I’m thinking how to make rear suspension for my Model A and have couple of questions. I like to use Cadillac rear end, cause I just happen to have one. Also I’ll use model A rear spring with reversed eays and some leafs removed, just cause I want to. Typical way to make suspension is to have ladderbars connected to X-member of the frame. But I don’t like the that all forces runs through the X-member that is made by me. It would make more sense to have forces running straight to frame rails. So I came up with idea to make triangular 4-link for it, using front wishbones as lower control arm, just for looks, and what ever pipe/rod for upper ones, cause they are hidden anyway. I don’t remember seen this kind of set up with transverse leaf spring, so do you know why it should NOT work? And please do not start discussion what is traditional or not. If model A with 270 red ram, four Stromberg 97s, drum brakes and 32 heavy axle dropped by me, ain’t traditional enough, then call me a street rodder! Pic of mock up, to give idea what i'm planning to do. Other question about rear end. As most of those “modern” rear ends, the Cad ain’t symmetric. Drive shaft runs center, as I want it to run, but pumpkin is off set. Does that hurt something else than looking stupid?
uppers should be 70% of lowers. I bought an Olds with ~36" lower arms and GM factory 12" upper arms and movement was locked up so removed uppers, welded lowers to rear and added a panhard bar
I have a triangulated 4 link with transverse spring setup. The spring is a '40 Ford front spring mounted behind the rear axle. Challenge is to keep suspension from binding during articulation, but in a lite car the suspension doesn't travel alot. Compared to a standard triangulated 4 link lay out your lower link is much longer, so could be a binding issue. I also question using the front wishbones. The offset pinion isn't a real issue as long as you can get the upper link attachments located correctly. So your basic concept works in a lite car. I would reconsider the design layout.
Thanks for the comments. And yes if i'll make this set up, the lower arms will be much shorter. In the picture there is a split front wishbone in original lenght, just to give idea what i'm thinking to do. That set has worn out brackets for axle mounting, so i could cut them to make lower arms. Any comments about using tie rod ends in front mount? I think should be strong enough, cause they work in front axle mounting where braking torque is acting on them.
I have a 1935 International truck that I put 1/4 eliptic springs for the lower bar triangulated upper bar works fine. Also have a similar setup on a rock crawler with 4 bars 2 springs on the rear works great lots of movement.
The bottom arms will have to be able to articulate at the axle with some kind of joint, and not solid with a yoke or similar. The tie rod ends used like you have on the bottom arms ( at the front) like you say are used on front split bones and will be fine if they are the larger truck (F1?) type. The threads are possibly 3/4"? You could use them at the rear too? Chris
The rear spring is going to keep the rear end moving in a single plane in it vertical movement. Your links are going to move thru an arc as they work, which should push and pull the rearend slightly fore and aft as it works. The longer the 4 link arms are, the less fore/aft movement as they work. I don't see where the shorter links actually accomplish anything, but "might" be problematic with their short arc working against the rear spring. Please don't consider what I'm saying above as being criticism, it's just what I would be thinking if I were doing it. It is possible that the movement might not be enough to create a problem, but it could increase bushing wear. As for the off set rear end. I'd save the Cad rear for another project. The exposed view of a rear end is one of the more noticeable things in a hot rod, and as you have already said, it will look "dumb". Save it or sell it and buy something else with the money, but its going to detract from all the other good stuff you have done. It's like that one ding in an otherwise perfectly straight panel..........thats what sticks in everyones mind when they see the car.
You might take a hint from Corvettes. I would support the rear end with bolts and biscuits to allow the rear end to move for and aft.
The main reason for trying to keep the upper and lower arms the same length is to keep pinion angle somewhat captured thru the rear-end movement. With much shorter uppers as the suspension moves it has a tendency to tilt the nose of the rear end down creating more pinion angle. This is one cause where I've actually had customers complain of driveshaft vibration on the hiway when they have a loaded car, (2 or 4 doors) with people in the backseat (if your car has a back seat). The extra say 600 pounds is enough to lower the stance to change pinion angle enough to have a vibration. I prefer trying to keep both upper and lower arms as close to the same pivoting length as I can. Also like the angles when the suspension moves separately side to side. But again everything is made up of compromises..... ...
If you are mathematically challenged, use a string line and an axle stand to mock up your upper links [visualization does wonders] Where the upper links intersect becomes the roll center You want the RC to be on the centerline /axis of the car [unless it is an offset /oval track car] The triangulated 4-link will control all lateral loads/ movement. To prevent binding with the spring use longer [more vertical] spring shackles shorter uppers will move the instant center down and towards the rear as suspension compresses.
Over the last 40+ years in the chassis business I've done quite a few buggy spring rears with both parallel 4 bars and triangulated 4 bars. Either worked well. My deuce 3 window has a buggy spring with parallel 4 bars, no panard and works great. In the 90's I built a chopped deuce tudor highboy with a 40 rear spring, 9 inch rear and triangulated 4 bars and drove it over 40K before I sold it. I agree, center the housing.
No need or want for a Panhard bar with a rear buggy spring as the spring mount will keep the axle centered. They run Panhard bars on Ford front buggy spring setups with cross steer because the cross steer wants to push the axle sideways on the shackles if you don't the majority of the time. That may be more noticeable with the spring in front of axle rigs with longer shackles than with the spring on top of the axle rigs.
Thanks for the comments everyone! So conclusion is that buggy spring and triangulated 4-link should not be a problem, just as i thought. But for centered rear end, if i'll find shorter (left side) shaft for the Cad rear, i could have the housing shortened on right side to make housing symmetric. But then drive shaft will be off center about 32mm (1 1/4"). That means about 2,2 deg angle from transmission center line. Then there will be around same angle vertical difference depends the final driving height of the chassis. Total angle is little harder to calculate, cause the plane of drive shaft is somewhere between vertical and horizontal planes. Could that total angle be a problem? I know that driveshaft angle should not be 0, cause then needles in universal joint will stay in one place and wear out the shafts. But i do not know maximum angle recommend for universal joints. Is there rear ends with same basic design (Ford 8" or 9", Mopar 8 3/4", some older GMs) that are symmetric from factory? The 9" under my 62 pick up seems to have off set housing also.
For argument's sake let's assume your driveshaft is 1200mm between the UJs. With 32mm vertical offset and 32mm horizontal offset, the overall diagonal offset would be about 45mm (two ways to do that: sin or cos 45° or Pythagoras). Then, arcsin (45/1200) = 2.15°. That's well within UJs' capabilities. At the risk of complicating @Kerrynzl's explanation, here is another diagram of how triangulated 4-link geometry works. The conventional setup has the upper links angled, with their axes converging behind the axle, the lower links parallel to the ground, all the links forwards of the axle, and a relatively high roll centre. Technically you could have any or all of that the other way around: but don't go there unless you understand how this stuff works.
Exactly my driveshaft lenght will be around 850mm, which gives angle of 3.03. That is just on limit 3 degree which i found on Dana Spicer web page. So i guess it will be ok, but i really do not know the vertical direction angle yet, so it would be more safe to have drive shaft in center. Or maybe i just worried too much....
I've done 100's of 28-34 chassis over my years in the chassis business using a housing centered 9 inch Ford rear which offsets the pinion yoke 2 inches to the right. This has been done since the since the inception of the 9 inch rear to countless 1000's of 9 inch rears with no ill effects.
Thanks a lot! That was what i wanted to hear. So i will get a symmetric rear end housing with offset pinion and stop worring this thing!
Just the lowers, no upper? What did you use to prevent axle twist under acceleration / braking forces?
Olds clamps axle to lower arms with square rubber bushing between steel halves. Welded axle half to axle so it is now a wishbone
The upper links need to be as long as the bottom! Or damn close to it. The amount of twist is going to eat bushings, unless of course you want to rubber mount the spring. I wish guys would quit copying the GM G body design.
This is an off topic drift truck but it works! Pinion angle is stable and it’s extremely strong. Poly bushings at the axle and proper poly lined automotive helms at the frame. Tubing is 1.312 cold rolled electrical welded. CREW. .120 wall.
Pardon the low res pics, these are scanned film These were taken back in the 80’s when I built my HotrodA roadster, before the HAMB. Adjustable Triangulated four bar with transverse spring. Rode great, hooked up, no issues in 30+ years. Lives in NH now. Still going.
As to your question of rear axles with centered pinion, Only early Ford stuff is like that or the early QCs like shown IIRC, nothing modern. I'd also prefer a centered diff, not pinion. It makes sense if you consider the internals.
Thanks guys for all that info. I thought it would be hard to find a left hand drive shaft for the rear end, when i do not even know which year it is. But i already found one in ebay, which has matching dimensions (-58 limo cad) and have a hint of one here in Finland, which is great cause shipping the shaft from States is not exactly cheap... So most probably solution will be centered Cad rear end, buggy spring and triangulated 4 link.
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