Very difficult to get into gear when cold

[Nordic]

My gf has a 94 Yj- now I know that this is a TJ forum, but the engine, transmission, and transfer case that are in it came out of my sister's jeep 98 TJ. The ax15 has about 170,000 miles on it. So a little while after the swap last year, the transmission started having issues going into 1st and 2nd. I did a fluid change with Redline-MT 90, and the shifting improved dramatically, no longer getting stuck. This was about a year ago. So anyhow, fast forward to 5 or so months ago, the not going into first and second issue starts coming back. Unfortunately I was overseas at the time, so I couldn't take a look at it until a couple of months after that. This time I was able to notice that the master cylinder had developed a leak, so I swapped it with a Dorman unit. This, again, improved the issue substantially at first, but now that it is colder in Colorado the issue has been happening again. Once the trans has warmed up a little bit it does get better and only sometimes won't go in, however she has major issues getting it into first and second before then- it's almost undrivable.
What should my plan of attack be here? I do have some Redline left over, so I could do another fluid change, and I also have a LuK clutch kit laying around which I could use, but I'm really unsure of whether this is the transmission going bad or whether it is the clutch which is not allowing it to go into gear. I do not know whether the clutch was ever replaced on it previously.

 

[NDSpeed]

Are you running full synthetic fluids? I’m not familiar with redline

 

[PatMc]

I would check to make sure the clutch (and pilot shaft) is able to dissengage properly at cold temps. Put it in 1st gear, parking brake off, depress the clutch and start it...does it try and lurch forward a bit?

 

[Jerry Bransford]

Are you running full synthetic fluids? I’m not familiar with redline

Redline is a top performing full-synthetic gear lube that works well in our Wrangler manual transmissions. Redline MT-90 for the AX-5 and AX-15 transmissions, Redline MTL for the NV3550 and NSG370 transmissions.

 

[NDSpeed]

I may have to change the fluid in my NSG370. I used Royal Purple when I installed the New to me Tranny. It isn’t exactly great. I’ll eventually have to have it rebuilt

 

[Goatman]

For some reason certain transmissions like to get real stiff in cold temperatures. I mean, they all do a little. The fluid is thicker and offers more resistance to the linkage and gears moving around.
But some, those early Hyundai gearboxes come to mind, get really stiff.
Assuming the clutch system is working properly I would drain the fluid, make sure it isn't full of metal bits, and go to a slightly thinner fluid. From a 80/140 to a 75/90 or something like that.

 

[Nordic]

Did a fluid change yesterday with more Mt-90, the fluid that came out was fairly dark, and a had quite a bit of brass in it, not a massive amount, but seeing as I last changed it 10k miles ago, it's more than I'd like to see.

Also, I should note that the new clutch pedal is difficult to push. It was very stiff to begin with and has lossened up some, but it's still harder than my OEM clutch in my TJ. Also, the cold just makes it happen more frequently and badly near startup, but then it will randomly happen throughout driving as well. I'm just confused as to whether this is a clutch issue or an issue with the transmission itself, as I've looked at multiple threads that have said the not going into gear issue is usually caused by the slave/master cylinder, but I've replaced those with only a little improvement.

I'm going to dry to do the whole start in gear thing today, I'll report back.

 

[PatMc]

The master and slave themselves will not have any influence on difficult the pedal is to push...The failure mode on these is simply leaking.

Galling/binding of the fork on the pivot ball, can cause resistance, dirt/hardened dried out schmoo on the front bearing retainer that the TO bearing rides on can cause resistance, and typically when clutch covers get a fair amount of miles on them they take more effort to disengage than they did when they were new....none of these though, will cause the clutch not to fully disengage if you CAN get the clutch pedal to the floor.

How many miles on the current clutch?...it might be time.

There are a couple schools of thought on use of lubricants during clutch installation...keeping in mind that the clutch will spend it's life in a hot enclosure full of flying abrasive dust...

1: Go in dry, no lube on the pilot shaft splines. This could eventually result in rust on the splines of the shaft and clutch which will cause the disc not to float between the flywheel and the pressure plate when the pedal is depressed..and could cause a light dragging.

2: Use lube on the splines, which will eventually collect a bunch of abrasive dust, turning it into a thick putty and causing the same thing.

In dry climates I typically don't use any lube...but guys in corrosive/wet climates lube the hell out of everything. There is no right answer here, it depends.

 

[Nordic]

Had a chance to drive it around this morning. Did the start in gesr with clutch depressed thing, did not cause it to lurch, but at that time when I started it, it was shifting fine. After about 30 minutes of driving was when it started acting all sort of weird this time around, at one point had to start it in third. The whole binding on the disengagement thing makes sense, but not sure why it happens so randomly. At this point, I think I'm just going to replace the clutch, unless anyone has any other thoughts.

 

[PatMc]

Had a chance to drive it around this morning. Did the start in gesr with clutch depressed thing, did not cause it to lurch, but at that time when I started it, it was shifting fine. After about 30 minutes of driving was when it started acting all sort of weird this time around, at one point had to start it in third. The whole binding on the disengagement thing makes sense, but not sure why it happens so randomly. At this point, I think I'm just going to replace the clutch, unless anyone has any other thoughts.

If you feel the clutch pedal is abnormally and excessively stiff, I would recommend this route. If you feel the clutch pedal is OK in terms of it's action...then you might try a quick fluid replacement and bleed...since you can do it in 20 minutes and it costs $5. There's a write up in the "how to" section...but it misses explaining the mechanics of the system, which can help.

Unbolt the slave from the bellhousing...let it hang. Using a syringe or whatever you have on hand (straw with your finger held over the top works in a pinch)...draw as much fluid out of the master cylinder reservoir as you can, then get a helper to compress the piston in the slave cylinder as far as it goes and hold it there while you draw the rest of the fluid out of the master reservoir. Fill the master cylinder with new fluid, then have your helper slowly release the slave cylinder. Add fluid as necessary to avoid the master running dry...you want the reservoir about 1/2 full when the slave is fully extended. As air rises, very carefully manipulate the slave cylinder such that the line fitting is as close to the highest point as possible...then cycle the slave cylinder a handful of time while a helper keeps an eye on the reservoir. It should appear dead clear while this is happening. If there are any bubbles, or what appears to be fog rising through the fluid...then you have air in the system and you're getting it out. Continue until it's clear. Bolt the slave back in, taking care to get the tip of the pushrod aligned appropriately in the clutch fork. See if it works any better.

We have seen old, moisture saturated brake fluid develop little crystaline frozen chunks in extreme cold temps, and excessive moisture contamination can also result in considerably lower fluid boiling points. One would not expect fluid to ever boil in a plastic system before the plastic melted, but stranger things have happened.

The fact that it worked fine when cold but had problems when it warmed up makes me lean towards hydraulics rather than binding...but there could be other things going on.

 

[TrueTexas]

The first Luk clutch master and Slave Cylinder I installed leaked right away so I guess it's possible the Doorman unit you got has gone bad.

However, your symptoms are almost exactly what mine was doing when I bought it. When it warmed up, it no longer went into gear.

I came to the decision that the input shaft was not being allowed to spin down either with the clutch depressed or in neutral. This meant the tranny was coming out. My initial guess was pilot bearing. Turns out that the input shaft seal on the tranny was leaking and the fluid was running down the inside of the input bearing retainer. It was then being kindly deposited on the clutch.

I certainly hope it's your Clutch Master and Slave but be prepared to pull the tranny and replace the clutch and related components

 

[Nordic]

So again, we put in a new sealed master cylinder/slave assembly about 1.5 months ago, and though maybe it changed the character a bit it didn't fix the issue. The only major change from doing it was that it became very stiff, whereas the clutch pedal before was super soft, due to a leaking master cylinder. I would think that if there was air in it, it would be super soft and spongy to push down, right? So unless the new doorman clutch was defective in a similar state to the old clutch, I'm thinking it's not the issue.

 

[TrueTexas]

I also started with a fluid change then clutch master and slave. Unfortunately, I think you may be looking at pulling the tranny.

After it is warmed up and is exhibiting the problem, have you turned it off and tried to shift thru the gears? If it lets you shift, then I would put my money on either the pilot bearing or clutch as it looks like one of these 2 things is not letting the input shaft spin down.

 

[Nordic]

I also started with a fluid change then clutch master and slave. Unfortunately, I think you may be looking at pulling the tranny.

After it is warmed up and is exhibiting the problem, have you turned it off and tried to shift thru the gears? If it lets you shift, then I would put my money on either the pilot bearing or clutch as it looks like one of these 2 things is not letting the input shaft spin down.

It shifts very easily when it's off, so I could definetly see that being the issue!

 

[TrueTexas]

You may want to pull the starter so you can feel or look inside the bellhousing for fluid everywhere. That's just 2 bolts.

That being said, if it's a seized pilot bearing, there may not be any fluid inside the bellhousing but the symptoms are the same. So pulling the starter may be inconclusive but that has to come off when you pull the tranny anyway