Hot Rods Axle clearances

I have a question regarding the amount of space between the axle and the frame. I have a 30 Model A chassis that will be running a 4" dropped tube axle with a link up front and a GM 8 3/4" rear end out back with parallel 4 link and coil overs. The body is a 27 T roadster and the power train is a small block Chevy with a TH350 tranny.
I'm looking to find out how much travel there should be between the frame and the axle once the car is sitting on the ground, under full weight load. I have it all mocked up sitting on jack stands with 4 inches of clearance

 

You probably need to kick up the rear frame a few more inches. A light car like your roadster would do well with quarter eliptic rear springs unless you just have to have the buggy spring.

 

The books I have on chassis setup use 2" between front crossmember and axle. Worked good for me!

 

There a few factors, and you are wise to consider clearance at this point in the build.
I've used the higher sidewall tires, to gain a bit of 'travel' when things were close.
(I'd want more than 2") Bader has a 'modest' copilot but no snow in his pic!

 

My A bone had a baby nail head in it when I got it and it came up 2.5" when I pulled the motor I wouldn't doubt that 2-3 inches of travel would be common with it.

 

Looks like you have a flat front crossmember there. Don't know what spring you plan to run but you'll need some space between the top of the spring and the bottom edge of the frame. Might need to notch the rails in that area.

As far as suspension travel goes how softly sprung the car is will help answer that question.

 

Also engine placement has a lot to do with it. Move the engine back and it unloads the front suspension a little bit.

 

dubie
On your frame; whether you c-notch, kickup, or do nothing on the rear, these low profile polyurethane bumpers work good for softening the bump back there. On my roadster, I have a c-notch, and these don't take up much room.
Pretty easy to use the nuts if your frame is not boxed, but if it is you can drll and tap the frames' lower flange.


These are made by Energy Suspension, available from Summit Racing, Jegs, etc.

 

I boxed in the frame already but we can cut and weld anything at this stage. I should have mentioned that the front suspension with be coil overs. I had bought and installed the flat cross member before i bought the axle and the axle came with a 4 link set up and mounts for coil overs. So it'll be similar to a sprint car set up.
The body on this thing is half touring roadster, half sport coupe all mashed together so the length of the body is a bit shorter than normal. Which is nice because it leaves a bit more room up front to slide that engine back a bit.

Any advice on coil over rates? I've been searching for a decent set of 4 to balance out the suspension but was unsure of the load rate. I've read about guys using to high of a spring rate on the back end and it feels like there's next to no give in the travel

I appreciate any advice guys, this is our first from the ground up hot rod build. Everything up until now has been 50's and 60's pickups where most things are plug and play set ups

 

2" from bottom of crossmember = at least 2-1/2" spring to axle,which is way more than enough. And we don't have much snow yet!

 

well I have mine mocked up a bit to height then. I'm sitting at close to 4 inches on the shop floor right now.

 

Many of "us" T-bucket guys run 150-175 lb coil-overs , at 2" clearance you'll use the bump-stops often , at 3" you're probably o.k. , the only proper way to determine spring rate & travel is to weigh the complete car w/4-wheel scales & do some math ..
dave

 

My vote would be 4" with 1/2" of that taken up by some sort of snubber / bump stop... and more if possible (why not?). Think about it... even at ride height in the garage while it is under construction, your car doesn't sit nearly as low as it would with a crew of two (+350 lbs?), full gas tank (12 gal @ 6.8 lbs per or about 80 lbs), luggage (40 lbs?), spare tire?, misc tools, cleaners, crap-ola? Gary

 

Not a T but the left frame rail on my 48 broke clear through from beating on the axle because I ever put a notch in it for clearance. Give yourself enough clearance so it won't hit.

Static height on the shop floor empty doesn't count for a lot as you need the height it will sit at with the weight of the driver and the regular passenger (s) in it to get the down the road ride height.