Grinding into 2nd manal ZF 6 gearbox

[Coltstingray]

Hi was wondering if anyone has had any work done on there gearbox or has any recommendations on where I should take it to get this problem fixed, the car still drives ok and i only get grinding every so often, I don't know if its rpm or speed dependent, but it will glide in lovely sometimes, the C A G S, plug seems to be unplugged, I can't really get in there properly to see the other end so I assume a previos owner unplugged it.
I live in Staffordshire area but don't mind travelling any help will be appreciated tha k you

 

[teamzr1]

How old or about how many miles on the tranny fluid ?
Possible needs to be drained and replaced

Issue could be the syncros as either fluid too old, damaged or a shift fork

As to CAGS (CARS)
you can either get a 1K Ohm 1/2 watt resister and push leads into the female pins on the wiring harness for that
and tape off and tie wrap the wire so not hanging down

Can buy a bypass like $20 US

Amazon.com

When tuning the C4 ECM customers ask me to turn CARS off, so wiring can be plugged in and 1 to 4th shift never happens

 

[Coltstingray]

Hi thank you for replying it's an 89 with 55000 miles and I have only just changed the trans fluid, no idea when it was changed before but I could see that someone had chewed away at the drain plug so it's been messed with before I have used amsoil manual transmission synchromesh fluid, at the moment it's not on the road as I'm updating the brakes so I can't test the gearbox yet.

As far as getting a resister and messing with the wires I'm not that technically skilled

 

[62 C1]

Hi - these guys in the US are very helpful when answering ZF 6 speed question. The websiet isn't pretty but has a ton of information. If you also email Bill be probably will give you the best UK contact he is aware of.

ZF S6-40 and T-56 6-speed Transmssion Driveline Specialists, Prototype and Manufacturing Services

ZR51 Performance repairs 6-speed manual transmissions (C4 Corvette - ZF 6-speed, C5 and C6 Corvette - T56 and T60 6-speed, Camaro/Firebird - T56 6-speed), spare parts sales, after-market parts design and fabrication, technical support

www.zfdoc.com

 

[Husaberg1]

Hi. I have a year 94, 40k miles with exactly the same problem is definitely the 2nd syncronizer ring is worn out. I am just trying to find solution via my mechanic to get touch with bill zf specialist in US. Please if you have got the solution let me know. Thanks

 

[teamzr1]

The ZF MN6 design is highly dependent on the correct fluid being used
The syncros are made of paper and wrong or old fluid can affect them

I know for a fact as having a new 1994 ZR-1 I got talked into by the owner of Redline oils to switch and test their fluid
He swore if any issues that he would pay for the damage and he lied
In short order I began to have syncro issues

Took the car to a dealer and GM saw the ZF not having OEM fluid and voided the GM warranty and cost me $5,000
where they swapped the ZF and also kept mine, plus my ZR-1 was tied up at the dealer for 5 weeks :-(
I sued GM for damages but the lawyer I got, sucked, and he lost the lawsuit :-(

Also, there was an issue with the shift forks,
The OEM ones were weaker and would slightly bend causing shift issues and replacement ones are stronger steel
to prevent that

First try and flush the ZF, use correct fluid and see if that helps, if not have your repair guy check the forks
but if the problem has been going on for some time, then might have to replace syncros

BTW ,when Redline put their product in my ZF they also replaced OEM engine oil with theirs to the LT5 engine
and their oil would find ways to leak out anywhere it could, total crap products

 

[Coltstingray]

I will definitely thank you for responding, and if you manage fi d a solution please pass it on thanks

 

[teamzr1]

FYI
ZF used an engine oil and not a normal tranny fluid
Question an owner asked ZF

(Q) I just bought, at the local BMW dealership, 3 liters of the Castrol TWS 10W60 oil.
I was surprised to see that it is motor oil. Not being a lubrication engineer myself, who did the investigation and determination that this product is compatible with and good for our ZF transmissions?

(A.) Jim, the C4 Corvette ZF S6-40 6-speed transmission uses engine oil for lubrication.

I was told by Jeff Henning, Warranty Administrator of ZF Industries North America, that Engineering of ZF Industries in Germany determined that the BMW imported Castrol (RS superseded by TWS) 10W-60 oil was the recommended alternative to the (GM P/N 1052931) factory-fill oil for use in the ZF S6-40 transmission.

TRANSMISSION OIL - Vascular flow of oil through the porous Phosphorus-bronze (Pb) material of each synchronizer is essential for effective British Thermal Unit (BTU) heat exchange occurrence
Frequent transmission oil changes will ensure lower Pb particle levels suspended in the oil. The ZF S6-40 6-speed transmission is lubricated by engine type oil.
Manufacturer recommendations specify the use of GM P/N 1052931 (5w-30) or BMW P/N 07510009420 (10w-60) oil.
Approximate oil capacity of the ZF S6-40 is 2.2 quarts.
FYI - the BMW 10w-60 oil is fully-synthetic and is used in the BMW M5 engine.

May find using the BMW oil works better than OEM since it is thicker or find worse than thinner OEM oil

Could also testdrive with the taking off the wiring connector for the CAGS (1 to 4th)
Or take the CAGS solenoid off, add a thicker washer so the plunger when engaged is not doing anything for a testdrive

 

[teamzr1]

Original fluid GM1052931 has been replaced by GM12345349

Also, could be a Hydraulic clutch system issue
The slave is on the left frame rail, but right near the exhaust pipe and causes the slave or fluid to overheat
Maybe luck out, but people never flush and replace the brake fluid that the clutch slave uses or even check the fluid level
I suggest normal maintenance is flush and replace the clutch fluid

I always wrapped the slave with a heat wrap to help deflect that exhaust heat

Also wonder if the shifter itself is out of alignment