what causes this?

Adger Smith · 07-14-2008, 04:36 PM

In a P/G the band is applied when it is pulled into low gear. Rolling forward is usually too low line pressure at the time you apply the Trans Brk or too much clutch clearance in the rev clutches. The low(forward band) is applied and the rev clutches must apply to hold or lock up the forward movement. If they(rev clutches) are late or slow applying you will roll/creep forward.Try changing the spring pressure or the size of the boost valve (.488 dia gets the most pressure) in the valve body to raise the line pressure. You might also try going to a higher apply RPM to get the pump spinning up the pump pressure-Vol. Low vol. or worn pumps require higher RPM to move the required fluid vol to apply the rev clutches. The hardest thing to fix is the rev clutch pack clearance. (requires complete transmission disassembly)The more clearance, the more fluid vol is required to apply the rev clutches. I usually work around .060 for pro tree and around .085 to .090 on .500 tree applications. With it doing it hot I would put a pressure gauge on the rev & check the difference in hot or cold pressures. You can also judge how fast the pressure rise is when you apply the Trans brake.
Good luck, hope this helps you solve your problem.

Bryan Gillespie · 07-14-2008, 04:57 PM

band adjustment (all the way in,then out 3 turns)
also change fluid and filter

Bob Verwold · 07-14-2008, 05:18 PM

Quote:

Originally Posted by Bryan Gillespie

band adjustment (all the way in,then out 3 turns)
also change fluid and filter

70 inch pounds in and 3 1/2 to 4 out is the way I adjust mine........

BIZMANRACING · 07-14-2008, 07:01 PM

i adjust my low band about a month ago. turned all the way in and then 4 complete turns out. i might add that it was a bitch with the CSI cover over the trans. its a little hard getting the allen head in there.

as for the line pressure being low and increasing the rpms. that might just be the only other thing to try. always some **** for me in the 3rd round. just finished practicing on friday. back to back to back runs just to see what the car would do if it had a good drivier. everything went fine and it repeated. now this.

well it will just have to rest until friday, then will do a little maintenance and put it away again until race day. see, bad thing about race cars is that you just can't take them out into the street and try them out. hell, it would blow the tires out anyway.....lol

SlickVic · 07-14-2008, 08:11 PM

Carlos, sometimes my trans rocks the car foward or backwards when engaging the trans brake. Ive tried adjusting an still does it. The way i fixed it was just to bring the rpms up a little before i stage. This brings the line pressure up and no rock. The nova also engages the line lock when the transbrake is engaged to keep it from rocking but becomes a pain when backing up w/ a hipster.

dak · 07-14-2008, 09:39 PM

I had run into this a couple of times when I first started racing ...1st thing I started doing was bringing the idle up 11-1200 RPM..the 2nd was before I would stage I would cycle the brake 3 or 4 times ...just press and release the button...I have no idea if any of those things helped ..maybe it was just a timing thing between going in the beams and applying the brake. but I know that once I started that routine the car never moved ... I still do it today

Adger Smith · 07-14-2008, 10:30 PM

Rolling forward when you hit the brake has nothing to do with the low gear band adjustment. Low gear band adjustment has everything to do with the timing of the low band dropping out & the High clutches applying. Any one that has really looked at a racepack graph of driveshaft RPM / engine RPM can see if the shift holds low too long or lets it loose causing a flare in engine RPM. Comp racers & savy .90 class racers chase the bump on the graph to get it as smooth at the shift as possible.
The low band is already in full apply when you are rolling forward into the beams. It is line pressure or fluid vol required for a loose reverse clutch pack that makes the car roll forward. The rev clutch pack isn't applying quick enough to lock the tranny up. The cycling of the T brake before the final apply is filling the rev piston cavity with fluid. So when you make the final apply it doesn't take a full load of fluid to move the piston forward to apply the Rev clutches.

07-14-2008, 04:36 PM	#1
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: what causes this? In a P/G the band is applied when it is pulled into low gear. Rolling forward is usually too low line pressure at the time you apply the Trans Brk or too much clutch clearance in the rev clutches. The low(forward band) is applied and the rev clutches must apply to hold or lock up the forward movement. If they(rev clutches) are late or slow applying you will roll/creep forward.Try changing the spring pressure or the size of the boost valve (.488 dia gets the most pressure) in the valve body to raise the line pressure. You might also try going to a higher apply RPM to get the pump spinning up the pump pressure-Vol. Low vol. or worn pumps require higher RPM to move the required fluid vol to apply the rev clutches. The hardest thing to fix is the rev clutch pack clearance. (requires complete transmission disassembly)The more clearance, the more fluid vol is required to apply the rev clutches. I usually work around .060 for pro tree and around .085 to .090 on .500 tree applications. With it doing it hot I would put a pressure gauge on the rev & check the difference in hot or cold pressures. You can also judge how fast the pressure rise is when you apply the Trans brake. Good luck, hope this helps you solve your problem. __________________ Adger Smith (Former SS)

07-14-2008, 04:57 PM	#2
Bryan Gillespie Banned Join Date: Dec 2006 Location: Maryland Posts: 456 Likes: 0 Liked 0 Times in 0 Posts	Re: what causes this? band adjustment (all the way in,then out 3 turns) also change fluid and filter

07-14-2008, 07:01 PM	#4
BIZMANRACING Junior Member Join Date: Oct 2004 Location: east brunswick, new jersey Posts: 62 Likes: 0 Liked 0 Times in 0 Posts	Re: what causes this? i adjust my low band about a month ago. turned all the way in and then 4 complete turns out. i might add that it was a bitch with the CSI cover over the trans. its a little hard getting the allen head in there. as for the line pressure being low and increasing the rpms. that might just be the only other thing to try. always some **** for me in the 3rd round. just finished practicing on friday. back to back to back runs just to see what the car would do if it had a good drivier. everything went fine and it repeated. now this. well it will just have to rest until friday, then will do a little maintenance and put it away again until race day. see, bad thing about race cars is that you just can't take them out into the street and try them out. hell, it would blow the tires out anyway.....lol __________________ S/ST 1739 Carlos Mendes

07-14-2008, 08:11 PM	#5
SlickVic Junior Member Join Date: Jan 2006 Location: Maryland Posts: 81 Likes: 0 Liked 0 Times in 0 Posts	Re: what causes this? Carlos, sometimes my trans rocks the car foward or backwards when engaging the trans brake. Ive tried adjusting an still does it. The way i fixed it was just to bring the rpms up a little before i stage. This brings the line pressure up and no rock. The nova also engages the line lock when the transbrake is engaged to keep it from rocking but becomes a pain when backing up w/ a hipster. __________________ 87 Cavalier, 92 Corvette, 72 Nova, 68 Firebird

07-14-2008, 09:39 PM	#6
dak Junior Member Join Date: Mar 2003 Location: west coast Posts: 26 Likes: 0 Liked 0 Times in 0 Posts	Re: what causes this? I had run into this a couple of times when I first started racing ...1st thing I started doing was bringing the idle up 11-1200 RPM..the 2nd was before I would stage I would cycle the brake 3 or 4 times ...just press and release the button...I have no idea if any of those things helped ..maybe it was just a timing thing between going in the beams and applying the brake. but I know that once I started that routine the car never moved ... I still do it today

07-14-2008, 10:30 PM	#7
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: what causes this? Rolling forward when you hit the brake has nothing to do with the low gear band adjustment. Low gear band adjustment has everything to do with the timing of the low band dropping out & the High clutches applying. Any one that has really looked at a racepack graph of driveshaft RPM / engine RPM can see if the shift holds low too long or lets it loose causing a flare in engine RPM. Comp racers & savy .90 class racers chase the bump on the graph to get it as smooth at the shift as possible. The low band is already in full apply when you are rolling forward into the beams. It is line pressure or fluid vol required for a loose reverse clutch pack that makes the car roll forward. The rev clutch pack isn't applying quick enough to lock the tranny up. The cycling of the T brake before the final apply is filling the rev piston cavity with fluid. So when you make the final apply it doesn't take a full load of fluid to move the piston forward to apply the Rev clutches. __________________ Adger Smith (Former SS)