Hot Rods Frame to rear axle clearance?

Here's where I am. Building hot rod RPU. Stock Model A frame, 3in dropped axle,327/350 combo,S10 rear and 4 bar with coil overs. Front half of frame has been boxed with 3/16. Going to start boxing and Z'ing rear half tomorrow. Don't want to get to carried away on Z so what is a safe distance for axle tube to frame clearance? I know this isn't a one size fits all answer but looking for opinions of what you guys have done. Thanks, Bill

 

3"-4" should work just fine.

 

I try not to build in less than 3". More is better but not necessary.
The Wizzard

 

My car has a stock model a frame i boxed ,
No Z , its sets low with 28 1/2 tall tire on rear ,
With QA1 coil overs , cheap triangular four bar about 1-1/2 between fender open top of tire , 255/70/15 , I started with about 2 inch between axle tube and frame ( rear cross member and rear body mout , ) it would hit some times from a dip / slite pot hole, so I notch axle tube close to axle ,
( about 4 inches along axle tub ,S-10 3:42 gear)
Now more clearance , all steel full fenders No chop 103 mph in 1/8 , 200 -300 miles a week

 

Thanks. Kinda thought 4in was ok ,just wanted to be safe.

 

I gotta ask....you say in your post you "notched the axle tube close to axle......" Do you mean, literally, you notched the axle housing tube to provide more clearance?....or do you mean you notched the frame/chassis tube to provide more clearance?

Ray

 

Good catch. I hope that is just a slip.

 

Stock rear crossmember and transverse spring, I have a bit less than 3” between top of the crossmember and top of axle bells.

 

3-4" as stated. Make sure you add bumps stops to underside of frame rails above rear axle, choose the correct length shocks and springs for your vehicle weight, suspension travel and ride height. Also don't lay your shocks over too far, I am for 20 degrees as this helps with lateral stability. Is it triangulated or parallel 4 bar? If parallel ensure that the panhard bar is horizontal to ground and parallel to rear axle centreline and as long as possible to keep the lateral movement arc shallow.

I'd also fish plate the frame where it is 'Z'd' for additional strength and double sheer all 4 bar mounting points.

Also make sure that you set the lower 4 bars up at the front and NOT down. At the same time set your pinion up 3 degrees to match the 3 degree down at the engine / transmission.




The lower 4 bar needs to point up or be horizontal to be geometrically correct and give you antisquat with the correct amount of pinion angle at ride height. Pointing the front end of 4 bars down causes the car to squat under load which will in turn causes the rear tyres to easily unload. The pinion will point down. The front pivot point needs to correspond horizontally with centreline of housing at ride height. With antisquat built in and bars pointing up at the front up, the wheels have a tendency to turn the axle in the opposite direction. This motion causes the bars to push the car up. With them pointing down the opposite occurs and the rear drops.


Forward mounting the shocks may offer slightly more travel and a better ride quality. Rear mounting the shocks offers more load capacity, a minor trade off? The further outboard the shocks are placed, the better the handling. Lay them over slightly (In at top) rather than upright, this will prevent lateral movement as you drive. Make sure upper mounting is parallel to lower or you will chew out the bushings.
Top bars in triangulated set up stops lateral, side to side, movement; hence no panhard bar as per parallel 4 bar.
In equal length parallel 4 bars the pinion angle will remain constant and not change throughout suspension arc.
The rake on the car however may change when raised or lowered. Unequal length triangulated 4 bar will alter pinion angle when car is raised or lowered. Also allow sufficient slip yoke travel.
Also be mindful of how much thread have you got inside the 4-bar tubes, the ends need to be screwed in 3/4 of their threaded length. That way you leave room for adjustment. Plus it's stronger with more thread engagement in the tubing.
Here are local requirements for 4 bars in our builds:-

• Front 4 bars:
  Up to 900mm long, tube OD 22mm, wall thickness 3mm, 5/8" UNF or 16mm fine (Metric)
  
• Rear 4 bar (Normal duty):
  Up to 900mm long, tube OD 22mm, wall thickness 3mm, 5/8" UNF or 16mm fine (Metric)
  Rear 4 bar (Heavy duty):
  Up to 900mm long, tube OD 25mm, wall thickness 3mm, 3/4" UNF or 19mm fine (Metric)

Lots of little things to factor in or consider. Do it once, do it right at the outset, you'll thank yourself later when you're driving.

 

WOW! This is some great info. You gotta love the H.A.M.B.ers!

 

Yes !!!! Notched the Axle tub, & welded box in the notch , it does not weaken the tub , Now I am not talking about planting 800hp @ wheels ( dead hook)
But if I had to , I would even do to 9 ford ,
In my Blown Altered I set wright over all most 2,000hp at wheels M-W's rear ,
If you ever get a chance to go to Don Garlitz museum in Florida there's a car top fuel dragster that was built in the late 80s early 90s by engineer by all engineer factors how it should be built , the car did not work !!!
The Hot Rodder WAY DID !!

 

Um, yes, it does indeed weaken the tube.

 

Let's not quibble here.....

Ray

 

One thing about it, if you don't have enough clearance you will know it every time the axle hits the bump stop or hits the frame. You just have to be careful how many Orca Betties you carry in the back at any one time.

 

You're right. Engineering and the advanced mathematical calculations required by it can all be overcome by hot rod ingenuity!

They are, after all, only The Friendly Suggestions of Physics!

 

If a Axle moves a 1/4 inch in side tube ,you have a problem!! We are NOT talking about a rear tube that's 30 inches or long on each end , model A tube length about 17 inches on Model A -32 33-34
Total length from axle flang to axle flang 54inchs ,
I am running about 450-480 hp at wheels
Threw a S-10 rear stock Axles posi 103-105 mph @ 1/8 , it might sound like BS , my Hot Rod is a race car on street driven 300-400 miles weekly ,with out all the bling bling , but I did swith over to EFI
( still a tunnal ram ) and also run a Datta logger , my green 1932 that I posted on here is going through a full makeover my goal is to Run 6:00 flat with no roll cage no slicks at 115 mph in the 1/8 all steel full fenders no chop ,
my 32 is going with a 9 inch ford 290 rear gear 30 inch tall tires 7 inch wide footprint 4 bar that is completely adjustable car should come in for all steel about 2600 pounds
There a few on here that seen me , met me
I Drive my car 30 pretty much everywhere, (N-Va)
I just have to change my vale springs about every 3 to 4 months

 

?????????


Sent from my iPad using The H.A.M.B. mobile app

 

What r u ????
The Few HAMB members on here that I mentioning if they want to chime in ,they can ,they see my car .

 

Clear, concise writing would help you to express what you mean. Please ask one of your friends to help you to make what you write more easily understood.


Sent from my iPad using The H.A.M.B. mobile app

 

Sorry ,, my grammar Suck's ,
I do think out side of box , fabricate & do thing people say will not work ,

 

S-10 stock rearend with 480 RWHP. You really do things people say won't work.