Car is probably right on the border of max power stock trans can handle at 890whp. Has a trans tune on it. Car drives amazing in all gears besides 5th. Only happens when full throttle. Even up to 70% 5th works fine. I rarely ever go into 5th wot and that's the gear that's not working for me while 1-4 get abused daily lol. Cars at 55k miles now and I'm assuming trans fluid has never been replaced. Gonna try that along with the weistec upgraded trans pan for better cooling. Not too hopeful but worth a shot before I have to resort to other costly options.

 

I assume the slipping happens at gear 6+ as well?

Your trans temps aren't high, and your ambient temps are quite low, i'm not sure how much a trans pan will help.

At 70% throttle, I'm not sure on your power curve, but are you accelerating at a higher rate than a stock car / stage 1 could in 5th? It could tell whether you are above the limit of the trans, or you are slipping at torque / acceleration rates consistent with a lower modded car which could highlight a problem with your trans.

I agree, start with the trans fluid and rear diff. You might need a true trans upgrade kit (new friction materials, etc.....)

 

I don't think 6th is slipping but I also haven't gone wot in 6th. Im hoping that the fluid change will fix it. Just doing the pan upgrade as well since I'm taking it off regardless. It just slips at full throttle in 5th wether I'm low in the power band at 3k rpm like video or I am going 140+. Trying to avoid having to do a trans upgrade but will if I have to

 

*****Once the pan is off inspect the bottom of the pan carefully for excessive friction material or obvious metal chunks. There are two magnets and if there is a bunch of metal on them including more than just metal "dust" the transmission should be overhauled/upgraded. On a car with 890whp - you are asking a lot of it driving it hard and having 55k on the odometer with no fluid change (presumably). Also, if the fluid smells burnt or is really dirty the friction material has roasted or simply been worn away from slippage enough that it should be replaced. You might get some miles out of servicing the transmission, but slippage as in your video would indicate worn clutch packs at the minimum, assuming fluid level is ok, or other related problems - perhaps with the pump not being able to properly feed the clutch pack fill times and maintain adequate fluid pressures under heavy loads.

The good news is the transmission can be rebuilt to be basically bullet proof with some new clutch packs, better machined pistons, better steels, and much much better clutch support to handle the increased HP and Torque of your car. Also replacing any hard parts that might have gotten heat damaged from all of the slippage and old fluids/debris floating around in there for 55k hard miles. Pic below of some of the parts to a rebuild kit - mostly clutch pack, gaskets and friction plates, etc.. Don't go cheap on the rebuild kit, get good quality parts and make sure whoever does the rebuild knows how to modify the valve body or pumps to optimize fluid flow for very high performance applications versus some old lady driving in Comfort mode to church every Sunday, and mebbe Applebees on Wednesdays to pick up young guys.

Expect to pay about 2k or so for a nice rebuild kit with everything you need, and another 2k for the actual rebuild using the nicer parts, any high performance mods to the valve body or pumps, etc.. pressure testing, and mebbe another 1.5k to install it all back in the car, and for proper engine and transmission calibration, road test, etc.. I'm familiar with American GM Turbo-Hydromatic transmissions (TH-350,400 and 200R4 like the GN/GNX had) used in old drag race muscle cars with standard torque convertors versus new wet-clutch systems which are hydraulic and offer some amazing advantages over old school torque converters. The 722.9 transmission I have looked over to see the tech and it was remarkably overbuilt for the C63s cars when they are stock, and have quite a bit of reserve capacity and safeguards built in but 890WHP is asking a lot of a stock transmission designed for a 550 flywheel HP car.

Good luck

 

Possibly could need re adaptations or tcu update? Have you spoke to your tuner?

 

thanks for all the info. Do you know who makes the best rebuild/upgrade kit? I would prob end up going with weistec

 

ya I tried that first no luck. Tuner said to flash tcu file to stock first. Gonna try fluid swap first if no luck try stock flash and again if no luck then prob build the trans

 

*****The Weistec kit seems *remarkably* over priced for what it seems to be on their website pics and description. The plates and clutch packs look like standard Raybestos GPZ which are really really nice along with gaskets and o-rings, etc... I don't see a filter or bellhousing or transmission pan bolts, etc... but perhaps they are not shown in the pic. I don't see K2, K3, or any type of clutch support cups or any type of re-worked pistons or valve body items, nor a new wet clutch pack, etc... Probably want to replace the wet clutch pack on a 55k mile transmission if you are overhauling it, as 890whp is not even remotely stock and the old pack got some miles on it - cheap insurance, and an easy install with the transmission apart anyway..

Other companies make HP application clutch packs like AMS/Exedy but I am not familiar with them, and not sure how much better they are, if at all, than Raybestos for a street driven vehicle. Once you start approaching 1000ft lbs of torque it's tough to keep things from breaking if you beat on the car enough..

Usually, the GPZ upgraded clutch pack modules go for about $380 or so, not including the nice steel modules and the overhaul kits with new pistons, etc.. which ups the cost some to about mebbe $680 give or take. You're gonna need new bellhousing and transmission bolts, and some other knick knacks that I don't see in the Weistec kit, at least in their pic. Perhaps they are all included, dunno. I'd strongly consider an new intermediate plate since the valve body is gonna come off during the rebuild anyway, and it's pretty cheap insurance. A decent rebuilder will clean and check the all important solenoids as well - a rebuilder would know this stuff though and replace anything out of spec.

Pics below of what a standard GPZ high performance pack kit comes with, and add in steels and the overhaul kit, etc... about $680-$700 ish. It's good quality stuff. A decent rebuilder familiar with HP applications may have their own preference and modifications they recommend for the valve body circuit as well as perhaps modifying pump line pressures, etc.. Anyway, whatever you decide, if you get it all rebuilt I would strongly recommend you change out the fluid at 500 miles or so to catch normal clutch pack and steel break in material so the transmission lasts a *lot* longer, and invest in a good transmission cooler as the one (at least on my C63s..) is uhhh..less than adequate for a higher HP build.

Plenty of companies sell the Raybestos or other kits for the 722.9 including PATC, and SHR (Southern Hot Rod), PAW, Oregon Performance Transmission, etc.. It is highly unlikely Weistec is making their own clutch packs,steels, gaskets and other typical transmission rebuild materials, but perhaps I am mistaken.

 

that shr setup looks pretty good I think I’ll go that route