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1925 Model T Front Suspension Options


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#1 rhs856

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Posted 24 September 2012 - 11:57 AM

I'm starting the AMT 1925 Model T (dropped frame, coupe body, Parts Pack Chevy 283 with the crank driven supercharger) and I'm not sure I like the look of the front suspension parts. Has anyone either made their own realistic front end or put on another front end from a different kit with any success?

#2 Ace-Garageguy

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Posted 24 September 2012 - 01:04 PM

I've done a suicide front end on that kit. I used a round front crossmember (which would be better in 1:1 because of the way it is in torsion) of styrene tubing and fabricated the spring perch from channel. The axle is a tubular unit from who-knows, but the principle would be the same for any transverse-sprung front end. Hairpins, split wishbones or a 4-link setup (which this car is getting) would complete the install.

One note....without stretching the chassis or moving the body rearward on the frame, the crank-driven blower won't fit unless you tunnel it under the firewall, which was done on some drag cars.

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Edited by Ace-Garageguy, 24 September 2012 - 01:09 PM.


#3 Art Anderson

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Posted 24 September 2012 - 01:08 PM

I'm starting the AMT 1925 Model T (dropped frame, coupe body, Parts Pack Chevy 283 with the crank driven supercharger) and I'm not sure I like the look of the front suspension parts. Has anyone either made their own realistic front end or put on another front end from a different kit with any success?


The AMT '25 T street rod version has a front suspension based on the '37 Ford tubular front axle. It's not all that bad, certainly considering that this kit was first released about this time in 1961, or 51 years ago. Given that this kit has a suicide front spring perch, you've got some real room for a fairly wide choice of front axles and springs. Here's one, the really nice dropped Model A front axle setup from the Revell '29 Model A pickup kit:

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Art

#4 rhs856

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Posted 24 September 2012 - 01:24 PM

I've done a suicide front end on that kit. I used a round front crossmember (which would be better in 1:1 because of the way it is in torsion) of styrene tubing and fabricated the spring perch from channel. The axle is a tubular unit from who-knows, but the principle would be the same for any transverse-sprung front end. Hairpins, split wishbones or a 4-link setup (which this car is getting) would complete the install.

One note....without stretching the chassis or moving the body rearward on the frame, the crank-driven blower won't fit unless you tunnel it under the firewall, which was done on some drag cars.


Thanks for the pics. It appears that I will be learning more about suspension than ever during this build. And thanks for pointing out the need to lengthen the frame - I'm one step ahead of you!

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The AMT '25 T street rod version has a front suspension based on the '37 Ford tubular front axle. It's not all that bad, certainly considering that this kit was first released about this time in 1961, or 51 years ago. Given that this kit has a suicide front spring perch, you've got some real room for a fairly wide choice of front axles and springs. Here's one, the really nice dropped Model A front axle setup from the Revell '29 Model A pickup kit...
Art


That reminds me... I have an old Ford truck glue bomb somewhere. I kinda like the look of that.

#5 Harry P.

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Posted 24 September 2012 - 01:26 PM

Stupid Question Department: Why is that type of spring perch called a "suicide" style?

#6 Jantrix

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Posted 24 September 2012 - 01:27 PM

Now if you really want to make a statement, maybe a quarter elliptical front end.

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#7 Ace-Garageguy

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Posted 24 September 2012 - 02:26 PM

Stupid Question Department: Why is that type of spring perch called a "suicide" style?


They got their name back in the wayback when a lot of the fabrication wasn't adequate on the back-yard cars. Because the front suspension loads are cantilevered out front with this particular arrangement, instead of being fed directly up through the crossmember from below, material choice and welding integrity on the spring perch and crossmember are critical. With engineering and workmanship being very often sub-par and leading to spectacular failures, the design soon came to have a bad rep, and somewhere along the line the term "suicide" was applied.

Art''s right about the kit axle being based on the tubular '37 Ford front axle that came under V8- 60 powered cars and soon became the racer's favorite due to its light weight. Unfortunately the effect is rather spoiled by the kit steel axle running through it. it takes some work, but it can be made into a nice piece with working steering knuckles.

The '25 T kit version is at top with the totally wrong steel axle running through it. Another '37 axle is below it, but I don't remember which kit it's from. These are the only two versions for the '37 axle I have come across so far.

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The two versions of the '37 in rework mode.

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Rob Mattis has a very good looking longitudinal quarter-elliptic spring setup going there. Unfortunately, in 1:1 it's a terrifying arrangement to drive. The axle is very far ahead of the front crossmember, and with virtually zero lateral location of it, steering is rather point-and-pray. Windup of the springs under braking is pretty thrilling too.

#8 Harry P.

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Posted 24 September 2012 - 03:33 PM

They got their name back in the wayback when a lot of the fabrication wasn't adequate on the back-yard cars. Because the front suspension loads are cantilevered out front with this particular arrangement, instead of being fed directly up through the crossmember from below, material choice and welding integrity on the spring perch and crossmember are critical. With engineering and workmanship being very often sub-par and leading to spectacular failures, the design soon came to have a bad rep, and somewhere along the line the term "suicide" was applied.


Ok, that makes sense, thanks for the history lesson.

That brings me to the obvious question: So what was the point of mounting the axle out ahead of the front crossmember in the first place?

#9 Ace-Garageguy

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Posted 24 September 2012 - 04:18 PM

That brings me to the obvious question: So what was the point of mounting the axle out ahead of the front crossmember in the first place?


It was a way to accomplish two things: One, to lengthen the wheelbase of the car without having to actually lengthen the frame rails, kinda like the extended forks on a chopper give a little more high-speed, straight line stability (but adversely effect handling). Two, and more importantly, to lower the car more, again without having to resort to major frame surgery like Zee-ing. For any given beam axle with a transverse spring, the raised perch ahead of the front crossmember will let the frame sit much lower relative to the axle than if the axle were mounted under the crossmember.

There are several variations of the geometry to choose from. The white un-chopped car of the OP has the spring mounted behind the axle, so requires less height on the perch to achieve the desired lowness. My chopped black car has the spring mounted directly over the axle, so the perch must be higher to get the same ride-height. On a 1:1 car, I tend to favor the second approach, as I rarely like the way the bolts, shackles and wishbones are loaded when the spring is behind the axle.

Edited by Ace-Garageguy, 24 September 2012 - 04:43 PM.


#10 Draggon

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Posted 24 September 2012 - 04:30 PM

Suicide style was named that, because if the spring perch failed, the front axle would be rendered useless, and the frame would dig into the ground, and presto, up and over the top! The benefit to the suicide perch is that the one could easily dictate the ride height simply by the placement of the perch. If you look at the 40 Ford setup, the spring is in front of the axle. If the perch was to fail, there would still be the spring and the axle to keep the frame off the ground and have some bit of control. While not so safe, the suicide perch has a great following among the traditional rodders, perhaps somewhat due to the sorta fearsome nature of the beast.

#11 Harry P.

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Posted 24 September 2012 - 04:34 PM

It was a way to accomplish two things: One, to lengthen the wheelbase of the car without having to actually lengthen the frame rails, kinda like the extended forks on a chopper give a little more high-speed, straight line stability (but adversely effect handling). Two, and more importantly, to lower the car more, again without having to resort to major frame surgery like Zee-ing. For any given beam axle with a transverse spring, the raised perch ahead of the front crossmember will let the frame sit much lower relative to the axle than if the axle were mounted under the crossmember.


Makes sense! Thanks.

#12 southpier

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Posted 25 September 2012 - 12:20 AM

i'm just dying to see this build completed

#13 Jantrix

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Posted 25 September 2012 - 12:49 AM

Unfortunately, in 1:1 it's a terrifying arrangement to drive. The axle is very far ahead of the front crossmember, and with virtually zero lateral location of it, steering is rather point-and-pray. Windup of the springs under braking is pretty thrilling too.


That's what I read when I was researching for this build. I don't think this is anything a sane person would drive. I found very few 1:1 examples in my Google searching.

#14 Art Anderson

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Posted 25 September 2012 - 07:17 AM

Ace-Garageguy, on 24 September 2012 - 03:26 PM, said:

Unfortunately, in 1:1 it's a terrifying arrangement to drive. The axle is very far ahead of the front crossmember, and with virtually zero lateral location of it, steering is rather point-and-pray. Windup of the springs under braking is pretty thrilling too.

But, you are missing a few details here:

For starters, transverse springs (which Ford used on all their production cars from 1906-1948) require radius rods (either the wishbone setup which was stock on a Ford) to single radius rods (split wishbone--which my '27 T street rod project has) to 4-link) which not only hold the axle square with the centerline of the frame, but also fix the relationship of the axle to the frame and to to the road surface in this way: A Ford front axle's radius rods actually set the caster angle of the front spindles very firmly--by absolutely preventing spring "wrap-up"--which you can see by looking at how that sort of radius rod is "clenching" the axle just as visibly as if you were holding it tightly between thumb and forefinger. There simply cannot be any distortion or twisting of the front (or rear spring) with proper radius rods. This didn't change with splitting the Ford front "wishbone" radius rods, nor does it change with the use of 4-link radius rods either.

This is entirely different from the "windup" that leaf springs can undergo with extreme acceleration (rear springs on any car using them longitudinally) or extreme braking (front and rear springs on any car with longitudinal springs on all 4 corners), absent any sort of traction bars.

As for any lack of lateral control, it doesn't matter whether the spring is mounted to the frame INSIDE the front or rear crossmember (or, the manner in which leaf springs were mounted to the frame of a stock '32 Ford, for example) or suicide style--in either case, the center of the spring does not move side-to-side, or front-to-rear, period. What does happen with ANY transverse sprung automobile is, that since both ends of the spring must be on shackles, with unevenness in the road surface, and certainly going around sharp corners, the transverse spring will "swing" side to side on the shackles perhaps an inch or so side-to-side. That made for some interesting gyrations (albeit within a very limited range) when driving on bumpy roads.

From the early 1920's until the demise of two-spring midget and sprint cars (and not a few Indy cars as well from the middle 1930's into the early 1950's) transverse leaf springs AND suicide front (and often rear as well) spring mounting in this manner ruled. However, given the oval track racing venues, left turns only, those old race cars had their springs shackled on the left side only, the right side used a conventional shackle (not unlike the leaf springs on most cars in the rear from the early 20th Century out to today on say, a pickup truck, shackled at the rear, solidly bolted to the frame at the front).

But in the bottom line, it was the radius rods that held the axle not only square with the frame, but also held the axle solidly so as to provide a constant caster angle to the front spindles.

Art

#15 Chuck Most

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Posted 25 September 2012 - 09:02 AM

Art- I believe Bill was talking about a quarter-elliptic setup, not a transverse semi-elliptic setup like the early Ford system.

#16 Ace-Garageguy

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Posted 25 September 2012 - 12:34 PM

Art- I believe Bill was talking about a quarter-elliptic setup, not a transverse semi-elliptic setup like the early Ford system.


Thanks Chuck...you're absolutely correct, as my post Art quoted begins with the words "Rob Mattis (aka Jantrix) has a very good looking longitudinal quarter-elliptic spring setup going there. Unfortunately, in 1:1 it's a terrifying arrangement to drive......."

And Art, I'm not missing a thing and am in fact quite familiar with the dynamics and design requirements of these and ALL suspension systems, and I agree with much of what you say above. Your failure to notice that I wasn't referring to YOUR model's suspension layout, but rather Rob's (about which my comment's are accurate) is my only gripe. I rarely write when I don't actually know what I'm talking about. (It HAS happened though) ;)

As an aside, there IS a decided twisting introduced into a transverse-sprung axle when the 'bones are split, and it's very well known and understood by people who actually build 1:1 cars.The original design controls the roll center of the vehicle with the center pivot point of the wishbone, either under the trans in front or attached to the driveshaft in the rear. When you split the wishbones and move their pivot points away from each other and outboard to the frame rails, the roll stiffness on that end of the car goes up dramatically. The triangle existing in one plane and formed by the axle and the radius rods, and free to pivot and remain in one plane, is transformed into a rough rectangle with two of its corners anchored to the rails, and the other corners (on the axle end) allowed to pivot and NOT remain in the same plane. Think about it.

This INVARIABLY introduces a twist into the axle as the vehicle rolls. (That's "roll" as in angular motion about it's longitudinal center, not roll as in 'roll over' or 'wheels rolling'.) As the old I-beam axles were not particularly rigid in torsion, this wasn't too great a problem. With the introduction of more tubular front axles which are by nature more rigid torsionally, the odd increase in roll-stiffness became an issue indeed. Increased roll-stiffness on one end makes that end tend to slip more. The race car guys noticed it first.....the 4-link setup that has become ubiquitous on solid-axle cars exists for just this reason. If you think through the motion of a 4-link, it becomes apparent that it allows a beam axle (the definition of which in this instance also includes tubular straight-axle) freedom to rotate about its center without twisting, by allowing the wheelbase to vary slightly from side to side in roll. Though they didn't make it to the majority of street cars before Pete and Jake's popularized them in the late '60s-early '70s, they were showing up on race cars with tube axles much earlier. Frankly I was kind of amazed when I noticed an early 4-link front suspension setup on a dirt track roadster in a black-and-white move from the early '50s.

Edited by Ace-Garageguy, 25 September 2012 - 12:41 PM.


#17 Art Anderson

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Posted 25 September 2012 - 01:29 PM

Art- I believe Bill was talking about a quarter-elliptic setup, not a transverse semi-elliptic setup like the early Ford system.


Well yeah, quarter-elliptic springs were iffy, unless the builder used two per side, in the manner of say, a Miller 91 front drive race car, even the Cord L-29 front drive.

Art

#18 Ace-Garageguy

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Posted 25 September 2012 - 02:01 PM

Well yeah, quarter-elliptic springs were iffy, unless the builder used two per side, in the manner of say, a Miller 91 front drive race car, even the Cord L-29 front drive.

Art


Nothing really all that bad about quarter-elliptics if one designs correctly, as in using something like a Watts link, or a Panhard rod to limit lateral movement (as I've even seen on '30s dry-lakes cars) as I'll be using here.....(there's no Panhard bar made up as yet....). Here the split wishbones would adversely effect the handling of this car on the street, but it's intended to be a straight-line car only.

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jantrix's quarter ellips would be scary because the springs are used for lateral location of the axle, and they do a very poor job arranged as shown. Looks cool though.

The quarter-elliptics, long traction bars, watts links and particular shackle arrangement on the rear helped the Mazmanian and Stone-Woods-Cook Willys gassers to launch well and consistently. The right suspension design for the particular application and intended use is the key.

Edited by Ace-Garageguy, 25 September 2012 - 02:05 PM.


#19 southpier

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Posted 25 September 2012 - 02:34 PM

Posted Image

#20 Fat Brian

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Posted 25 September 2012 - 02:50 PM

Gee, that looks terrifying. :o