short shifting 1-2 off the transbrake issue?

[JDSfastGN]

Alright so I’m finally getting around to fixing a few small things with my Buick now that a buddy is talking a bit of smack. I have probably built 30ish 200-4rs with great success in the past so it feels weird asking the questions but I will readily admit I am not a valvebody guru and am looking for any hints or pointers. I launched off the Stage-rite Tbrake on my first pass of the day and all went well; 1-2 at 5800 and 2-3 at 5700. After that I had 3 more runs and gave the transbrake a try each time. As soon as I launched, the car was instantly in 2nd gear and first was nonexistent. Obviously this killed my 60 fts. I run a KC valve body as well as a deep pan and filter set, full billet internals, dual fed, CK servo etc….. It runs great on the street and all the shifts are quick and firm like my other builds. I use CKs shift kit but I blocked off my 1-2 accumulator. It does seem to quick shift into 2nd earlier than before those passes if I start to lean into it or if the tires break loose in 1st, but on the street it’s hard to tell. Does an issue like this ring a bell for anybody? The transmission shifts and acts completely normal under all other driving conditions. I plan on pulling my PTC to have it stalled a bit tighter soon and was hoping to get a few ideas before just replacing seals and clutches and hoping for the best if I don’t find something obvious.

 

[TT/Ameasap]

I just installed (1st timer) and raced mine a month or so ago. Had no problems with it.
Are you shifting from 1st to 3rd?

 

[JDSfastGN]

yeah I am. Ive raced with it for years with no problems. Im 90% sure the issue is in the valve body and the only reason I noticed it was because of being at the track on the Tbrake. On the street the tires break loose so quickly that 1st gear is just a blur of tire spin anyways. It would probably do the early shift even off the footbrake. I just didn't get a chance to try it at the track.

 

[TexasT]

Can you log the tps sensor? Is the t brake hitting so hard that your foot lets the pedal up a bit and the tv allows a short shifts. Just a thought.

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[larrym]

Can you log the tps sensor? Is the t brake hitting so hard that your foot lets the pedal up a bit and the tv allows a short shifts. Just a thought.

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My buddy did that bottle launching his Malibu slide back enough to release the nitros car basically hopped wheels up than took off.

 

[JDSfastGN]

Can you log the tps sensor? Is the t brake hitting so hard that your foot lets the pedal up a bit and the tv allows a short shifts. Just a thought.

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I wish that were the case but its not. My TPS does drop to 3ish on the runs right at launch but just judging by how soft it felt right off the brake It was in 2nd almost instantly. I backed off a bit thinking maybe I had blown the tires off but after watching vids it wasn't the case. I do have issues not putting my foot through the floor especially on shifts but Ive raced the car for a long time and it doesn't usually do this off the brake. Here are a couple logs from my passes that day. The first is when it had 1st gear and the next are basically a 2nd gear start right off the brake. They were all 11.1-11.0 runs.

 

[TexasT]

Next thought is the tv valve might be sticky. Do you have the spring in the bottom of the tv spool to force the valve back allowing pressure to go down enough to get back to first? I have had the 2nd gear start due to the pressure being to high but I think mine was a sticky valve not going back and causing the high pressure. I pulled the tv cable sharply several times to clear it. It seemed to be better but I haven't driven it much. Yours might have gotten some crudge in it causing some stickiness.

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[JDSfastGN]

Yes I run the return spring. I don't think it's a second gear start though. It always starts in 1st on the street. It just hits second a split second after the launch. I have thought about a tv issue but again normal driving the shifts are timed perfectly. The TV is all factory KC.

 

[TT/Ameasap]

Turn your boost down and let the tires hook. Then you will know without spending $25 for TNT.

 

[TexasT]

My next thought is the vb might be leaking between a pair of places and the shift is getting pressure from something next to it making it shift. I will try to remember to look tonight when I get home at what is next to the 1-2 shift in the worm casting.

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[JDSfastGN]

My next thought is the vb might be leaking between a pair of places and the shift is getting pressure from something next to it making it shift. I will try to remember to look tonight when I get home at what is next to the 1-2 shift in the worm casting.

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Thanks for all the help and ideas TexasT. Really I just need to pull it and get the converter tightened up a bit and go through it to see if anything is amiss. Its been 4-5 years and quite a bit of racing so its probably due anyway, but I'd hate to miss something and get it back together only to still have it jump right into 2nd gear. It killed my ET up in Oklahoma at the Buick vs Ford last year and I'm sure effected my trap speeds that were down 4-5 mph from previous best.

 

[JDSfastGN]

Turn your boost down and let the tires hook. Then you will know without spending $25 for TNT.

I really have some suspension work to do as even wtih a 315/35/17 NT05 on an 11" wheel it wont hook even with a half throttle 0 boost/0vacuum launch. I plan on double adjustable shocks and installing some lower control arm relocation brackets Ive had for a while. The car is lowered a lot and I believe the rear geometry is pretty off.

 

[TexasT]

Did you do anything to help get the pinion angle back after lowering it? What are you using for arms and bushings. Adjustable uppers work wonders to get you back to a driveline angle that hooks. Also boxing or replacing the noodle lowers helps keep the rear under control. I sent you a pm.

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[bison]

It's unlikely it's going to second unless there's is a cross leak in the vb. Try disconnecting the wastegate and leaving the clamp off the compressor outlet and do a flat foot trans brake launch and see if it's in second.


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