MYblu69

I understand the advantages to my 7 speed and I like the transmission.
However, this Tremac along with my 6 speed Tremac in my08 would still crunch from time to time going from 1st to 2nd even with the tranny fluid changed out to Red Line synthetic. So can some one tell me why this happens? Intrinsic to Tremac? Design of the gears? What?

JerryU

I'll try. The Tremic trans handles a lot of torque. It has very big gears and gear clusters. The gears don't move but the spinning gear cluster has to change speed from a Z51's 2.97:1 1st gear 30% going into 2nd. The 2nd gear syncro's have to change the rpm for the whole gear cluster. Even though it has 3 synco cones (unlike the usual one in a lower hp car) it still must change the rotational speed of that large heavy gear cluster in a short time.
When the fluid is cold, don't care if it is Red Line, it's thicker.
I have found when the trans is cold that it does require more force and a faster pull. One of those 3 synco cones is carbon faced so it should be able to take it. I get no crunch, just a harder feel of the synco catching 2nd gear. Here is a pic of the gears.

jcp911s

The torque multiplication (e.g. difference in gear ratio) is always greatest in the 1-2 shift, and this is the shift that occurs most often in DD driving, so the 2nd gear synch takes the most punishment.

Decades of driving Porsche 911s, I use 1st to get the car moving, and shift immediately into 2nd.

Corvettes have enough torque (I have a '71 4-speed btw), that you really only need to use 1st for parking... I always drive the car in 2nd. Saves the trans.

rdrnr

Good explanation and one thing I picked up on was your comment on requiring more force and a faster pull. I recently found out that when I shift faster from 1st to 2nd, the shift is less "crunchy".

bob guzzy

Another thing you might consider is if you change fluids the trans may not work correctly.

By changing your fluid to a different type you may have created your own problem, for what it would cost you, I would change back before I put any money in the trans.

Bill Dearborn

The 7 speed in my new car seems to be similar to the M6 and M12 transmissions I had in my C5 and C5Z. A little hard to get into low gear and if you don't ensure the shifter is all the way forward the trans will pop out of gear when you let the clutch out. The trans in my C6Z was much easier. No issues ensuring it went into gear it just went kathunk and was in. The C5 transmissions and C6Z transmissions would nibble the gears on the one two shift in cold weather but as long as you were slow in making the shift the first few times the nibbling went away as soon as the fluid warmed up. Then, you could jam gears. The 7 speed will nibble on the one two when it is cold and that will go away after a half mile or so of easy shifting but on mine there is clunk that wasn't there with the other three transmissions. Even after miles of driving I can feel a momentary catch when making the 1-2 shift and I think if I had the window open I could hear it as well. I drove the car around town for a couple of hours today and that clunk and what I think may be an associated noise was there on every 1-2 shift. I tried shifting hard a couple of times but there is a feeling that this is something I need to get checked out. I am pretty sure it isn't shifter related since the C5/C6/C7 shifters have been nothing but a shaft through a hole since the C5 came out in 97. People have come up with different designs but in the end they are nothing but a shaft through a hole and will not catch on anything no matter who makes them. The shift linkage running from the bottom of the shifter to the rear along the top of the transmission could be causing a problem since it is a more complicated assembly than the shifter.

Bill

JerryU

I'm reminded of watching technicians at the Lenco booth at a national drag race repairing manually shifted transmissions brought in by racers. Although totally different construction than the C7's, when I asked what causes that bullet proof trans to fail, he said it happens when they don't pull the shift levers fast enough! The Tremic is the not the same design but the syncro teeth have to engage quickly and they are beveled to help. But in that more difficult 1st to 2nd shift pulling faster makes them engage without slipping (or at least not as much) over each other making that grinding sound. The syncro's triple cones, one carbon faced may even have less wear when engaged more quickly. Once the trans fluid gets hot I have no problems shifting fast or slow.

MYblu69

I took your advice of just starting off in 1st gear. I have to say wow! Smooth as silk. I notice no lugging or higher revs needed to start moving.
There seems little difference between the two gears actually.

MYblu69

Whoops! I meant to say start off in 2nd gear!!

C7Joy

When my car is cold I avoid forcing 2nd gear and never really get a crunch. Sometimes I avoid 2nd and just shift right up to 3rd. If the car is designed to do 1-4, 1-3 is certainly ok.

MYblu69

What I have tried and it works every time, is pull it out of first and for a moment, let the spring push the shifter to the right, in neutral then slip it into 2nd. Perfect. Now I'm no engineer and have no clue how this works but it does. Give it a try!