DukeDiablo

Dear Forum-

I changed the ZF6's lube this morning and all I can say is wow.

I'm not sure of the previous interval or what was used; however, the improvement in shifting is dramatic.

I'll have to see just how long this improvement lasts, but either way, I'll be ordering more of the Castrol TWS Motorsport 10W-60 in about 10-15k miles.

Yall have a good one and thanks for the advice.

StealDads67

It feels great when I changed it compared to whatever else was in it, But seems to be a little on the stiff side when its cold. When its warms up though so smooth and nice.

Perfusion

Mine's always been stiff when cold too, but after a recent fluid change, it does feel great when warmed up.

mitchcole

I just noticed an ever so slight smoothness increase. Better - but not in the "unbelievable" category.

KP Texan

In order to refill the transmission, did you use the tube and funnel technique or did you use a hand pump? I'll be putting fresh TWS 10W60 in my transmission next week and I'm just trying to figure out the right tubing size to fit in the fill hole before I actually start doing the job. Anybody know what size plastic tubing works best? I would hate to buy some that is too large and have it not fit in the hole. Also did you need to replace the drain plug with a new one? I've heard that sometimes they get ground down so much that they need to be replaced.

Thanks,

Wes

StealDads67

Well first thing you should do is make sure you can get teh side plug out first before you drain the oil. IF you drain the oil and the side plug doesnt want to come out your in trouble.

My drain plug has never seen the ground and was in perfect condition, but on my old vette, it was ground down a lot.

I dont remember the sizes off hand but its pretty simple. I have a pump that i fill with the oil and fill teh tranny up, took like 5 minutes all together

DukeDiablo

KP-

I used a cheapo "Suction Gun" you can get at just about any auto parts store.

http://www.speedwaymotors.com/produc...HQ31GJABCJ754E

It sucks up nearly one pint per...uh, suck, and then you just push the lever in slowly and pump in the new oil. I bought mine at Advance Auto for $8. It came with a nice 12" length of flexible tubing that fit perfect.

My C4 has a reman (blue tag) ZF6, so the plugs weren't "gorilla torqued" on.

I did have to purchase another cheapo item...a three piece Allen Socket set from Autozone. It came with a 9,14,&17mm allen socket...all for $5. Made for 1/2" drive ratchets...I didn't have to grunt much.

Unfortunately, I only accomplished one of my three objectives for today. I had all of my parts to change the diff gear oil as well as the fuel filter; however, I ran into a problem with the diff plug (couldn't get my ratchet on it!) and I threw in the towel for today.

Best of luck on your projects.

Oh and I would say not much more than 1/2" diameter tubing would work best for fitting in the hole and flexibility.

C4DC

I didn't notice any difference with the TWS. I changed it at ~50k. I shifted fine before and just did it from what I have heard here. Still nice to know the fluid is fresh...

SLOWRIDE

LT4BUD

I noticed a definite improvement in shifting smoothness when I did mine at about 30k miles....

DukeDiablo

Well this one has 95,700+ now (about 80,000+ on the ZF6)...so maybe you will begin to feel more of a difference down the road.

Yall have a good one.

VR'92

I think it makes more of a difference on the high milage cars. It has really improved mine!

SouthernSon

Duke, the TWS is synthetic. I plan on leaving mine in for 50K. I have changed the fluid before with the GM stuff. I noticed no difference using a fresh GM fill but,WOW, that TWS 10-60 really smoothed up the shifting. Of course, the GM is a straight 30 grade (although synthetic).
I got the stuff for $8.05 a quart from an import indy.

DukeDiablo

Southern Son-

It's my understanding that even though the TWS is synthetic...the problem with the ZF6 isn't a breakdown of the oil...but a build-up of bronze in the synchros.

I agree...a synthetic in a gearbox shouldn't require 12k change intervals; however, the problem seems to merely be a build-up of bronze.

Regardless...I'll definitely wait until I can feel a difference before I decide to drain/fill again.

Yall have a good one.

2manyfuncars

My ZF has TWS in it right now. 3rd gear syncro is worn, but otherwise shifting is still good. The TWS didn't make any real impact. I'm wondering if the synthetic BG syncroshift or the dino GM syncromesh might help that third gear syncro a bit. Anyone try either one?

I'm finishing a build of a 400 solid roller motor and I really don't want to rebuild the ZF at the same time. I'd rather postpone the transmission issues for a little while. (I may go TKO 600 for the next one instead of big $ for rebuilding the ZF. Then I could use a regular scattershield too.)

Thanks

rocco16

Interesting. It's my understanding from an old post here that lubricant breakdown IS the issue. Regardless, I'd think a good synthetic like the Castrol should go 30K miles.
I changed the trans lube in my 70K mile 'Vette to the Castrol. Didn't feel any difference. Still, it's good to know that the lube is fresh.

Larry

DukeDiablo

Larry-

You're probably right; however, I was pulling knowledge from the ZF Doc FAQ page...particularly #8:

(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? Jim – Grand Sport Registry
(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 superceded 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. In effort to verify ZF Industries alternative lubricant recommendation, we ran our own test series on the BMW imported Castrol TWS 10W-60 oil. Independent testing of the transmission oil samples was sub-contracted out to CTC Analytical Services. The test series went as follows:
<1> Spectrographic analysis indicated that it is has full synthetic composition.
<2> After 2 hours of operation, approximately 100 miles, oil sample analysis tests indicated that the viscosity rating was reduced from 60 down to a 43 level. No need to worry, this is a normal occurrence for this heavier type of oil. I attribute this to microscopic-level lubricant-strand trimming through operational loading where all of the oil contents has been passed through gear pressure-loading regions at least a few times.
<3> At 200 miles, the viscosity level stabilized at a 42 level viscosity since the 100 mile oil analysis test results.
<4> At 5000 miles, the oil analysis test results indicated a 40 level viscosity.
The test-transmission was completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 4% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent)
gap wear/mass measurements.
<5> At 10,000 miles, the oil analysis test results indicated a 39 level viscosity.
<6> At 12,500 miles, the oil analysis test results indicated a 37 level viscosity.
<7> At 15,000 miles, the oil analysis test results indicated a 34 level viscosity.
The test-transmission was again completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill 30 oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 17% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent) gap wear/mass measurements.
<8> At 15,000 miles the oil had enough phosphor-bronze particles suspended
in it that deposits began building up inside of the synchronizer sliding
sleeves from the normal centrifuge-like rotational occurrence.
In Conclusion, until someone invents a copper magnet, we recommend that the ZF S6-40 6-speed transmission oil be changed at 10,000 - 12,000 mile intervals so as to minimize the amount of deposits of the suspended spent synchronizer material from collecting in critical component contact surface areas.