The_7

I'm in the process of installing my GSLSE rear end and I'm going to be doing the Nylock nut mod from the PB&J Racing write up. I was thinking about the binding issue and if there were any other cheap ways to improve it. As the upper and lower links rotate to allow the rear end to move up and down, they don't trace a vertical line obviously, but instead an arc. So as the rear end is moving up and down, it is also moving parallel to the ground (front to back motion). However, the watts link is trying to restrict the motion to purely vertical, which is one source of binding. In addition to the PB&J Racing idea of softening the upper link bushings, what if you installed a rubber bushing or spring on the watts link main bolt (the one attached to the rear end) between the watts link piece and the nut. The idea is that this gives more front to back compliance and reduces binding. What do you guys think - would it help at all?

NewRXr

I my opinion that would hurt more than help. Yes the rear axle moves up and down in a small arc but it's not great enough to overtravel the existing compliance in the Watt's Link. The Watt's Link isn't there to keep rear axle movement purely vertical (viewed from the side) and it doesn't even try. It's only keeping the rear axle centered under the body side to side (vertical from the rear or front view). It holds the rear between the frame when high cornering forces try to push the body outwards while the tires are gripping to hold the rear in place on the road. If you were to soften up any of the Watt's Link mountings you would allow the body and rear to separate more side to side during cornering. This separation would cause more binding in the control arms than the Watt's Link ever did because they are only designed for straight up and down travel and then they would be forced to deal with side to side loads that the Watt's Link had been isolating them from. The control arms are parrallel to the frame, alone they can't and won't stay parallel to the frame with any significant side to side loading. If you look at a suspension of a lesser sports car such as the popular Fox Body Mustang you notice the lack of a axle centering device like a Watt's Link or Panhard bar. Instead the Ford has upper control arms at a 45* angle to the frame, so they must do both jobs holding the body and axle apart vertically and horizotially. They are overworked and easily smoked in the twistys. You have to take away all resembilence of a comfortable ride to get competitive cornering out of that chassis design. Lot's of binding there with the control arms having to hold the body and axle centered in all directions.

Also if you were to support the 7 up and put a jack under the rear axle then remove all four control arms you would be very suprised how easily you could roll the rear foward and back with the Watt's Link still firmly attached. It would surely move freely fore and aft more than the axle ever would when cycling up and down with the control arms attached. The Watt's Link has rubber bushings you know, there is plenty of give. Even with solid bushings you coun't remove all the slack. Think about it, the links are opposite the frame, not parrallel. Little slack opposite the frame, some with it. Where as the control arms are in the opposite position, little slack with the frame direction, some opposite.

You need both control arms and Watt's Link working properly to reduce binding, if one is loose the other will bind.

Vernon

The_7

I considered that there might be enough slack already in the watts link from the way the links are situated, but wasn't sure so it was just a thought.

The PB&J write up talks about drilling holes around the bushings in the upper arms to soften them - this seems to help. I know there is more than one source of binding - which one does this help reduce?

I got the idea that if softening the upper bushings reduced binding, then maybe if you softened some of the watts link bushings it would help also, but I considered it might cause to much slop. Like NewRXr said, if you soften the watts link, the side to side movement increases and causes more binding in the upper and lower links.

peejay

The suspension bind has NOTHING - ZERO - NADA to do with the bushings.

The problem is twofold: Unequal-length non-parallel 4-links inherently do not want to "rotate" in chassis unless the two non-parallel links coincide with the axle centerline.

In other words, in a one wheel bump, or in body roll, one of the upper links will be trying to stretch, and the other one will be trying to compress.

This is why you *need* to run gooey bushings in the upper links. If you don't, the suspension won't be able to move.

The "loose bolts" fix only works because it trashes the bolt holes in the chassis. So the compliance comes from being really loose. The geometry is still awful, only now you're inducing wheelhop under acceleration and destroying your bodyshell.

The Watts linkage is another, different, yet related problem. Any non-parallel four-link will have its own defined roll center. The Watts link is defining one of its own as well. The two aren't in the same spot, so binding occurs. This is still ignoring the more important problem with the Watts setup - the roll center is just TOO FREAKIN' HIGH in the first place.

The SOLUTION is to THROW THE UPPER LINKS AWAY and go to a three link system. The roll center can become livable if you un-slam the rear suspension, too...

jgrewe

iTrader: (1)

peejay has it explained the best. I'll just add that the compliance of bushings is the only way that the system works at all. The stiffer the bushings the worse the problems. In order to do the rearend right you have to get rid of the problem links(uppers) and replace them with something else. The easiest way is a single center link(tri-link). Any other cure that just deals with bushings is going to create other issues, none of them good.

The_7

I know that regardless of what you do with the bushings, it is still not near the handling quality of a good tri-link and panhard setup, but I don't have the money for that now, so I'm just looking for some other economical ways to improve handling. My question is that in addition to the Nylock mod and softening the upper bushings, if you soften the other bushings - do the pros outweigh the cons? Is the binding that is reduced worth the new problems created? This for a primarily street driven car - some aggresive driving and maybe an auto x every once in a while. Eventually I will upgrade to the GForce setup, but for now I'm looking for the best and most economical compromise.

Boswoj

Seems like I've explained this about a billion times, but peejay did a very nice job of it this time.

A soft bushing at the watts link pivot would only serve to prevent the only positive thing that the watss link does, which is accurately locate the rear end side to side. It would be one more "spring rate" that would have to take a set before steady state cornering could proceed. It would have the additional disadvantages of loading the upper arms unpredicatably, and introducing a random and possibly unpredictably dynamic rear wheel steering system into your car. It's highly likely that your car already handles as well as it is EVER going to need to for road use. The famed snap oversteer characteristic that 1st gens are famous for is something that eventually must be handled on our race cars, but if you are finding it on the street then you need to concern yourself with the function of the car more than esthetics and raise it up a little and /or you need to slow the f*k down before you kill yourself or someone else. If you are autocrossing the car and are reaching the limits, consider one of the big Racing Beat front sways which will bring the car a long way back toward neutral and unlike a third link and panhard, really isn't that expensive or difficult to install.

jgrewe

iTrader: (1)

Yea, just put a sway bar as big around as your arm(racing beat) on the front so it breaks loose the same as the rear. Not a very elegant solution but it has worked for years on some pretty fast cars. You will also get a more fun 'feel' out of the car because it will be more responsive to turn inputs. You won't reach the limits that you can with the Gforce set-up but it will be suprisingly balanced. And I'll second Boswoj's "keep it off the street" statements. These are very fun cars to drive fast, just do it where the only person at risk is you.

Hyper4mance2k

iTrader: (40)

Panhard is by far not the best option, It jsut happens tobe the most economical solution for our bunding problem. A properly designed watts link or any mumford link is about 1123843490 times better than a panhard bar. Because the pan hard bar will cause the axel to now have a vertical arc. A good 3 link and a mumford would outperform a panhard by soooooo much.

DriveFast7

iTrader: (1)

Replacing the Watts with any of the available Panhard Rod's is the first step in making the rear handle better. Try it, you will like it.

If you have more time and $$, get a real watts link custom fabbed in there with centrally located piviot point and equal length links. But it's overkill for street use. Real solution is adding a 3 or well designed 4 link or better yet a Lotus Link; all of which would be best suited for track use, and too much investment for street use.

Rx7carl

Whoa there partner, I specifically tell people they MUST restrict the bolts from rotating so that the holes do not become elongated and so that the nuts wont work loose (and they WILL if you do not restrict the movement). If thats unclear in my article, please let me know why.



Again, Ill say it for the millionth time, this is nothing more than a cheap band-aid fix that works reasonably well. Its certainly not the best solution.

Hyper4mance2k

iTrader: (40)

My personal sugestion is why go back intechnology when mazda did not. They could have put the much cheaper to produce panhard bar on the rx, but they didn't because the watts is simply better at controling side to side movement. And again I say nothing compairs to a Mumford link. Thats what most solid axle race cars use GT4&5 cars now GTL. But hey if you like the panhard feel free, NASCAR uses it with a 2 link. LOL!!

The_7

Hey carl, speaking of bolt rotation - I don't have a welder, so i was thinking of drilling a hole in the bracket right beside the bolt head. Then I would cut a piece of metal rod to use as a pin and JB weld it in there. I was thinking 1/8 to 1/4 inch diameter pin. What do you think?

I completely agree that this is a "band-aid" as carl said, and doesn't match the performance of a complete geometry change. However, it does offer moderate improvement over stock for relatively no cost. The latter is nice because I'm a poor college student on a VERY tight budget.

RacerX7fb

What is the primary purpose of your car you guys? A street driven, spirited driven perhaps occasional autocross car?

My guess is that it is not for serious road racing (Improved Touring, E-Prod) or a national or regional championship autocrosser for that matter.

That being said, then how can one who is on a tight budget necessitate the need for a tri-link/ panhard setup?

If your are driving your car on the street hard enough that rear end binds and causes the famed 1st gen snap oversteer, you are pushing the car dangerously passed your own driving ability.

The_7

No, my car is not for serious racing. Of course I'm not going to be pushing the traction limit on the street - just looking for some more predictable handling. I will take it to autox whenever I can find one in the area. The PB&J racing mod improves the handling somewhat for a very minimal cost. However, if I had the money, I would go with a trilink etc - even if it was still a street car. Most corvette (viper, jag, etc) owners dont use the full power of the engine on the street - does that mean people who don't race shouldn't have corvettes?

jgrewe

iTrader: (1)

I think its more of trying to justify the expense of redesigning the rear end suspension for driving on the street and the occasional auto-x. A RB front anti-roll bar would do what you want. As for all the options available for how to locate the rear end, you are dealing with a series of compromises throughout the whole car. While a mumford link may be the best, a whole lot of fabrication would be needed to put one on the car. Is all the weight and expense worth it? probably not. If you are building a full tube frame and can start with a blank sheet of paper, go for it. There are enough other things that are less than ideal on the car(struts!) that having the ultimate rear suspension doesn't matter that much. If a mumford link gave even a noticable advantage G-Force Eng. would offer it. As it is, for the effort, expense and weight a panhard bar is fine and a new watts link isn't even worth it. This isn't just a guess, I built two FB's with Jim at G-Force when he started developing the suspension he sells. I've seen the computer models and helped construct the first tri-links. If you see his car, that is one of our cars from the business we had.

DriveFast7

iTrader: (1)

panhard adds least unsprung weight of all later axel locators discussed. A good panhard will only allow 1/8" lateral movement through the rear's entire range of movement. From fully compressed to fully uncompressed. A racecar typically does not go though that range either.

Rx7carl

Not sure it will hold. Also the "pin" you would install would go thru the bracket and into the end of the link, causing it not to want to rotate. Take a close look and you'll see that your idea may be tricky to make work.

peejay

I don't have the money for it right now either, but I'm going 3-link. Out of necessity more than anything...

Shouldn't cost more than $50, and that is using Super Mega Ultra-Duty rod ends. If I wanted I could just grab an old lower link, cut it to length, and be done with it... but the suspension will be all rod ends eventually, might as well do it right the first time.

peejay

The side-side motion of a Panhard is next to negligible even with a relatively short length rod in a long travel setup.

Take a yardstick, pin one end to the ground, and swing the other end up and down about 3 inches either way. That's describing what a Panhard does in the "real world". Not very much motion. And, actually less than what our Watts has!

The Watts is not "better", it was just a method of space reduction. If Mazda used a Panhard, they would have had to make the car a couple inches longer in order to get sufficient crush space between the rod and the gas tank, whereas the Watts could be half-assed and mounted ahead of the axle centerline. You can look it up, this is the reason why Mazda used the Watts. It's not a secret.

The Watts sucks, mainly because the roll center is too high.

Mumfords are neat, but *jeez*.

The_7

The pin wouldn't go into the rod end, just into the bracket. The entire pin's length would be about the same as the thickness of the bolt head. I know with the pin only going through the thin bracket, there's not much support - but I think it would be enough to keep the bolt from rotating. The JB Weld holds the pin firmly in place and the pin pushing against the bracket provides the force to stop the bolt from rotating.

Where do you get $50 from? The GForce Trilink is $290. I don't have enough fabricating experience to make a custom one if thats what your thinking.

DriveFast7

iTrader: (1)

Quality large heims go for $45-80 each.

The one from my panhard was $48! and my tri link one is even larger.

Rx7carl

Yea Pete is being over optomistic on that price, or hes getting a helluva deal. You are correct however, Jim states the lateral play of his panhard to be like 0.02" or something like that. Negligible.

The_7

I thought of another idea to prevent bolt rotation. After some thinking I figured that the pin idea would hold up for a short while, and then the JB Weld would crack and the pin would work it's way out. My new idea is to fab up some simple brackets from sheet metal and bolt them up - make them long enough so the bolts are past the rod ends so they dont get in the way. This way they will definatly stay put and keep the bolts from rotating.

Lots of good info in this thread, thanks for the posts. I just installed the SE rear end with all the nylock nuts and my modded upper bushings. It was a tight fit to get the watts link main pivot piece in after everything else was installed, had to use the rubber mallot alot. Somehow I lost one of my rubber spring seats when I tore the car apart last summer so now I have to wait to put my RB springs in. The rear suspension will be all done very soon, then its off to work on the SE tranny .

Any links to info about the mumford link? Just curious - I found some pics but no detailed explanations of how it works.

peejay

$16 each for 27,000lb yield strength rod ends, times 2: $32
$1 each for jamnuts, times 4: $4
3/16" flat stock for bracketry: $6-8ish
(will also use some 1/8" that happens to be lying around)
1" square tube stock: $7ish

Still under $50... will also need some grade 8 5/8" bolts (have plenty on hand...) and some angle iron for the corners of the new floorpan / crossmember brace dealy (have plenty on hand...) and some sheet stock for the rest of the floorpan rebuild (plenty on hand: computer cases and old microwaves).

I'd rather fab my own, since the G-Force unit, besides being prohibitively expensive, has a big ol' bend in the middle. Seems like a Bad Idea when it comes to encountering wheelhop (under accleration *and* braking) on rouch surfaces.

Besides. It's just a hole in the floor, some bracketry welded to a couple crossmembers and the rearend, and a linkage rod. Piddly crap... much easier than fixing the bin rust.