Lost my overdrive the other day, while just cruising along easy. No noise, no grinding, just all of a sudden gone.. I am told about a week to rebuild it, or i can drop in a used one. I can't really afford to be without my truck for a week, and it has always had some slop in it. Is that common for these 6 speeds? should I keep my old one for a spare? Or is there a common problem for the overdrive to just kind of slip out, and maybe it is a cheap fix? I have a bunch more questions about this, but i will wait on them. Thanks!

 

UGH!
I didn't want to hear this, I'm sensing something has gone haywire with my OD gear as well. No grinding, but a vibration that follows engine speed , not driveline speed, and the higher the gear I'm in the more pronounced the vibration with OD being the worst at around 1800 rpm under load. Take my foot off the throttle and it's instantly smooth as silk. Back on the throttle and the vibration returns. And sitting in neutral there is a growling, grinding noise that I cannot decide if it's the spring pack on the clutch disc or if it's truly a failed bearing. Putting the transfer case in neutral so that it allows the transmission to freewheel doesn't change the noise. But then putting the transmission into any gear, with the transfer case in neutral eliminates the noise. But that also puts a slight load on the clutch hub, which would help to quiet the noise if the source of the noise is the clutch. But that would also cause a bad bearing to quiet down if it wasn't spinning in neutral either.

I cannot afford to be without my truck for long either, as it is my daily driver right now. (Saving money to buy my wife a new car, her's is old and the transmission on my old commuter took a dump and it wasn't worth rebuilding..)
You can get a rebuilt exchange unit from here, an FTE sponsor, and a Ford authorized parts outlet.
http://www.trademotion.com/partlocat...99&catalogid=1

 

Yikes! I guess i have to go with a used one... I found one locally that was driven only on sundays, for under $2K. I also found a LS rear axle for about $750, and was considering replacing both at the same time. Does yours have the LS? Any downside to replacing the whole axle? Am I asking too many questions at once? I am still running the truck, I just try to stay on secondary roads, and under 55. The truck is due for a bunch of maintainence, as it has 110K on it. The rear axle seal leaks, and the e-brake doesnt hold very good. This has been my year for repairs.

 

Replacing the rear axle can be both easier and faster than changing rear end parts....especially if you don't have any experience setting up the gears.

 

I also have a 6 spd that started vibrating in overdrive returning from vacation this summer. It has gotten louder, but has seemed to be the same lately. It can be noticed in other gears, but is very pronounced in OD. Coincidentally, it started about 500 miles after I had the clutch changed (2 days before leaving on vacation). The shop left the 2 bolts loose on the swing bearing, 1 fell out, and allowed my driveshaft to whip all the way over to the exhaust. I pulled over and replaced the bolt, and all was well for 400 miles or so until the vibration in overdrive started.

The driveshaft turns true, and I don't see any problems there. I also had the four bolts that bolt the driveshaft to the tranny come loose last month, 1 fell out.

The shop claims it is in the tranny, and they're not responsible. The shop originally put a Zoom variable torque clutch in, but it made a knocking noise when you let the clutch out, even in neutral. I would not take it like that, so they replaced the Zoom with a stock clutch, and it quieted down.

If you hold pressure on the shift lever, you can almost make the noise go away, but this can't be good. Any ideas short of pulling it out and going through it?

 

raduenz, Welcome to FTE.

I'm still trying to decide what the vibration is on my truck in OD. It showed up right after I returned from a long pull with the trailer as well. I'm kind of in denial about it, because I don't want it to be the transmission. It was just fine before I left and this was the first time I pulled the trailer after modding the motor for more power.
If it turns out that the OD truly is bad, then I will be forced to admit that the ZF6 is not as good as I had hoped and will regrettably have to restore my engine to stock tune.

 

Thanks for the reply. At least I know I'm not alone. I just pulled it out, and will tear it down tomorrow. I'll let you know what I find.

I have been running the Superchip tuner in tow mode for several years. However, my stock clutch would slip when going over overpasses on the interstate when I had cruise engaged. This started about 2 years ago (at about 90K miles), and I finally decided to change the clutch (at 120K). When I would put the factory setting back in, the clutch wouldn't slip. I kept my old clutch, and except for a little wear, it looked fine, but the new one doesn't slip. I know it was loading up the motor, but since I'm running the lowest power setting, that should not have been a problem for the supposedly indestructible 6 speed.

That was one of the reasons I bought the standard in the first place, to ensure I could tow my 37' fifth wheel, with the expected reliability. I'm sure parts will not be quick to get, but we'll see what I find.

 

I will await your report.

 

My money is on the pilot bearing in the back of the crank. What does it look like?

 

Thanks, I hadn't got around to looking in there yet.

I looked at the pilot bearing, and it appears new. The rollers are all intact and have grease. However, there is some scarring on the input shaft (and it appears new) where the rollers contact. It looks as though the new bearing is riding in a different place than the old, like the new one wasn't driven in far enough, or it isn't square in the flywheel.

Thoughts?

 

What's the scarring look like? Is the shaft rough? I wouldn't worry about a wear pattern, you'll get that with any bearing. As long as the contact area is nice and smooth, it should be ok and not the cause of your vibration.

 

I'm not familiar with the insides of the Manual 6 speed ZF box in your 6 litre Ftrucks stateside. Theres reasons for that:-

1. We don't get the 6 litre downunder, only the 7.3 PSd
2. We also don't get the 6 speed manual, only the 4r100 Auto are ever imported.

That said, I've towed a lot of smaller boats with smaller turbo diesels 4wd's with manual grearboxes and 5th gear overdrive in years gone past, having owned a pair of Mitsubishi Triton 2.5 tubo diesel 5 speed manuals for 12 years each!

The result was I ended up rebuilding one gearbox 3 times and the other twice!

So, please treat my comments/suggestions with the well intentioned manner in which they are delivered...as just some advice learned the hard / expensive way that may or may not be applicable to this situation!

What was killing these small gear boxes with the 5th over drive gear was towing a heavey 16 ft boat in overdrive 5th gear!

It was a design shortcomming in the gearbox - that the output shaft bearings for 5th gear were a needle roller type - while the direct drive 4th gear output shaft had a full ball bearing roller race, and could take pretty much any abuse without failing!

Eventually, the repair facilities - devised a "cure" by turning out the end of the gear box housing where the overdrive output shaft needle roller bearing fitted, to a larger diameter and fitting a non standard Ball bearing race in that turned out space, to support the 5th gear overdrive output shaft!

Like I said - after destroying 5 such gearboxes, I think this advice is pretty valid probably!

The golden rule ended up being, "Do not tow in overdrive" to the point I had stickers made up for the dashboards of both vehciles, to remind myself (and others) "don't tow in 5th overdrive, thickhead".

Never had any problems after that, with either vehicle...whether the new oversized ball bearing race output shaft bearing was the cure all, or the fact we only ever towed in 4th gear - we never spent any more $ on gearbox rebuilds for the 2 tritons (I still have one of them to this day with +500,000k's on it)!

The problem is that the turbo diesels make so much low down torque that you don't feel a need when towing in overdrive, to shift down a gear on small inclines - hills etc, so you get lazy and just coast up the hills, rather than shift down gears because the engine doesnt die, it keeps on pulling due to it's low down torque!

Sadly those iddy biddy needle rollers on the overdrive output shaft - can't take the low down torque load from the deisel and keep pulling the loaded trailer weight behind, something has to give, and the needle rollers just crush under the load into a sort of metal paste....and then you are in all sorts of bother!

I suspect from what I'm hearing that maybe the 6 speed ZF is suffering a similar probem maybe?

Anyone have a schematic of the insides? (or photo's of one pulled down)? - what type bearings support the 5th & 6th speed over drive output shafts?

Maybe therein could lurk your problem!
Then again - i could be waaay off course and totally wrong!
Likely it's worth investigating tho!

Maybe if it's a needle roller bearing problem, MAYBE theres room in the end of the gear box housing to turn out the bearing race and install a larger dia aftermarket ball bearing race, rather than a new needle roller bearing, if the riginal fails and you don't alter towing habits then likely the replacement will, likewise fail, unless you over engineer it!

Just ignore the above if the premise of needle rollers bearings proves incorrect for the ZF 6 speed box!

Only trying to help out with a suggestion from past expensive overdrive towing experience!!

Cheers!

 

The scarring is definitely rough where the two ends of the roller bearings run. You can see the wear pattern from the previous bearing, and it was smooth, just discolored. This could be some of the problem. The fact that the shop also pulled the tranny after replacing the pilot bearing the first time, to change clutches. I wonder if they put a bind on the pilot bearing the second time, and somehow messed it up.

I know this is not normal, but the tranny does seem to have a lot of looseness in it, so I'll probably tear it down anyway to have a look. I really suspect something like Flywest suggested, that I have bearing problems on the overdrive shaft.

I'll keep you posted as I find out more.

 

If we could get some close up photo's of what you describe this might aid a lot in determining causal factors!

Something else I can tell you we learned the hard way from rebuilding the triton gearboxes!

The gear gogs run on lay shafts inside the box! You remove this lay shaft by unscrewing a soft alloy end cap, out of the rear of the box. When you place the gears back on their layshaft and secure it back in place with the soft alloy threaded end cap, it controls end float and secures the lay shaft in place - its position also determines where the gears "Run" inside the box!

In order to stop it comming loose (unwinding) in the box housing, you are supposed to instal it with locktight, and then - looking in thru the top opening of the box - your sposed to take a long centre punch and "peen" the threaded cap on the inside to burr the thread in 3 places around the cap - to stop it moving back out of the Box housing, allowing excessive end float of the shaft and hence movement of the gear cogs!

Well my mechanic never did these 2 steps...and my end cap on the lay shaft DID start to unwind and move backwards out of the box housing...allowing the lay shaft to move backwards, and take the cogs with it!

On a longish country drive (60 miles)...in 5th overdrive gear - the excessive end float on the lay shaft allowed the face of 2nd gear cog to rub against the face of the 5th overdrive gear, creating a LOT of excessive heat!.

This ecessive heat basically welded the 2nd gear cog to it's lay shaft!

When the vehicle stopped - and changed to first gear, it took off into traffic (in front of a laden truck bearing down on it) went for second gear - only to have the gearbox seize - the rear wheels lock up - and be stranded broadside on to the now fast approaching truck.....

Luckily the truck driver managed to spy what was happening with the smoke off the rear tyres and go around!

So...

When it does come time to put that sucker back together again = pay very close attention - to how you secure those lay shafts into position within the gear box housings, and don't be shy to use locktite and peen the threads inside the end cap to keep it where you want it to stay!

That little oversight alone cost a good $3000 to fix!

Rebuilding gear boxes is a good way to tear up a lot of $100 bills in a big hurry! Rebuilding them 5 times @ $3K per box classifys you as an "expert" - a substantially poorer expert!

Cheers!

 

My manual states this on one of the steps to dissassembly of the transmission:
µ 20. Remove the retaining ring, fifth gear and needle bearing.

The pictures are too crude to really tell.