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cornwall 02-05-2014 06:41 AM

Jeep 4.7 Grand Cherokee Ltd Gearbox
Hi all

My first post here as until now my Jeep has been faultless, yippee

The Jeep is a 2001 4.7 Grand Cherokee Limited all standard apart from LPG conversion, everything else works faultless

But now I have a real fault, wonder if you can all help a Jeep novice like me

As I said Jeep driving great

Then suddenly if selected drive would only go in first, no change up at all

Put gear selector in second and would only drive in second

Reverse etc worked

Reading around forums it looked like the two speed sensors were on their way out, I did the key thing to see codes and got the P7000 return

Had the 2 sensors changed yesterday by a local mechanic

Now I went for a drive, to start with very sluggish and slipping no power to the wheels

After a minute running I lost all gears apart from first, no reverse, in fact selecting reverse I could still drive forward

Neutral seems OK so does park

Anyone any ideas on what to do, or is the gearbox totally blown

Thanks all for your help

Frango100 02-05-2014 07:30 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Welcome to the garage.
Your jeep has the 5-45RFE transmission. This is a fully electronic controlled transmission. However reverse is completely mechanically selected. For that reason it is strange that your jeep still goes forward when reverse is selected.
I would have a look first at the gear selecting cable and the lever where it is mounted to on the transmission.
The P0700 code only means that the TCM (transmission control module) has set a fault code(s) and need to be scanned with a scanner which can read those codes.
First get the code(s) to know where to go from there.
Also check the fluid level, colour and smell at this time, because it can tell more on what is going on.
Also it can be that the transmission is in limp mode. This is 3rd gear when D selected or 2nd when 2nd or 1st is selected. The torque converter will do its best to move the jeep, but it will be more sluggish and it will not change any gear, unless you go from D to 2nd or 2nd to D.

cornwall 02-05-2014 09:09 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Thanks for the welcome and the reply, it is appreciated

It is a really weird fault I know I haven't come across it before

I just went down to the jeep and since changing the speed sensors, it is permanently stuck in first, even in reverse, and neutral I think even in park it is trying to drive but the brake is holding it

I am wondering if there is something that the mechanic could have inadvertently dislodged while under the car

I am slow to just jump in and say the gearbox is broken and replace it if there is something in the control department that is giving the electronics weirdo signals

I have checked the fuse and the relay seems to be ok, any suggestions welcome please

Frango100 02-05-2014 09:34 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
1 Attachment(s)
Both speed sensors are mounted on the left side of the transmission housing, one in the front (input speed sensor) and one more at the rear (output speed sensor)
To change these sensors normally nothing else has to be removed (at least how it is mounted on mine), but the aft sensor sits close to the shift manual lever. The fact that in Park the jeep doesn´t move and it does when not in Park, means that at least the shift cable is connected to the shift lever on the transmission. Was it maybe removed and installed wrongly?
In Park a mechanical pawl inside the transmission will hold the transmission output shaft fixed.
I won´t expect this to be an electronic control failure, because reverse is just a mechanical input from the shift lever to a mechanical valve inside the transmission valve body. I expect a mechanical failure or just mechanically something installed wrongly ( ie the lever on the transmission.)
Attached a page from the manual showing how the manual lever on the transmission should be mounted.

cornwall 02-05-2014 11:31 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Hi Frango

Thanks for the greeting and info

The 2 speed sensors were changed and I am led to believe that to get to one of the sensors the bracket by the forward speed sensor that holds the shift lever has had to be undone and replaced, the mechanic definitely removed the bracket and refitted it

I wonder if this has not been put back correctly or can the cable become detached from the end when the bracket is removed ?

If this cable does detach then I have a sneaky feeling that if it was in first gear when he replaced the speed sensors then that is where it is stuck and no matter what I do with the lever it possibly isn't connected properly at one end

Does that sound possible ?

By the way, I went back to the jeep and it does still drive forward in park, in fact it is in first no matter where the lever is, which is pushing my thoughts towards the cable thing

Frango100 02-05-2014 02:26 PM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Another strange thing is that the jeep only should start in Park or Neutral. The switch to achieve this sits inside the transmission and is in fact actuated via the movement of the shift lever. So how can it start and still drive when it doesnt seem to be in Park? Maybe the cable is not well attached, which caused a shift in the shift lever movement? I would start looking at the bracket which you mentioned to see if there is something obviously wrong.

cornwall 02-12-2014 10:42 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
I have been and had a double check with the transmission fault, although the mechanic is going back under this afternoon to double check things, we have been held up here due to flooding in the car park

I also double checked and the car starts in neutral and park and no where else, but only drives forward in any selector including neutral, and will not kick out of first, also when in reverse it still drives forward

This is a weird one

I will let you know what he finds :confused:

Frango100 02-12-2014 12:26 PM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
1 Attachment(s)
I wonder what he will find wrong there. Did he check the TCM fault codes, because that can also help for trouble shooting.
If the shift linkage is mounted ok, then the only thing i can come up with is a broken pin from the manual valve inside the valve body (see item 5 on attached page. This is the manual valve and at the end you will see the small pin which is used to move the manual valve) With this pin broken, the manual valve will not move anymore and stay in the last selected position. The TRS selector plate will still move and actuating the switch for the starter circuit and also you will feel in the shift lever the shift detents, which also come from the TRS selector plate.

cornwall 02-12-2014 05:01 PM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Hi Frango

The cable appears to be fine, everything is moving when the gear linkage operates at the handle

I am thinking that your idea of the pin could well be the problem, just to clarify that, I take it that no matter where the shift plate moves this pin doesn't move the piston so no gear changes happen even if the plate moves, and I can feel the detent of the plate at the handle

This would also stop the reverse from engaging ? hence the forward drive when the selector is in reverse ?

I guess it is a large job to strip and replace the pin or the valve body, that is if there are any spares available ?

Even if there are spares available and it is a reasonable job to do, I bet a box from a breakers yard would be cheaper than the part, or are they a reasonable cost in USA ?

Thanks for all your help

Frango100 02-13-2014 01:49 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
The manual valve pin moves in a track in the TRS selector plate. So when you move the shift lever, the selector plate moves and the shape of the track will set the manual valve in its desired position. The manual valve is used to select reverse, but it also will be in a certain position for Drive, manual 2nd and manual 1st.
Maybe the manual valve got stuck and for that reason the pin broke. Never heard it before, but its a possibility.
Its not such a large job to remove the valve body, its just a bit more work then a fluid change. When the transmission pan is down, you only have to remove the large connector on the left side of the transmission and then you can remove the valve body by removing 6 bolts.
Maybe something else is wrong, but the problem seems to be at least with the valve body. I would remove it and inspect it.
Did the mechanic check the TCM fault codes?

cornwall 02-14-2014 06:54 AM

Re: Jeep 4.7 Grand Cherokee Ltd Gearbox
Hi Frango

First of all thanks for all your help, it is appreciated and people like you who share their knowledge are what makes forums successful

As for the gearbox, it is totally broken, and is being replaced with a used unit next week

Diagnosis from a local auto specialist (he knows these gearboxes very well) is that the first clutch has jammed in position, this is probably due to crap in the oil and lack of maintenance before I owned the vehicle, he says this is the only thing that would allow forward drive while selecting reverse at the gear selector

As I have only had the Jeep a few months and was going to service the gearbox soon, I even have the filters, sump pan gasket and oil sitting here waiting for a dry day this has been an expensive delay on my part

The expert says that the gearbox oil should be changed about every 30 to 40,000 miles, my Jeep has about 87,000 on the clock and I seriously doubt that it has ever been changed

He does say the gearbox is bulletproof if maintained properly, but rubbish if neglected, and he does say he has a Jeep gearbox come in about every 14 days with different problems, all caused by lack of oil changes

I have been lucky, I have found a nice gearbox with warranty that is at a very good price from a breakers, the donor vehicle had a full main dealer service stamps so hopefully they will have changed the oil when needed

My local garage says they can change it out in about 6 hours, I am giving them the filters and gaskets so they can service it at the same time, does 6 hours sound about right ?

The moral of the story, don't forget to change your gear oil, it may seem expensive, but not as expensive as a gearbox change

sanjuro77 02-14-2014 07:00 AM

It really is amazing how many folks ignore regular maintenance!

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