Rear subframe conversion ruminations

5109 Views 83 Replies 10 Participants Last post by Duncan, 3 mo ago

Tremelune

Discussion Starter · 4 mo ago

Cars with live rear axles make for frustrating conversions, mainly because you have to keep a manual transmission up front. Adapter is a grand or two, and the 2:1 TorqueBox is $4k (plus custom driveshaft). If you ditch the axle, you have to reengineer the suspension, which involves much more than cutting and welding.

Enter the rear subframe swap. Many conversions will take a Tesla subframe and stuff it in the rear. The difficulty here is that Teslas are wide, and many of the cars I'd like to convert are narrow. It also makes using different wheels tricky.

Has anyone successfully gotten an electric motor and gearbox into something like a Miata rear subframe? E30? What are some other rear subframes that are narrow with pickup points that a Leaf/Tesla motor could bolt into without moving the suspension pickup points?

What are the implications of changing the rear suspension geometry and travel while keeping the front stock? For a sportscar it would make me nervous, but for a daily driver or cruiser...not so much—just get over these bumps!

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olegil

· #61 · 3 mo ago (Edited)

remy_martian said:
Why do you want to center leafs with a panhard bar when the shackles and front spring mounts hold the car laterally? I'd think it would bind up.

The entire point of this setup is not to do any suspension mods/fab to the originals in the car. It's also arguable you could mount the drive unit to the Dedion tube - not that great for unsprung weight, but zero mods to the car, in theory.

A panhard bar might lock up, but a Watts linkage certainly wouldn't. I didn't see it mentioned that the frame had to be pristine.

Here's why you want to add some stability to leaf springs:

remy_martian

· #62 · 3 mo ago

EV West Guy bolted his in...leaf springs is key to simplicity, imo.

You can't reuse anything from the old solid axle, unfortunately. You need splined hubs out there and outer CV joints.

Yes, it doesn't come for free. Still a lot of fab. I like it because no butchery of the car to speak of. For an old car, I would mount the DU to the Dedion tube and attach it all to existing leafs....anyone see any gotchas other than unsprung weight?

remy_martian

· #63 · 3 mo ago

^^ I'm not sure what we're looking for in that video.

The operator drives like a girl is all I see so far 😂 and the camera mount creates an illusion there's transverse wobble in the rear axle.

olegil

· #64 · 3 mo ago

remy_martian said:
^^ I'm not sure what we're looking for in that video.

The operator drives like a girl is all I see so far 😂 and the camera mount creates an illusion there's transverse wobble in the rear axle.

Maybe I misunderstood their point and what we're seeing is sidewall flex rather than lack of a watts link or panhard bar.
But I don't understand your fear of adding some centering. It's standard on all modern cars with live or dead rear axles and leaf springs, and at highway speeds I would think any stability improvement was welcome. It's also both cheap and easy, if you understand a tiny bit of geometry.
Why would a panhard bar lock up the leaf springs in a 60s vehicle but not a modern one? All it does is reduce lateral movement. Are you depending on lateral movement in any way?

Here you can actually see both the sidewall flex and the lateral movement of the rim while cornering:

The rim moves much more than the sidewall flex. Yes, obviously this is on track, not highway. But still.

remy_martian

· #65 · 3 mo ago (Edited)

The bar goes through an arc. The old leaf spring cars never had them.

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olegil

· #66 · 3 mo ago

The old cars never had a lot of really nice things. Electric motors, for one. A properly set up panhard bar has WAY less lateral movement than any bushing and shackle would flex, and a Watts linkage has essentially none. A panhard bar of 40 inches (a reasonable length) allowing +/-4 inches of suspension travel (a ridiculous amount) would have a total lateral movement of about 3/16ths of an inch (40, 4 and 40.2 being the three sides of the triangle). Show me an old leaf spring setup that moves less than 0.2 inches sideways while cornering hard.

The Ford Ranger EV had a Watts linkage on its De Dion with Leaf springs.
40's Cadillacs came from factory with leaf springs and panhard bars. This makes sense, as they wanted the smoothest handling on the premium brand.

I think you're mistaking "could get away with not spending the extra cost" with "doesn't improve handling".
Now, of course, if you LIKE your rear axle to float about on the old leaf springs, noone is forcing you to do anything. My point was originally that if you're making a De Dion you can easily add a Watts linkage to it, which would be a double improvement to the original, with lower unsprung mass and less lateral movement.

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brian_

· #67 · 3 mo ago

Panhard rods are sometimes used with leaf springs, normally for higher lateral stiffness, and only when suspension travel is relatively short. This is the sort of thing usually found on race-prepared production cars from decades ago (such as the early 1970's Datsun a friend of mine had, which was race-prepared around 1980), not anything in street use and not anything recent at all.

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remy_martian

· #68 · 3 mo ago (Edited)

The idea is not to fabricate anything you don't have to. One principle on restomodding is reversion - putting the car back to its original condition, which some people want for whatever reason. Not one new hole drilled is their rule.

To Brian's point, if you're building a race car that whips into curves at the edge of traction cutting loose, yes squirm could break tires loose. For road cars, it's unnecessary....even pickup trucks that do towing don't have them....not even my 4 wheel steer trucks have them.

Hard bushings can accomplish the same goal, btw.

Coil spring cars have to have them, though.

Electric Land Cruiser

· #69 · 3 mo ago

brian_ said:
Panhard rods are sometimes used with leaf springs, normally for higher lateral stiffness, and only when suspension travel is relatively short. This is the sort of thing usually found on race-prepared production cars from decades ago (such as the early 1970's Datsun a friend of mine had, which was race-prepared around 1980), not anything in street use and not anything recent at all.

That's not true. My Land Cruiser has a panhard bar and it has tons of suspension travel. A brand new 2023 Land Cruiser also has them. Most all 4x4s with solid axles have them from the factory.

Also Camaros and Mustangs from the 2000s. Crown Vic. Etc. Tons of cars have them and modern cars too.

brian_

· #70 · 3 mo ago

olegil said:
...
But I don't understand your fear of adding some centering. It's standard on all modern cars with live or dead rear axles and leaf springs...

There are no modern cars with beam axles and leaf springs. There are many trucks (light and medium duty) with basic beam axle and leaf spring suspensions, but they don't have Panhard/track rods or Watts linkages... just look at any pickup truck or van (such as the Tacoma).

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remy_martian

· #71 · 3 mo ago (Edited)

Electric Land Cruiser said:
That's not true. My Land Cruiser has a panhard bar and it has tons of suspension travel. A brand new 2023 Land Cruiser also has them. Most all 4x4s with solid axles have them from the factory.

Solid axles with coil springs.

Plus, you wouldn't need a panhard if you had leafs...you drive like a girl 😂

Electric Land Cruiser

· #72 · 3 mo ago

brian_ said:
There are no modern cars with beam axles and leaf springs. There are many trucks (light and medium duty) with basic beam axle and leaf spring suspensions, but they don't have Panhard/track rods or Watts linkages... just look at any pickup truck or van (such as the Tacoma).

Tacoma, 4Runner, Sequoia, etc all had panhard bars at least until 2016. Ford Bronco, Chevys, Ram. Practically every truck has them.

brian_

· #73 · 3 mo ago (Edited)

Electric Land Cruiser said:
That's not true. My Land Cruiser has a panhard bar and it has tons of suspension travel. A brand new 2023 Land Cruiser also has them. Most all 4x4s with solid axles have them from the factory.

Also Camaros and Mustangs from the 2000s. Crown Vic. Etc. Tons of cars have them and modern cars too.

Electric Land Cruiser said:
Tacoma, 4Runner, Sequoia, etc all had panhard bars at least until 2016. Ford Bronco, Chevys, Ram. Practically every truck has them.

Those vehicles have coil springs and control arms, not leaf springs, except the Tacoma (which doesn't have a Panhard rod). Here's your 80-series, with visible rear coil springs, no leaf springs... and yes, a Panhard rod. Did you just not notice that we're talking specifically about the use of a Panhard rod with leaf springs?

That includes GM full-size SUVs with beam axles (Yukon, Tahoe, etc) and even Ram light-duty pickups. "Practically every truck" would be only Ram trucks and the 2023 Tundra, because they're the only ones with coil springs. While a Tahoe had (until it went IRS) a rear beam axle with coil springs and links including a Panhard rod, but the Silverado of the same platform series has leaf springs... and no Panhard rod.

Of course a lateral location function (Panhard/track rod, or Watts linkage, or angled upper arms, or upper A-arm) is required with coil springs.

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remy_martian

· #74 · 3 mo ago (Edited)

Electric Land Cruiser said:
Tacoma, 4Runner, Sequoia, etc all had panhard bars at least until 2016. Ford Bronco, Chevys, Ram. Practically every truck has them.

More deceptive remarks from you.

None of my leaf spring Chevrolet trucks has them.
Early Mustang/Falcon didn't have one
Bronco uses coil springs afaik
Some Land Cruisers have coil springs
Dodge Ram uses coil springs afaik
Tacoma I don't see a panhard bar:

Wheel Tire Vehicle Tripod Automotive tire

www.tacomaworld.com

What do I need to replace leaf springs?

I plan to buy some used rear leaf springs. Do I need to purchase additional hardware? Keep in mind I'm trying to be as frugal as possible. Can I just...

www.tacomaworld.com

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Tremelune

Discussion Starter · #75 · 3 mo ago

I think we've gone a bit too far into the weeds here—the point of this thread is specifically to avoid re-engineering suspensions. Let's stay focused on subframes that would be advantageous for EV swaps into narrow RWD cars.

remy_martian

· #76 · 3 mo ago

We are focused.

No subframe solutions are being posited as superior to subframes in many restomods in that next to no modifications to the target conversion's suspension and chassis is needed.

Whether to include a panhard bar in a leaf-springed Dedion setup is being discussed.

Duncan

· #77 · 3 mo ago

My tuppence worth on the Panhard rod

I am building a Marlin kit car - the kit was made in 1995 - after several people faffed about and spent money but did not finish it I am finally getting it on the road

This Marlin has Morris Marina suspension - leaf springs and a live axle
One of the previous owners had fitted a Panhard Rod
That was one of the first things I threw away!!
As built and installed it would have severely restricted the rear suspension
I'm sticking with the live axle and leaf springs

Leaf springs
One of the great things about leaf springs is that you can add or subtract leafs to change the spring rate

Corrosion between the leafs and stiction can be a problem - I have used some Teflon sheet cut into strips between the leafs - it was sold for use in Barbeques

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brian_

· #78 · 3 mo ago

Tremelune said:
I think we've gone a bit too far into the weeds here—the point of this thread is specifically to avoid re-engineering suspensions. Let's stay focused on subframes that would be advantageous for EV swaps into narrow RWD cars.

Fair enough - the original subject is clearly using a complete subframe-mounted suspension. That will be independent, not any kind of beam (including a de Dion beam).

The beam axle - and then de Dion - sidetrack started with a post by olegil. The specific issue of a Panhard rod with leaf springs was also raised by olegil in another post, and compounded by his comments in another post and yet another post and the apparent inability of Electric Land Cruiser to understand the difference between leaf and coil spring suspensions. With any luck, we're done with that, and everyone understands that a beam or de Dion system may be a sensible alternative for some vehicles, but is not intended to be the subject of this thread. The Comet project build thread (1962 Mercury Comet + 2013 Nissan Leaf) is a good place for that discussion.

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Electric Land Cruiser

· #79 · 3 mo ago

brian_ said:
Those vehicles have coil springs and control arms, not leaf springs, except the Tacoma (which doesn't have a Panhard rod). Here's your 80-series, with visible rear coil springs, no leaf springs... and yes, a Panhard rod. Did you just not notice that we're talking specifically about the use of a Panhard rod with leaf springs?

That includes GM full-size SUVs with beam axles (Yukon, Tahoe, etc) and even Ram light-duty pickups. "Practically every truck" would be only Ram trucks and the 2023 Tundra, because they're the only ones with coil springs. While a Tahoe had (until it went IRS) a rear beam axle with coil springs and links including a Panhard rod, but the Silverado of the same platform series has leaf springs... and no Panhard rod.

Of course a lateral location function (Panhard/track rod, or Watts linkage, or angled upper arms, or upper A-arm) is required with coil springs.

Actually, you wrote a couple run-on sentences that could be interpreted in a few different ways. I'll let you have the win because I'm busy. I'm on another adventure with my DIY Electric Car. Much more fun than talking on the internet!

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remy_martian

· #80 · 3 mo ago

Pretty clear what Brian wrote.

I for one don't consider driving cars on trailers everywhere to be useful or fun. The entire point of an electric vehicle is lost when you're getting 9mpg hauling it around with an ICE for 10x or more of its range.

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