Rear End for Drag Racing
09-18-2009, 05:15 PM
#21
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It's really not too hard to get traction on a Vette...it's being able to do it multiple times!!
I got by with a stock diff for a long time. I had rebuilt it and set it up well....but otherwise all stock hard parts. The 427 I used to have ran low 11's with it, but I was launching relatively easy with it to save parts. I DID break outer stubs a few times! Inners never broke on mine.
On the other hand a buddy of mine has broken 4 of them with his 327 smallblock on street tires! Along with some stub axles! I tell him he doesn't have enough power to spin the tires and thats the problem!!
JIM
I got by with a stock diff for a long time. I had rebuilt it and set it up well....but otherwise all stock hard parts. The 427 I used to have ran low 11's with it, but I was launching relatively easy with it to save parts. I DID break outer stubs a few times! Inners never broke on mine.
On the other hand a buddy of mine has broken 4 of them with his 327 smallblock on street tires! Along with some stub axles! I tell him he doesn't have enough power to spin the tires and thats the problem!!
JIM
09-18-2009, 07:50 PM
#22
Burning Brakes
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Stiffer spring help plant tires better too. Our stuff works a little different since trailing arms really can't transmit motion like a 4 link or a regular leaf spring setup. As the rear of the car goes down the spring *pulls* downward by the end bolts which forces traction. The more of that motion you use up by squatting is just that much less force applied to the arms initially. Don't get me wrong...there are cars that 60' very well with a significant amount of squat....but it's wasted motion and hard on parts as mentioned. Some drag folks extend snubbers so the car rides out solid on them...but that is pretty harsh and not as consistent. It's especially hard with a stick car. If spring is weak and you get good traction you will get into a *porpoise* mode where the car loads and unloads pretty violently. I've been there and while wild to watch....it's not much fun to drive! When you really get traction you won't know which lane you're coming down in!
Mine uses a steel 5 leaf Daytona spring with an added thick main leaf for 6 total. Vette brakes made it for me. I use QA-1 adjustable shocks, stock trailing arms and no added traction bars etc. The front end is critical...you want some lift. I use Moroso springs just like Olivier and I have CE 90/10 front shocks. Otherwise it's just stock arms etc.
I have Tom's outer axles and custom made 3.5"x.134 wall halfshafts with 1480 series u-joints. My differential is a custom built Hemi Dana 60 made into an IRS configuration.
Alignment is important here too. Vette's go through some wild toe in issues on launch with lots of bump steer. The front ends gain positive camber on lift vs going to negative as Camaro's and most everything else does. Not bad...just need to set it up to make it drive OK.
JIM
Mine uses a steel 5 leaf Daytona spring with an added thick main leaf for 6 total. Vette brakes made it for me. I use QA-1 adjustable shocks, stock trailing arms and no added traction bars etc. The front end is critical...you want some lift. I use Moroso springs just like Olivier and I have CE 90/10 front shocks. Otherwise it's just stock arms etc.
I have Tom's outer axles and custom made 3.5"x.134 wall halfshafts with 1480 series u-joints. My differential is a custom built Hemi Dana 60 made into an IRS configuration.
Alignment is important here too. Vette's go through some wild toe in issues on launch with lots of bump steer. The front ends gain positive camber on lift vs going to negative as Camaro's and most everything else does. Not bad...just need to set it up to make it drive OK.
JIM
JIM
AS USUAL, YOUR RESPONSE IS CLEAR AND TO THE POINT.
I'VE BEEN TRYING TO FIND OUT HOW FORCES APPLY TO OUR VETTE REARS UPON LAUNCH FOR A LONG TIME. MOSTLY, THE REPLIES MAKE GENERLIZATIONS, BUT DON'T GET INTO SPECIFICS.
YOU EXPLAIN HOW FORCES APPLY WHEN A C2-C3 REAR LAUNCHES SO THAT WE CAN UNDERSTAND IT.
JUST WANTED TO SAY THANKS, AND PLEASE KEEP THE INFO COMING.
BILL SR
09-18-2009, 09:39 PM
#23
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New rear stock leaf spring
Standard rear shocks
Rear stabilization bars (QA1) (connecting the trailing arms with the differential case)
Moroso Trick Springs - front, with 1-2 coils cut off to lower the height
I drive it on the street with no issues. It is a street racing car that morphed into a race car.
Standard rear shocks
Rear stabilization bars (QA1) (connecting the trailing arms with the differential case)
Moroso Trick Springs - front, with 1-2 coils cut off to lower the height
I drive it on the street with no issues. It is a street racing car that morphed into a race car.
09-19-2009, 11:39 PM
#24
Team Owner
Eliminating (or at least reducing) rear squat, and thereby keeping the halfshafts straighter under power reduces the strain (and consequent breaking) of the halfshaft U-joints because of the severe angle incurred.
Stiffer shocks are also needed to aid the leaf spring in this task.
Stiffer shocks are also needed to aid the leaf spring in this task.
12-08-2009, 11:33 AM
#25
Le Mans Master
Bump for a good thread. Starting to research modding my stock rear on a budget to help it survive a few passes on drag radials or slicks behind an auto. Those Duntov rears are pretty interesting in the fact they are not upgrading them to 12 bolt internals. Still would like to do the 12 bolt but...$$$$
12-08-2009, 12:01 PM
#26
I think Jim is correct about the axles being the first weak part. That's all I used to really have a problem with with my old motor. It was about what you guys are talking about HP wise. I used to race all the time and ran Sportsman Pro's (before the drag radial existed). I think if you just go to a heavier spring, some good adjustable rear shocks, and solid U-joints you'll be fine for quite a while with an automatic anyways. I would recommend a set of loops for the halfshafts for safety. If something does go, it won't be pretty with out them.
12-08-2009, 12:23 PM
#27
Burning Brakes
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I agree, stiff rear spring, shocks and solid U joints. The spacer under the strut rod bracket and an automatic foot braking it and you should have no problems for a long time.
12-08-2009, 01:10 PM
#28
Le Mans Master
currently, my car has a 340#trw fiberglass spring and KYB shocks on it. I will probably throw some QA1s on the rear to help stiffen it. I am also gonna run either some locally built thick walled 3" halfshafts with solid spicers or get some 3" shafts from dragvette. I will add toms loops at the same time . Hopefully that will get me by for a while. I won't be racing it a lot, just a few times a year but it will get a lot of street race action. I probably won't leave REAL hard on it at the strip to help keep it from breaking.
12-08-2009, 03:41 PM
#31
Burning Brakes
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One other thing you need to check and or re support is the chassis bracket that the pinion mount on the rear end mounts to. I have crushed the bracket on the chassis so much that the rear end yoke came through the floor. See picture below. Also make the side of the pinion bracket thicker where the two long bolts go through the rear end. They will start to oblong. I think some of the bracket already have extra metal added in that area. This all happened in my 67 when I was racing it with a 4 speed and the current motor that is in my 80. When you start leaving hard things are going to break!!!
Last edited by L79racer; 12-08-2009 at 03:45 PM.
12-08-2009, 03:56 PM
#32
Le Mans Master
Oh I do want a 10 sec slip, and I know it's gonna take 1.50 or better 60' to get it. Eventually when I get the loot to completely R&R the rear end and rear suspension, I will hammer down on this biotch. For now, I just want to play on the street some with some decent tires that halfway hook up so I can do some 30 mph roll on racing. But before I really even start beating on it hard at all, I want to atleast do the halfshafts and loops.
I called a local drivetrain shop, they wanted $290 EACH to build 3" halfshafts, .083 wall with solid spicers and flanges. I can get them from Dragvette for $400. Prolly just go that route to keep it simple. I will get the loops from Tom if he still sells them, I couldn't find them on his site, gotta call him later.
I called a local drivetrain shop, they wanted $290 EACH to build 3" halfshafts, .083 wall with solid spicers and flanges. I can get them from Dragvette for $400. Prolly just go that route to keep it simple. I will get the loops from Tom if he still sells them, I couldn't find them on his site, gotta call him later.
12-08-2009, 04:04 PM
#33
Le Mans Master
L79racer,
great pic of the 67!
I will check the pinion mount and bolts etc. I know Jim tore up that pinion mount on the frame you are talking about. I am sure mine is probably fine for now. My car has never been raced nor has it ever made anything over 200rwhp...with an auto at that. I don't think it had enough power to break or distort anything stock. Hell I could barely get it to do a burnout in the waterbox at the track...right before it's record setting 15.01@91mph pass....lol
great pic of the 67!
I will check the pinion mount and bolts etc. I know Jim tore up that pinion mount on the frame you are talking about. I am sure mine is probably fine for now. My car has never been raced nor has it ever made anything over 200rwhp...with an auto at that. I don't think it had enough power to break or distort anything stock. Hell I could barely get it to do a burnout in the waterbox at the track...right before it's record setting 15.01@91mph pass....lol
09-07-2010, 08:14 AM
#34
7th Gear
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Nine Inch
Heres a vette with ..ahem ..a Nine Inch conversion, a Ford part granted, however a 31spine Detroit Locker is nice insurance...
It has Toms 31 Spine outer axles & 3" Shafts
It has Toms 31 Spine outer axles & 3" Shafts
09-08-2010, 12:56 PM
#35
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09-08-2010, 01:30 PM
#36
Team Owner
The only things to ever fail in 22 years were the posi units, of course 1350 U-joints, one 3 inch half shaft, and the outer axils
I just pulled out my 4.11 gears this spring and the gears and yokes still look new after all these years of big slicks. I just put in a new toms posi and US gear 3.55 to go with my 5 speed OD tranny.
09-08-2010, 01:37 PM
#37
I bought a rebuilt rearend with 4.11 richmond gears in 1988. I had the custom hardened yokes which now sell for about $299 each from mid-America. As power went up things things failed. So when the first posi (auburn)failed. I went to www.tomsdifferential.com and I bought billet main caps and the $800 posi units.
The only things to ever fail in 22 years were the posi units, of course 1350 U-joints, one 3 inch half shaft, and the outer axils
I just pulled out my 4.11 gears this spring and the gears and yokes still look new after all these years of big slicks. I just put in a new toms posi and US gear 3.55 to go with my 5 speed OD tranny.
The only things to ever fail in 22 years were the posi units, of course 1350 U-joints, one 3 inch half shaft, and the outer axils
I just pulled out my 4.11 gears this spring and the gears and yokes still look new after all these years of big slicks. I just put in a new toms posi and US gear 3.55 to go with my 5 speed OD tranny.
09-08-2010, 02:23 PM
#38
Team Owner
Before I got smart my smaller solid roller motor with 4.11, 700R4, 3500 stall, goodyear slicks was a very consistent 11.70's drag racer. I got tired of sitting in the staging lanes with sweat running down in my eyes watching some dumb *** farmers doing a one wheel burn out with their 18 second pickup truck.
So I now drag race out of each corner and then stomp on the brakes and drag race again till the next corner!
It's called Road Racing on real tracks. I can go nearly 50 miles in 30 minutes of "Drag Racing" the real way.
It is extremely hard on the drive train compared to 11 second 1/4 miles. My 7500 rpm 434 ci small block is probably in the mid 600 hp at the crank and my car weighs @3000 pounds
These are my big 335 X 28 inch dia slicks compared to my 335/35/17 street tires. Both of these tires hook up pretty good.
So I now drag race out of each corner and then stomp on the brakes and drag race again till the next corner!
It's called Road Racing on real tracks. I can go nearly 50 miles in 30 minutes of "Drag Racing" the real way.It is extremely hard on the drive train compared to 11 second 1/4 miles. My 7500 rpm 434 ci small block is probably in the mid 600 hp at the crank and my car weighs @3000 pounds
These are my big 335 X 28 inch dia slicks compared to my 335/35/17 street tires. Both of these tires hook up pretty good.
09-08-2010, 02:35 PM
#40
