T18A Shifting Difficulty in 77 CJ5 - JeepForum.com
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post #1 of 21 Old 08-03-2020, 10:22 AM Thread Starter
cyates13B
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T18A Shifting Difficulty in 77 CJ5

Hello all! Trying to diagnose an issue with my T18A (AMC 304 V8 if engine size is needed). It seems to have an intermittent "hard shifting" issue. It becomes more noticeable once I've driven for awhile (after engine gets to operating temp), although it isn't permanent. For the first 5-10 miles it shifts like a dream (relative to a T18A); but after that it starts to get spotty. Sometimes it'll shift fine and other times it takes two hands to pull it into 2nd at a stop light. It sometimes gets better if I downshift 4th->3rd->2nd; but not always. I don't exclusively double-clutch; but haven't noticed that double-clutching makes it go away. I use Pennzoil gear oil (recommended for older transmissions), and the transmission was re-built about 6 years ago (replaced a gear and one or two collars). The fact that it occasionally shifts fine makes me think it isn't a clutch adjustment issue; and maybe the 5-10 miles thing is a coincidence. Doesn't appear to be losing gear oil (I use the un-scientific "pinky finger in the top plug" method to measure). Have others had this issue? If so, what ended up being the root cause/ fix? I've had other Jeeps with the T18A and it wasn't ever this difficult.

Thank you in advance for any help!

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post #2 of 21 Old 08-03-2020, 06:01 PM
adman02
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What kind of gear oil are you running in it? It should be GL4 IIRC. I put GL4 in mine and it seems to help with the shifts (still fees like driving a school bus though).
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post #3 of 21 Old 08-03-2020, 06:44 PM
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I never understood "fingering" your fill holes, the manuals say otherwise.

If it don't run back out, it's not full enough.

Here's the manual explanations.

----JEEPFELLER
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post #4 of 21 Old 08-03-2020, 06:49 PM Thread Starter
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Iíll top it off. Do you think that would explain my issue? Or could it just be a contributing factor?


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post #5 of 21 Old 08-03-2020, 06:50 PM
oldschool74cj5
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hello

i saw that you said you used pennziol gear oil. if it is the pennzoil snychromesh that could be part of the problem because it is to thin of a oil the snychros wont work properly. the t18 is a old iron granny transmission. the oil that needs to be used is a 80w90 gl4 gear oil. i would look at the stalube 85w90 gl4 gear oil.

oldschool
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post #6 of 21 Old 08-03-2020, 07:25 PM Thread Starter
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Originally Posted by oldschool74cj5 View Post
hello

i saw that you said you used pennziol gear oil. if it is the pennzoil snychromesh that could be part of the problem because it is to thin of a oil the snychros wont work properly. the t18 is a old iron granny transmission. the oil that needs to be used is a 80w90 gl4 gear oil. i would look at the stalube 85w90 gl4 gear oil.

oldschool

Yes, itís the Pennzoil Synchromesh, as I believe it was recommended at NAPA for ďolderĒ transmissions. As far as Stalube, it says itís for hypoid gears, which I was under the impression wasnít ďrightĒ for this transmission. Not arguing, just trying to verify. Could that be part of the fact that it seems to occur more after driving for awhile? Being too thin and not working well with the synchronizers makes sense (perhaps temperature is effecting viscosity?).


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post #7 of 21 Old 08-03-2020, 07:33 PM Thread Starter
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Originally Posted by adman02 View Post
What kind of fear oil are you running in it? It should be GL4 IIRC. I put GL4 in mine and it seems to help with the shifts (still fees like driving a school bus though).

Itís Pennzoil Synchromesh. I believe it was recommended at NAPA for the transmission (due to being safe on yellow metal). Another comment mentioned it was too thin, which makes sense in my mind for why it seems harder to shift after running for a bit.


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post #8 of 21 Old 08-03-2020, 10:54 PM
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Quote:
Sometimes it'll shift fine and other times it takes two hands to pull it into 2nd at a stop light.
Sounds a bit like a clutch issue. When this happens I would try to shift into reverse. If it grinds, then the clutch isn't disengaging.


As for oils, straight 50WT engine oil has been found effective for smoothing balky shifting T18's.

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post #9 of 21 Old 08-04-2020, 03:04 AM Thread Starter
cyates13B
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Originally Posted by jeepdaddy2000 View Post
Sounds a bit like a clutch issue. When this happens I would try to shift into reverse. If it grinds, then the clutch isn't disengaging.


As for oils, straight 50WT engine oil has been found effective for smoothing balky shifting T18's.

Iíve not trie to shift into reverse when this happens; but I have gone back through the gears (4->3->2) and sometimes that helps.

What could be the clutch issue? Could the linkage be out of adjustment - or something else?

Iíve seen posts about 50W engine oil in the past. If I go that route is there anything specific I need to do differently (shorter intervals between transmission oil change)?


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post #10 of 21 Old 08-04-2020, 04:26 AM
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Jeep also advised for the T18 using 85w90 GL5 lube, just to confuse us. I woudl stick with GL4 if that was the recommendation in your year.

Take your pick but it does sound either the lube is giving problems when it heats up or the clutch is not adjusted properly.

Transmission oil changes are every 27,500 miles. No matter what oil you use this should be fine unless you have been through a river and water has got into the oil. I check mine every 6 months and change about every 4th year on the whole fleet, just easier to get them all lined up.
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post #11 of 21 Old 08-04-2020, 04:36 AM Thread Starter
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Originally Posted by BagusJeep View Post
Jeep also advised for the T18 using 85w90 GL5 lube, just to confuse us.

Take your pick but it does sound either the lube is giving problems when it heats up or the clutch is not adjusted properly.

Yeah, the current gear oil has been in for over a year, so if comes down to changing it, thatíll be alright.

Iíll try adjust the clutch linkage first to see if they helps. Normally, I adjust the linkage where I feel it disengage when the pedal is about halfway down or so. If that helps, I can take it out to see how it shifts.

Iím also leaning towards the lube being an issue once it heats up. The earlier comment about the Pennzoil Synchromesh being too thin seems logical to me.


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post #12 of 21 Old 08-04-2020, 05:29 AM
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Originally Posted by cyates13B View Post
Iíve not trie to shift into reverse when this happens; but I have gone back through the gears (4->3->2) and sometimes that helps.

What could be the clutch issue? Could the linkage be out of adjustment - or something else?
A solid transmission with operating syncro's won't allow you to shift into gear without the clutch being disengaged. It won't grind, it simply won't go into gear. This is where the reverse shift comes in. Since reverse isn't syncro'd, attempting to shift into it will produce one of two results. Either it will go in smoothly (clutch operational) or it will grind (clutch dragging). The vehicle, of course, must be stopped when doing the test.



Quote:
Iíve seen posts about 50W engine oil in the past. If I go that route is there anything specific I need to do differently (shorter intervals between transmission oil change)?
The swap to 50WT addresses another issue. T18 are balking shifting transmissions on a good day. moving to a thinner oil allows the syncros to operate better and the transmission to shift faster and smoother (especially in cold weather). It is the recommended "go to" solution for many IH owners, where T18's were a staple transmission.

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post #13 of 21 Old 08-04-2020, 07:14 AM Thread Starter
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Originally Posted by jeepdaddy2000 View Post
A solid transmission with operating syncro's won't allow you to shift into gear without the clutch being disengaged. It won't grind, it simply won't go into gear. This is where the reverse shift comes in. Since reverse isn't syncro'd, attempting to shift into it will produce one of two results. Either it will go in smoothly (clutch operational) or it will grind (clutch dragging). The vehicle, of course, must be stopped when doing the test.
I generally get a little bit of grinding (less than a second before it goes into gear) when I shift into first/ reverse. Sometimes it doesn't; but it generally does. I always chalked that up to it being non-synchronized. I don't recall if it gets better after I've adjusted the clutch linkage.


Also is the 50W thinner than the Pennzoil Synchromesh? An earlier comment mentioned the thinner Pennzoil lube could be part of my problem.
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post #14 of 21 Old 08-04-2020, 12:19 PM
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The stuff I posted (even up above-with gear oil specs) is from the 1977 AMC JEEP service manual.

I also have a paper version of the '79.

Both manuals state that the free play in the clutch pedal should be .88"- 1". This means from the top (idle pedal at rest), as the pedal is depressed it will start pushing the pressure plate from 1 inch of travel and on (this means the plate, not the throwout bearing) The throwout is being moved during the 1 inch of freeplay.

So in short, the JEEPFELLER interpretation, your pedal is at the top, your clutch disc should be disengaged before your pedal is pushed halfway down (or sooner).

As far as a tough, hard to push clutch, if you are mainly a street and mild off road kind of Jeep guy, I recommend that the next clutch you install be a diaphragm type.

If you'll look this over, you'll also find ways to make/ and keep the linkages always reliable and EZ to push.

https://www.jeepforum.com/forum/f8/o...bolts-4397129/

----JEEPFELLER
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post #15 of 21 Old 08-04-2020, 12:40 PM Thread Starter
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Originally Posted by JEEPFELLER View Post
The stuff I posted (even up above-with gear oil specs) is from the 1977 AMC JEEP service manual.

I also have a paper version of the '79.

Both manuals state that the free play in the clutch pedal should be .88"- 1". This means from the top (idle pedal at rest), as the pedal is depressed it will start pushing the pressure plate from 1 inch of travel and on (this means the plate, not the throwout bearing) The throwout is being moved during the 1 inch of freeplay.

So in short, the JEEPFELLER interpretation, your pedal is at the top, your clutch disc should be disengaged before your pedal is pushed halfway down (or sooner).

As far as a tough, hard to push clutch, if you are mainly a street and mild off road kind of Jeep guy, I recommend that the next clutch you install be a diaphragm type.

If you'll look this over, you'll also find ways to make/ and keep the linkages always reliable and EZ to push.

https://www.jeepforum.com/forum/f8/o...bolts-4397129/

----JEEPFELLER
Great information, I really appreciate it! It's sounding like my clutch isn't correctly adjusted. I will adjust it this evening and see if I can get a better adjustment. Just to make sure I'm understanding correctly, pretty much as soon as I start pushing the pedal in, the linkage should be moving the throw-out bearing, right? So that by the time I get close to the bottom of the pedal, everything should be totally disengaged. I just want to make sure i'm not "riding" the throw-out bearing.

If properly adjusted, would my pedal stop moving before hitting the floor? I can't recall off-hand if it does or not; I'm just curious if the pedal stopping above the floor would be a sign that I was a bit more properly adjusted.

I also have a couple quarts of the synchromesh gear oil - so I'm planning to top off the transmission and t-case (until it starts to spill out) to see if that, along with adjusting the clutch linkage, helps my issue. I would just rather try this approach instead of draining and re-filling everything if it was a linkage issue all along.
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