[quote author=Scotty link=board=4;threadid=11912;start=75#122300 date=1049072248]
I took out the shifter and added some friction modifier today.

Now theres no notchy shifts...I had a bit of a grab in 4th...silky smooth now.
[/quote]

Hate to say it, but you're going to tear up your synchros with the friction modifier. The synchros must have a specific property or coefficient of friction to engage properly. Here you go, from the Redline site:

"All oils are slippery, and with most lubricated components, the slipperier the better, but this is not so with manual transmissions. The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. Few modern transmissions use sliding gears to change gearing other than for reverse gearing. Synchromesh transmissions have the gear pairs constantly in mesh. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear.

The time this process takes depends on how easily the synchro ring moves and the rate of frictional energy transfer between the two synchronizer surfaces. Higher viscosity lubricants slow the sliding of the synchro ring on the input shaft and require a longer time for the oil to be squeezed out from between the mating synchronizer surfaces. After the lubricant is squeezed out, the coefficient of friction of the lubricant determines the rate of frictional energy transfer between the two surfaces. Slippery lubricants such as hypoid gear oils and ATFs can take too long to synchronize the gears, which promotes synchronizer wear.

Some motor oils have an adequate dynamic coefficient of friction, but most have problems with the static and low velocity coefficient of friction which can result in clashing.

Clashing of the gears (actually clashing of the synchromesh gears, since the drive gears are always in contact) can occur if excessive shift effort is used in order to shift the locking ring into place before the surfaces have achieved equal speed. It may also occur at the end of a reasonably smooth shift if an instability exists in the coefficient of friction, causing stick-slip to occur. In this form of clashing, the ring slides on the mating synchro gear, but a sudden slippage causes a grinding of the gears. In order to prevent stick-slip from occuring and the gear clashing which results, the coefficient of friction should inflect downward as the relative speed drops to zero."

Sorry about the lengthy quote, but blending seems kind of risky. I don't think NVG's response is very helpful, either. It just means that they've made a decision to test only one lube. The oil they recommend has inferior specs to other oils on the market.

ascraeus

 

Hey, everybody. My dad, who is Gear Poet, sent an e-mail to NVG a couple of weeks ago on this issue. They didn't get back to us, and I've been telling him about the posts on this thread. So he and I sent a "strongly-worded" e-mail to NVG last night. Here's what we got back today from an NVG engineer:

"The NV5600 transmission has seen some improvements on the friction material that is used on the synchronizer friction rings (inner blocker rings). There was a material change that took effect on the 2002 model year transmission. This change was to the improve durability of the synchronizer friction material. Please note that adding friction modifier to the transmission would only adversely effect this condition.
The friction material used on the NV5600 synchronizer friction rings is not compatible with the friction modifier used on our other transmissions. NOTE: DO NOT USE FRICTION MODIFIER IN A NV5600 TRANSMISSION."

"If a friction ring is burnt up and the unit starts to clash into gear, only the friction ring in the synchronizer assembly should need to be replaced. As long as the gear set has not seen heavy gear clashing or clutch tooth wear it should not require replacement. Most service transmissions should not require transmission replacement. The dealers have the capability of repairing these transmissions. The 3rd speed
synchronizer assembly would be the exception due to hydraulic press requirements to disassemble the countershaft. Therefore a service part is available to replace the entire countershaft assembly in the event of a 3rd gear clash condition caused by friction ring wear."

So there was a problem, and it was fixed in the 2002 model year. If you've got an '02 NV5600, you've got stronger synchros.

And apparently the friction modifiers used in the NV5600 are not the same as in other NVG transmissions. That's pretty strong statement about not using friction modifiers.

And finally, the infamous 3rd gear grind is apparently caused by the inherent design.

ascraeus