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ZF Six Speed Problem

Thank you for all of the replies. I called Bill Boudreau (the "ZF Doc") and spoke with him about the transmission. He was helpful. I took his advice and had the 75W-90 drained and I had the transmission refilled with the Castrol 10W-60 that Bill and BMW recommend for the transmission. The car shifts much easier now than it did with the 75W-90. Bill told me that the major problem with using 75W-90 is that the oil is too thick. Being too thick, it does not flow as well as the lighter weight oils that are recommended for the transmission. Therefore, the oil does not get into areas that it should as easily, and will not dissipate heat from parts of the transmission that is should. Over time, this may lead to premature failure of the transmission.

I also had the transmission specialist at the Chevy dealer drive the car. He has worked on (and rebuilt) many of these transmissions himself. He claimed that the transmission was not making any unusual noises for this transmission. He said that he had recently placed a remanufactured ZF transmission into a 1994 Corvette and that it made more noise than my transmission.

As far as the metal in the transmission fluid, it was more like what you would find on the magnet on your oil drain plug. So, I would figure that this would come with normal wear of metal parts.

Also, people have commented about there being noises that come from the transmission while it is in gear at a stop or in neutral with the engine idling. I don't hear any odd noises during either of these conditions. The transmission seems to be pretty quiet.

The transmission seems to make more noise in first through third gear and seems very quiet in fourth through sixth. I think that part of the reason for the increased noise in first through third gear is because the engine turns a higher amount of rpms in those gears. Typically, once I am in fourth gear the engine is not turning as many rpms. Again, I am a poor judge of how much is engine and how much is transmission noise with this being my first car with a manual transmission. At this point, the car is mine and the only thing that I can do is drive it. If the transmission gives out, I'm screwed. Right now, the transmission is only one of two major things that I am worried about with the car. I have only driven the car about 300 miles, but so far I am only getting about 11.5 to 12 miles per gallon driving around town (mostly stop and go driving). The mechanic that I have dealt with at the Chevy dealer with my previous car (1999 Camaro Z28) seems to think that this is most likely due to a bad sensor (most likely 02) and not plugs and wires. I did not have the car scanned to check the sensors because he said that they would probably charge an hour ($100) of labor to do it. I did find a leak in one of the tubes attached to the intake (looks like part of the PCV system) and fixed that leak. I don't know if that had any affect on the mileage. So, that is another mystery I will have to tackle. Other than all of this, the car seems to run well. Did you ever think that you made a major mistake buying a vehicle? I'm getting to that point. Thank you all for your help and letting me vent a bit.
 
Nick S said:
.

At this point, the car is mine and the only thing that I can do is drive it. If the transmission gives out, I'm screwed. Right now, the transmission is only one of two major things that I am worried about with the car.

Other than all of this, the car seems to run well. Did you ever think that you made a major mistake buying a vehicle? I'm getting to that point. Thank you all for your help and letting me vent a bit.

Sounds like you really don't have a problem with the transmission......

Take the car on a trip driving interstates around a CONSTANT 65-70mph and check for mileage......should be 25mpg plus...pretty close to 30

11mpg sounds low, but in city driving who knows...

Take care to Autozone or similiar that will scan for codes at no charge..

I DON"T THINK YOU MADE A MISTAKE!!!!! The LT4 is a fantastic engine!!!
 
Autozone scans for FREE! Take it there and let them hook it up. 12mpg is terribly wrong. One should get 18 or better even in town. I used to get 25 mpg on the interstate at 78 mph before the HOT cam installation. I now get at best 21 mpg with the cam. Still, in town I never fall below 16 mpg (and that is even goosing it a little and having fun.)
 
I read in the owner's manual "SAE 5W-30" (GM Part No 1052931). Why am I reading "10W-60" all over the place here???

Cheers,

Selim
 
SSTibet said:
I read in the owner's manual "SAE 5W-30" (GM Part No 1052931). Why am I reading "10W-60" all over the place here???

Cheers,

Selim
it's better :) --many times car companies use thinner oils to get better gas mileage... this could be the case here.

As far as gas mileage goes... I have gotten as bad as 5 MPG with various C4's... Depending mostly on how long the trips are. I used to have a daily 'commute' of less than a mile, that is when my mileage was the worst.... I currently get between 8-18 in town, depending on how long my trips are more than anything else. My commute now is under 5 miles.

As stated before, the only way to really check the mileage is to get on the highway:)
 
My commute is ten miles each way. Two lane highway with stop lights. The speed limit is 50. There is a lot of stop light to stop light sprinting. Get the car up to 50-60 mph for a mile, then stop, and repeat.
 
Nick S said:
My commute is ten miles each way. Two lane highway with stop lights. The speed limit is 50. There is a lot of stop light to stop light sprinting. Get the car up to 50-60 mph for a mile, then stop, and repeat.

"sprinting" does not get good mpg.......sounds like 11 might be expected......I doubt if you really have a problem....."sprinting" is fun, but sprinting costs..

ENJOY......
 
TrackDayLT4 said:
Hi Hib,

Just Curious, you wrote in another thread that you use Redline Light Shockproof in your zf's, why?
Red Line Light Shockproof is an even more robust lubricant than MTL. It's calcium-based EP additive package and its gel-based lubricant are the ultimate for a manual trans in extreme duty. There is a small downside of LSP and that is, a ZF's shift effort is incrementally higher when the lubricant is cold than a ZF with MTL in it. Some people don't like the higher cold shift effort so that's why I recommend MTL for general use in ZFs and Light Shockproof for extreme duty.

What are the advantages and disadvantages vs MTL or MT90
MT90 is a higher viscosity version of MTL. That's the only functional difference.
The reason I ask is that I recently went to a single mass flywheel and with MTL the trans has A LOT of gear clatter. I am looking for a different oil to quiet the trans a little. Someone suggested redline 75W140NS but that seems a bit to thick.
If you want a lubricant to help with gear rattle, use Light Shockproof. It will slightly decrease the rattle. In fact, that's another reason I use it.
Thanks for the info, it looks like the 75W90 GL4 GL5 thing is not as straight forward as I thought it was. In my garage I have a bottle of Motul 75W90 which is rated as a GL4 and MT90 is rated as a 75W90, and GL4 so I thought that 75W90's were GL4.
Cheers,
Lawrence
DO NOT use a GL5 in the ZF S6-40, or any other manual, for that matter. GL5s are intended to lubricate hypoid ring-and-pinion gearsets in rear axles and, thus, have far more EP additives than do GL4s. In fact, most GL5s will increase shift effort and reduce shift quality because they have so much EP additifves that synchronizer action is degraded. Use only lubricants rated GL4 in a ZF.

All 75W90 Gear Oils are not GL4s. In fact, many are GL5s, however, you may find transmission lubricants that are rated as 75W90. Admittedly, this is confusing but at least Red Line brands it's high vis. GL4s something other than "75W90" but notes on the label that they also rate as 75W90.
 
Nick S said:
I have only driven the car about 300 miles, but so far I am only getting about 11.5 to 12 miles per gallon driving around town (mostly stop and go driving). The mechanic that I have dealt with at the Chevy dealer with my previous car (1999 Camaro Z28) seems to think that this is most likely due to a bad sensor (most likely 02) and not plugs and wires. I did not have the car scanned to check the sensors because he said that they would probably charge an hour ($100) of labor to do it. I did find a leak in one of the tubes attached to the intake (looks like part of the PCV system) and fixed that leak. I don't know if that had any affect on the mileage. So, that is another mystery I will have to tackle. Other than all of this, the car seems to run well. Did you ever think that you made a major mistake buying a vehicle? I'm getting to that point. Thank you all for your help and letting me vent a bit.

I get 11 to 14 around town and I think that's about right. If you drive it like there's an egg under your right foot you might get 16 around town (and use the 1/4 cags shift pattern).

But what the heck fun is that?

My 02 Suburban gets better mileage than my LT4, it's the nature of the beast.

Depending on how you want to use the car you may have done better choosing an automatic with the LT1 engine. It'll get better mileage around town & still walk away from a lot of cars.

The LT4 is about performance not mpg.

Either way you should own/drive a car that you enjoy. Maybe sell the LT4 & try something else? Miata's are fun & get great mpg.:)
 
Nick S said:
My commute is ten miles each way. Two lane highway with stop lights. The speed limit is 50. There is a lot of stop light to stop light sprinting. Get the car up to 50-60 mph for a mile, then stop, and repeat.

Do you shift through all the gears? meaning, 1-2-3-4-5-6? if so, try shifting 1-3-5-6 or 1-2-4-6. the car can handle skipping a gear with ease, and should give you a bit better gas mileage. I actually think the car is a bit easier to drive in town like that, because you shift less. The other question is, what RPM do you shift at?
 
froggy47 said:
The LT4 is about performance not mpg.
.:)

Actually the LT4 is a wonderful balance of performance and economy!!!!!!!

When mine was stock, I easily got 28-32mpg highway in the 65-80mph range..

Personally I never got less than 20mpg between fill-ups........

I still suspect the low mileage here is related to repeated "spirited" starts over and over again all the way to work.

Must be a lot of fun......does anyone ever actually beat you from the red lights???

Enjoy!!!!!! You have one of the most remarkable cars ever built!!!!
 

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