Quick backstory, I have been planning on making my truck into a 400 rwhp daily driver/ farm work truck. Unfortunately I am super tight with money and have not been able to convince myself to buy much for the truck yet. As of right now though, it has the stuff you can see in my signature. Eventually I would like to add stage 2 sticks, an upgraded turbo and gauges, but I may have run into some issues recently. So here goes:

1. Transmission Concerns -
a. Vibrations - under all driving conditions, as long as I can remember there has been slight subtle vibrations I can feel through my shift stick. To me they seem like the vibrations I am used to feeling when there is a dry-ish bearing or slight unbalance in the PTO driveline on a piece of farm equipment. Are these vibrations normal or are they something I should worry about?

b. 4th(direct drive) gear - Back in August I was in my 65 hp DD tune and got on it pretty hard headed out of town, when I was at about 6 my transmission suddenly jumped out of 4th gear, scared the crap outta me. At the time I attributed it to not having the lever all the way in to the correct spot. I hit the clutch shoved it into 5th (OD) and continued on home, no issues. About 2 months later the transmission jumped out of 4th again on me, and a few days after that it did the same. The truck still drives fine in 4th, except for its tendency to hop out of 4th. Now when I put it in 4th gear and rest my hand on the lever, it feels like a multiple-lobe cam is hitting the lever and shaking it. Also, for at least a year the truck has always made a lot of noise when no-load decelerating in 4th. I think it sounds similar to "gear rollover" noise, but I'm not sure that is how to describe it. However if you have a slight push, such as downhill decelerating, or slight drag, such as the brakes, you can't hear the noise until about 1100-1200 RPM. Did I seriously mess up my transmission? Is a rebuild in my future?

2. Transmission Questions -
a. Is it crazy to try for a 400 rwhp manual truck? Can I expect a healthy zf6 to take that much power and torque?

b. Are there any changes or modifications that get done to these transmissions to make them stronger, or more reliable?

I always thought the manuals were supposed to be a very reliable transmission, but these issues make me question if I'm shooting for something out of reach of this transmission. That being said, this truck has never left me stranded anywhere in the 2 years and 37,000 miles I've put on it.

I apologize for the small novel I wrote, but I am still not overly knowledgeable about these trucks and I would like to learn everything I can about my beast. Also I am not very hot on the idea of increasing the power she puts out just to eat up the transmission.

Thanks,

Baatzy

 

Maybe Chris (F350-6) will chime in here, he's got a ton of experience and miles on the ZF6. Here's my take:

1.a. - the needle pilot bearing in the ZF6 sucks. Mine was nothing but dust when I swapped my clutch. There are several fixes out there, from oversize needle bearings, to machining the flywheel to accept a cartridge ball bearing, to the cheap yet effective oil impregnated bronze bushing from Dorman (which only costs $4!). Your vibration could simply be related to the pilot bearing allowing slop in the input shaft, or grinding up what's left of broken needles. Or, it could be something deeper. Even with my toasted pilot bearing, I never noticed excessive grinding or ever popping out of gear, though. If you're gonna pull the tranny to swap the clutch (see clutch comments below), definitely have a pilot bearing fix (whichever one you choose) ready to go.
1.b. - I'll let someone with more experience comment on that.
2.a. - absolutely, a healthy ZF6 will handle gobs of power. I'm not sure what the upper limits are, but I don't think 400 or 500 is anywhere close. I'd love to hear from someone who's gone big with power mods, and who's driven plenty of miles after, comment on it. You WILL need to upgrade the clutch to handle 400hp, just like I did after my injectors/tuning (I'm guessing I'm around 375-400hp). I'd spin the clutch when I got on it hard. I also had 167k on the factory clutch, so maybe the factory could handle it for a little while, but I'd plan on being ready. This goes back to my comment in 1a - you'll be pulling the tranny to swap clutch/flywheel, so you can do your pilot bearing swap at that time. My sig has the South Bend clutch/flywheel kit number. That model is rated for 425hp. It's been an ideal match for my mods.
2.b. - there are some great rebuilders out there. I'm hoping not to talk to any of them anytime soon! Chris directed someone to Midwest Transmission in MN. Give them a call. They'll be happy to give you info on upgrades they do.

In summary, the ZF6 is an awesome workhorse, and (with proper clutch) can easily handle what you're thinking. If yours does need a rebuild, do it and be happy for another 200k, 300k, or 400k miles!

Chris, hope I'm not stepping on your toes, throwing your name and past comments around.

 

Feeling vibrations with your hand on the stick while driving isn't unheard of.

What do you mean by this? Not 6,000 rpm's I hope?

Sounds like a worn synchro. Years ago, I had a 64 pick up (three on the tree) where I had to rest my arm on the gear shift so it wouldn't pop up out of third while driving.

Don't know if you messed it up, but if you hit 6k rpm's, I'd be more worried about the motor. If it jumped out of gear at that high an RPM, I'm surprised it didn't bend a push rod.

But yes, it sounds like at least a new synchro is in your future.

No.

Yes.

If you want to talk to the ZF expert, call Dan at Midwest transmission and talk over with him what your plans are and what he recommends. He call sell you all the parts to do it yourself, or probably ship you a rebuilt transmission to install if you can't do it yourself.

Nothing lasts forever. My manual has only lasted 493,000 miles so far. Change the fluid every 50k. Looks like I'm gonna have to do it again soon.

 

Thanks for the responses. I had a good 400 mile drive home today and had plenty of time to simmer ideas in my mind about the transmission

The needle pilot bearing sounds like it could possibly be the most logical issue, as the vibrations occur in any gear, and seem most related to RPM from what I could tell today. Is there any other sign or test I can do to more specifically tell me that is the issue?

For the 4th gear problem it looks like my mind was talking faster than my fingers, I meant to say 60 mph. I can't even imagine 6k RPMs, I think that literally would have put a brown streak in my pants, and left me looking something like that guy --->

For another question, do you think rebuilding/fixing the potential issues, such as the needle bearing and synchronizer are something that could be attempted at home? Or would there be so many specialized tools and close tolerances and what not to make the job more of a hassle than what its worth? Just for reference as to my abilities(luck), last winter I pulled the engine to do fuel and oil o-rings and give it a bath.

I'm very happy to hear a healthy zf6 should hold up to what I want, I was worried I might be expecting too much there for a bit, again I must've been a little off my rocker when that went through my mind.

Lastly, if the needle pilot bearing and synchronizer are the issues, how long can I drive the truck in this shape before I really hurt her?

Thanks again,

Baatzy

 

There's no way to check the pilot bearing without pulling the tranny out. Once the tranny is off, it's easy to see. And there's no way to check syncros without a) driving it and knowing what to look for, or b) opening the tranny. I've never cracked open a transmission myself. I did my own clutch, flywheel, and pilot bearing fix with the help of a friend. Pulling the ZF6 is fairly straightforward, though it is a heavy beast. A tranny jack is helpful, but we manhandled it with a regular floor jack. We left the transfer case attached, which adds a lot of torque and makes it want to roll off the jack, so be ready if you go that route. Three people to get it lined up when putting it back together would be a bonus. If you pulled the engine, you can surely do the transmission. As Chris said, give Dan at Midwest a call and talk about rebuild options - since you have plans on investing in the truck, I'd suggest doing the rebuild now, do your clutch/pilot, and be done with that side of things. Also, before you do the rebuild (or throwing any more money at the truck), do a compression test and make sure you're investing around a solid engine (if you haven't already tested it).

 

I think the biggest obstacle to rebuilding the ZF-6 is just it's size. It's very big and it's very heavy. But it's still just a manual transmission and doesn't have all the crazy stuff inside you have to worry about like the auto's do.

Shouldn't be any tolerance issues to worry about unless you're checking for a worn part or something. Everything comes apart and goes back together. Call Dan and talk with him, then decide how to proceed.

 

Chris, I am certainly not trying to pick a fight but have you ever taken a manual transmission apart? They are worlds more tedious than an automatic in every regard. In addition, every modern manual transmission (because of the way the case is assembled) requires some kind of holding fixture so the main, counter, and input shafts will line up properly upon reassembly.

 

No offense taken at all Cody so don't worry. Perhaps it has to do with the way my mind works. I've seen the guts of an auto transmission and all the clutches, etc. that go in them. While I've never taken one apart myself, they just seem more complicated to me.

Yes I have taken a manual apart. Starting with the 64 I mentioned earlier that I pulled in the parking lot, toted upstairs, and took apart in the living room of my apartment, then rebuilt with junkyard parts. I didn't have a manual on how to do it so I just laid everything out on newspaper in the order it came apart to aid in the re-assembly that came 2 weeks later after I got a ride to get the parts.

Perhaps I'm oversimplifying the process. The ZF-6 doesn't have the short, bolt on input shaft up front that some others do so maybe more caution should be taken.

Personally I wouldn't be scared to tear into the ZF-6 but wouldn't consider trying it on a 4R100, but that's probably because I've torn into many manuals and zero autos.

At least I recommended he call Dave before making up his mind. If it's something he shouldn't try at home, I'm sure Dave would set him straight after a short conversation to determine the tool and skill set.