Hi all,

This stumped all my friends and my transmission guy is looking into it (didn't know either) but i'm hoping someone here might have an answer.

Info: recently professionally rebuilt 700r4.. upgraded clutches, hard parts, shift kit, corvette 2-3 servo, sonnax 4th servo. 12" tc with 2800 stall. has cooler in place (plumbed correctly). engine has: holley stealth ram, headers, 24lb injectors, etc. car does 14.6 in the quarter consistantly (needs a tune bad) so i am not running a 600hp beast here.

Issue: at the track this weekend I was running good, but when I attempted to shift with the engine at 5500rpm the tranny "stuck" between gears.. engine revving, no shifting, car slowing down. as soon as i dropped the rpms to 53-5200 it slapped right into gear chirped the tires and ran perfectly. If i shift it under the 5500rpm limit it works perfectly with no slipping or lag; it drops right into gear with a firm shift. i did some tests on the next few passes and found this is something i can replicate, and can happen on the 1-2 shift and the 2-3 shift.

anyone here have any idea wtf is up? apart from that weirdness this transmission works awesome which is why i'm stumped.

thanks all,

Jason

 

Check fluid level, if you are low you will not be able to build enough pressure to shift at higher RPM and loads.

It could be a valvebody issue, but i'm not very well versed in the valve body schematics.

 

the fluid level is good, checked both before and after my day at the track. in addition the fluid is clean, new and does not smell burned. tv cable is adjusted correctly as well.

 

sprag?

 

I am not a transmission expert but I would say line pressure/valvebody issue. Either the pump is sloppy or there may be a sticking valve. Again, this is just my opinion. You could try hooking up a trans pressure gauge to check your pressures while driving. I have had to do this a couple of times. The guage isn't expensive at all.

 

if the car runs and drives fine other than this one issue, i wouldnt think the line pressure is the problem, especially at high rpm when it should be the highest. If the clutches were slipping due to low pressure, i dont think it would completely freewheel either. It would be more of a lazy/soft shift.
I personally think the forward sprag is spent. These things are notorious for that, and it would only happen in 1-3, probably under a torque change (like shifting gears).
But yea, i would probably throw a gauge on it for *****-n-gigs before i pulled it.

 

ok.. that kinda frustrates me. i've only been running this newly rebuilt tranny for 3 weeks. he used all new sprags.. what could trash the sprag in 3 weeks?? I had good fluid, i didn't push it until I had about 600 miles on it. hell, its got about 1500 miles on it total and the track this past weekend is the first time i've actually hammered on the thing full throttle.

anyone recommend a particular gauge? there are so many different ones (mechanical, electric, etc) i'd rather grab one someone has tested and likes. as i plan on racing this i'd like one that will last me a while.

 

well i could be wrong. I'm no expert, but i did just rebuild mine so the mechanics of it are still sorta fresh in my head.

How much do you trust your tranny guy?
Maybe the problem was there since the initial rebuild, and the problem is only showing now since you said this was the first time you actually hammered on it.

 

I'm not questioning you man.. just bummed my tranny is not workin 100%. this guy has a great reputation and did the tranny for my friends 10 second GTA (works great) as well as a few other very fast cars at the track so i was hoping mine wouldn't be f-ed up.

i was so hoping i wouldn't have to pull the tranny again. how much of a pain is it to swap out a sprag? at least they aren't expensive

 

well i would question me lol
definitely run it by a few other tranny guys before you pull it out or bust his *****. (wow, that sentence could DEFINITELY be taken out of context)

The sprag is in there... approximately the middle of the trans. Not horribly hard to get out, other than the fact that you actually have to pull the trans and rip into it.
Basically you pull the pump out
remove the reverse input drum (may have to remove the servo and/or the valve body in order to get the band loose enough to get the drum out).
remove input drum
remove clutches and steels from input drum
remove sprag
reverse proceedure for installation

actually it isnt too bad at all, all you would probably need is the pump gasket. You wouldnt need a spring compressor or a seal tool to do that job. A pump puller is recommended, but i just used a power steering pulley puller, slightly moddified.

 

I'd just bring it back to the TransGuy. Have HIM drive it, if there is any kind of warranty work have him pull it and fix it (hopefully for free).

For as much as a transmission costs to rebuild, they should honor if it hasn't been a long time.

Any good trans guy should be able to narrow down a list of things that could cause your symptoms. If you understand how the transmission works, you should be able to diagnose an issue with a degree of certainty.

 

well, I called my torque converter company (CTI out of nedrow, ny) and Darren helped me eliminate the torque converter and forwarded me onto a company called Clark transmission. Guy named fred answered and after describing the issue he gave me two possible scenerios. the more remote possibility was getting air in the tc when spinning that high and under heavy acceleration.

the thing he told me was most likely the issue though is a problem with the governor not being calibrated right. he said if the inner weight is too light, i'll get stuck in the lower gear as it will require an even higher rpm to shift. he said to re-check my cable to confirm it didn't stretch or slip and that i should grab another governor to test with if my tranny guy has one handy. is swapping out the governor easy?

 

Yes. Under the domed cover, driver side rear of tranny.

RBob.

 

Yes, swapping out the governor is easy. Just make sure that when you put the dome plate back in, it seals tight. If that plate comes off at speed you will lose fluid pressure and likely fry the transmission before you can shut it down. Ask me how I know.

 

well i upped my rev limiter to 6000 and did some testing on the highway... it DOES finally shift.. but at about 5700-5900 rpm under full throttle (well after the power band).

its gotta be the governor. under almost full throttle it allows me to click it up a gear, but under full throttle it waits until almost 6k before allowing it to shift. it seemed to be stuck between gears because it was making so little power that high (factory tune with a hsr, head work and other upgrades) that it actually stops accellerating before the tranny lets it shift into the next gear.

is there a complete idiots guide to governor weight and spring selection or should i just bring it to the tranny shop to make the adjustments? i want to drop the full throttle shift to a max of 5500rpm

oh, and thanks for the heads up man... i definitely don't want to smoke this thing. i'm too broke to rebuild it again

 

You can a weight and spring kit to recalibrate the gov.Get ready to pull that thing at least 5-10 times while adjusting.B&M has one.Also superior sells one.

 

rather than doing all that, wouldn't it just be easier to grab a corvette one from patc or probuilt and throw it in? or would that not work right either?

 

Great thread...I've been having the same issue with my 700R4 and was continually told it was my TV cable that required adjusting - which is hard to do unless you can spend a day at the track adjusting after every run until you get the trans to change gears. Normal driving and it changes perfect -- drag strip, hangs onto 2nd, can't hit 3rd -- I never even thought about the Gov.

Thanks! Great help.