Reverse Clutch or Low/Reverse Brake:
In reverse, the only systems that operate are the "reverse clutch" and the "low and reverse brake". If the reverse clutch is slipping under normal pressure, the friction plates are worn and need to be replaced. This requires a replace/rebuild. But why would the reverse clutch pack burn out? It is rarely used and is used under mild acceleration. However, when the ATF is cold and viscous, the clutches are less likely to slip. When it is warm and runny, they are more likely to slip. This fits my symptoms. The Low/Reverse Brake (a clutch that connects to the case) can't be the problem as it also operates during 1st gear which has no problem. If a clutch or brake is the problem, this requires replace/rebuild.

Reverse Band:
The shop I went to said this was slipping and was the reason for my problem. This can't be the problem though because there isn't a "reverse band". There is a "brake band" that surrounds the reverse drum but it only operates in 2nd and 4th gears NOT during reverse.

Other Hydraulic Problems:
Solenoids help route hydraulic fluid from the pump lines through the maze-like valve body to the appropriate pistons and clutch packs. They should throw a code if they are malfunctioning. I don't have any codes. Maybe though the solenoid is functioning but a seal around a solenoid or valve is allowing oil to leak elsewhere. If there is a problem with a solenoid or valve or clog in the valve body, this can be fixed by pulling out the valve body through the pan -relatively easy.

Service Manual:
The service manual has a section "Does not creep backwards in R". The recommendations are to do a stall test. If 1st gear is good but R is bad (as is my experience) this is suggested:
*Remove control valve body and inspect line pressure stuff
*Remove the whole transmission and inspect oil pump, torque converter, reverse clutch and high clutch
I don't know why they recommend inspecting the high clutch here.


Plan:
*Inspect shift lever linkage
*Test line pressure to detect a hydraulic problem.
*Use TransX (for older transmissions) to increase friction, recondition seals, clean any buildup.
*If this resolves the issue then I'll replace the oil/filter and add TransX again and monitor.
*If it doesn't resolve the issue and there is a pressure problem then I'll remove the valve body and poke around including testing the solenoids.
*If it doesn't resolve the issue and there isn't a pressure problem then I'll have to go for the replace/rebuild.
 

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Discussion Starter #2
This thread of a Frontier with a similar problem has some good information in it: Cant understand the RE4R01A in my truck ?

As of this point, most likely there is a problem with the rotor in the oil pump which causes low oil pressure. The forward gears require lower pressure than the reverse gear does to activate the clutches. The cold/more viscous oil can also engage reverse more reliably under this low pressure.

I'll get back after I do the pressure tests.
 

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I've continued to post on the clubfrontier.org thread I linked above because I was getting some help from a member there. I just did the pressure test and will copy the same post from over there.

***

Line Pressure Test Results (with and without dropping resistor):

I had an issue taking off the shift cable bracket to get at the forward gears test port (see here: Can't remove AT shift cable bracket) but finally was able to do a line pressure test. The results weren't what I expected in that the D, 2, 1 test port pressures were normal! I expected them to be low also.

REVERSE:
In reverse, at the "Test port for the R position" (aka "3 -> 4 & N -> R accumulator back pressure", see above), I found that when cold, the pressure could go up to 80 PSI idle and when giving gas it would bounce between 25 and 80 PSI. I could get movement on flat ground if over 25 PSI.

When warm, the R pressure was usually 0 to 10 PSI at idle, 0 to 25 PSI when giving gas and 65 PSI during stall test (I didn't do this but twice because I knew the clutches were slipping.)

When I unplugged the dropping resistor (which should give maximum line pressure), there was virtually no change. Sometimes when giving gas, I'd get between 0 and 25 and sometimes up to 50. I didn't do a stall test with the resistor unplugged (didn't want to burn the clutches).

FORWARD:
Very normal. I only tested D selection. I had 70 PSI at idle, between 75 - 125 PSI when driving normal and 150 PSI at stall. With the dropping resistor removed, the shifts were crisp but not hard (only tested when warm). The pressure hung around 125 PSI and went to 150 PSI at stall.


Discussion:
I'm a little upset that pulling the resistor didn't increase pressure in the reverse line. It would be nice to have a temporary solution to this. It seems the pump is cranking enough to get up to 150 PSI so I would assume that we would see at least that pressure in the R line. I don't know that this rules out a problem with the pump but I'm less suspicious of it.

So, there is loss of pressure in the R line. What could cause this? Of all the solenoids, gaskets, valves, springs, steel balls, accumulators, orifices and tubes, I suppose it could be anything. I can focus on those things related to the R line though. One place to start may come from the manual where it calls the R test port "3 -> 4 & N -> R accumulator back pressure". I have not seen a problem with 3 -> 4 shift. Another aspect to investigate is why can I achieve higher pressure when the oil is cold?

Plan:
Now that I have a base line, I'm going to add K&W TransX (75K) and see if anything changes.
Study the R line hydraulic lines and components.
Pull the valve body and fish around for problems.

*

I think I'll need some help studying the hydraulic lines.
 

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No Reverse in 2004 4x4 SC
Transmission: RE4R01a
Engine: VG33ER

I'm going to be very detailed to help others who may experience this. If you have input, of course I'd like to hear it.


Symptoms:
Last weekend, I started my vehicle from cold, shifted into reverse to back out of the driveway and noticed a 2 second delay. The vehicle drove fine for 20 minutes where I parked and shopped for about 1 hour. When I got back out to the car, it wouldn't engage in reverse. Everything else was normal including a soft clank that I had always heard when shifting into reverse. Since then, I've noticed that the Xterra will usually shift into reverse when cold and rarely when warm. When it does engage, sometimes it is immediate, sometimes there is a slow buildup. I haven't noticed any other problem with the transmission.


History:
I've owned the vehicle for about 7 years and have put 50K miles on it. It has 190K miles. The oil has 40K miles since replacement. I pulled a heavy trailer about 5 months ago for 1000 miles including some mountain passes that were very taxing; no problems or over heating were seen. Rarely, I'll notice a clunk from the transmission when I accelerate but for some reason have to abruptly (traffic stops or misjudged oncoming car) stop accelerating and apply the brakes; I think this is normal.


Current Findings:

Codes:
No "service engine soon" light nor ECM or TCM codes were found. The procedure for getting the TCM codes was wrong in my Chilton manual and on one page I found in this forum (a sticky). The service manual procedure accessed them correctly.

Oil:
It was a little low, I topped it off. It is a rust color and smells similar to new oil.

Stall test:
RPMs were a little low but consistent in all forward gears.
RPMs raced in reverse gear.

Oil pressure:
I've purchased a test kit which will arrive this week.

Cruise Control:
Normal

Transmission Specialist:
Looked at the oil and symptoms and told me there is some friction material in the oil and the reverse band is slipping. I need to replace/rebuild. Didn't do a pressure test. (BTW, The brake band doesn't engage in reverse.)


Considerations:
I knew almost nothing about automatic transmissions before last weekend. I've researched by watching videos, reading websites and reading the official service manual which has been the most helpful.

Before dropping $3000 on a repair, I want to make sure this isn't something that can be fixed otherwise. When a gear doesn't engage, one thinks that either the clutches are slipping or there isn't enough hydraulic pressure to push the clutches together hard enough for them to grip. If the clutches are slipping under normal hydraulic pressure, then you would need to rebuild that transmission -very difficult/expensive. If there isn't enough hydraulic pressure getting to the clutches, you might be able to resolve this through the oil pan -relatively easy/cheap.

Pump Problem:
User Ignotus posted a very similar issue here (2002 2WD XE V6 - No Reverse) 4 years ago. His issue seems exactly like mine. He attempted a valve body cleaning and solenoid replacement which did not resolve the problem. Eventually, during a rebuild, his mechanic told him that the problem was the stator which "related to the pump" and was replaced along with the rebuild. He was also told there was some wear on his reverse clutch. His problem resolved.

I really don't see how the stator would have been the problem. As I understand it, the stator allows torque multiplication and sits in the torque converter. In the automatic transmission service manual, "stator" is listed once. Maybe there is something inside the oil pump called a stator as a stator can be any stationary part of a rotary system. Someone mentioned that the pump could be providing decreased pressure that is not enough for the R clutch (needs 210 psi) but is enough for the forward gears (need 150 psi). I don't think this correlates with how it works when cold but not when warm. If the pump is the problem, this is a replace/rebuild fix because you have to remove the transmission to get to it.

Slipping Reverse Clutch or Low/Reverse Brake:
In reverse, the only systems that operate are the "reverse clutch" and the "low and reverse brake". If the reverse clutch is slipping under normal pressure, the friction plates are worn and need to be replaced. This requires a replace/rebuild. But why would the reverse clutch pack burn out? It is rarely used and is used under mild acceleration. However, when the ATF is cold and viscous, the clutches are less likely to slip. When it is warm and runny, they are more likely to slip. This fits my symptoms. The Low/Reverse Brake (a clutch that connects to the case) can't be the problem as it also operates during 1st gear which has no problem. If a clutch or brake is the problem, this requires replace/rebuild.

Reverse Band:
The shop I went to said this was slipping and was the reason for my problem. This can't be the problem though because there isn't a "reverse band". There is a "brake band" that surrounds the reverse drum but it only operates in 2nd and 4th gears NOT during reverse.

Other Hydraulic Problems:
Solenoids help route hydraulic fluid from the pump lines through the maze-like valve body to the appropriate pistons and clutch packs. They should throw a code if they are malfunctioning. I don't have any codes. Maybe though the solenoid is functioning but a seal around a solenoid or valve is allowing oil to leak elsewhere. If there is a problem with a solenoid or valve or clog in the valve body, this can be fixed by pulling out the valve body through the pan -relatively easy.

Service Manual:
The service manual has a section "Does not creep backwards in R". The recommendations are to do a stall test. If 1st gear is good but R is bad (as is my experience) this is suggested:
*Remove control valve body and inspect line pressure stuff
*Remove the whole transmission and inspect oil pump, torque converter, reverse clutch and high clutch
I don't know why they recommend inspecting the high clutch here.


Plan:
*Inspect shift lever linkage
*Test line pressure to detect a hydraulic problem.
*Use TransX (for older transmissions) to increase friction, recondition seals, clean any buildup.
*If this resolves the issue then I'll replace the oil/filter and add TransX again and monitor.
*If it doesn't resolve the issue and there is a pressure problem then I'll remove the valve body and poke around including testing the solenoids.
*If it doesn't resolve the issue and there isn't a pressure problem then I'll have to go for the replace/rebuild.
 

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Dude, I'm an OLD ASE Master Mechanic. ( which means I passed a few tests) Transmissions typically require a specialist. You stated:

"I knew almost nothing about automatic transmissions before last weekend. I've researched by watching videos, reading websites and reading the official service manual which has been the most helpful."

My hat is off to you! I just pulled/replaced this same transmission last weekend in a pathfinder. The difference is, it was for a special family member, (daughter) and SOMEBODY else rebuilt it! :)
 
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