Trans issues

[project 92z]

Hey Everyone. I got a bit of an issue. Trying to find out how big of a deal this is... I got a 92 Z34 with about 190k on it. I haven't done a trans fluid change cause I don't know much about the past. I don't do much banging on it from a dead stop but rolling punches are the norm and I've topped out on more than a few occasion.
All that being said, I've noticed what seems like slipping coming out of passing gear. It shifts fine 1-4, fine 2 into passing gear, fine passing gear into 4th (when topping out) but if I'm in passing gear and let off b4 it kicks down on it's own, it seems to slip. Any insight? I know it's possible I'm looking for an excuse to rebuild my tranny so that I can do upgrades, but I really don't have the extra$$ now. Can I get away with a trans flush or do I not need to worry at all?

[farley463]

So your basically saying that the 3rd-4th gear upshift feels sluggish? I'm no transmission expert but it sounds to me like it might be a bad vacuum modulator. How does the fluid look?

[project 92z]

To me the fluid looks dirty and a little foamy. A friend of mine told me that for a trans with 185k that was pretty normal, but that was b4 I noticed everything else. But is the vacuum modulator external or internal. does it require a rebuild.

[farley463]

Foamy sounds like it might be a little burnt, but I could be wrong. The vacuum modulator is the canister looking thing held by a bracket on the transmission, on the drivers side facing towards the front of the car. It has a vacuum line on it that goes to the intake manifold. What it does is it adjusts shift firmness based on engine load. If your going wide open throttle, you have no vacuum, so it'll give you firm shifts. When your cruising at say 15-20% throttle, you have a lot of vacuum, so it will then give you soft shifts. It shouldn't be an expensive part, and its very easy to change, so its one of those things where you can't go wrong.

[project 92z]

Thanks! Modulator seems to have done the trick. aftermarket ones are a lot smaller and kinda confused me for a minute, but like I said, it worked. Installed in about 5 minutes, too. As far as the fluid is concerned, I'm not sure about doing a trans filter and flush because I don't know much about what was done previously. Is our trans notorious for failure after filter/flush?

[farley463]

Glad I could help!! Anyways, what you want to do is drop the pan and change the filter and fluid. The worst thing you can do with a transmission that hasn't been kept up on fluid changes is flush it, because what happens is varnish builds up on the seals, and when you flush that out the seals start leaking, and the next thing you know is your spending 6-800 bucks getting your trans rebuilt. If you do the fluid and filter change be sure to keep up on it every 50k miles, and your trans should last as long as you don't beat the hell out of it like I did to mine. That was a 600 dollar mistake ill never make again. But anyways, I'd just do the fluid and filter. If you have any other questions about anything, don't be hesitant to ask!! Good luck!!

[Schurkey]

The only difference between a "pan drop" fluid and filter change, and a PROPERLY-DONE trans flush...is the quantity of old fluid removed, and new fluid added. Pan drop = approx. five quarts of fluid, while a flush removes virtually all the old fluid.

Be aware that many shops performing "fluid flushes" DON'T change the filter, or clean out the pan. These folks are criminals who need to have their business license revoked.

If the only thing holding your transmission together is the "varnish", you need a trans overhaul anyway.

[robertisaar]

^ some people may call this guy an asshole at times, but he isn't wrong very often.

if a flush kills a transmission, it was either done VERY wrong or it was going to let go soon anyways.

the MC essentially flushed itself out when the cooler lines rotted and dumped the entire contents of the pan in my driveway. did a filter change shortly aftwards(original pan gasket was leaking too, replaced with a WIX cork one, even with 1 stripped pan bolt, no leaks after a retorque after some heating and cooling happened), i seem to remember needing about 8 quarts? that was 7 years ago though, so your experience may vary.

[project 92z]

OK now I'm confused again. Do I risk it with a 20 year old 4T60E trans that may not have had servicing before or not. If I'm seeing slight browning or greying in the fluid and some foaming, am I better off riding it out? I don't do N drops often but hitting it hard from 40mph isn't rare at all...

[Schurkey]

OK now I'm confused again. Do I risk it with a 20 year old 4T60E trans that may not have had servicing before or not. If I'm seeing slight browning or greying in the fluid and some foaming, am I better off riding it out?

I would drop that fluid like it was a broken rubber. And I'd refill with whatever brand of Dex/Merc (Dexron III equivalent) was on sale at the time. I would buy a trans filter kit that uses a big piece of cardboard to support the gasket so that the gasket IS NOT FOLDED-UP AND CRAMMED INTO A TINY BOX. If the filter kit happens to be Made In USA, even better.





Loosen pan, drain most of the fluid. Remove and clean the pan and the magnet, install fresh filter, reinstall the pan using NO sealer on the gasket. Some or all of the pan gasket bolt holes will be slightly undersize, use the undersize holes to retain some of the pan bolts for easy alignment of the gasket as you install the pan. Fill pan with fresh fluid through the dipstick tube--about the same amount back in, as you drained out. Let it settle for five minutes.

Then you've got options:

1. Start engine, run it through the gears. Check fluid level. Since the fluid isn't fully warm, It SHOULD read a bit low (1 pint or so) on the dipstick. Drive car no less than 10 miles. Check fluid level again--should be at "full hot" mark. Adjust level as needed.

OR

2. Figure out which trans cooler tube is the OUTLET from the radiator. Remove that tube from the radiator. Install temporary tube purchased from parts store (typically about 2--3 feet of 5/16 double-wall seamless steel tubing with a 45 degree double-flare end, although there are other styles especially on newer vehicles) into radiator, with the tubing bent as needed to direct the fluid into a big drain pan. Open a few more quarts of fluid (5 recommended), and place them in close reach on a stable surface. Have a helper start the engine. Fluid will shoot out of the temporary tube into the drain pan. Dump the fresh fluid into the dipstick tube as fast as you can, while ALSO watching the fluid squirt out of the temporary tube. When the fluid shooting out of the temporary tube is bright red, clean and virgin-looking, have the helper shut off the engine. Re-connect the cooler tube to the radiator. Start engine, run it through the gears, check for leaks and check fluid level. Adjust fluid level as needed. You just flushed the transmission and the trans cooler. Have a beer and enjoy the rest of your day knowing you accomplished something worthwhile.

I don't do N drops often but hitting it hard from 40mph isn't rare at all...

Don't EVER do a "N drop". This is extremely hard on the trans, and on the fluid. It is a wonderful way to burn clutches, burn fluid, crack drums and shells, and tear splines from shafts and hubs. Whacking the throttle at any speed is no big deal if the trans is suitably warmed-up. Beating on a cold engine or a cold driveline is not recommended.

^ some people may call this guy an asshole at times, but he isn't wrong very often.

Thank you. Now I have a signature line. Appreciated!

[Schurkey]

Thank you. Now I have a signature line. Appreciated!

Took awhile for the signature to show up. Apparently, it's only added to new posts, not the existing ones.