fatboyuk

last couple of runs at the strip I've been hitting the rev limiter on 2-3 shift and have to drop off to get it to change - dropped the shift points a couple mph and its ok for a run or two then same again. Rev limiter set at 6600 with hpp3 with 3.73's in a series 2 carrier. Normal driving is no problem. Is it likely to be the clutch?

WJ SOM SS

iTrader: (11)

Go down more on 2-3 shift points until it acts properly. You have heads, cam, and valvetrain mods? If not, better go down to 6300 limit... WJ.

Jammer

iTrader: (1)

Let me guess...stock transmission fliud pan. I was told that the 2-3 shift problem in many of our cars is due to the pick-up being in the front of the pan and fluid going to the back..letting off the gas allows fluid to move forward and into the pick up. Was told the best solutionis to try the ..I think..98 Tahoe truck pan (one of the few with a stock drain plug too) as the pan angles forward. I'm gonna try it. This came from a very reputable source who owns a pontiac/gmc dealership.

Colonel

Sounds like the clutches are trying to give up to me. You might buy a little time by doing a tranny flush. Always run with the selector in OD.

Brains

iTrader: (7)

why OD?? I've always heard to run in regular ol' D (3rd gear position) as it applies the overrun clutch through all forward gears, taking some of the stress off the sprag.

Colonel

Brian, my track experience tells me that running it in D causes a higher RPM on the shifts because you have more slippage (appearantly due to lower line pressure but not necessarily because of this reason.) It will seem to flair up higher on the shifts when in D than in OD. This has been observed many times by many people over the years. It's why you so often see people complain of hitting the rev limiter at the track but not on the street. They run D at the track and OD on the street. Once they realize this (as I did years ago), they solve the mystery.

Try it a few times while Autotapping the RPM paramter only. You'll see.

TA/30th 1002

I think ...

WJ 99 SS: is most correct with it being a tuning issue.

Jam Master: has a good point on the filter. From what I've seen of the different filters; the stock GM filter is well designed with an integral pick up tube and pulls very tight off the bottom of the sump. The aftermarkets "Carquest" I've seen pull from a broader area. ... But still I don't think that much oil will get tied up in the trans. A problem like this would be more pronounced on a 1-2 shift when you're pulling more G's. And also by simply adding a pint of fluid would support this type of prognosis.


Colonel: I agree with on the OD shift mode. We've all been down that road with stock trans tuning. I think with the manual valve in 3rd it's GM's idea of a performance shift mode. The shifts are managed by RPM's instead of TP and MPH. When the shift is called for @ie:6k, the trans actual shift time exceeds the engines rev time to rev limiter settings. ... If you delete TM you'll decrease the engines rev time to rev limit. If you're 3-4 clutches are getting loose "like the Colonel also stated" you'll increase the trans actual shift time, both of these issues will aggravate this 3-4 shift phenomenon.

My TA hit the rev limiter on the 2-3 in the performance shift mode right off the show room floor. I fixed it with Edit by bumping the rev limiter up a little. ... When I installed 3:73's it happened again when the trany was cool. I bumped the rev limiter up some more and that fixed it. ...

With 3:73's, your 2-3 WOT shift set at 6K, your rev limiter set @ 6.6k and your stock 3-4 clutch clearance with-in GM spec of 0.080 ish ... you should stay off the rev limiter.

... Ron

Brains

iTrader: (7)

Interesting If I remember, I'll atap it and see how much the RPM rise is... Does it seem to affect ET much, if it doesn't actually smack the limiter?

z2beat

I had the same problem after I installed a 3.42 rear. I tried it in OD & problem solved

Jorday

Yah, I always race in OD. Tried D a few times and the car seemed to act funny. It does sound to me like you may be getting a little bit of slipping going on.

PunkNPonys

iTrader: (2)

I am having the same problem. It makes me mad because my car only has 33,000 miles on it. At first i thought it was because i was low on tranny fluid but i checked it and i wasnt. I was told it is the 3rd gear clutch pack that goes out all the time. So does that tranny pan thing really fix the problem. My car just started acting up, it wont shift from 2nd to 3rd at WOT and it acts funny at normal driving its like i can hit the gas a little bit and the rpms jump to like 4000rpm. What should i do?

TA/30th 1002

redlsz28: In what position do you have your manual valve in when you don't get a 2-3 wot shift?

When your rpm's jump to 4k during normal driveing, what gear is the trans in?

Under moderate accelleration, 50% throttle; how would yo rate your 1-2, 2-3, & 3-4 shifts? ... positive, smooth, or hardly noticeble.

... Ron

Colonel

"Does it seem to affect ET much, if it doesn't actually smack the limiter?"

No.

If your clutches are slipping too much on the 2-3 shift, no oil pan is going to help. Going to a fluid that has less friction modifiers may buy you a little time (like Ford F-type or Trick Shift) but the clutches will need to be replaced soon.

PunkNPonys

iTrader: (2)

Well my 1st-2nd shift is fine and normal but then when it trys to go to 3rd it hestitates and sometimes it takes awhile to actually go in, i can give about 30% gas in 2nd and the rpms will just keep climbing and it wont shift. Its like i have a stall converter in 2nd gear and i think i can do the same thing when it finally does go to 3rd. I am not sure what you are talking about when you say manual valve? Can you explain? Thanks for the replies and any help.

TA/30th 1002

Manual valve is what your console shifter moves inside your trans. When your in OD up top, that is in what position your manual valve is in inside the trans, and so on. Sorry to confuse you on that. With the manual valve in 3rd you bring in anouther clutch for additional holding force. This practice can sometimes help diagnose internal trany problems.

It's hard trouble shooting a trans this way. But from your last post: it realy sounds like its makeing the 2-3 shift and then just smokin right through the 3-4 clutch pack. When you let off some it grabs, but with a little power your just walking right through the clutch again. Your trany fluid must be burnt.

... Ron

Colonel

"With the manual valve in 3rd you bring in anouther clutch for additional holding force."

You lost me here. For holding the 3rd gear you have 6 clutches (when stock) and they all apply regardless of if the selector (never heard it called a manual valve) is in 3rd or 4th.

A true manual valvebody is one that gives the user FULL control over his shifts. If he has it in 3rd it will actually start off in third. It requires the user to shift manually. These are best for track only cars in my opinion.

From what you describe, it sounds like your 3-4 clutchpack may be toast. Like Ron said, your tranny fluid will smell (and look) burnt if this is the case.

TA/30th 1002

Sorry Colonel for the more confusion. Some times I just get to rambling. The manual valve is the only valve in the valve body controlled by the operator. Every thing else in there is governed by the PCM or pressure/spring differential. I know my LS1-Tech nomenclature may not be correct all the time, coming from a mostly Caterpillar background. ... Yes I'm with ya on a full manual valve body and I hope this clears up any confusion of my reference to the "manual valve".

BTW: A full manual valve body configuration in a Cat dozer is called a Power Shift. The name alone sounds awesome ... "Power Shift"

>>Bringing in another clutch in manual 3rd<<: I wasn't referring to applying more discs within the same pack. With the manual valve in "OD" position, the trans operating in 3rd gear mode; Forward Clutch &amp; 3-4 Clutch are applied, Forward Sprag Clutch is holding. With the manual valve in the 3rd position; trans operating in 3rd gear mode; all of the above components are applied or holding to include the Overrun Clutch. ... The only time the Overrun Clutch is ever used is if the operator selects the manual valve to the "D", "2" or "1" positions. ... If you were road testing a trans; by applying the Overrun Clutch your could more accurately trouble shoot certain internal components.

... Ron

Colonel

Good info. I've had my tranny builder explain all of that stuff before but I gotta admit, it's been awhile.

Ron, do you happen to know why we see more slippage on the 2-3 shift when the gear selector is in D rather than OD? All I know is that it IS the case (which results in more RPM flairup on the 2-3 shift), but I don't really know why. This phenom is not hard at all to detect, especially with Autotap.

TA/30th 1002

I think the only difference between OD and D is the WOT 2-3 shift when in D is initiated at a little bit higher RPM. ... I'm talking stock programing here.

I think we see the rev limiter bumped because the PCM initiates the shift electrically but the hydraulics take time to dump off the 2-4 band and pressure up the 3-4 clutch. ... I understand the shift to happen like this: The stock 3-4 clutch clearance is something like 0.080". So when the 3-4 clutch plates finally get close to engagement the shuttle valve lets go of the 2-4 band and we try to drive power through the 3-4 clutch. During the time the 3-4 clutch piston is moving that 0.080" were still accelerating to the rev limiter. The 3-4 clutch accumulator has to load up to give us a smoooth shift. During the time were filling that 3-4 clutch accumulator we don't have full apply presure and were slipping the 3-4 clutch pack.

When I put my 3:73's in my rev limiter bump came back. I believe is was due to my revs accelerating quicker waiting for 2-3 shuttle valve movement. If the engine makes more HP during this 2-3 shift via: TM, cam, 422cid ... I think it highlights this event even more.

The quick fix is getting the rev limiter out of the way. A better fix is a shift kit. An even better fix is a built trany (not built to tight though!)

... Ron

Magnus

iTrader: (4)

Hmm... so there will be on harm in driving in D all the time as opposed to OD to avoid excess 3-4-3-4-3 shifts?

The real question is, is the same amount of fluid pressure applied weather the shifter is in 3 or 4.