ZF Six Speed Problem

[Nick S]

I bought a 1996 Corvette with the LT4 engine 8 days ago. The car has 55,000 miles. I decided to start having the different fluids in the car changed, since I did not know how frequently the previous owner changed them. I decided to start with the transmission fluid. I took the car to an AAMCO to which I have taken my previous cars. I told them to drive it and make sure that everything seemed fine. The technician brought the car back and said that the transmission whines in 1st and 3rd gear. I then went out with the technician so that he could point out the sound to me. Never having driven a manual transmission before, I thought the transmission sounded fine. I mean, a little noisy, but no different than my friend's four cylinder Toyota pickup. Anyway, he pointed out the sound and I guess I could hear what he was pointing out. He said that if it were the rear differential then the sound would not go away when the clutch is depressed. When we got back, the owner sent another tech out to see if he could hear the noise. That tech said that it was louder in 1st and 3rd, but that he could hear it in 2nd and 4th also. Well, we changed the fluid (75W 90 synthetic, the transmission was full of fluid when checked before the change) and according to the technician and the owner it did not make a difference in the noise. Also, there was a little metal in the fluid that came out. That did not seem totally unusual to me. Not much different from when changing rear differential fluid. Well, the owner tells me that the bearings are probably going, that the noise will just get worse, and that it will eventually need a rebuilt transmission.

After this, I took the car back to the Chevy dealer that I bought the car from. My service consultant and a couple of techs that drove the car told me that it is actually quieter than a 2004 C5 that they recently drove and a 94 Corvette that they recently put a new transmision into.

My question is, is this sound normal? I know these transmissions are supposed to be noisy. I just don't know who to believe at this point. Obviously, the dealer would have a vested interest to say that it is normal noise. It is also possible that the AAMCO dealer is not familiar with this transmission and thinks that the normal noise is an indicator of a problem. This dealership deals with Corvettes all of the time. They had two C4s and a C2 in the garage tonight when I was there. It seems hard for me to believe that they are lieing to me. Geeez, so confusing. Please help. Thank you.

Nick

 

[jwilliams]

Nick S, Your local AAMCO may be a fine transmission shop, but...I strongly suggest you get an opinion from someone who is very familiar with the ZF6. It may be hard to find such a shop. Your sig does not show your location, you may want list it as others on the CAC may be near you and can offer resources, shops to vist, etc....my personal experience is that the ZF6 is very strong, it makes noises that others may think are not right. I have an 89 with a ZF6 that is only used for autocross. It has 128,000 miles on it. I just had the clutch replaced and by all appearances it was the ORIGINAL clutch to the car. I autocrossed it all last year and know for a fact that the previous owner made several passes at the local drag strip during vette magic a few years back. I'm sure alot of others will ring in with opinions, advice, etc...

 

[Nick S]

Thank you for the reply. I am in Herndon, Virginia. Herndon is a suburb of Washington, D.C.

 

[Dean Barker]

My 96 LT4 coupe with 35,000 miles has some transmission noise. Whine is usually gear noise due to inaccurately cut and heat treated gears. Bearings are usually more of a growl or rumble. I wouldn't worry about it. You're doing the right thing by changing all the fluids. You will love that car!!

 

[jrp]

I'm no expert, but would give pretty good odds that the sound is normal for our 6-speeds. Especially if you would describe it as a whine. Mine does it, and it did take some getting used to since I've never really noticed that kind of thing in any other car.

jwilliams is right that you'll want to take your car to a shop that is familiar with the ZF6 and that AAMCO, diplomatically speaking, probably has not been given many opportunities to service them. In the meantime, I would take some comfort in the fact that the dealer techs say it sounds normal based on some recent experience. These places aren't exactly in the business of telling you nothing is wrong.

 

[Nick S]

The Chevy dealer that I bought the car from has a reputation for selling and working on Corvettes. If you go there, you can always find at least half a dozen Vettes either being worked on or sold new or used. I just figured that they might have an interest in saying that it is normal since they sold it. If there is something wrong, then they would have to pay at least half of the repair on the transmission. They did offer to sell me an extended warranty on the car. I initially bought it, then canceled it. The used car manager said tonight that they could still sell me an extended warranty for just the drive train. The full warranty was $3,000 and covered everything on the car until 100,000 miles. I would assume that the drive train warranty would be cheaper. I may have to look into that tomorrow to find out the details.

 

[Nick S]

One other thing, the service consultant at the dealership told me tonight that he would take the car to another shop and ask their opinion on the transmission too. He figures that another shop would find the noise normal too, but he figures that it is best to check around if I don't trust their opinion.

 

[vetteguy]

Nick, I think it is normal for the ZF6 to whine alittle. I have seen many threads to this effect. Cant really be sure about yours without actually hearing it. Maybe find another and listen and compare. Try http://www.tonyscorvetteshop.com/ I have never been there but hear good things about them. Not sure how far that is for you. Good Luck, Guy

 

[markone]

Hi:

I have a '92 with 11K on it and the whining is normal with the 6 speed. In fact if you get your hands on the original information tape that came with the car it tells you that due to the high performance nature of the transmission you are to expect it to whine, mine does it also. Hope this helps...the car is a beast...thrash it through the gears and enjoy it. At the risk of insulting any reputible AAMCO owners, the only experience I ever had with AAMCO was a bad one, I wouldn't set foot in another one, especially with my 'vette.

markone

 

[mnl119]

My owners manual calls for 5W 30 weight oil in the ZF-6 transmission on my 1994 ZR-1. 75W 90 sounds like the wrong fluid.

 

[Jeffvette]

My owners manual calls for 5W 30 weight oil in the ZF-6 transmission on my 1994 ZR-1. 75W 90 sounds like the wrong fluid.

No, it doesn't. 5w 30 is motor oil for the lt1/4.

The ZF requires GM #1052931 or BMW (preferred) M5 motor oil which is 10w 60.


Nick, dump the fluid and go get 3 bottles of the bmw fluid and swap it out, the oil they put in is way to thick.

 

[mnl119]

No, it doesn't. 5w 30 is motor oil for the lt1/4.

The ZF requires GM #1052931 or BMW (preferred) M5 motor oil which is 10w 60.


Nick, dump the fluid and go get 3 bottles of the bmw fluid and swap it out, the oil they put in is way to thick.

Yes it does. Here's a quote from the ZF doctors web page about GM ZF-6 transmission fluid:

http://www.zfdoc.com/techinfo.htm

"TRANSMISSION OIL (status) *-* 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 (15K-30K miles)*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."

 

[Roadster Guy]

Nick, I suggest you check out this thread a little further down in the LT4 Forum called "Best Tranny Fluid".
http://www.corvetteactioncenter.com/forums/showthread.php?t=59924

And then get your hands on a copy of the book "101 Projects for your Corvette 1984-1996 by Richard Newton. There is a very informative section in there on the ZF tranny as well as sections on other areas of your C4. Oh yeah, and do go with the BMW Castrol TWS 10W-60 synthetic as someone suggested earlier. Put it in mine this fall.......great results and it is what is recommended in the book.

As for the whine sound in a couple of gears......too bad you can't get yourself into another ZF equipped Vette to compare and/or another Vette owner with a ZF into yours. Contacting your local Vette club may sort that one.
RG

 

[wx briefer]

Mine actually has gotten better over the milage. It whined much more at 10k than it does now at 90k. I also have switched to the BMW TWS 10-60. I like it. GM's is a straight 30 grade synthetic from my understanding. Of course, the transmission is adapted from a truck tranny. It is going to make some whine.

 

[LT4BUD]

I Well, we changed the fluid (75W 90 synthetic, the transmission was full of fluid when checked before the change)
Nick

75W90 synthetic????????? Not the correct lubricant...Find a new shop....

www.zfdoc.com

 

[TrackDayLT4]

75W90 synthetic????????? Not the correct lubricant...Find a new shop....

75W90 synthetic is fine for the zf6. Gear oil viscosity is different from motor oil viscosity, 75W90 gear oil is equivalent to 15W40 Motor Oil.

As to the original post, the zf6 has a lot of gear whine. If it was not loud enough to concern you the first time you drove the car, it is fine.

Cheers,

Lawrence

 

[mnl119]

75W90 synthetic is fine for the zf6. Gear oil viscosity is different from motor oil viscosity, 75W90 gear oil is equivalent to 15W40 Motor Oil.

As to the original post, the zf6 has a lot of gear whine. If it was not loud enough to concern you the first time you drove the car, it is fine.

Cheers,

Lawrence

It is? Try taking 75W90 gear oil and 15w40 motor oil and pour them out next to each other, see if they flow the same.

 

[Hib Halverson]

One of the potential problems with this thread is transmission noise diagnosis by laypeople and technicians inexperienced with ZF S6-40 six-speed is very subjective.

It is true that the ZF emits higher amounts of certain types of transmission noise than other manuals, however, if the gear "whine" is unusually loud, it still would be indicative of a problem.

But, let's consider the obvious issues first. Lubricant...if AAMCO put a 75W90 gear lube (synth. or otherwise) in the ZF you need to drain that and replace it with either of the ZF-recommended lubricants, which are acceptable and certainly better choices than 75W90, or Red Line MTL synthetic which is even a better choice. A 75W90 is unacceptable for two reasons: 1) it's way too high a viscosity and will make the transmission hard to shift and 2) it's a GL5 lubricant intended for use in rear axles. ZFs need a GL4 and use of a GL5, also, increases shift effort because of faulty synchonizer function. I should add: that AAMCO not having the forethought to open the car's owner's manual to see what the recommended lubricant is shows that company is unsuitable for work on manual transmissions. Low viscosity manual trans lubricants have replaced 75W90 or 90 gear lubes in passenger car and light truck manuals starting about 20 years ago. Today there are virtually no pass. car and light truck manuals using 75W90 or 90 GL5 gear lubes as factory fill. Most use specific low vis GL4s and some even use ATF.

Secondly, it was said that a small amount of metal came out in the drain oil. If this metal was in the form of a grey or bronzey colored very, very fine powder or paste and came in a very small amount---seeminly suspended in the lubricant, there's probably nothing wrong. But, if it came out as metallic particles or (worse yet) chips not suspended in lube, but carried out as debris in the drain flow, then you've got problems.

Third, nothing here was mentioned about gear rattle and growl in low gears when the car is underway, the most pervasive of ZF noises and usually far more noticable than any whine. A certain amont of gear rattle at idle and growl in first gear as the car accelerates are normal.

ignore anything AAMCO tells you about ZFs, clearly, they are ignorant on those subjects. Then, I'd change the lubricant ASAP and road test the car for a while to further analyze the noise. If you need the trans overhauled, I'd have a Corvatte-savvy service shop remove the trans and ship it to ZR51 Performance (aka ZF Doc) in Arizona for rebuilding. Bill Boudreau (the "ZF Doc") does all my ZF work and is one of a few ZF-specific shops in the country which really know that transmission. ZR51 Perf. is at (602) 319-6575 or billb@ZFDoc.com

 

[korvettekarl]

I would listen to what Hib has to say. He is one of the most informed Corvette enthusiasts around as well as a damn fine journalist.

 

[TrackDayLT4]

Hi Hib,

Just Curious, you wrote in another thread that you use Redline Light Shockproof in your zf's, why?

What are the advantages and disadvantages vs MTL or MT90

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.

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