3-link or 4-link rear?

So, on the monstrous MG project, I think I'm going to go with a live axle. The sudden appearance of an S10 Blazer rear end seems to be involved - thanks for the tip on that one.

I'm now trying to figure out how to tie it down. It'll have coilovers, I can't bring myself to retain the leafs (interesting, not leaves. Kinda like the Maple Leafs. Hmm, are they named after a suspension component?). But should I go with a three- or a four-link system? Both are available on the aftermarket if I want to purchase them, or I can use the copious and detailed photos as inspiration for my own version.

Three-link: Easy to work out the geometry. No chance of bind. Lots of really good pictures on how to do it . But I'm not thrilled about the concept of a Panhard rod and the associated lateral axle movement. Is this noticeable at all from a handling perspective? Is the simplicity worth the (potentially theoretical) downside?

This is one of a bunch of pictures of the commercial setup. Note the big bend in the Panhard rod to clear the diff. I'd probably try to run it behind the axle so I could use a straight one. Many more high-quality pictures of this setup.

Four-link: Actually, a modified four-link with non-parallel upper joints. Herb Adams calls this a "Satchell link". Better axle location and much more pleasing from an engineering aesthetics perspective, but I think there's real potential for bind if you don't get it right and that has me a little spooked. If I choose to shell out for it, then my geometry concerns aren't really valid, but the roll oversteer designed into this one isn't quite what I was looking for. More on this commercially available setup, along with a few pictures.

Thoughts? Advice on setup? Preferences?

As a mustang owner, I say stay as far away from a non-parellel 4-link setup as possible. A panhard bar should have no lateral axle movement (well, other than bushing slop), which you'll see a lot of with a NP4L.

I'd go 3-link (assuming you also have some way to stop axle wrap?), or parellel 4-link with a panhard or watts link (a la AE86).

might look into what some of the old mustang folks do to update the old leaf sprung setups. here is a site that details a few of the options out there for the mustang to pull ideas from. (like using the forward leaf spring mounts to locate your lower control arms)

The only advantage of a four link over a three link is not needing a panhard bar. We ran them for years and lateral movement is very slight, especially if you go behind the axle and use a long bar. If you are rally concerned about it you could go with a watts linkage, I don't have any experience with them but I'm sure someone here could tell if they did/didn't make a difference for them. Four links do like to bind which is one of the problems we had starting with GM chassis. If I were starting from scratch I would look at a three link or torque arm like a late model Camaro as the torque arm seems to help with whel hop if you have the room for it. Tommorrow I'll try and find what info I have on setting up three links, there are several good books that deal with it, though they are mostly based on circle track building.

My wife and I stopped by a race team that had two former trans am cars on our last trip to Puerto Rico. One was a 3 link, the other a 4 link. They seemed to like the 3 link a LOT better.

There were a series of articles in Racecar Engineering, where you could partially eliminate torque wedge using a properly designed 3 link...

And on Corner Carvers (which i'm NOT a member of just looked), there was an interesting discussion about the 3 link set up.

BWT, while there is an arc with a panhard rod, I'd bet you would not notice it at all. And if you don't like that, use a Watts link.

Eric

A parallel 4 link, like a 1st gen RX7, still needs a side to side location device like a Watts or Panhard. It also has a good bit of roll steer compared to a 3 link or Satchell. A Satchell link, due to packaging requirements, generally requires the upper arms be angled instead of the lower and on a B that means the mounting will take a LOT of fabrication. The upper links should be somewhat shorter than the lowers to get the roll steer right, meaning you now have to move the lower arm front mount points further forward than the stock B leaf spring mounts or deal with a good bit of roll steer.

Ideally, a 3 link has pretty long lower links as well but you can get away with all 3 being nearly the same length.

The Jensen Healey has a Satchell link setup, two parallel lower trailing links and angled uppers. Yes, it does bind with rubber bushings and the roll center can't be changed without major work, so I am ditching it in favor of a 3 link with a Panhard. In my case, the lower links are already plenty long enough and I have the luxury of having to fabricate only the upper center link and brackets. If the Panhard is as long as possible, the side to side movement is minimized. There should be enough room under a BGT to run the Panhard behind the axle, thus simplifying its design and construction.

A Satchell can be done with rod ends but that's noisy as hell in a street car.

A Watts link is certainly an option, but now you have to fabricate two frame brackets, an axle housing bracket, a swivel center link and all the associated link bits and pieces, plus you have to re-engineer the whole thing if you want/need to move the roll center. I'm just going to run my Panhard as far as possible out to the left side of the axle as viewed from behind.

The guy I got the car from had already fabbed a (to me) too short Panhard setup that he used in conjunction with the original Satchell link and rubber bushings meaning the axle moved too much from side to side as it moved up and down causing binding. He had also installed a rear anti sway bar thus jacking the rear oll stifness even more, for some reason he complained of a tendency for the car to oversteer.

By the way, that Panhard shown on the 3 link pic in your OP jacks the roll center way up.

Google the Factory Five Racing three-link setup. It's pretty well thought out and is supposed to be very effective.

Reverend Dexter, a three-link has three links plus a Panhard rod. There's one on the top of the axle in the center as well as the two lower ones. Axle wrap is not a problem. The lateral movement comes from the arc of the Panhard rod as the axle moves up and down.

Jensenman, the guys who put together that three link setup claim a RC right at the middle of the axle, same as a stock MGB. But that's easy to fix, as the RC simply comes from the Panhard location if I remember right.

Also, there's not much fabricating to put a Satchell link on an MGB, check out the link I posted for the commercial setup. It's a nice packaging job, but I think the roll steer isn't quite thought out.

Sounds as if the downsides to the Panhard rod - assuming it's as long as possible, which is what everyone recommends and which makes sense - are not worth worrying about.

I had a good experience with a 3 link, straight panhard behind the axle, on my FB Rx7. The standard 4 link upper arms were not parallel and therefore caused binding.

Well, if you're really concerned about the roll center, there is always the Mumford Link

More Pictures

My thoughts about that bolt in 4 link: binding due to the urethane bushings and as you noted weird roll steer because the upper links are so far out on the axle housing and the links are pretty short. To get a reasonable roll steer, the links would have to be moved in quite a bit and also made longer meaning fabrication of a crossmember etc.

That setup would probably be OK on a street car or even a drag race car but I see evil in the twisties.

The three link Panhard looks like it's super high, I guess it's just the picture angle. Maybe if they had run it BELOW the axle in the front...

As much hardware as that Mumford needs, it oughta be able to cook dinner and fetch your slippers too.

The Panhard in that setup is curved to go over the diff - which has me worried about bending. But it does hide the true path of the bar, which is delineated by the location of the ends and not the craziness in the middle. I would change that.

Jensenman wrote: My thoughts about that bolt in 4 link: binding due to the urethane bushings and as you noted weird roll steer because the upper links are so far out on the axle housing and the links are pretty short. To get a reasonable roll steer, the links would have to be moved in quite a bit and also made longer meaning fabrication of a crossmember etc.

When we were forced by rules to run the four factory arms the urethane bushings seened to make the binding worse, we would either leave the rubber busings in the top of the axle housing or replace the bushings in the upper right arm with foam rubber, which made it simply decorative to meet the rules, and helped the car turn left while accelerating, which was good for a circle track car, but bad anywhere else. Neither setup worked as well as the three link though.

1st gen RX7 4 links are known for the binding problem. Energy Suspension released a 3 part bushing to try to combat this, it's a hard disc about 3/8" thick which goes in the middle of each arm link. It's then sandwiched by two pieces of very soft feeling urethane and then has a steel sleeve through the middle. It's better than the stock rubber setup but not by much, the rear still binds when the body rolls. About the only way to 'fix' it is to run a horkin' HUGE (like 1 1/8"!) front sway bar to cut down on body roll.

Or run a 3 link.

3 link gets my vote. You need to think hard on where to locate the 3rd link as it will efect the tire loading under power and braking. Longer the panhard rod the better and it should be as close to level as possible to eliminate lateral movement and help keep the roll center near the same spot.

44 PS: PM SENT

i have no issues with my panhard bar moving the axle laterally enough to feel it or cause tire rub, and my tires are within 3/16 of the quarter lip. i set it up so that the bar is dead level at ride height - which was simple to do since i built my 4 link with the trunk cut out of the car.

for a watts link, the junkyard might be your friend as all 98+ crown vic/grand marquis have them to locate the axle. it's actually a nice rear setup if you crawl under one.

I'm a big fan of 3-link and watts. This one worked VERY well and didn't take up that much space.

http://www.usa7s.com/forum/uploads/slngsht/modernbeat/default.asp?f=modernbeat

Very nice, that's the first time I've seen one on the bottom of the rear end. It looks like it limits the amout of travel you would have, but that doesn't look like a problem for what your doing.

Wally wrote: Very nice, that's the first time I've seen one on the bottom of the rear end. It looks like it limits the amout of travel you would have, but that doesn't look like a problem for what your doing.

Theres a bearing in the center of the watts link (where the oil drain plug is), so the suspension has travel (the rod ends, bearings rotate, just the axle doesn't move laterally).

This is the same suspension I had on the the rear of my tricked out spridget. Nice low roll center & never picked up a wheel.

Kendall

There are endless possibillities with rear end design, but I always go with proven set ups used by pro racers. From what I can gather, generally a 4 link is favored by straight line drag racers and a three link is good everywhere else. If the suspension on a Cup car can keep those tires stuck to the pavement, I'd go with a similar design. The bend in the panhard bar is not a concern. It's a pretty common design. Check this out - http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/truck_arms_independent_rear_three_link.html

modernbeat, that's a very nice setup. I think I might have flipped the rod ends for the center link 90 degrees (so they'd be parallel to the outer rod ends) just to be 100% sure there was no bind but you can't argue with results.

Given the choice, I'll take a straight Panhard rod over a bent one. It'll be stronger. It'll come down to the packaging on my particular car, though. I'll also have a look to see if that Watts setup is a possibility with my axle and frame.

Three shall be the number of the links and the number of the links shall be three. Four shalt thou not link, neither shalt thou link two, excepting that thou then proceedeth to three.

(Five is right out.)

The Watts link on the bottom of the axel housing is quite common on tube frame race cars. Early Jack Roush built Trans Am cars used a panhard bar and 4 links. They later change to a 3 link and a Watts link mounted on the bottom of the axel housing. I have seen these cars up close as I worked on both a Roush built car from 1983 and one built in 1995. Both cars are still owned by a guy I know that used to race in the Trans Am series. My opnion is to use a 3-link and either a panhard bar as long as possible or the Watts link.