Automatic transmission fine in reverse, but nothing in drive

ZamWrangler

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Jan 9, 2019
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Zambia
Hi Guys,

Followed this forum for a while, but first post. Warning - long post ahead.

A bit of history about my Jeep. I bought my 97 wrangler sahara 4.0 auto in November 2018. It was being sold after being parked for two years due to erratic shifting. While looking it over I discovered the TV cable bracket had come loose, so I was certain that was the issue. Got the jeep home and started work on it. Re attached the bracket and put in a new cable for good measure. It ran fine through all the gears although I couldn't get it to hold a gear past 4000rpm. At the same time i noticed there was a slight leak from the auto sump.

Fast forward till this last week. The jeep had been parked for weeks as I was doing other work to it and waiting for spares. We moved house and I needed to move the jeep. Started driving from the old house but as soon as i went round the first corner the auto started sliping. Checked the level and it was low. I topped it up and it shifted fine till the new house. After using it for a few days I decided to do a filter and ATF change. The sump had some sludge in it and the filter clogged up but not too bad. Put the new filter in topped up to the correct level. I did find a very concerning head for a nut in the sump though.

Decide to give it a test, goes into reverse no problem, put it in drive, it starts to whine and shudder, i give it a bit of gas and it feels like its not in gear. I decided to give it a flush, disconnected at the cooler outlet, start it in neutral, nothing comes out. Disconnected at the inlet and it comes out fine. I blew air backwards though the cooler reconnected and tried again. Pumped through fine, checked the return line to the box and it was clear. Flushed with 12L.

Checked the level and gave it a test. Again, reverse perfect. Put it in drive, slight delay then engages good. As soon as i give it a bit of gas, feels like its slipping with a bit of juddering, build up to 1500rpm and it starts taking better, over 2000rpm as it should be. Took it round the block to see how it goes. Performs the same though all the gears. Pull back into the drive and suddenly loose all drive and a faint whine can be heard. I checked the cooler outlet again and pumping fine. Double checked level and spot on.

I'm lost with where to look next. There are no transmission shops close to me and a 2nd hand box is close to $3000 here.

All ideas welcome.
 
Pic for attention.
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20190101_123840.jpg
 
The only nut I can think of is for the jam nut for the internal band adjustment. I don't have a pic handy here at work, but there are several threads on how to make band adjustments. Seems like an odd thing to have loosen up but there really aren't any nuts inside the tranny, just lots of bolts, screws and clips.
 
The only nut I can think of is for the jam nut for the internal band adjustment. I don't have a pic handy here at work, but there are several threads on how to make band adjustments. Seems like an odd thing to have loosen up but there really aren't any nuts inside the tranny, just lots of bolts, screws and clips.
It is actually a head for a bolt rather than a nut. About a 6mm head.

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When you are checking its ATF level, is the engine running and is the transmission in Neutral while you're checking its dipstick?

If the engine isnt running or if the transmission is in Park while you are checking its ATF level, the dipstick will give an erroneous indication of more fluid being present than there really is.
 
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When you are checking its ATF level, is the engine running and is the transmission in Neutral?

If the engine isnt running or if the transmission is in Park while you are checking its ATF level, the dipstick will give an erroneous indication of more fluid being present than there really is.
Yes running and in neutral.

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So the only logical reason i can think of the transmission behaving like it is, is that I have a blockage somewhere or a seal is gone.

I am going to drop the box and rebuild it myself. Looking at getting a rebuild kit from www.transpartsonline.net

Looking at either the MRK deluxe master kit or the Red eagle master kit.

What else will i need to do while it is out. Should i consider replacing the pump? Also will i need any specialist tools.

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Sorry for not responding sooner, been traveling for work.

First, look at this video. It provides a pretty good explanation of how typical 3 speed autos like ours work.


You can see that everything is controlled by fluid pressure taking different pathways through the valve body to a series of pistons that actuate clutch packs and bands. In the video, you can see a representation of the fluid movement for all gearshift positions (Drive 1-3 is the transmission automatically changing gears and Select 1 & 2 are positions 1 & 2 on the gear selector lever). Notice on the Select 1 & 2 fluid pressure is used to both actuate the pistons and prevent the upshifts. The transmission uses various strength springs so as pressure increases due to the movement of the throttle position cable (TV cable), the fluid can move into different pathways to actuate the correct pistons / valves. This is why having the TV cable correctly adjusted is so important.

You will see in the video that the Reverse gear uses a separate band actuated by fluid moving a specific pathway through the valve body. This is why your reverse seems to work fine. It is also why most rebuild kits only come with one band - the reverse band doesn't get much use/abuse.

If I understand your issue, it is an intermittent issue that can be corrected by letting it sit. This, to my less than expert brain, says there is an issue with a blockage in the valve body. Inside the valve body are a number of small ball bearings that are really check valves. If there is sludge in there the balls won't move freely or seal properly. A fluid flush seems to fix the problem temporarily until the sludge moves itself back to the valve and the problem reappears. This is also why people argue not to flush their transmissions. They believe it "causes" transmission issues. You have to understand that the sludge is the friction material worn off the bands and clutch packs. If you have sludge, you already have a problem and will need a rebuild.

If it was my Jeep, I would start by disassembling and cleaning the valve body. If you are thinking about rebuilding the transmission anyway, you will have to do this as part of the rebuild. The upside is that the valve body can be removed and cleaned without pulling the transmission. You will be out some time and a few quarts of transmission fluid. There are many videos online that walk you through this process. It is the part that the filter attaches to. The hardest part is the small detent ball that the shift actuator connects to. Hard, but certainly not impossibly difficult to do by yourself. It is more of a coordination thing. Have a buddy help hold things.

Once it is clean, you will know the fluid is moving properly to control everything. This may solve the problem. If not, the next step would be a rebuild. You will know if it worked because the transmission will slip as it shifts to second or once in third. The full rebuild will replace all the O-rings that allow the pistons to hold enough pressure to function properly. It will also replace all of the friction material (Clutches and bands) in the transmission.

Part of the rebuild kit will also replace the o-ring and bushing at the pump. The pump is gear driven and likely won't have to be replaced unless the gears are out of tolerance, which seems pretty rare from my investigation.

I have a bad transmission in my 2000 Sahara that slips as it shifts into second. If I keep the RPMs smooth it shifts fine but if I am accelerating quickly it shudders and slips like crazy. Luckily it is my son's Jeep and h is just learning to drive so the Jeep doesn't get used much and rarely sees speeds over 45. I am waiting until the weather breaks a bit since winters here are very cold and even with a garage, not much fun to turn wrenches in. For the record, I have only helped rebuild a similar TH350 transmission before but they are all pretty much the same 3-speed autos.

As far as tools, you will need to be able to measure the end-play of the shaft so you will need a dial gauge and a micrometer to measure thrust washers, etc. Pretty cheaply found. A vice is also nice to have and a 1/4" inch-pound torque wrench.
 
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Sorry for not responding sooner, been traveling for work.

First, look at this video. It provides a pretty good explanation of how typical 3 speed autos like ours work.


You can see that everything is controlled by fluid pressure taking different pathways through the valve body to a series of pistons that actuate clutch packs and bands. In the video, you can see a representation of the fluid movement for all gearshift positions (Drive 1-3 is the transmission automatically changing gears and Select 1 & 2 are positions 1 & 2 on the gear selector lever). Notice on the Select 1 & 2 fluid pressure is used to both actuate the pistons and prevent the upshifts. The transmission uses various strength springs so as pressure increases due to the movement of the throttle position cable (TV cable), the fluid can move into different pathways to actuate the correct pistons / valves. This is why having the TV cable correctly adjusted is so important.

You will see in the video that the Reverse gear uses a separate band actuated by fluid moving a specific pathway through the valve body. This is why your reverse seems to work fine. It is also why most rebuild kits only come with one band - the reverse band doesn't get much use/abuse.

If I understand your issue, it is an intermittent issue that can be corrected by letting it sit. This, to my less than expert brain, says there is an issue with a blockage in the valve body. Inside the valve body are a number of small ball bearings that are really check valves. If there is sludge in there the balls won't move freely or seal properly. A fluid flush seems to fix the problem temporarily until the sludge moves itself back to the valve and the problem reappears. This is also why people argue not to flush their transmissions. They believe it "causes" transmission issues. You have to understand that the sludge is the friction material worn off the bands and clutch packs. If you have sludge, you already have a problem and will need a rebuild.

If it was my Jeep, I would start by disassembling and cleaning the valve body. If you are thinking about rebuilding the transmission anyway, you will have to do this as part of the rebuild. The upside is that the valve body can be removed and cleaned without pulling the transmission. You will be out some time and a few quarts of transmission fluid. There are many videos online that walk you through this process. It is the part that the filter attaches to. The hardest part is the small detent ball that the shift actuator connects to. Hard, but certainly not impossibly difficult to do by yourself. It is more of a coordination thing. Have a buddy help hold things.

Once it is clean, you will know the fluid is moving properly to control everything. This may solve the problem. If not, the next step would be a rebuild. You will know if it worked because the transmission will slip as it shifts to second or once in third. The full rebuild will replace all the O-rings that allow the pistons to hold enough pressure to function properly. It will also replace all of the friction material (Clutches and bands) in the transmission.

Part of the rebuild kit will also replace the o-ring and bushing at the pump. The pump is gear driven and likely won't have to be replaced unless the gears are out of tolerance, which seems pretty rare from my investigation.

I have a bad transmission in my 2000 Sahara that slips as it shifts into second. If I keep the RPMs smooth it shifts fine but if I am accelerating quickly it shudders and slips like crazy. Luckily it is my son's Jeep and h is just learning to drive so the Jeep doesn't get used much and rarely sees speeds over 45. I am waiting until the weather breaks a bit since winters here are very cold and even with a garage, not much fun to turn wrenches in. For the record, I have only helped rebuild a similar TH350 transmission before but they are all pretty much the same 3-speed autos.

As far as tools, you will need to be able to measure the end-play of the shaft so you will need a dial gauge and a micrometer to measure thrust washers, etc. Pretty cheaply found. A vice is also nice to have and a 1/4" inch-pound torque wrench.
Thanks for all this information.

It pulled the valve body today and started cleaning. Not too much sludge but it is there.

My big concern can be seen in the pictures. Its been worked on before and shortcuts taken. Could the bare wires or cracks cause this issue? Could the missing pieces of tape be sucked up and block something? Or would it have been stopped by the filter?

Looking at the poor workmanship i'm sure i will just pull the transmission and rebuild for peace of mind.
52d99cef7d1ce5e6b889d39af2b12c09.jpg
cc1266c12730d9299db037593b29c85d.jpg


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The tape probably didn't get into the valve body but who knows where it ended up inside the rest of the transmission. Any contamination on the friction surfaces of the bands and clutches could easily glaze them up and reduce their effectiveness. The bare wires are obviously a concern as are the cracks. Since everything is pressure controlled, anything that can affect the consistent pressure to the actuator pistons will cause the bands and/or clutches to not be held as tightly as needed. Voltage issues and shorting of the wires will cause all kinds of pressure inconsistencies.

I would solder/shrink wrap the wires, replace the O-rings and that cracked part and then give it a test run. You will still ultimately need to rebuild it, but it may put the schedule more on your terms rather than an immediate need. Worse case, you have to pull the transmission now, best case, you can take the time to plan the rebuild out. There is nothing you can do to hurt the transmission anymore at this point.

Have you separated the valve body into two halves? How did the internal channels look? Did the check balls move freely or was there any sludge in there?

Also, make sure you clean the inside of the valve body with lint free cloth. When it is all clean and dry, blow it with air to remove anything that may be in there. You cannot make it too clean! Same goes for the valves themselves. Any trapped debris will prevent them from moving freely and will stop the fluid from moving as needed. If the valve can only open partially, the loss of pressure will affect the overall ability to "tighten" the band and clutch packs.

As I have done more learning, the pressure is very important but the speed at which the pressure builds is equally important. The faster the pressure builds and actuates the internal mechanisms, the quicker the transmission shifts. Faster shifts mean less heat and less wear. Think about a clutch in a manual. Rev up the engine and release the clutch slowly and the clutch gets destroyed. Same thing happens in our transmissions. If the clutch packs or bands tighten slowly, they spin excessively, glaze over and lose their friction properties. Hope that helps.
 
Last edited:
Sorry for not responding sooner, been traveling for work.

First, look at this video. It provides a pretty good explanation of how typical 3 speed autos like ours work.


You can see that everything is controlled by fluid pressure taking different pathways through the valve body to a series of pistons that actuate clutch packs and bands. In the video, you can see a representation of the fluid movement for all gearshift positions (Drive 1-3 is the transmission automatically changing gears and Select 1 & 2 are positions 1 & 2 on the gear selector lever). Notice on the Select 1 & 2 fluid pressure is used to both actuate the pistons and prevent the upshifts. The transmission uses various strength springs so as pressure increases due to the movement of the throttle position cable (TV cable), the fluid can move into different pathways to actuate the correct pistons / valves. This is why having the TV cable correctly adjusted is so important.

You will see in the video that the Reverse gear uses a separate band actuated by fluid moving a specific pathway through the valve body. This is why your reverse seems to work fine. It is also why most rebuild kits only come with one band - the reverse band doesn't get much use/abuse.

If I understand your issue, it is an intermittent issue that can be corrected by letting it sit. This, to my less than expert brain, says there is an issue with a blockage in the valve body. Inside the valve body are a number of small ball bearings that are really check valves. If there is sludge in there the balls won't move freely or seal properly. A fluid flush seems to fix the problem temporarily until the sludge moves itself back to the valve and the problem reappears. This is also why people argue not to flush their transmissions. They believe it "causes" transmission issues. You have to understand that the sludge is the friction material worn off the bands and clutch packs. If you have sludge, you already have a problem and will need a rebuild.

If it was my Jeep, I would start by disassembling and cleaning the valve body. If you are thinking about rebuilding the transmission anyway, you will have to do this as part of the rebuild. The upside is that the valve body can be removed and cleaned without pulling the transmission. You will be out some time and a few quarts of transmission fluid. There are many videos online that walk you through this process. It is the part that the filter attaches to. The hardest part is the small detent ball that the shift actuator connects to. Hard, but certainly not impossibly difficult to do by yourself. It is more of a coordination thing. Have a buddy help hold things.

Once it is clean, you will know the fluid is moving properly to control everything. This may solve the problem. If not, the next step would be a rebuild. You will know if it worked because the transmission will slip as it shifts to second or once in third. The full rebuild will replace all the O-rings that allow the pistons to hold enough pressure to function properly. It will also replace all of the friction material (Clutches and bands) in the transmission.

Part of the rebuild kit will also replace the o-ring and bushing at the pump. The pump is gear driven and likely won't have to be replaced unless the gears are out of tolerance, which seems pretty rare from my investigation.

I have a bad transmission in my 2000 Sahara that slips as it shifts into second. If I keep the RPMs smooth it shifts fine but if I am accelerating quickly it shudders and slips like crazy. Luckily it is my son's Jeep and h is just learning to drive so the Jeep doesn't get used much and rarely sees speeds over 45. I am waiting until the weather breaks a bit since winters here are very cold and even with a garage, not much fun to turn wrenches in. For the record, I have only helped rebuild a similar TH350 transmission before but they are all pretty much the same 3-speed autos.

As far as tools, you will need to be able to measure the end-play of the shaft so you will need a dial gauge and a micrometer to measure thrust washers, etc. Pretty cheaply found. A vice is also nice to have and a 1/4" inch-pound torque wrench.

My 2001 4.0 TJ 32RH is doing the exact same thing as your 2000. Way worse going up steep hills. Would adjusting the bands help?
 
Well, to add to the thread my story....I recently did a tranny oil flush with tranny oil filter change. Everything went awesome, except approximately a week ago when I shifted to reverse and it started slipping and shuddering (not much power at all) 1st and 2nd are good to go when shifting, 3rd or (OD) shudders when shifting but not always. Is it time for a tranny overhaul? What could be the culprit after the oil change? BTW: Oil level is on spot!
 
Something to try is to add a little more ATF+4 to bring it right to the full line. I've seen slippage on the trail being as little as a half-quart low.