HardTopC4

My '90 6-speed balks (no grinding) occasionally when upshifting from second gear to third gear. It works best if just relying on the spring loaded shifter mechanism, and pushing straight forward out of second gear (slowly enough to avoid going into first gear). Downshifting from fourth gear into third gear is perfect. This transmission never grinds. The clutch is good, with no crunching/bad noises when shifting from first into reverse. The car has approximately 20k miles, the CAGS bung has been removed, and the spec gear lube level is full. Has anyone else experienced and remedied this problem, and if so, how? Thank you very much!

WVZR-1

You only mention it's "full" but you don't mention ever servicing the trans so ............. if you feel there's no clutch issues you service the ZF with proper fluid and reassess your ZF "suspected" issues. Does the ZF still have the "lift-ring" for reverse?

mickey5

Gripping the **** when doing a 2-3 shift always gives me trouble finding the 3 gate. By pushing the **** with the "V" between thumb and pointer finger lets the spring do its job rather than you aligning the 3rd gate. My experience over 27 years of shifting my ZF.

billschroeder5842

Funny, me too. I'm glad to see someone else doing this.

HardTopC4

Thank you, all.
The transmission fluid was last changed 700 miles ago, and the change made no difference in the shifting. What other servicing is required beyond keeping the fluid fresh?
I will try the "V" technique. I should have noted that the pushing straight out of second was for total avoidance of any side-to-side shifter guidance, and this is how the shifting works best, but it does not eliminate the random third gear balking which occurs around 5% of the time.
Thanks again!

mickey5

To OP: When moving the shifter from 2nd to 3rd do tyou pause in neutral before moving into the third gate? What happens when it "balks"? (I assume you mean lockout) Do you release pressure on the shifter momentarily and then try again?

Kubs

What fluid did you use on the change?

QZRBLU

I don't want to alarm you but my '90 6-speed had a very similar problem with about 2,500 miles on it. The dealer replaced it with a brand new ZF 6-speed under warranty.,
At that time they were not allowed to open the transmission to attempt a fix. Haven't had a single problem with 3rd gear since. I assume it was a failed 3rd gear syncro. Happened about once a week in daily use. I've changed fluid twice with AmZoil MTL. I'd suggest ZF Doc in AZ for a consultation/fix. www.zfdoc.com

HardTopC4

Thank you, all. Fluid is Castrol synth 10-60 engine oil sourced from a BMW dealership. Have heard +/- about it, together with all the others, e.g., GM Synchromesh/Pennzoil. Shift lever movement is two-part; out of second gear into neutral, and out of neutral into third gear, with an imperceptible pause in the neutral detent neutral, like shifting dog ring/teeth type synchros. The balk going into third gear feels like the shifter is running up against a stop at the point at which is should be selecting/engaging third gear, about half way between neutral and all the way home in the third gear position. Sometimes I return to neutral and then reattempt and complete the third gear selection; sometimes I just go to fourth gear, situation dependent. In any event; third gear does not get forced. Thanks again!

WVZR-1

I asked if it still had the "lift-ring" for reverse as well as had it been serviced. Being a '90 and if there was NO "lift-ring" then you could assume the shifter is aftermarket and maybe a flawed install. There's shims, stop-blocks and pivots in the shifter. If the lift-ring is there I'd say that the shifter was OE and certainly less likely to have shifter issues. You mentioned that the CAGS had actually been removed so I thought maybe aftermarket shifter also. You mentioned "bung" removed but I took that to actually mean solenoid. What is actually removed?

20K miles is maybe irrelevant, check the tag on the transmission for an assembly number. Post up the tag information.

Kubs

I figured you were going to say that. I have heard nothing but bad things about the Castrol in a ZF, including shifting issues similar to what you describe. It is too heavy to properly lube everything. Not to mention it is engine oil, not gear lube. It is designed for a different task.

I have ZERO issues running AMSOIL Syncromesh in mine, and I use it hard on the road course for long periods of time.

https://www.amsoil.com/shop/by-produ...716&zo=1934716

A fluid change is cheaper than a new transmission. I would try something different first.

DGXR

The 3rd gear notchy shift is well known in the ZF S6-40. In mine it only happens during an upshift (from 1st or 2nd), never during a downshift and only happens about 10-20% of the time. Otherwise perfect shifting in all gears... clutch and all hydraulics are working properly. I run the Amsoil MTF linked in Kubs' post above.

I suggest bleeding the clutch hydraulics first (which is a good PM idea anyway). If that does not help, drain the engine oil you have in the transmission and put in something suited for the task. Personally I would (and have) put in Pennzoil Synchromesh before putting in engine oil.

HardTopC4

Thanks all for your continuing input!
WVZR-1, Sorry I failed to respond to your reverse lift ring question. Yes, this transmission still has the original shifter, complete with the lift ring and rubbery feel. The CAGS solenoid and related "lift out parts" were removed and replaced by a CAGS delete screw plug. The following is from the transmission tag: TYPE S6-40, PARTS LIST No. 1052 000 36, TRANSMISSION No. 012319, CUSTOMER'S REF. No. 101 50 047, TOTAL RATIO 2.68 --- 0.5. Remaining tag cells are not populated.
QZRBLU, Kubs, & DGXR, Thanks for your Amsoil recommendation! The hydraulics are good, and even though DGXR notes the same issue I have with the upshift to third gear even using Amsoil, it sounds like it's worth a try. Thanks again!

HardTopC4

Just an FYI, the following Forum discussion is what drove my Castrol 10-60 engine oil selection for this transmission's lubrication, based on the authorities cited, particularly the information sourced from the ZFDoc noting ZF Engineering. Are there equally authoritative published updates available?


https://www.corvetteforum.com/forums...-capacity.html

Kubs

There are no write ups that I know of.

The Castrol or Mobil engine oil mentioned in that thread may be the correct weight oil, or even provide decent lubrication to the areas needed, but transmissions have lots of dissimilar metals. Brass, bronze, nickel, alloys, steel, aluminum, etc. Transmission fluids have additives to help these different metals and keep them from corroding and pitting under extreme pressure and stress. Using oil that is designed around that particular function is much more ideal than something that was designed to do another task, but is OK for other things.

HardTopC4

I couldn't agree more with the sensitivity to weight and GL spec for the reasons you cite (dating back personally to Alfa Romeo's shift from Dentax to Spirax with their mid-60s gearbox metallurgical enhancements), and following the manufacturer's recommendation for what should be used in their product. So, when ZFdoc cited ZF engineering as identifying the Castrol motor oil as meeting their specifications, I went with it. As you know, manufacturers specifying engine oil for transmissions is not without precedent, e.g., Volvo in the mid 60s calling for Valvoline non-detergent 30 Wt in their manual transmissions, according to their Phoenix dealership's then service manager. This said, the Castrol info is now more than 10 years old, and I would hope that in the ensuing period a better product has come to market for this application, supported by engineering data. We've all got anecdotes, and all though a different product and application, I'm a little skeptical of the Amsoil product line based on a BMW cam lobe occurrence many years ago, reportedly involving their engine oil. Thanks again!

HardTopC4

Problem solved. Draining the previously recommended Castrol 10-60 and refilling the transmission with Amsoil Synthetic Manual Synchromesh Transmission Fluid immediately and totally cured the problem. I have since tried to induce the previous fault while shifting and been unable to do so. I have no relationship with the product and bought it from a dealer who was a complete stranger, and frankly, I was more than a little skeptical. The fluid meets GM specs 9985648, 9986105, and 9985535 according to the manufacturer. The label also references GM part numbers 12345349 or 12345577, 12377916, and 1052931. The manufacturer's product code is MTF-QT.

KyleF

3 years later and you come back to post. Awesome, hate when threads like this die without resolution. That doesn't help the next guy out, this does

VikingTrad3r

thanks for this

QCVette

Thanks for posting the results.

I had a similar problem when shifting from 1st to 2nd when it was cold. I also switched to Amsoil fluid and the problem went away and never returned in the last 5 years.