How durable is the T56 transmission? I have the Z51 ratio and I heard it's not as strong as the base/Z trans? I'm looking to put about 500/450 rwhp/tq thru it from a H/C package. The car is mainly a street car with maybe 1-2 road course days if schedule and budget allows. I wont be hitting the drag strip much if at all.

So how are these things holding up? Has anyone blown one up or had any issues around these power levels?

Search didn't help too much.

Thanks

 

i believe if you know how to shift and dont powershift, it will take the 450rwtq no prob

 

I'm fairly competent shifting and I don't powershift. To me the abuse is not worth the slight reduction in shift time.

Does anyone know how much (if at all?) weaker the Z51 trans is compared to the base/Z?

 

Mine seems to be doing just fine.

BJK

 

you are fine to about 700rwhp 600rwtq... after that go 6060...

 

I don't think I'll be anywhere near that.

Thanks for re-instilling my confidence guys.

 

I've never heard of the z51 tans being weaker then the base, it is the same transmission. Just different gearing.

 

Because the input gear on the Z51 transmission is smaller and has less teeth engaging so the stresses are increased (the stress isn't spread out over as large an area {teeth}) Supposedly the Z51 transmission has a lower torque rating than the base/Z trans. How accurate or how much weaker it actually is, and if it's something I should be concerned about, was my question.

 

That's my favorite quote from a dumbazz salesman as I was looking at two radios on display with different model numbers..."they're the same, just different!"

It's the gearing of the MZ6 transmission that makes it weaker than the base transmission. The base/Z06 transmission is rated at 500 LB-FT and the Z51 transmission is rated at 428 LB-FT...that's just the way it is. For a given transmission with the center spacing, gear tooth width, and materials the same, the torque capacity decreases as the 1st gear ratio increases (numerically). For the gear ratio to increase numerically, the larger gear gets larger while the smaller gear gets smaller...the gear tooth stresses on the smaller gear increase causing the torque capacity to decrease.

PS For things you've never heard of, try doing a Google/Yahoo search first...it won't take you long to realize how little we really know.

 

I plan on having upper 500's in the hp/torque range. I have an 05 z51 should I keep the trans or will it give?

 

Good info

 

The 05-07 C6 T56 are same as C5 T56 as far as the gears are concerned. The 06-07 Z06 T56 have 30 splined main output shaft that increases the TQ rating. Starting on 08 GM went to TR6060.

Generally, T56's will be good from 600 to 700 RWTQ but that differs with application such as drag racing.....For the street, it will take more. IMHO there is really not a limit to what the T56's can hold. I have seen street cars with 800+ RWTQ holding it well.

 

Transmissions are rated based on fatigue strength and 1st gear is the "weakest link" based on that analysis. While 6th gear is probably used more than 1st from a time-in-gear perspective, 6th gear typically sees no more than 75 lb-ft during 99% of its life span. Contrast that to the many times 1st gear is exposed to full throttle max engine torque (470 lb-ft in the Z06). With steel, as long as you stay below the endurance limit (EL), you'll never have a fatigue failure. The EL is typically 50% of the ulimate tensile strength (UTS) for fully-reversing bending fatigue. For high strength steel like 9310, the EL can be as low as 35% of the UTS but the since the UTS is much higher, the EL is still above lower strength steel. It should be noted the stresses inside the gear teeth are actually zero-max-zero as each pair of gear teeth mesh and unmesh and the EL will be higher. At the gear tooth interface (surface of the gear teeth) where there is compression loading, EL values for hertzian (contact) stress can be substantially higher.

An interesting side note is the maximum input torque at which catastrophic/immediate gear tooth failure occurs can be approximated using a few conservative assumptions. For the ZR1 gearbox with a 9310 steel gear and using the fully-reversing bending fatigue factor of 35% with the 600 lb-ft torque rating, the max engine torque the gear tooth will sustain is 600/.35= 1714 lb-ft. Using the zero-max-zero fatigue factor will yield a higher number and that calculation does not apply to the shock loading that would occur from dumping the clutch.

For your case, you can see from above your transmission will handle upper 500's LB-FT easily without catastrophic failure. The torque capacity GM assigns to a transmission is for infinite fatigue life of the gears/shafting (but not the bearings, synchros, or seals). As you exceed that rating, the clock starts ticking on the fatigue life...the more you exceed it, the faster the clock ticks.

 

The material and material process for 1st gear was also changed to handle the increased torque of the LS7.

 

Before I bought my vette I did tons of research, but I never ran across the z51 trans being weaker. Ok I get the less teeth making contact being weaker then a set of gear teeth making more contact being stonger. It is the same reason a 4.10:1 rear axle ratio would be weaker then a 3.73. The question now is, is it really that much weaker to actually worry about?

 

Great info!

 

Asked and answered:

 

I just had to replace the entire manual transmission in my Corvette 06 Z51 M6. The trouble ticket indicated the transmission was stuck in 3 gear/synchro was stuck and all gears were overheated. I sent GM a note requesting that they share in some of the $4800.00 replacement cost pain since I have never popped my clutch, tracked it, raced it or done a burnout. I essentially drive my car back and forth to work. I just spoke to GM and they indicated since my car had been modified they would not proide any reimbursement and that was the final decision.

I should not whine since I accepted the risk that something might happen requiring me to have to take my car back to the stealership and them discovering the mods I have. It will make me think before I do another mod or maybe I should look into a Z06.

It does make me wonder if the clock is now ticking for another transmission failure since GM told me my transmission failure was the direct result of my power adders. I do not believe this to be the cause of the failure but just interested what the more mechanically inclined folks believe. Should I be worried about another transmission failure in the future?

 

Sorry to hear that.
What mods do you have and what kind of power are you putting down?

 

Thanks.

I am only putting down 446 RWHP and 404 RWTQ so it really seemed odd that my transmission would let go at only 41K miles. I have had my mods for around 2 1/2 years (see signature). I am sure with GM a mod is a mod is a mod no matter what the cause of the failure is. I asked about adding a Z06 clutch while they had everything pulled apart and they said that would be $1500 more.

Looking back I should have probably put my car on a flatbed and hauled it to a performance shop. When it comes to beefing things up I am not so good at making those decisions. I would have thought my transmission could have handled much more. I am just really fearful that this could happen again to me but if that were the case I would believe that we would see more see more posts about transmission failures. I have done some searches about transmission failures and really do not see much.