Crm318

I have just installed a brand new Bowtie Overdrives stage 3 2004R in my 1977 Corvette with a blueprint 383 and a brand new 3.55 differential. I just got everything installed and the TV cable was perfectly calibrated, verified visually by watching the travel in the pan and by pressure gauge. I took it for a spirited drive today and tha car performed phenomenally. I did a few full throttle runs starting in 1st gear with out a hitch, it when ever I dropped from 4th gear to 2nd on a full throttle run, I heard a loud bang and then the engine revved high. I then had no gears, forward or reverse. What could cause this? It's a stage 3 build dyno tested to 600hp. My engine dynoed at 436hp at the crank. What could have happened?

txfatboy1

Hard to tell exactly, but if you have no forward or reverse, the sprag in the torque converter or low/reverse drum, or input shaft are all possibilities I think.... and I'm sure there may be others. Keeping in mind, even if the trans was dynoed, any manufactured part can have an internal flaw that can fail... Happens a lot even with new OE or brand name parts in the repair industry.

ajrothm

The 4-2 wot downshift is the killer of many OD transmissions. It likely broke the band. Out it comes and back to Bow Tie. The trans “should” be able to handle WOT downshifts, but it’s NEVER a good idea to do a full throttle 4-2 shift. It’s best to take it out of OD manually, then either put it in 2nd and nail it or let it down shift from 3-2 at wot.

Either way Bow Tie should stand behind this.

Buccaneer

^^^THIS^^^
Even with a 700r4, you never want to do a WOT pull from OD, not a good idea. Always pull it out of OD before hitting the loud peddle hard. Good luck with the warranty work and hope it goes well.

CA-Legal-Vette

Check you U-joints before you pull the transmission. A lot less work to fix.

REELAV8R

i didn’t know this. So if put in a 2004r I gotta manually shift down if I’m cruising along and just hammer the throttle?
Don’t like that at all. And I was considering putting one in.

guess I’ll stick with the th350

Motorvation

This I've preached for years with any high performance transmission. "Let off the gas, manually move the selector, then stand in the throttle as required!" 350TH, 400TH, OD's. Bad things can happen in the overlap period of the downshift. You are throwing all the power and revs into the planetaries not relieving them like an upshift.

Steve O.

gkull

Generally I would say that the sprague. In the TC shattered. What kind of TC was it

TimAT

There is a selective thrust washer between the front shaft and the rear shaft. When it fails (often, it's plastic) the forward drum slides back and opens all the oil passages on the front pump. Pressure dumps and no gears. That "bang" you heard/felt could have been that washer shattering. That washer is in the th200, th200-4R and the th375-4L

'75

That much power on a non billet input shaft could also be the issue. You got a list of the special parts in it? I do the 4th to 2nd or 4th to 1st downshift every now and then, no issues, but then I'm only running around 325 hp.

71 Vert LS1

Didn't know about moving out of OD before nailing it. I had a 67 Nova with a LS2 sleeved and stroked to 427 cubes. Chassis dyno HP was 490 hp. Built 4L60E behind it and many down shifts from 4th to 2nd without any issues. Never broke. Maybe due lack of traction? 255 -18 tires on the back. Good info.

Motorvation

BTW, my guess is the hub on the cornvertor broke. No pump drive, no go....

Steve O.

ajrothm

Naw.... Its definitely either the band or the plastic washer Tim was talking about... Its not really because of how much power its making or the traction it has, its more about the transition components going from 4th down to 2nd and skipping over 3rd. Its a killer. On bone stock engines its a lot less likely to hurt it but...

I had a $5k RPM Transmissions Level 7 4L60, and from the start RPM told me no WOT downshifts from 4th and no chasis dynoing. 3-2 WOT downshifts are fine, and I did hundreds of them. But it literally takes ONE hard 4-2 down shift when making 900 rwhp to break the trans.

WOT throttle down shifts on T350s and T400s are fine, they are designed and equipped for it. They are not dealing with tiny little bands trying to hold the drum and tiny little 3/4 clutch packs.

Even on my new C7Z with the A8, I won't let it do a full throttle down shift. I'll manually shift it down to the gear I want to hit it from and go from there. Can you imagine how hard it would be on it to go from 8th to 3rd on the highway at WOT?

naramlee

Im very glad to be reading this info here since I will be running a PATC lvl-5 700R4 and 600ish... I didn't know any of this about the whole downshift buggery... is there any countering this with the TV kickdown or a throttlebody mod? or is it simply a poor design of high pressure fluid slamming into 2nd?

Buccaneer

Yeah, a 700r won't take it if you start doing those type of down shifts for very long. Mine is a very much built 700r with the extra wide band and host of up grades and the builder said to refrain form doing that or I will be back sooner than expected with tranny issues. With 600ish to the rear, I would definitely not do the 4th to 2nd or 3rd WOT downshifts until you yank it out of OD manually, then mash the loud peddle. I never use OD in town only when I get on the freeway. I plan on getting back into the trans sometime this year and check things inside and do a couple more mods to make it as good as it gets. The PATC 700 looks like a beast of a tranny and hope it does what it says. For that price...It should.

bfit

in curious what is the reasoning to down shift 4/2 at WOT , I'm hard pressed to find a good reason.

Bfit

Kacyc3

cruising along down the road and something pulls besides you and picks a fight before you can manually drop it, is my guess.

naramlee

Uh... i do it all the time in my mustang when some old guy in a new vette pulls up next to me and wants race... then i have to wait for him to catch up to see the look of disgust on his face... makes it all worth while 😁

Honestly tho, if i had known about this issue i never would have gone the 700 way... i would have put a built T5 in it and been done, after all, isnt that the point of an automatic??? Not having to manually shift it?

Crm318

Sorry to keep yall guys waiting, I've been at work for a few days in some desolate areas with out cell or internet service. I failed to mention that there was a split second that I did shift into 3rd on my way down to 2nd gear. The torque converter is from Cliff Ruggles, the quadrajet expert. Since this is a non lock up application, they said that the warranty was void when I ordered it, but that would cause a wear issue, not an internal fragging. We'll have to see. I'm going to get a hold of Cliff first and then with BTO no later than tomorrow. I will keep yall posted and thank yall for the responses.

DorianC3

Mmmm, I had that once... it was the retaining clip to the output shaft. No real damage to the trans.

I just can't see this happening to a built 200-4R behind an NA 383. It doesn't make sense. I don't think this is a total frag. Something else is up.