Mine has the opposite problem - I get a quick little "grunch!" sound when upshifting to 2nd or 4th about half the time. I also switched to Mobil Synthetic ATF and it didn't help, but it doesn't seem to have made it worse. Mine is for sure a synchro going, if I shift to neutral, pause, then go to 4th, it doesn't do it. But it's been a couple of months now and it hasn't gotten any worse, so for now I am just ignoriing it.

 

There are sliders on the mainshaft that are composed of a sliding sleeve, synchro body and synchro. When the slider moves toward the gear when you shift, the synchro, through friction, equalizes the speed of the gear and the mainshaft so the gears don't grind. The synchro you're looking for should be on the back side of 2nd gear on the mainshaft and you may be able to see it from the PTO port. Look at #s 52-61 in the diagram:

 

how hard would that be to change out a synchro? would that be something that someone with average to good mechanical knowledge be able to tackle? or are we talking transmission shop?

 

Nighthawk:

You know what you are doing and I'm sure you could replace a synchro. I don't necessarily think this is something that has to be done by a shop. You just had the trans rebuilt so the bearings seals, etc. should be in good shape. Years ago I put new synchros in a 4 speed Muncie M-21 and it was a 2 hour job. In the Ford shop manual the ZF looks a little different and more involved. You remove the bolts holding the rear case on the transmission and lift the front case straight up. You then have the "gear pack" -mainshaft, countershaft, and shift rails sitting in the rear case. Ford has a special tool called "gear pack holding fixture" and nylon sling that are placed around the gear pack and the assembly is then removed from the rear case. Once it is removed, you could take the mainshaft out and replace the synchros. I could scan the ZF transmission disassembly/assembly instructions and email them to you if you decide that's what you want to do. Send me a pm or email with your address. I've learned if it's got t!ts or tires it will give you trouble.

What about the place that rebuilt the trans? Will they fix it?

 

that place will probably fix it, only problem is, I'm here in LaGrande at college, and the place I had rebuild it is 300 miles back home... If you could do that with the instructions, that'd be great, I can do this this summer when I have some downtime.....This probably can't be done in-frame can it?

Did you get that image out of the shop manual?? As I was looking at it, there at the bottom, it said that the taper was too smooth after a few thousand miles, and to try some hard shifts at high RPMs and see if that fixes it... I tried it, went up to 4200RPM (cringe) in first, shifted to second, went to 4200 again (cringe more), and then up to third. Did that a few times, and for now, I can downshift again normally, so it might be fixed for now, but that's probably an indication of them being going and it'll need to be done soon.

 

I gotta try that on mine too. But for a 300, "high rpms" would be about 3 grand.

 

yeah, I hate hitting anywhere above 3 grand with mine too, 3500 tops

 

I don't think it's possible to replace the synchros without removing the trans. I can get you a copy of the instructions in PDF format. It will take a while to scan so I won't have it together tonight or maybe even this weekend. Let me know where you want me to send it. Yes, that info came out of the shop manual and that corrective action looked like the most fun way to try to fix a problem that I ever saw in a shop manual.

 

Hey nighthawk I asked my brother about your problem. He's got a 97 F250 Powerstroke with ZF and he said you problem is pretty common amongst ZF owners. He frequents a forum on ford-trucks.com under the avatar PSDFreak. Anywho, he said a lot of ZF's have problems shifting down into 2nd and most guys just avoid doing it all together. My brothers ZF, though, usually has no problem shifting into 2nd, but he still says he doesn't do it since 3rd rides him down far enough. He says that most say the ZF should take ATF (like you put in) but he uses Redline MTL and his transmission loves it. So he recommended that you change your fluid to MTL and fill it through the boot in the cab, as opposed to the fill plug on the tranny; this way you can get a full 4 quarts in, instead of 3 1/2. A gallon of MTL should cost you $20-$25. I trust my brothers opinion, hes quite the wizz when it comes to the 7.3L and the ZF, although not ALWAYS right . I figured this would be worth a try before you dump money into replacing the synchros. Keep us posted on what you find out.

-Chris

 

thanks chris, I appreciate every bit....where can I find that stuff, I haven't seen it around here at any of the parts houses

 

You can use their dealer search on the site to find the dealer nearest you:

http://www.redlineoil.com/dealers.asp

Hope that helps.

-Chris

 

MTL is actually not a Redline exclusive product, stands for Manual Transmission Lubricant (duh), I'm sure there are other brands that are easier to come by if you search around. Redline can be a b*tch to find sometimes, but my brother loves their lubricants, high quality stuff.

-Chris

 

I had similar troubles when I tried synthetic gear oil in my Toyota Tacoma 5 speed. Started to have 4-3 downshift grinding. Switched back to dino oil and seemed to fix the problem. I've read that some synthetics and additives can be too slick and synchros have a harder time getting speeds matched.