ZF-6 grinding into fourth
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Freshman User
Joined: Oct 2006
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From: On a farm
ZF-6 grinding into fourth
A couple of weeks ago the ZF-6 transmission started to grind into fourth when I didn't use the clutch to shift lately it has been grinding every once in a while even when I use the clutch. I do not know how many miles are on the transmission but the clutch has been recently serviced and transmission fluid changed this last winter less than 10,000 miles ago to amsoil synthetic. The truck does have 350,000 miles 160,000 on rebuilt engine not sure about transmission. Any help on why the transmission is grinding is greatly appreciated.
I have a early 99 7.3 4X4 DRW.
I have a early 99 7.3 4X4 DRW.
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Freshman User
Joined: Oct 2006
Posts: 39
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From: On a farm
May be, I guess after diving hundreds of thousands of miles in a Kenworth it is a habit to shift without the clutch. I did not think it was a problem beings it was not grinding into gear.
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,112
From: Rio Rico, AZ.
You need a tranny. Sorry but if it's isolated to just one gear like that, it's always a problem inside the trans.
I replaced my ZF-6 last year due to the pilot bearing failing and ruining the OD bearing at the rear of the input shaft. You could hear it rumbling with the clutch out in neutral and when underway the whole truck would shudder if I gave it light throttle.
I bought my tranny from Fleet Pride for a very good price: $2400.00 + refundable core.
Shipping was free because I happened to be close enough for them to put it in a pickup truck and bring it out to me. Your location may change that.
While it's out, get a new clutch and pilot bushing. Don't use the bearing.
I replaced my ZF-6 last year due to the pilot bearing failing and ruining the OD bearing at the rear of the input shaft. You could hear it rumbling with the clutch out in neutral and when underway the whole truck would shudder if I gave it light throttle.
I bought my tranny from Fleet Pride for a very good price: $2400.00 + refundable core.
Shipping was free because I happened to be close enough for them to put it in a pickup truck and bring it out to me. Your location may change that.
While it's out, get a new clutch and pilot bushing. Don't use the bearing.
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,112
From: Rio Rico, AZ.
Originally Posted by powerfarmer
May be, I guess after diving hundreds of thousands of miles in a Kenworth it is a habit to shift without the clutch. I did not think it was a problem beings it was not grinding into gear.
One of the "issues" that I have with ZF over the transmission design is the fact that the cases are made out of aluminum. There is NO WAY that you can make a tranny last unless you make the gear case out of steel. Pretty soon everything starts to loosen up around the bearings and then the shafts begin to telescope in and out.
The tranny still works for a while, but it just gets "soft".
I know that an iron tranny case would be 500lb and cost more to machine, but I would be willing to pay for that to get the longevity.
Post Fiend
Joined: Mar 2007
Posts: 26,966
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From: Texas
Originally Posted by Kwikkordead
I know that an iron tranny case would be 500lb and cost more to machine, but I would be willing to pay for that to get the longevity.
That thing looks like it weighs 500 lb with the aluminum case. I can't imagine what it would weigh with a cast iron casing.
As far as the grinding it does sound internal. Either take it easy and shift 3-5 or grind through it until you can afford that new transmission.
Post Fiend
Joined: Feb 2007
Posts: 14,541
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From: Dallas-Ft. Worth
Originally Posted by powerfarmer
May be, I guess after diving hundreds of thousands of miles in a Kenworth it is a habit to shift without the clutch. I did not think it was a problem beings it was not grinding into gear.
"The synchronizer<sup id="_ref-0" class="reference">[1]</sup> has to change the momentum of the entire input shaft and clutch disk. Additionally, it can be abused by exposure to the momentum and power of the engine itself, which is what happens when attempts are made to select a gear without fully disengaging the clutch. This causes extra wear on the rings and sleeves, reducing their service life. When an experimenting driver tries to "match the revs" on a synchronized transmission and force it into gear without using the clutch, the synchronizer will make up for any discrepancy in RPM. The success in engaging the gear without clutching can deceive the driver into thinking that the RPM of the layshaft and transmission were actually exactly matched. Nevertheless, approximate "rev-matching" *with clutching* can decrease the general delta between layshaft and transmission and decrease synchro wear."
Definitely sounds like torched synchros. I never understood the desire to not use a clutch by so many drivers. Why risk it?
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Elder User
Joined: Apr 2005
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From: sycamore, illinois
i just put a clutch in mine it isn't light by any means, it doesn't help if u do what i did which was leave the transfer case bolted on, the only trick is getting it lined back up b/c to have it balanced u can't get the rear of the trans high enough but i managed to do it by useing a come along warped around the frame rails and a block between the cable and tailshaft slide right in
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Logistics Pro
Joined: Jun 2005
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From: AZ
Originally Posted by Izzy351
I never understood the desire to not use a clutch by so many drivers. Why risk it?
Elder User
Joined: Apr 2005
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From: sycamore, illinois
we tell all our drivers to not shift with the clutch and we had trucks that had over 800,000 miles on them and never had a trans and some of them never had a clutch too, the one i remember that didn't have a clutch put in it had like 650,000 it had a solo self adjusting cluch in it that quick adjusting and we were able to ge it to adjust enough to engage the clutch break and sent it to sales lot in iowa
Last edited by justblowin'smoke; Aug 21, 2007 at 09:33 PM.
Cargo Master
Joined: Apr 2004
Posts: 3,162
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From: Vilonia Arkansas
It's a hard habit to break but a tranny with synchros just won't handle it like the non synchros in the big trucks. As far as driving without a using the clutch in a big truck when your running up through an 18 speed or any of the others thats alot of in and out on the clutch and hard on the leg . Besides that its just plain cool to sit back drop the hammer and run though the gears like it was a automatic tranny click click.
Post Fiend
Joined: Feb 2007
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From: Dallas-Ft. Worth
Well admittedly, I don't know how the trannys work in big trucks, but I was referring to our trucks. I've broken enough manuals speed shifting to know what's in 'em (which is why I switched to a C6 in my 'stang!!) and how nasty it looks in there after a gear or two break. 
I just wouldn't do that with our trucks.
I just wouldn't do that with our trucks.
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Freshman User
Joined: Oct 2006
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From: On a farm
Thanks for all the replies. As of the last couple of days I have been driving the pickup around and trying to use the clutch for all gears and the grinding does go away, but if I forget and grind fourth then it will grind in fourth untill I let the pickup sit for awhile. I hope that maybe if I do use the clutch for all shifting I can get a couple more miles out of the transmission. Sometimes old habits are hard to break.
thanks
thanks
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