408/ 904 trans

-
skrews said:
I think you'll find on tracks with poor prep the car will have start line issues. On a good track it will work fine. My car has a 530ish HP motor, 5800K converter, low first gear 904, 4.56 gear, and 28x10.5 tire. It will 60 in the 1.39-1.4 range on a good track, but on a crap track it will 60 in the 1.5+ range. The high and rear location of the instant center of the A body rear suspension leads to a violent hit at launch which is compounded by a high start line gear ratio.
Click to expand...
The instant center does concern me
 
Going to get the car as low as I can and look at some good shocks
Would have loved to just 4 linked the car
But I feel like I will street drive it
Also would like to use a longer front spring segment but crap that is a lot work

all A body’s have the same length front segment??
 
Last edited:
o1heavy said:
Going to get the car as low as I can and look at some good shocks
Would have loved to just 4 linked the car
But I feel like I will street drive it
Also would like to use a longer front spring segment but crap that is a lot work

all A body’s have the same length front segment??
Click to expand...

Yes, 20" the short front segment ever used.
 
A63BDDCB-10C8-460C-97FA-7242A9DB24AC.jpeg
92CDD4AC-B19A-4AF3-88A8-964C673BB590.jpeg
BC56EB3C-9215-42C4-A062-E43729A941B9.jpeg
54BC8714-451F-4986-BF2E-FA332BF50CD1.jpeg
57CDDF9B-1D77-444B-AA49-ADEDFBF48E58.jpeg
4 link it . I did mine w Riley Motorsport 4 link kit. You can put It Where do you like it
 
I went from a W2 head 363 with 450 torque with 4.88s my 60 foots were 1.49- 1.50 ( on throttle stop) to a R3 block Indy 360-1 head 408 502 torque two years ago I was reving well over 7 grand at the stripe I went to a 4.10 gear and my 60 foots are the same as with the 4.88s because of the 52 more pounds of torque 1.49-1.50 I recently went to a 4.30 gear for more stripe rpm ( 6200) picked a up a little but 60 foots are the same i tried a low first gear set In my 904 years ago and saw no difference but that's my combo yours could be different .. ProTrans is top notch and long time Mopar racers

IMG_0332.JPG
 
skrews said:
I think you'll find on tracks with poor prep the car will have start line issues. On a good track it will work fine. My car has a 530ish HP motor, 5800K converter, low first gear 904, 4.56 gear, and 28x10.5 tire. It will 60 in the 1.39-1.4 range on a good track, but on a crap track it will 60 in the 1.5+ range. The high and rear location of the instant center of the A body rear suspension leads to a violent hit at launch which is compounded by a high start line gear ratio.
Click to expand...
Do you foot brake yours??
 
skrews said:
yes
Click to expand...
I’ve considered staying with my old 727 and just footbrake it lord knows I would save a ton of money
But not sure I would be competitive in our area we use a pro 400’s tree
And really need a .020 just to go rounds
 
I run line locks front and rear in conjunction with a 2 step. I call it the poor mans trans break.
 
B3422w5 said:
If the convertor is right, car will 60 foot the same off the brake as off the foot
Click to expand...
Probably better with the foot brake
The Transbrake seems to really only help the reaction time especially when using a leaf spring on a mopar
Helps with r/t and at the same time creates a suspension problem, if I had to do it over I would just 4 link the car but I’m in it to deep

There’s a reason most of the mopar guys are not using a Transbrake
I’m gonna get the best shock I can and hope for the best

Just another small factor why we are getting left behind
 
B3422w5 said:
If the convertor is right, car will 60 foot the same off the brake as off the foot
Click to expand...

^^^ This is what I've seen for the most part. My double line lock 2 step deal doesn't work the same as a trans brake. It is just a way to come off the brakes and rev limiter simultaneously, and I found it easier to cut a light coming off a button vs foot braking.
 
Probably better with the foot brake
The Transbrake seems to really only help the reaction time especially when using a leaf spring on a mopar
Helps with r/t and at the same time creates a suspension problem, if I had to do it over I would just 4 link the car but I’m in it to deep

There’s a reason most of the mopar guys are not using a Transbrake
I’m gonna get the best shock I can and hope for the best

Just another small factor why we are getting left behind
Click to expand...

^^^ Agree. The Mopar A body has terrible suspension issues arising from the VERY POOR instant center location that causes too much hit and separtion. 4 link or ladder bars will fix it but are a big and expensive undertaking for most. This is why so many of us run Caltracs or some variation of Caltracs, they are relatively inexpensive and easy to bolt on. Unfortunately Caltracs do nothing to relocate the instant center in the car regardless of the propaganda out there to the contrary. The best thing one can do is keep the cars ride height low, set the Caltracs to induce the least amount of hit as possible (lower hole with gap), and run a good double adjustable shock. I'm looking to upgrade my Viking shocks to custom valved Crusader series in the near future.
 
skrews said:
^^^ Agree. The Mopar A body has terrible suspension issues arising from the VERY POOR instant center location that causes too much hit and separtion. 4 link or ladder bars will fix it but are a big and expensive undertaking for most. This is why so many of us run Caltracs or some variation of Caltracs, they are relatively inexpensive and easy to bolt on. Unfortunately Caltracs do nothing to relocate the instant center in the car regardless of the propaganda out there to the contrary. The best thing one can do is keep the cars ride height low, set the Caltracs to induce the least amount of hit as possible (lower hole with gap), and run a good double adjustable shock. I'm looking to upgrade my Viking shocks to custom valved Crusader series in the near future.
Click to expand...
I’m gonna move forward with the Transbrake
Plans and get the high dollar shocks and do the best I can with
I know this is crazy but
Jason digby and his 69 dart uses the stock front segment and Caltrac’s system dart leaves absolutely beautiful
Can’t really find out a whole lot about the rest of the rear system though
And probably using a glide
 
When the track is good my car leaves awsome, but when the track isn't good my car leaves like ****.
 
Last edited:
skrews said:
^^^ Agree. The Mopar A body has terrible suspension issues arising from the VERY POOR instant center location that causes too much hit and separtion. 4 link or ladder bars will fix it but are a big and expensive undertaking for most. This is why so many of us run Caltracs or some variation of Caltracs, they are relatively inexpensive and easy to bolt on. Unfortunately Caltracs do nothing to relocate the instant center in the car regardless of the propaganda out there to the contrary. The best thing one can do is keep the cars ride height low, set the Caltracs to induce the least amount of hit as possible (lower hole with gap), and run a good double adjustable shock. I'm looking to upgrade my Viking shocks to custom valved Crusader series in the near future.
Click to expand...



Have to disagree with ya there. The A body has lots of rear overhang and makes an excellent racecar. Thats why if you go to any bracket race, you see more Dusters than Carter has liver pills.
I raced a 70 Duster for many years in various forms, the last few years with a 9 sec stroker smallblock.
I had 002/003 leafs and CE 3 way shocks on all 4 corners and the car would hook on ice with 28 by 10 bias ply DOT tires. Anywhere. Won races and went rounds with that car. It was better than the driver( me.. lol)
I find more posts from guys who have bought Cal tracs and put them on A bodies and cant get the car to stick than anything, over the years. I got my pinion angle set at 5 degrees down with the S/S springs, and let her rip.
A bodies make GREAT race cars, and Mopar S/S springs work outstanding well into the 9’s.... even on a small tire. Thats fact
 
B3422w5 said:
Have to disagree with ya there. The A body has lots of rear overhang and makes an excellent racecar. Thats why if you go to any bracket race, you see more Dusters than Carter has liver pills.
I raced a 70 Duster for many years in various forms, the last few years with a 9 sec stroker smallblock.
I had 002/003 leafs and CE 3 way shocks on all 4 corners and the car would hook on ice with 28 by 10 bias ply DOT tires. Anywhere. Won races and went rounds with that car. It was better than the driver( me.. lol)
I find more posts from guys who have bought Cal tracs and put them on A bodies and cant get the car to stick than anything, over the years. I got my pinion angle set at 5 degrees down with the S/S springs, and let her rip.
A bodies make GREAT race cars, and Mopar S/S springs work outstanding well into the 9’s.... even on a small tire. Thats fact
Click to expand...

My point is when you look at the thrust vector in the chassis its all wrong because of the instant center is well above the center of gravity of the car. This makes the car more sensitive to track conditions. As you pointed out more guys have problems with caltrac A bodies than any other suspension, thats the reason. The Chevy and Ford cars have 25+ inch long front spring segments (which puts the instant center in a far better location in the car) as opposed to the 20" Mopar, and thats why those car work well with Caltracs.
I'm looking at going back to SS type springs next year, I've had enough of the Caltrac KoolAid
 
Man don’t go back to ss springs just buy some good shocks we as mopar enthusiast
Need to move forward not backwards

Why not just buy some good shocks
Look up the toothjerker he is running a Caltrac type system on a monoleaf spring
Wish I had more details
He is on a different level and is moving forward I fully expect his dart to run into the 3 on a leaf spring
Just saying my friend
 
skrews said:
My point is when you look at the thrust vector in the chassis its all wrong because of the instant center is well above the center of gravity of the car. This makes the car more sensitive to track conditions. As you pointed out more guys have problems with caltrac A bodies than any other suspension, thats the reason. The Chevy and Ford cars have 25+ inch long front spring segments (which puts the instant center in a far better location in the car) as opposed to the 20" Mopar, and thats why those car work well with Caltracs.
I'm looking at going back to SS type springs next year, I've had enough of the Caltrac KoolAid
Click to expand...

Right. Guys with Mopars have problems because when swapping from stock leafs or even S/S springs all the sudden more thought and adjustment is required, and many get lost.
But Dusters, Darts and Demons make great race cars. If i got to where S/S springs didnt work, i would jump straight to a ladder bar or 4 link.
As mentioned, good shocks are an excellent investment. With my 002/003 leafs i never had hooking issues so fortunately didnt have to upgrade what worked.
 
A pic of what some of the faster A body guys do to make Caltracs run well. Relocate the front spring eye.
2012-10-27223349_zps88a494b2.png
 
My Caltrac's took me the better part of a race season to sort out, but now that I did I wouldn't change it. They are super consistent now, even in hot greasy conditions...but I foot brake....most of the folks I have heard that are having issues use a T-brake.
 
You must log in or register to reply here.
-

Back
Top