TH400 doesn't hold the gears

gbak

Well-known member
Joined
Mar 24, 2008
Messages
89
My gearbox doesn't hold the second gear when dragracing.

Everything is warmed up and I always do a 1 sec burnout just to remove dirt from the tires.
I have tuned the govenor with lighter springs and weights, instruction tells it should be possible to hold the gears longer if doing so.
Modulator is new and also tuned, but I don't think it will have anything to do with this problem.
I have also installd a B&M shiftkit.

At the line I hold the car at 1800 rpm before take off.
First gear pulls fine up to 6500 rpm.
Then I shift manually to second gear.
But two of three times the gearbox itself goes directly up to the third gear and the race is lost as I loose the power and must build it up again.
The gearbox is except for the govenor, modulator and shift kit pure stock.

What is wrong? Can it be so that the speed is to high when I upshift from first to second?
Or is it time for a big rebuild of my gerbox?

I don't know nearly anything about gearboxes so you have to guide me here!
 
Last edited:
I've been thinking about this one for a couple of days. To miss 2nd gear, the 1-2 and 2-3 shift valves have to be moving, which leads me back to the shift kit. I've never used a B&M kit so I'm not up on the works there. I would think about getting a Trans-Go kit and a new spacer plate and redoing the valve body. I'd also think about opening the trans and checking the sprag on the intermediate drum- if it's slipping then a host of other problems will develop.

Just for info- the 74 Coupe I just got has a TH 400- I' have it hanging on the bench right now and I plan to rebuild it in the next couple of weeks- with pictures and tips.
 
TimAT:
As I'm a TH400 newbie I would be more then happy if you do a "How to rebuild TH400" thread with photos.
A rebuild would be a nice job when the winter and snow comes here in Sweden.
Any difficulties or special tools needed for a rebuilding/strenghten the gearbox?

Talking about brands; are Trans-Go the way to go?
What about all the other brands, are they not good enough for our HP Corvette's?

Next question:
When I manually shift on WOT (when racing), is there anything in the gearbox that decide's that "now it's time to upshift"?
Or should the gearbox hold the 1'st gear until I decide to upshift at any rpm/speed?

Last question:
As I understand there is a lot of slip on converters.
Any recomendation of which brand to use to minimize the slip?

A lot of questions and I hope someone (TimAT?) can answer them so we all can learn something here!
 
It don't seem to matter what tranny it is.....there is ONLY ONE SHIFT KIT...and that's TRANS GO.....the rest suck.....end of conversation...

get that heavy duty TG kit in there and that sob will squall rubber from there to China....

:shocking::shocking::search:
 
I've been thinking about this one for a couple of days. To miss 2nd gear, the 1-2 and 2-3 shift valves have to be moving, which leads me back to the shift kit. I've never used a B&M kit so I'm not up on the works there. I would think about getting a Trans-Go kit and a new spacer plate and redoing the valve body. I'd also think about opening the trans and checking the sprag on the intermediate drum- if it's slipping then a host of other problems will develop.

Just for info- the 74 Coupe I just got has a TH 400- I' have it hanging on the bench right now and I plan to rebuild it in the next couple of weeks- with pictures and tips.

Tim, we need the same for the 350, 200 4r, 700 r4, 4l60, 4L80e......

Pretty please.....please....huh ???
:smash::smash::fishing::lol:
 
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