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Honey monster thanks for that sterling effort you do deserve a prize! Your also right about the good advice in this thread (thanks guys) i knew you could all help. HM as you also said its the designing and installing that needs to be done correctly and your bang on again - i have know dought i could fit the stuff its just a case of fitting it right. I feel another MS paint based diagram coming up  |
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1mzmk1
Part of things
Posts: 205
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An interesting read! I have a 4 door chevette but i'll be using the usual manta axle as i don't intend huge amounts of power. However, i also have a toyota kp30 which i'll be fitting a different axle to, and had looked down the same routes mentioned above but i really don't want to cut the floor about. I then discovered the Asymmetric 3 link setup. As far as i can see it has major benefits in being able to fit the links to a normal road car, plus the geometry itself if set up correctly can cancel out all driveline torque. It requires very careful planning by the looks of things, and the single top link is subject to high loadings so the mounting point on the floor must be very rigid. A brief read here: home.earthlink.net/~whshope/id16.htmlI did find some more info a few months back when i looked into it but cant remember where now. I'm hoping to test the theory on the toyota when i eventually get around to it! Andy |
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hilux
Part of things
Posts: 12
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Think I would 4 link and panhard rod it. Standard bottom mount and boxs in the floor by those chassis rails and your done. Me and a mate (royal we) are gonna put a beam axle in a golf and use the stock mounts at the bottom and after the tank is out there is loads of room for top links or even an a frame. You deffo like has been said need rose joints at at least one end. Also an easier way of having adjustabilaty especially if you rose joint both ends with left hand thread one end and right hand the other. Anyone know the legalities of rose joints on a road cars? Do you need dust covers? Agree entirely especially if the rose joints on the rear of the trailing links are adjustable, you can set the diff nose angle perfectly as against fixed length bars - I`d bush the fronts and rose joint the rears but there are rose joints and rose joints - don't skimp on them and fit covers Same with the panhard rod. |
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a few of the pics you have got there are from retropower I see,I work there,best thing to do is give nat a bell for a chat,I'm shure he'l help u out or even do the job for you  |
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Well you will mess with these cars....
Mk4 golf gttdi highline. Mk2 golf 1.8T
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Hi Gaz thanks I was planning to give you guys a call as there are some other bits I want to talk about too. I love your coupe btw |
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Cool!,he's just about got it rebuilt for big horsepower! ;D,fitting dry sump ect,running out of space in the engine bay!! ;D
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Well you will mess with these cars....
Mk4 golf gttdi highline. Mk2 golf 1.8T
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What turbo's he running now? I will be able to help if hes looking to change?
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Its a GT35 "equivalent" (but I can't remember the housing and wheel specs I'm afraid) from our friends in the far east. keep twisting his arm to spend a bit more on it but he keeps pointing out that they don't seem to go wrong.
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PS re. rear suspension. There are a million permutations, and a million people claiming "theirs" is the best!
I won't claim anything, BUT I know of plenty of track record holding cars that use very basic 4 bar and panhard rod setups, and even a couple using 3 bar and half width panhard rods, which is even less geometrically correct!
Re. panhard rod and roll centre height. To my knowledge the only live axle lateral location setup that is in common use that allows rear roll centre adjustment is the mumford link. While this is VERY useful on extremely low circuit cars where the CofG is much lower than the axle centreline, its less useful on a road car where the couple around the cofg and roll centre is much less.
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Thanks for the reply Retro power i will try and give you guys a call later ref the above although i'm very busy right now
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Re. panhard rod and roll centre height. To my knowledge the only live axle lateral location setup that is in common use that allows rear roll centre adjustment is the mumford link. While this is VERY useful on extremely low circuit cars where the CofG is much lower than the axle centreline, its less useful on a road car where the couple around the cofg and roll centre is much less. The point where the panhard rod intersects the vertical axle centre line is your roll centre (or thats how it seems in my head!). Therefore you can easily set and adjust it by adjusting the panhard mounts. Roll centres are crucial in any car that wants to handle well... EDIT: You may be getting confused with the fact that the mumford link doesn't have a physical roll centre and therefore it can be anywhere (ie, below ground) which makes it useful on cars with low CoG. Its quite common on clubman racers. Nice little write up on it in last months Racecar Engineering. |
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Last Edit: Nov 9, 2011 23:30:23 GMT by Adam
1997 TVR Chimaera
2009 Westfield Megabusa
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CIH
Posted a lot
Posts: 1,466
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Nov 10, 2011 14:10:09 GMT
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Personally I'd be more interested in making sure it's in and located straight than roll centres and the like.
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Nov 10, 2011 14:30:14 GMT
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Re. panhard rod and roll centre height. To my knowledge the only live axle lateral location setup that is in common use that allows rear roll centre adjustment is the mumford link. While this is VERY useful on extremely low circuit cars where the CofG is much lower than the axle centreline, its less useful on a road car where the couple around the cofg and roll centre is much less. The point where the panhard rod intersects the vertical axle centre line is your roll centre (or thats how it seems in my head!). Therefore you can easily set and adjust it by adjusting the panhard mounts. Roll centres are crucial in any car that wants to handle well... EDIT: You may be getting confused with the fact that the mumford link doesn't have a physical roll centre and therefore it can be anywhere (ie, below ground) which makes it useful on cars with low CoG. Its quite common on clubman racers. Nice little write up on it in last months Racecar Engineering. Not confused, as you say, the panhard rod mounts set the roll centre height, but although you can chop them and move them about, or even use an adjustable rod mounting tower, you then run into problems with sideways axle movement as you get further away from a "sensible" axis. The mumford link allows lots of adjustment without axle centring issues. Anyway, as somebody else has now put, all fairly irrelevant in the real world and a road car. Its amazing what works when it is very far from ideal! Having spoken to the "asker" of the original question, the question was really about ability to handle a given amount of power, in a sensible package for road and limited trackday use, and to that end, a little "uprating" of a combination of std manta and kadett/chevette rear axle parts will be plenty strong enough and do the job very nicely, and a lot more cheaply than any of the upgrades that are possible. Whenever road use is the main target, and our roads are now pretty horrendous in terms of bumps, then IRS has a huge benefit. on a track this is not so much the case, as with IRS the overall weight "usually" goes up, (though obviously with reduced unsprung weight). While I have now fitted IRS to a few cars which were originally fitted with live axles, to do it "right" and not just chuck it in is a little time consuming, and not very cheap if you are paying for the hours! |
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Nov 10, 2011 15:39:21 GMT
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Thought is just chuck in the word woblink, being the ultimate in solid axle sideways location.
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muttley racing ftmfwmf
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Nov 10, 2011 17:12:37 GMT
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First off let me say a big thanks to Nat at retro power for thaking the time to run through all of what i wanted to talk about as it was very helpfull and has potentially saved me time and money at this stage.
Further from this conversation it appears i may be able to get away with fitting a manta A axle instead of the scimitar axle (and the 4 link) that i have planned on as long as i don't hike power past 200 ish hp, so i will try this first.
To go back to my original query i basically wanted to know how to go about setting the car and axle up to fit the 4 link system accurately. As this seemed the best way to get the power i intend to run to the road.
I understand now that there are many ways to secure a live axle to the car however the 4 link seemed the most straight forward and available plus its proven etc etc (let the debate continue on that one)
So to confirm (and please correct me if i'm wrong), the axle nose should sit up at around a 3 degree angle when the car is at ride, both the bars should be parrallel to each other and the same length (on the set up i was looking at) now do the bar 'cages' sit at a 90 degree angle to the link bars on the axle? And finally would you fit the link boxes first once their position was worked out and at what angle would they be positioned - parrallel with the links?
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Nov 17, 2011 15:23:31 GMT
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This article explains the workings of the 4-link suspension and the tuning methods used to maximize its performance under various track conditions. This information applies only to 4-link rear suspensions having links floated on the rear axle (via birdcages) with all links running forward.
The 4-Link Difference Upper Links Lower Links Indexing AFCO Springrod AFCO Clamp Brackets
The popularity of the 4-link suspension is due primarily to its ability to let the race car turn freely in the middle of the corner without compromising forward bite. To understand how a 4-link can be made to provide such handling, you must first understand a few basics about rear suspensions.
Realize that you can increase forward bite on any type of rear suspension by angling the trailing arms upward toward the front of the race car. Trailing arms mounted in this manner cause the rear tires to try to drive underneath the chassis as the rear axle pushes the race car forward (See illustration 1). As a result, the loading of the rear tires (during acceleration) is quickened and forward bite is enhanced.
Illustration 1.
There can be a handling trade-off, however, to the forward traction gained by running the trailing arms upward to the front of the race car. During chassis roll, trailing arm/s mounted upwards will cause the right rear tire to move rearward (until the arm/s reach a level position) and the left rear tire to move forward. The condition is referred to as "loose roll steer". (See illustration 2A.)
Loose roll steer causes the rear axle to steer towards the outside of the race track. If excessive, loose roll steer can cause a loose handling condition that negates the benefits of the forward bite gained by running the trailing arms upward towards the front. However, the right amount of loose roll steer can help a race car to turn the corner correctly. At best, any trailing arm arrangement is a compromise between forward bite and roll steer.
The 4-Link Difference
A well designed 4-link provides good forward bite and the proper amount of roll steer. The two most critical factors to the performance of a 4 link suspension are the link lengths designed into the suspension and the angles to which the links are adjusted. The key to correctly designing and tuning a 4 link is to understand the significance of these two factors.
Upper Links
We stated earlier that trailing arms mounted upwards to the front of the race car enhance forward bite by using axle thrust to quicken the loading of the rear tires. Primarily, we use the upper links on a 4-link suspension to enhance the forward bite. A good starting point for upper link angles is from 15º to 18º on the right and 24º to 26º on the left provide good forward bite. A good starting point for both links is 15º upwards (to the front).
Be aware that trailing arms angled uphill too steeply can hold the chassis up during acceleration which can reduce the effectiveness of the shocks and springs. This condition will cause loose handling-especially on rough race tracks. Keep in mind that trailing arm angles can become excessive if the rear of the chassis lifts a lot during acceleration.
The length of the upper links should be at least 17" . We can reduce loose roll steer by making the lower links shorter than the upper links (more on this later). If the upper links are shorter than 17", the lower links have to be extremely short to minimize loose roll steer. But extremely short links change their angles radically whenever the suspension moves. When the rear links are too short forward bite and roll steer are overly affected and handling becomes inconsistent.
Lower Links
We can use the lower links of a 4-link suspension to help offset the loose roll steer tendency caused by the steep angles of the upper links. The following examples and illustrations should help you to understand this important function of the lower links. You should pay close attention to how the lower link adjustments change the paths traveled by the bottom of the birdcages during chassis roll. Keep in mind that any change to the path traveled by any trailing arm will affect roll steer.
For example, in illustration 2A, both the top and the bottom links move the birdcages (and the rear tires) rearward on the right side and forward on the left side during chassis roll. This action will cause loose roll steer.
We can reduce loose roll steer by lowering the bottom links at the chassis. You can see how this adjustment works in illustration 2B. We've lowered the bottom links to a level position and now the bottom of the right side birdcage moves forward during chassis roll instead of rearward as in illustration 2A. On the left, we have reduced the forward movement of the bottom of the birdcage. As a result, loose roll steer is reduced.
Basically, we've position the bottom links to counteract the forward(L.S.) and rearward (R.S.) movements of the birdcages caused by the upper links. As a result, we reduced loose roll steer. We can reduce loose roll steer further by lowering the bottom links further as shown in illustration 2C. Notice how this adjustment, positioning the lower links 5ºdownhill, causes the bottom of the right side birdcage to move forward more during chassis roll than in illustration 2B where the links are level. On the left side, the bottom of the birdcage now moves rearward (until the link reaches a level position) instead of forward as in illustrations 2A and 2B. Consequently, a further reduction in loose roll steer results.
Generally, bottom link angles from 0º to 5º downhill (to the front) are used to help control loose steer. Some forward bite may be lost when the bottom links are lowered but the effect on forward bite is usually minor relative to the overall handling improvement that is realized by reducing loose roll steer.
Another method used to reduce the loose roll steer of a 4-link suspension is to shorten the bottom links. Notice, in illustration 2D, how the shortened bottom link pulls the bottom of the right side birdcage forward during chassis roll more than the longer links in the other illustrations. The bottom of the left side birdcage does lose some of its rearward movement because of the shortened bottom link. But since left side birdcages typically move down much less than right side birdcages move up during chassis roll, the overall effect, when shortening the lower links, is a reduction in loose roll steer. However, if the left rear of your chassis hikes up during cornering, loose roll steer may increase whenever both bottom links are shortened!
We could reduce loose roll steer even further by combining the long bottom link arrangement of illustration 2C on the left side and the short bottom link arrangement of illustration 2D on the right side. The preceding paragraphs should help you understand why.
The length of the bottom links are dependent on the roll steer and traction characteristics desired by the chassis tuner. For most track conditions, bottom links 2" shorter than the upper links work well. Short links( from 3" to 4" shorter than the upper links) generally work best for tight, flat race tracks or on any track where the chassis tends to be loose. Long bottom links (equal in length or no more than 1" shorter than the upper links) work best for fast tracks or on any track where the chassis tends to push. You should use the information in this article to determine the correct link lengths for your application.
However, a proven 4-link arrangement includes 15 1/2æ bottom links, mounted 5º downwards to the front, coupled with 17 1/2æ top links, mounted 15º upwards to the front.
Indexing
A 4-link birdcage rotates or "indexes" on the axle tube whenever the suspension moves (unless both upper and lower links are equal in length and parallel to each other). Indexing is greatest when there is a lot of length and/or angle difference in the upper and lower links.
Typically, indexing causes the coil-over mounts, if located on the front of the birdcages, to rotate against the shocks and springs during suspension bump (compression) movement. As a result, the springs and shocks are compressed from both ends at once and the suspension becomes very stiff. (Try to bounce the rear of a car with a 4-link rear suspension).
During chassis roll, indexing loads the right rear tire and unloads the left rear tire and wedge is reduced (40 lbs to 80 lbs is typical!).
Indexing can improve driveability by keeping the race car flat in the corners. However, indexing can cause the rear suspension to be too harsh on rough race tracks. When selecting springs for your 4-link, you should keep in mind the effect that indexing has on suspension stiffness.
AFCO Springrod
The AFCO Springrod (see the AFCO Catalog) is used to replace the right side upper link when tighter handling during acceleration is desired. The operation of the springrod is simple. During acceleration the springrod compresses and allows the right rear tire to move forward. This movement steers the rear axle to the inside of the track and tightens the race car.
When the springrod compresses it causes the birdcage to rotate away from the right rear spring (if the coil-over unit is mounted ahead of the axle). As a result, the right rear tire loses some of its load (the left rear tire gains load) during acceleration and handling becomes tighter off the corner. The AFCO Springrod can provide a significant handling improvement.
AFCO Clamp Brackets
AFCO Clamp Brackets (see AFCO Catalog) are used to mount the coil-over units directly to the axle housing. When clamp brackets are used in front of the axle, axle wrap-up during acceleration causes the rear axle & chassis to separate. The rear axle (and tire) are forced towards the race track.
Clamp brackets are sometimes used on short, slick tracks to improve initial forward bite. Mounting the left coil-over unit ahead of the axle (on a clamp bracket) generally tightens corner handling. Mounting both coil-over units on clamp brackets and ahead of the axle can improve forward bite on stop and go or slick race tracks. On extremely slick race tracks, you can tighten overall corner handling by using clamp brackets to mount the left coil-over unit ahead of the axle and the right coil-over unit behind the axle.
Suspension movement usually increases when the coil-over units are taken off birdcages and mounted to clamp brackets (since there's no longer any indexing of the springs). Consequently, it may be necessary to increase rear spring rate when making this adjustment.
You should keep in mind that any loading of the rear tires caused by clamp brackets during acceleration will be accompanied by an unloading of the rear tires during deceleration This unloading can upset the race car upon corner entry -especially when both coil-over units are positioned ahead of the axle and attached to clamp brackets. You may be required to make chassis adjustments to correct any corner entry handling problems caused by clamp brackets.
Final Points
The 4-link is a relatively complex rear suspension that is very sensitive to adjustments. A link length change of 1" or a link angle change of 2.5º can make a noticeable change to handling. When designing or tuning a 4-link, it is important to understand the relationship between link lengths and angles and how the relationship affects roll steer, indexing & drive angles.
As we stated earlier, the 4-link is a fairly complicated rear suspension. We hope the information in this article, combined with your efforts, will provide you with an AFCO advantage!
Tuning Tips • Increasing the upward angle (to the front) of any link will enhance forward bite and increase loose roll steer.
• Decreasing the upward angle (to the front) of any link will decrease forward bite and reduce loose roll steer.
• Suggested angle adjustment parameters:
• Upper Links: 20º to 28º (upward) RS 10º to 18º (upward) LS
• Lower Links: -5º to +5º
• You may need to reduce link angles when using clamp bracket/s and/or when running on rough race tracks.
• You may need stiffer rear shocks when using clamp brackets (to control wheel hop).
• You can correct roll steer handling problems by leading or trailing the right rear tire (or left rear).
• Shortened bottom links (especially R.S.) tend to reduce loose roll steer and tighten deceleration handling.
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Nov 17, 2011 16:07:14 GMT
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Nov 17, 2011 19:27:57 GMT
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cheers mate. i had a go lol I'm not good with computers
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Nov 25, 2011 12:03:47 GMT
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Chambers1984: That's a good article. It's amazing how complex a four link system can get when you start adding rotating birdcages onto the axle. The thing with the four link system is that lots of clever people have been optimising them for their own type of motorsport (dirt cars, nascar, rally cars, etc) for years, so all the stuff you can find out and read can get a bit bewildering. Retropower is right - everyone thinks theirs is the best system! Countvauxalot: If an uprated stock system with Manta A parts will cope with the power, that's got to be the easiest thing. If not, I'd plump for a four bar and a Panhard rod. Perhaps not theoretically the best, but realistically pretty good. And when you get bored with it, you can always experiment with Watts or Mumford linkages later. (as an Engineer, I'd like it if you made all 3, and did back-to-back tests around a track - proper data!) In answer to your other questions: - Yep, if you get the bars parallel to each other and the ground, you won't go far wrong.
- Fit the axle brackets such that the centreline of the mounting holes is perpendicular to the bars (and therefore the ground)
- The holes in the chassis/body mounts should be parallel to the holes in the axle (ie, in this case, perpendicular to the ground)
- If you're buying link boxes with pre-drilled link bar holes, that kind of sets where the rest of the box will be.
- If it was me, I think I'd do what Ford did with the Works Mk2 Escorts and make a separate bracket for the front of the links - basically you hack holes in the floorpan to take this and to let the link bars through. Measure and align the bracket properly and weld in place.
- Then you can move the axle to the highest position it can ever be, allow an extra inch above it for clearance and then make templates for the shape of the link boxes to clear this, cut from steel, weld in place, job done.
Diff angle: There seems to be a lot of confusion about this. The suspension doesn't care what the diff angle is set to. You're setting the differential angle to ensure the UJ's in the propshaft can work properly and don't bind up as the suspension moves. Someone can tell you to install the axle with the nose pointing down by 3 degrees but they may as well tell you to point it at the moon - they don't and can't know: unless they happen to have the same engine and gearbox installed into the car in the same way. - That article I linked to before (http://www.carcraft.com/howto/91758/index.html) was a bit wordy, but it's right.
- This picture spells it out: www.carcraft.com/howto/91758/photo_08.html
- The angle of the output shaft of the gearbox needs to match the angle of your diff pinion shaft. That would be the perfect case, but a tolerance of a degree or two would be close enough.
- The propshaft doesn't have to be inline with your gearbox and diff pinion shaft. In fact, I've heard it's better if the propshaft isn't inline.
- As you're putting a new engine and gearbox in the car, the angle of the gearbox tail shaft is a bit of an unknown. So you'll have to measure it. Difficult to do this on a gearbox, so stick an inclinometer upright on the back face of the bell housing (or if you're a cheapskate like me, you'll use a spirit level, a tape measure and some trigonometry) and measure the angle. This is the starting point of what to set your axle to.
- Theoretically, you'd set the vertical face of the diff flange to match the angle you've measured from the bellhousing. But, in the real world, when you apply torque through the rear wheels, the axle twists, tending to angle the nose of the diff upwards. This is why people set the nose of the diff down by 2-3 degrees (from the measurement from the back of the bellhousing) to allow for this.
- This axle twist is worse for leaf sprung suspensions. With a four-linked axle, there's only going to be a bit of twist (basically taking slop out of joints and deforming the small rubber bushes at the link bar ends), so I reckon two degrees down from the measured angle will be fine.
- For those interested (or suffering from insomnia) lots of scary techy propshaft information at Bailey morris website: www.baileymorris.co.uk/technical5.asp
Countvauxalot, sorry if it sounds a bit complicated. Some people do just take it all for granted and just angle their diff up towards the gearbox. They might get away with it too, but either that's through luck, or the fact they only do a few hundred miles a year. Having seen your excellent work on the manifold, I figured you'd like to know the correct way to engineer the axle installation. |
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Nov 25, 2011 20:12:48 GMT
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[/li][li]The angle of the output shaft of the gearbox needs to match the angle of your diff pinion shaft. That would be the perfect case, but a tolerance of a degree or two would be close enough. [/quote] This is what i've always been told, although i would describe it as the U/J's on the propshaft should be at the same angles. Just incase you have a 2 piece propshaft on your car |
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