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Old 05-15-2014, 06:23 AM
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WJ Reverse Gear Issues when Warm

Hi All
New to this site so hello from Australia.
So I have an issue with my 2001 GC WJ 4.7 with a 545RFE transmission.
When started from cold no problems, drives and shifts very smooth.
After a drive and warmed up, sometime the transmission does not want to select reverse. Just idles like its in N. When revved it will usually jump in.
When it is in, there is no slip.

This has been going on for a couple of years. Took it to a shop who did a service and the problem went away. I came back a month ago, so I serviced the transmission with genuine parts and fluid at $$$.
The drain pan was very clean inside, the magnet only had a light covering of grey deposit.
Since the service it has only done this twice in 8 trips.
Checked the fluid level using the correct method and all good and clean.
But its still there !

Oh no codes

Any Ideas would be very appreciated

Thanks
Jon
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Old 05-15-2014, 06:48 AM
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Re: WJ Reverse Gear Issues when Warm

Welcome to the garage Jon.
The 5-45RFE transmission is a fully electronically controlled transmission, except for reverse. When moving the shift lever to reverse, the manual valve in the valve body is moved, so that the clutches used for reverse are pressurized. A slight misalignment of the control cable could cause the valve to not be exactly in the position it should be. Thermal expansion (from engine and transmission) could be the reason its still ok when cold, but acts up when hot. Also check the routing of the cable, that its not stuck somewhere halfway and could change the output of the cable due to the thermal expansion.
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Old 05-15-2014, 06:53 AM
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Re: WJ Reverse Gear Issues when Warm

Quote:
Originally Posted by Frango100 View Post
Welcome to the garage Jon.
The 5-45RFE transmission is a fully electronically controlled transmission, except for reverse. When moving the shift lever to reverse, the manual valve in the valve body is moved, so that the clutches used for reverse are pressurized. A slight misalignment of the control cable could cause the valve to not be exactly in the position it should be. Thermal expansion (from engine and transmission) could be the reason its still ok when cold, but acts up when hot. Also check the routing of the cable, that its not stuck somewhere halfway and could change the output of the cable due to the thermal expansion.

Hi Frango thanks for that information. I'll check that out, is there a way to make sure it's aligned?



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Old 05-15-2014, 07:05 AM
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Re: WJ Reverse Gear Issues when Warm

You should remove the cable end from the transmission lever (in Park position) and see if you can move the lever more aft. Also if the lever moves a bit when removing the cable end and/or it doesnīt align perfectly when you want to reinstall the pin, then its slightly misaligned. The adjustment must be done from under the shiflever floor console. There you will find an adjustment screw. If this seems to be perfectly aligned, then there must be a problem at the valve body or internal shift mechanism.
There is a remote possibility that there is a problem with the reverse clutch, but i wonder if that would be temperature depending.
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Old 05-16-2014, 04:31 AM
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Re: WJ Reverse Gear Issues when Warm

Thanks I'll take a look over the weekend and let you know cheers


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Old 05-17-2014, 01:43 AM
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Re: WJ Reverse Gear Issues when Warm

I checked out the shift cable and it looks like the adjustment is ok
I went on a good trip and got the tranny up to temp, checked the fluid and all ok.
Got home put it into reverse and it just sat there. Tried different combinations of selecting gears
From park to drive to reverse and 1 and 2 still just sat there in reverse. I blipped the throttle slightly and in it went.
Think it might be a pressure issue, could it be the pressure sensor reading slightly high therefore keeping the actual pressure low?
Would a line pressure booster mod do the trick ?
Trying to avoid a rebuild !!
Cheers
Jon


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Old 05-17-2014, 07:27 AM
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Re: WJ Reverse Gear Issues when Warm

The 5-45RFE uses a closed loop system for the pressure regulation. The line pressure sensor (which sits on the right hand aft side of the transmission, close to the exhaust hanger) measures constantly the line pressure and the TCM will send signals to the pressure regulation solenoid to regulate the pressure depending on which gear its in. Disconnecting the line pressure sensor connector will make the TCM to send a default signal to the pressure regulator solenoid and a fixed pressure is regulated for all gears. So you could try this out, however i wonder why only in reverse the problem would be there.
Regarding the cable adjustment, did you check it at the moment the problem is there? (hot). On a cold transmission reverse works, so if the problem is caused by thermal expansion, it could eventually be that the cable has a slightly different position hot compared to cold.
For reverse gear, the reverse input clutch and the Low/reverse holding clutch will be pressurized. The reverse input clutch is only used for reverse gear, so normally would not wear out that soon (unless you only drive backwards with your jeep). The Low/reverse clutch is also used in first gear, so since first gear doesnīt have problems, that one is ok.
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Old 05-17-2014, 08:32 PM
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Re: WJ Reverse Gear Issues when Warm

Yeah I checked the cable when cold and hot and when the reverse issue was happening and all seem ok. I will try the pressure sensor disconnect and see what that does. If I turn off and restart the engine when it happens, the reverse is ok again !
Got me stumped


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Old 05-18-2014, 06:24 AM
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Re: WJ Reverse Gear Issues when Warm

And in D it never presents any problem? If disconnecting the line pressure sensor connector doesnīt help, i would suspect a problem with the valve body/manual valve.
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Old 05-18-2014, 06:26 AM
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Re: WJ Reverse Gear Issues when Warm

No problems at all, it drives really well and shifts very smoothly.


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Old 05-18-2014, 07:51 AM
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Re: WJ Reverse Gear Issues when Warm

I was looking into the hydraulic schematic diagram and maybe found the culprit of your problem. There is a small shuttle valve in the valve body, the so called LR switch valve. When in first gear, the LR clutch is activated via the LR solenoid and the LR switch valve is in one position. When you select reverse, this same LR clutch must be pressurized, but then it is selected via the manual valve and the LR switch valve should move over to the other side. This valve gave more problems of binding due to contamination. When you buy the transgo shiftkit, then it comes with a modified LR switch valve, which is less fulnerable to binding. So it could be a good idea to check this valve, if the trick with the line pressure sensor didnīt work out.
To check this valve, the valve body needs to be removed from the transmission and it should be split, to be able to remove the LR switch valve. If you would decide to do so, i could give you some tips.
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Old 05-18-2014, 04:27 PM
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Re: WJ Reverse Gear Issues when Warm

Hi Frango thanks for the info that's very useful and does sound like it could be the problem. I going to do the line pressure mod with a resistor to see if that helps it. I'll look at doing the valve or installing a shift kit next fluid service. Cheers I'll let you know if the mod works.


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