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Discussion Starter · #1 · (Edited)
Potentially a silly question- Is there a general rule of thumb with how many inches can I expect the car to drop with an engine installed?

specifics are as follows:

- Leaf spring assy from a 1957 1/2 ton chevy truck.
- going on my '55 chevy
- engine will be a V8. not sure yet if SB or BB

When I go to build my frame rails and attach this front axle assy I'm wondering how I can reasonably expect where the vehicle will sit when the engine is in it. I don't have the engine yet, but I'd like to have an idea as that can help me determine how large of spacers I need to make before welding this together.

Or am I going to have to have the engine and all the weight in it to know for sure?

Just wondering how you guys have done it.

Thx,
-Brendon
 

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GOOD ? question ?

I "assume" there is a "rule of thumb" GUESS-TI-MATE on how much a suspension will DROP once a complete engine & tranny is installed... (small or BIG block) even i think the other suspension part variables would make it difficult to guess a semi-accurate number. but then ANY NUMBER might get-ya-close enough to 'TRY' something
 

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Oh yea you are going to need the weight of the drive train on the leafs you are going to use.....but you can make adjustments by having the springs re arched...but getting it as close as possible is the best way to go to avoid putting blocks under it... to long of a shackle on.... or perch towers that are long and ugly...dont forget the back end height will make a difference on how high the front will look...as well as effect castor....if you are stubbing it then it should be a piece of cake.....yea like that really happens
 

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On cars I've setup I always try to set the engine in to simulate weight, or put planks across the frame rails and add weight to simulate what my engine will weigh. I've used concrete or sand bags and whatever I could pile on the planks. On my last build (my '63 Falcon) I went BBC, and I bolted some box tubing to the engine mounts and just sat the weight in place. Then I temporarily set the sheet metal on to see how the stance was.
Hard to say what to guesstimate, as it depends on spring rates, and engine weight. It can also change a little with brand new springs as they settle a bit. A year after the build the springs might settle 1/2"-3/4". I'd rather error slightly high, and then see how it sits. If it's a little high I usually remove a leaf spring to get it to lower, and also soften the ride. Ended up taking 3 leafs out of my Austin because of the very light frontend. The first two leafs didn't even change the ride height.
 

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I guess you could say.. take the original curb weight (or if you know the weight of the car) you can divide it by four. take that number and find a spring rate for that number. you could even find similar vehicles with the same curb weight and you could experiment with it. see what leafs fit and what don't.
 

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Discussion Starter · #6 ·
Cool, thanks, guys. Yeah, it sounds like I'll just need to either simulate the weight or get an engine in there. This is what I was thinking, but I wanted to make sure I wasn't overlooking something...
 

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It's one of those areas where calculations and such just don't seem to take in everything you need to correctly set things up. Engine setback, or rear spring rate, chassis setup, rollcage, frame, etc. Can all affect the stance, and spring rate. So trying to guess how much it will settle can be catastrophic if you don't actually simulate it with the rear engine/trans, or some equal weight in the same location.
Every time I think I've got a hold on it and can guesstimate how high it should sit before the engine is in, it bites me in the butt, and then I end up having to make changes somewhere in springs, or mounting points.
 

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Discussion Starter · #8 ·
It's one of those areas where calculations and such just don't seem to take in everything you need to correctly set things up. Engine setback, or rear spring rate, chassis setup, rollcage, frame, etc. Can all affect the stance, and spring rate. So trying to guess how much it will settle can be catastrophic if you don't actually simulate it with the rear engine/trans, or some equal weight in the same location.
Every time I think I've got a hold on it and can guesstimate how high it should sit before the engine is in, it bites me in the butt, and then I end up having to make changes somewhere in springs, or mounting points.
Yeah, you're totally right- there are so many variables to consider. That's what was in my head which is why I was wondering (and started this thread) if there was such a way to calculate because I sure didn't know it. I should still have enough time over the course of my holiday break to make the front frame rails and I'll make something for the front end as I need to start somewhere and only tack it in place. I'll probably base it off of pics I see online with vehicles that have a stance similar to what I'm looking for.

Thanks again!
 

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Considering what you've done so far, I'm sure you'll get it right. One thing I do when setting up the axle and spring mounts is to tack everything good, but not weld anything solid that I might need to adjust. Build the frame stubs solid, as they wont change. But tack all the rest until you can check it with weight, and see if it sits right. Then it can be finish welded, or adjusted and finish welded.
 

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Discussion Starter · #10 ·
Considering what you've done so far, I'm sure you'll get it right. One thing I do when setting up the axle and spring mounts is to tack everything good, but not weld anything solid that I might need to adjust. Build the frame stubs solid, as they wont change. But tack all the rest until you can check it with weight, and see if it sits right. Then it can be finish welded, or adjusted and finish welded.
Sounds like a good plan to me!
 
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