2” drop rear springs ‘70 A body - Chevelle Tech
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post #1 of 57 (permalink) Old Jan 6th, 20, 5:50 PM Thread Starter
 
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2” drop rear springs ‘70 A body

Hi All, new member, first post.
Happy New Year!
Wondering if anyone’s using UMI 2” drop rear springs (or similar) 4051R in the rear of a ‘70 A body (mine’s a GTO) with 275/60/15 or 295/55/15 M/T ET Street?
No frame or wheelhouse mods. Have UMI 2 way adj uppers & lowers, will use UMI or H.R. rear anti roll bar. Would like to tuck them in and get the rear down to improve IC. Any suggestions appreciated.
Thanks in advance.
Jordan
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post #2 of 57 (permalink) Old Jan 6th, 20, 6:23 PM
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Re: 2” drop rear springs ‘70 A body

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Originally Posted by TheGrudge View Post
Hi All, new member, first post.
Happy New Year!
Wondering if anyone’s using UMI 2” drop rear springs (or similar) 4051R in the rear of a ‘70 A body (mine’s a GTO) with 275/60/15 or 295/55/15 M/T ET Street?
No frame or wheelhouse mods. Have UMI 2 way adj uppers & lowers, will use UMI or H.R. rear anti roll bar. Would like to tuck them in and get the rear down to improve IC. Any suggestions appreciated.
Thanks in advance.
Jordan
Welcome aboard Jordan. Are you wanting to improve the IC location for the drag strip, or just for some better straight line traction on the street? Or are you just wanting the look of the lower ride height?

70 Chevelle SS clone (632 CI powered).
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post #3 of 57 (permalink) Old Jan 6th, 20, 7:26 PM
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Re: 2” drop rear springs ‘70 A body

I've got 2” BMR springs and 275/60r15s on 9" Prostars with 5.5" BS. I had to get the axle centered on the frame and the body centered just right but they fit pretty good. There's a not great picture in my profile. There was no gas in the tank, and the back window and rear seats were out when that picture was taken so it's probably an inch lower fully dressed. There's 2.5” spindles on the front.

Mine is a '69 but the wheel well seems to be the same. Fit exactly the same on my Camino when all the parts were under it too.

70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt

Last edited by Tommy the Cat; Jan 6th, 20 at 7:54 PM.
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post #4 of 57 (permalink) Old Jan 6th, 20, 7:50 PM Thread Starter
 
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Thanks for your reply Billy,
car will be 50/50 street strip so straight line traction is no.1; front has 2” drop spindles so I’m working off a 2” drop in the rear to even things out + lower the front pivot points of the rear arms. Not against the idea of no hop bars but won’t use them if I don’t have to.
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post #5 of 57 (permalink) Old Jan 6th, 20, 7:53 PM Thread Starter
 
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Thanks for the info Tommy (dig the Primus reference btw). I’ve replaced the body mounts & have new QP 9” ready to assemble so I’m prepared for a bit of a jiggle to centre everything. What are your trailing arm angles like upper & lower?
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post #6 of 57 (permalink) Old Jan 6th, 20, 8:45 PM Thread Starter
 
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Re: 2” drop rear springs ‘70 A body

Quote:
Originally Posted by Tommy the Cat View Post
I've got 2” BMR springs and 275/60r15s on 9" Prostars with 5.5" BS. I had to get the axle centered on the frame and the body centered just right but they fit pretty good. There's a not great picture in my profile. There was no gas in the tank, and the back window and rear seats were out when that picture was taken so it's probably an inch lower fully dressed. There's 2.5” spindles on the front.

Mine is a '69 but the wheel well seems to be the same. Fit exactly the same on my Camino when all the parts were under it too.
Thanks, that pic gives me a good indication. Tucks in well so clearance shouldn’t be a problem with correct backspace.
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post #7 of 57 (permalink) Old Jan 6th, 20, 8:46 PM
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Re: 2” drop rear springs ‘70 A body

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Originally Posted by TheGrudge View Post
Thanks for your reply Billy,
car will be 50/50 street strip so straight line traction is no.1; front has 2” drop spindles so I’m working off a 2” drop in the rear to even things out + lower the front pivot points of the rear arms. Not against the idea of no hop bars but won’t use them if I don’t have to.
I'm not postive on this, but you might be making it tougher for yourself at the starting line by having drop spindles. I could be wrong about that. The one thing I DO know is that for drag racing the front suspension is as important, or in some cases, even more important at the drag strip than the rear suspension and your IC location is. You really NEED to have the front suspension working freely, so that the front control arms are NOT binding up nor being hindered at all from their movement during the launch. And using front coil springs with the factory stock rates is a no no for drag racing.

What power level are you at under the hood? And do you have factory stock type front control arms or aftermarket ones?

70 Chevelle SS clone (632 CI powered).
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post #8 of 57 (permalink) Old Jan 6th, 20, 8:54 PM
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Re: 2” drop rear springs ‘70 A body

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Originally Posted by Tommy the Cat View Post
I've got 2” BMR springs and 275/60r15s on 9" Prostars with 5.5" BS. I had to get the axle centered on the frame and the body centered just right but they fit pretty good. There's a not great picture in my profile. There was no gas in the tank, and the back window and rear seats were out when that picture was taken so it's probably an inch lower fully dressed. There's 2.5” spindles on the front.

Mine is a '69 but the wheel well seems to be the same. Fit exactly the same on my Camino when all the parts were under it too.
Tom, I fully understand what you mean by centering the body on the frame, but how would you center the rear end "in the frame"??? The rear end housing is anchored to the frame by the upper and lower control arms. So what would you be able to do to change that? Am I having a brain fart here and overlooking something obvious? Or did you simply explain that a little wrong?

70 Chevelle SS clone (632 CI powered).
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post #9 of 57 (permalink) Old Jan 6th, 20, 9:18 PM
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Re: 2” drop rear springs ‘70 A body

Quote:
Originally Posted by TheGrudge View Post
Thanks for the info Tommy (dig the Primus reference btw). I’ve replaced the body mounts & have new QP 9” ready to assemble so I’m prepared for a bit of a jiggle to centre everything. What are your trailing arm angles like upper & lower?
Not too many catch the Primus reference. I already like you. I'll try to get some angle measurements for you but it'll be a day or two.

Quote:
Originally Posted by BillyGman View Post
Tom, I fully understand what you mean by centering the body on the frame, but how would you center the rear end "in the frame"??? The rear end housing is anchored to the frame by the upper and lower control arms. So what would you be able to do to change that? Am I having a brain fart here and overlooking something obvious? Or did you simply explain that a little wrong?
Adjustable upper control arms are used to set pinion angle and center the axle in the frame. When I installed them I adjusted them the same length as the stock arms and it was about a quarter inch offset to the passenger side and the tire rubbed when I cycled the suspension with no springs. Lengthened the passenger side arm, shortened the driver side and it was centered. Then just adjusted both the same amount to set pinion angle. Make sense?

70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #10 of 57 (permalink) Old Jan 6th, 20, 9:24 PM
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Re: 2” drop rear springs ‘70 A body

I used the drop spindles with the intention of using the longest, lightest front spring possible, not to lower the front end. It's down a little from stock but not a lot. The weight transfer of the long, soft spring is the advantage I'm after. Sits pretty level with a 26x6r15 front tire and the 28” rear tire.

70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #11 of 57 (permalink) Old Jan 6th, 20, 9:41 PM
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Re: 2” drop rear springs ‘70 A body

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Originally Posted by Tommy the Cat View Post
Not too many catch the Primus reference. I already like you. I'll try to get some angle measurements for you but it'll be a day or two.



Adjustable upper control arms are used to set pinion angle and center the axle in the frame. When I installed them I adjusted them the same length as the stock arms and it was about a quarter inch offset to the passenger side and the tire rubbed when I cycled the suspension with no springs. Lengthened the passenger side arm, shortened the driver side and it was centered. Then just adjusted both the same amount to set pinion angle. Make sense?
Oh, OK. It sounds like you're actually talking about the rear end originally not being square in the car, and you were able to make it square with the adjustable control arms, eh? That makes sense. I never even considered using adjustable rear control arms to square the rear in the car, but it sounds to me by what you've described, that it worked good.

There are two ways that I know of to check that the rear is square in the car: One is the most accurate but also the most work, which is having the car high up on jackstands, and using a chalk-Line and a plumb bob and drawing lines on the garage floor, (kinda involved, but very accurate when done correctly). And the other way is the quick and dirty way: Measure from the end of the passenger side axle tube, ( close to the brake drum) on a diagonal angle to the tail of the transmission, and then doing the same on the drivers side, and comparing the two measurements, (suposed to be within 1/2" of the two measurements, otherwise the axle tubes are either bent on atleast one side, or the rear is not square in the car).

But as you probably already know, the rear being square in the car is also important for getting the car to launch straight.

70 Chevelle SS clone (632 CI powered).
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post #12 of 57 (permalink) Old Jan 6th, 20, 9:50 PM
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Re: 2” drop rear springs ‘70 A body

I actually haven't checked whether it's square or not yet.. haven't got that far. The upper arms will center it side to side but to square it I believe I would need adjustable lower control arms which I don't have at this point.

I'm hoping it's square now. I'm tired of having to buy parts twice. I will say it launches dead straight right now. But with at least 150 horsepower on tap it could be WAY off and still launch straight!


70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #13 of 57 (permalink) Old Jan 6th, 20, 9:53 PM Thread Starter
 
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Re: 2” drop rear springs ‘70 A body

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Originally Posted by Tommy the Cat View Post
I used the drop spindles with the intention of using the longest, lightest front spring possible, not to lower the front end. It's down a little from stock but not a lot. The weight transfer of the long, soft spring is the advantage I'm after. Sits pretty level with a 26x6r15 front tire and the 28” rear tire.
...exactly my idea behind drop spindles, was going to use factory 6 cyl soft springs up front. Replied to Billy but the post disappeared??!?

...anyway, tube arms in front, no sway bar, motor in the 550-600hp NA range (not dynoed yet)..
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post #14 of 57 (permalink) Old Jan 6th, 20, 9:58 PM
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Re: 2” drop rear springs ‘70 A body

Quote:
Originally Posted by Tommy the Cat View Post
I used the drop spindles with the intention of using the longest, lightest front spring possible, not to lower the front end. It's down a little from stock but not a lot. The weight transfer of the long, soft spring is the advantage I'm after. Sits pretty level with a 26x6r15 front tire and the 28” rear tire.
I'm pretty sure that drop spindles lower the front ride height without compressing the front coil springs anymore than they would be with stock height spindles. The height of the car is dropped by the dimensions and geometry of the drop spindles and I believe is unrelated and uneffected by what spring is used.

I do know that using a taller UPPER ball joint, ( you can use a 0.5"+ with factory upper control arms, and 0.9"+ taller with most aftermarket upper arms) you create more room between the underside of the upper control arms and the top of the frame, in order to allow the arms to move downward a greater distance before they make contact with the frame and prevent anymore front suspension travel. That allows you to make more use of the greater amount of "stored energy" in a taller/lighter front coil spring for weight transfer during the launch.

So as far as I know, the drop spindles are only helpful for better handling around turns. What I'm not sure about is if the drop spindles will hinder weight transfer during the launch or not.

70 Chevelle SS clone (632 CI powered).
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post #15 of 57 (permalink) Old Jan 6th, 20, 10:00 PM
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Re: 2” drop rear springs ‘70 A body

I have Moroso Trick Springs in mine but I can't remember what rate. I'll have to dig out some receipts. Seems like they were lighter than any that were listed for an A body. Might have been intended for a G body. I'll probably have to trim them a touch when the new engine goes in. It's going to lose about 75 pounds on the front.

70 Camino...Roller

69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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