about a year ago I swapped a ZF S5-42 into my 95 F250 and everything has been working great.


I have been running Amsoil syncromesh oil its been quite and shifting smoothly until last weekend I was towing about 6 thousand pound to my camp about 2 hours away. when I got there after running about 65-70mph in overdrive (about 2000 rpm) it wouldn't shift into first or second real easy at all when I came home it was shifting fine until about the time I got into town and the same story.


I dropped my trailer and drove around a bit trying to figure it out and then thought about heat. I climbed under the truck and the trans was about 130* maybe hotter I couldn't leave my hand on it. so I checked fluid level and I put alittle less than half a quart in it. its been shifting fine now but I have really towed anything with it.


Is this early signs of needing syncros or was the fluid level the problem. or maybe I should try some other fluid. Or maybe I just need to just slow down haha What do yall think

 

Is your clutch disengaging properly? How far do you have to let the clutch pedal come up before the truck moves when taking off from a dead stop?

 

Ill have to pay attention to that when I drive it tonight.

 

My ZF wouldn't shift for beans when I got my truck going, it had an unkown gear oil in it. Once the truck got warmed up second was useless. I dumped the gear oil (thats when I found out it had gear oil in it) and went to full synthetic ATF like what is called for. I think I used Valvoline Maxlife ATF Full Synth. cause I stock it here at work.

Instantly the trans shifted smother with less effort being required to grab each gear. I have about 5K on the fluid in the trans now and plan on dumping it and putting fresh in it again as when I dropped the gear oil it was very nasty.

 

You really shouldn't be towing a 6,000 lbs camper overdrive, even on flat ground. That can overheat your transmission big time. Use 4th gear and keep it under 65.

 

Bullhocky!!>

I tow a 14k deckover trailer all the time in OD and it is just fine.

This is not one of those old autos you may be familiar with

 

+1 on the wrong stuff.

AMSoil has the following recommendations for ZF-42s:
Manual Transmission,S5-42 (5-SPD)......MA
All TEMPS......
Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid (ATF) (ATFQT)
OE Multi-Vehicle Synthetic Automatic Transmission Fluid (OTFQT)
Torque-Drive Synthetic Transmission Fluid (ATD1G)

I was struggling with cold shifting in mine and just put in the SS ATF last weekend with very positive results. I haven't towed yet or temped anything, but I'm shifting much more easily and getting better power.

 

X2 not an e40d And even if it was locking out of overdrive is only necessary when the trans is constantly shifting gears

 

I guess I stand corrected. I did used to tow in 5th gear with my previous truck that had 4.10 gears and a 7.5L and never had a problem. That being said I only did it towing less than 5,000 lbs and on flat ground. I used 4th for the 8,000 lb trailer I sometimes had to tow for my job at the time. Maybe I was being overly cautious. The speed limit in California for any towing is 55MPH and believe me they are strict. I got a ticket for going 61MPH. I can only dream of towing in 5th with my current 5.8/3.55 gears...

That being said, you absolutely will create more stress and heat towing in 5th than 4th. 4th gear simply locks the input shaft to the output shaft, so it is the strongest gear and creates virtually no wear or heat because there is no friction between gears taking place. In 5th gear the power flow is running from input gear to countershaft gear then countershaft gear to output gear. More heat is created and it is weaker. Can the ZF-5 handle it? Apparently Yes. So my point is not necessarily relevant. Diesel Brad it would be interesting to hook up a temperature gauge when towing your 16,000 lb trailer in 5th and see what temp your trans is running. Just out of pure curiosity.

 

I have. 190* just cruising with towing nothing and approx 240-250* when going up an down hills loaded. And when downshifted to 4th on the BIG hills(8-10%) the temp never changed

 

so I checked out my clutch engagement and it is super low maybe an inch or two from bottom out until it starts moving the truck.


I would rather tow slower but every time I look down im doin 70. I wish my crusie control worked so I set it at 60 cause I get way better millage but I still haven't figured the cruise out

 

So I finally got around to bleeding my clutch and the fluid was coming out with the black tint to it but it pedal felt good and everything shifted fine for about 15 more miles and then it went back to doing what it was doing before were it didn't want to go into gear from a stop

Do you all think my slave cylinder is going bad or is the fluid just Burnt and doesnt have the viscosity like it should

 

I would try the synthetic ATF as stated in earlier posts. If the manufacturer recommends a certain lubricant in their equipment, it is almost always for good reason. Ford calls for ATF in the ZF because that is what it was designed for.

 

I was thinking clutch hydraulics as I read thru all of the posts on here. 1st and 2nd gears can get ugly with bad clutch hydraulics...

 

When you say it went back to doing what it did before, not going into first and second, is your clutch still engaging near the floor when this happens? Or is the clutch pedal closer to the middle of its travel? Obviously, if the clutch is near the floor that's the place to start. But it is definitely worth it to change the fluid to a good quality ATF. I just put synthetic in my ZF, and shifting under load improved immensely, especially 1st - 3rd.