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MG MGB GT V8 Factory Originals Technical - lowering rubber bumper crossmember
|If your car is fitted with a rubber bumper crossmember it can be lowered by fitting shorter front springs.|
Sadly they make the wishbones angle up and are stiffer.
Dropped stubaxles are available from the USA but are expensive.
A less expensive alternative is to fit a chrome bumper crossmember with the rubber bumper rack. The rack needs to be rotated about its axis, so it is lowered in the direction of the universal joint (easy to do)and the pinion shaft needs shortening by 2 inches and resplining.
This method ensures correct steering geometry, restores original chrome bumper ride height and is cheap.If you want any more info ring me on 01244 341484
|How do you know the rick is in the right place to stop bump steer|
|The standard chrome bumper cars at standard ride height do not suffer from bump steer. |
This is however one of the big problems encountered with lowering any MG by simply using shorter springs.
As bump steer tends to get worse at the ends of the suspension arc and with shorter springs you are nearing working at that point.
By rotating the rack about its axis you are not alterering any relationships within the suspension set up. Indeed the rack could be upside down without upsetting anything. It is only when you try to reposition the rack either forward or backward that problems occur.
I can help you locate the parts required if you wish 01244 341484
'The rack needs to be rotated about its axis, so it is lowered in the direction of the universal joint'
I am very interested in this because I am am a firm believer in the need to get some spring length back.
Could you please explain the first sentence a little more.
|Dick at MG Limited in Greenfield, WI makes a modified stub axle that drops the car to chrome height - just bolt them on your existing rubber bumper suspension beam!|
|What some do not realize is that a lowered swivel axle alone will usually result in additional bumpsteer, beyound the bumpsteer found when a car is lowered with springs, unless the rack is relocated or the steering arms modified, or flipped side for side and the tie rod end inverted. |
Remember that you've now changed the relationship between the locations of the control arms and the steering rack, and you need to address these changes to prevent initiating a new problem while trying to solve an old.
|greg fast - ?|
Greg has posted here before. He seems knows what he is talking about. I will not deal with Dick or discuss him on this BBS.
|David - understood but I still have the same '?' for Greg as I don't see what he's talking about - all the modified stub axle does is move the location of the hub upwards...it doesn't change the location of the steering lever, its relationship to the tie rod ends is the same....it doesn't change the kingpins' relationships with the upper trunnion or the lower control arms (and I'm using a complete custom coilover system designed by Hawkes Engineering over in the UK)....so, I can't see how it changes anything except ride height|
I've seen the "dropped" spindles that Dick supplies up at his shop. They are standard spindle/kingpin assemblies that have been modified. Material is removed from the top of the spindle and a like amount is welded (& machined) on the bottom. This has the net effect of moving the spindle upwards. The downside is the mount for the steering arm also moves up - hence the potential problem with bump steer. Dick addresses this by removing the tie rod ends and replacing them with aircraft style rod ends. They are attached with straight bolts after the steering arms are drilled out. He has to position them on the opposite side of the steering arm. This gets the geometry close to original. How close I didn't see since he had the parts sitting on the bench.
My personal preference is to install a chrome bumper cross member with the shortened pinion on a RB rack. Of course the pinion will need to be resplined.
|Tom....thanks for the explanation...I'm going to be visiting Dick in the Fall & will look that setup over...I went out to my setup last night & really couldn't see the effect of the modification (of course that might be because my entire setup is so custom))....as for 'bumpsteer' - I don't think normal to hard street driving will necessititate changing to Dick's aircraft tie rods (plus, normal driving would cause those aircraft tie rod ends to get contaminated - rain, etc)...if anything, I'll just heat mine & bend them a bit....I think we've gone beyond daily driving problems & have entered the world of F1 driving when we're concerned with this minute of an adjustment! (MHO)|
If you don't have it already, get a copy of Fred Puhn's book "How To Make Your Car Handle". My copy is about 25 years old, but I believe it is still in print. It has a LOT of info, particularly about cars and suspension of the vintage we're talking about. One item of interest is the method and fixture (it's dead easy to make) to check for and measure bump steer.
One item he stresses is: If you heat the steering arms to bend them they MUST be heat treated afterward to eliminate the real possibility of failure in use! It's not advisable to bend them cold either. This is a safety item and should be approached with extreme caution. At work we've had parts fail due to incorrect heat treating - it's not an issue to take lightly.
I want to keep the stock type sealed tie rod ends for the very reasons you mention. That's why I'll stick with the mix and match between new and old parts. Plus I can respline the steering shaft myself.
|Please excuse my misunderstanding, but could someone tell me in more detailed terms what "The rack needs to be rotated about its axis" means. I would really like to lower my 75 mgb roadster without causing any other problems, now or in the future, from doing so. This seems really interesting because I have a CB parts car that I could use the crossmember from. I also have a friend who can respline my steering shaft. Any information will be greatly appreciated. Thanks in advance.|
|What you need is something to hold the rack in place while the mountings are cut.|
Using a C/B crossmember.
What I did was to cut a temporary support using angle iron, cut the same length at the tube part of the rack between ally mountings. with the crossmember removed from the car bolt the rack in place then tack weld the angle iron under the rack so that when both mountings are cut the rack will stay in exactly the came position. Bolt the crossmember up to the car. Sit the rack in the angle support. now it can be rotated to get the correct angle and measure where the new spline needs to go. Get splines sorted then sit the rack in the angle support with splines going into U/J. now get the best position and tack on new rack bracketts. Remove crossmember and weld up and remove angle iron support. Bolt it all together.
It worked for me.
perhaps someone has a simpler method.
|My first attempt was to move the rack forward and down slightly but this was a disaster with horrendous bump steer. It was awful to drive.|
It needs to be done right.
The only downside is reduced clearance between rack and sump about 5mm on my factory V8.
|For Ian Buckley & T Johnson, Florida|
Mark has explained how to rotate the rack ok, but I suppose I know what he means. So in case anyone is still unsure here goes...
With a chrome bumper crossmember OFF the car and ANY MGB steering rack bolted to it (rubber or chrome bumper)cut an additional temporary support using angle iron and clamp it to the underside of the round tube part of the rack housing. Then weld a couple of pieces of angle iron between the piece you have clamped and the crossmember.
Remove the clamp.
Remove the rack, leaving the welded support in place
cut off the tops of the rack mounting pads from the crossmember.(Dont cut the whole of the rack mounting off just the bit where the bolts go through)
Now the rack can be 'rotated about its axis' ie downwards in the direction of the universal joint as it is still supported by the angle line you welded in place
Bolt crossmember on the car and place a Rubber Bumper rack on the angle line support
Rotate the rack downwards to line up with the U/J and cut the pinion to the correct length
Respline the end of the pinion
Tack weld on rack mounting pads at the altered angle
Remove rack and seam weld rack mounting pads
Then build up the steering and suspension as normal
I can help with the pinion resplining.Al 01244 341484
|much simpler to remove the rack & cut the mounting bases at the greatest angle possible with a hack saw. Use an electric drill & the correct size bit to angle the holes in the base so you can still bolt it to the mounts on the crossmember. Insert 1 bolt per mount with only a turn or two to locate the rack so you can measure how much to cut off. Once you have resplined or installed the new U joint (so many different ways to handle tis part), install the rack with all 4 bolts snug. Shim the rack as required. |
Excluding the U-joint deal, this is about 1 hour of work, & the biggest shim I have ever had to use was 1 AN washer. It may take another hour to get the shims right so your steering is free. I have done 4 cars this way with no problems & several hundred thousand miles on them.
This is an old Glenn Towery trick & he has done lots of cars & miles using this method.
No welding, no bump steer, simple hand tools.
|I'm not following logic !!|
Lowering car upsets all geometry!
The MG limited solution offers to greatest possibilty of restoring the geometry back to original!
I assume that all who have lowered car have considerd bump stops in the equation.
greg fast is my true name- great grandad Fast was with a group of Dutch Mininites who immigrated to the US in the 1880's and settled around Henderson and Grafton Nebraska. Grandad moved his family to Dallas OR in the '30's- at one point, if you were named Teason, Freizen, or Fast, you were ralated to 1/3 of the town.
You caught me in a mis-satement- "changed the relationship between the locations of the control arms and the steering rack."
What I should have said is "changed the relative locations of the outboard pivots of the control arms and steering rack" - minor error on my part, but mis-leading nonetheless.
As later posters have noted, this is in fact a problem. The distace between the upper and lower pivots on the kingpin scales about 8 7/8 inches, and relocating the steering arm an inch higher along this distance will cause a noticable increase in bumpsteer.
Perhaps a better description of one potential method to address this is to flip the steering arms side to side. This will put the taper on the steering arm facing down, rather than up. Using the stock tie rod end, mounting beneath the steering arm, you'll be a lot closer to maintaining the factory relationship.
Personally, not a fan of using spherical rod ends on street cars. A couple concerns that are unrelated to the thread.
Paul in Surrey-
There is no impact to factory bump stops, as the relationship of the control arms to front crosmember remains unchanged. Shock motion should remain as per the factory. Lowered spindles only move the swivel axle higher along the kingpin shaft (which causes the bumpsteer issue initially listed).
If the installer (and ultimately the owner, who must take responsibility for any changes he authorizes on his vehicle) thinks through the changes he/she/they make, lowering will not "upset all geometry".
They sky will not fall, the world as we know it will not end, and, while I'm not personally familiar with it, I'm sure that "The MG limited solution offers to greatest possibilty of restoring the geometry back to original!" is most probably an exageration.
Race shops and enthusiastice drivers all over the world recognise that the MG front suspension geometry does have limitations. A fine piece of work in 1962, it lacks enough negative camber to work modern tires well, and has inadequate negative camber gain in roll to afford best grip. Not talking just race rubber here, this is true for street tires also.
Initial post was to advise the unsuspecting of a problem previously unidentified in the thread (and I don't recall it on previous dropeed spindle threads.)
Long post, apologies for that, just got started and didn't know when to stop.
As one of the objectives is to keep track rods and upper and lower wishbones as near horizontal as possible then the modified king pin is best placed to achieve this if the track rods are also modified.
For road use a number of owners use the neg camber lower wishbones to give about 1.5deg neg camber, and the Hoyle front set up is adjustable.
The front bump stop will also drop with lowered springs, and in addition the spacer can swell. Competition bump stops are available which leave out spacer.
I accept and use lower control arms that are longer than stock to achieve initial negative camber. My premise is not that there is anything wrong with starting with these- I use them. But they are just a starting point.
Don't know or care about Hoyle's permutation- can't use it, seen pix, looks to me like they went half the distance (like almost every aftermarket MG suspension manufacturer- If I'm going to spend that kind of money, I want ball joints so I can get adjustable caster.) Don't have an opinion (hard to belive, eh?) howimpacts front suspension geometry as I don't know pivot locations
I also accept that lowered bump stops are available- aparently I was not clear in stating that these lowered bump stops are not required if you lower using the dropped spindle method. They are clearly required with lowered springs.
I do not agree that the premise needs or wants to be that keeping the control arms horizontal as viewed from the front should be the first best goal. I believe that statements such as that reduce the thought process involved in generating good suspension geometry.
What I am looking for is good initial camber (1/2- 1 1/2 degree negative, with an increase in negative camber gain in roll. Typically, a VERY short upper link would be required to achieve this is the control arms are parallel and horizontal. What I am looking for is the lower arm to droop toward the outside, and the inner arm to tilt up toward the outside. This generates a condition where as the car rolls in a corner, the lower arm first pushes the bottom of the knigpin away from centerline of the car, while the inboard pivot moves closer to verterline. Meanwhile the upper arm inner pivot is pushed away from centerline, while the outer pivot is pulled inboard due to the initial angle of the upper arm. What one tries to do is strike a balance so the increase in distance parallel to the graound on the lower arm is greater than the distance the inner pivot is pulled inboard- while the opposite condition occurs on the upper arm.
Layout the geometry of the inner and outer pivot locations while the car is at static ride height. Then rotate the car (and the pivot positions around the ceterline) while compressing the outboard suspension and see what happens to that nice initial degree or two of negative camber. I can see the outside wheel going 3-4 degrees positive on pictures of the race car (yes, I'm using bigger sway bars and shock valving and some other stuff that's not supposed to work.)
The basis for re-thinking my front suspension was that I want negative camber ALL the time, without starting with 5-7 degrees negative the the Macpherson Strut guys are compelled to.
So for me and the little green money pit.....
I've taken the front (CB) crossmember and pushed the body bounts an inch lower and sectioned a corresponding inch from the center of the crossmember. So without any other changes (except the need to rotate the rack to bring it's shaft into position vis-a-vie the coupler), I've bought an inch of drop. No geomtery change required, thank you very much. Cheating? or creative rules interpretation? Sanctioning bodies I run with- the tech inspectors appreciate creative thought process more than blindly following the crowd. And I'm stiil in techical compliance- Can't move the pickup points- and I haven't. Moved the crossmember instead
So I'm still too high, and negative camber gain in roll still sucks. So I grab a pair of MGA lower trunnions, and rather than use the MGA kinpin, I have 'special' pins turned up from some good induction hardenable steel. Using a stock swivel axle, I grab another 1 5/16" drop, but will need to flip my steering arms. These specials are an inch and a half longer than a stock MGB kingpin, thanks to the screw together nature of the MGA trunnion/kingpin.
So now I've bought over 2" drop w/ basically level lower control arms, upper arms are tilted up as you move away from centerline of the car. Good ride height, better negative camber gain in roll, and as for upper/lower control arm swing arm length- well, some of us spend time using Staniforth's "string computer" and bump steering on the shop (or in my case, driveway) floor.
Once again, way too long and dry. Apologies to all who need to scroll through.
Once again, on re-reading, I replaced a mis-satement- with a new, improved mis-statement- "changed the relative locations of the outboard pivots of the control arms and steering rack"
What I really should have said is "changed the relative locations of the outboard pivots of the control arms and outboard pivot of the steering rack- the tie rod end". If I mis-state often enough, sooner or later I'll stumble on the truth.
|<<Perhaps a better description of one potential method to address this is to flip the steering arms side to side. This will put the taper on the steering arm facing down, rather than up. Using the stock tie rod end, mounting beneath the steering arm, you'll be a lot closer to maintaining the factory relationship.>>|
I like this idea and may try it. Will it work w/14" wheels?
I lowered my '79 MGB w/ springs in the front & blocks in the back. The bump steer is quite noticeable. I worry that my wife may not be able to hold the line on a bumpy curve.
Thanks for the info, Greg. Great thread.
"The installer (and ultimately the owner, must take responsibility for any changes he authorizes on his vehicle) who thinks through the changes he/she/they make, lowering will not "upset all geometry". "
I cannot take responsibilty or liability for the design of a modified suspension system.
That being said, you have 2 q's here
1) Will flipping the steering arms work for me and
2) will they fit 14" rims
1) I've never tried it on a stock suspension lowered w/ springs only. You can assemble it this way and measure the distance between the lower inner pivot and the upper inner pivot, and measure the distance between the lower inner pivot and the swivel where the tie rod come out of the steering rack. Then measure the distance between the outer lower kingpin pivot and the outer upper kingpin pivot, and measure the distance between the outer lower kingpin pivot and the swivel in the tie rod end.
Divide the distance between the lower iinboard pivot and the steering rack swiver pivots by the distance between the upper and lower pivots, for both the inner and outer pivots. The closer these numbers are, the lower the bump steer.
2) I run 14" Panasports w/ alot of offset. They fit this wheel, your wheels may vary
So spending way too long to answer, the answers are:
1) I don't know
2) I don't know.
All suspension changes need to be thought out to predict impact, and take appropriate countermeasures to reduce consequences of negative side effects.
It's unortunately impractical to ask someone unfamiliar with the details of your specific suspension what happens when some change is made. I unfortunately have neither the time or resources to investigate details and recommend changes. Much as I might want to be an internationally recognized suspension guru, I'm just a guy working 9-5 who tries to science stuff out during his lunch break.
Sorry I can't be more specific, but it would be improper for me to suggest a detailed plan. I can only speak in generallities about this stuff and hope to get people look at options for themselves
Are you in race mode?
Static camber is available to 3deg
For UK road use lowering car 2ins will probably give problems with speed humps.
Two other thoughts on set up are, adding neg camber under braking may not be advisible for a road car, and there would be an increase in height of front roll centre. My prefernce would be to use Mumford link to reduce rear roll centre.
Am I n race mode? Well, I do race an MGB, but the points I'm trying to make on bump steer are applicable to both race and street cars.
With a recent increase in interest in handling street cars in the US (the so-called g-machines, a really stupid title the US hotrod press has assigned cars with fat tires at both ends), there has been an increased interest in cars that can make the turn at the end of the quarter mile. I'm putting a set of tall spindles on my daily driver (an el Camino to those familar with now obsolete GM models) to give the fronts a chance to grip in a turn.
The changes previously described re xmember and kingpin changes, yes, I'd make the crossmember change to a street car and use a dropped spindle, probably not the special kinpin (cost me too much for moderate gain.) I'd make further modifications on street x member that I can't for the race car, moving the lower inboard pickup higher, and probably need to relocate the steering rack for bumpsteer attenuation.
But that doesn't impact my street MG's because they are an MGA and an MGC. The hot street MGB is still a pipe dream, either an FI 3.5 rover V8, or a turbo FI 18V. Maybe buld the 18V with a twincam head. Real easy to plan these things when you're not paying for them.
race mode or street? don't really know if there's a difference, except for rules conformance. And cost.
Static camber arms available up to 3 degrees- no big deal. you can extend the lower arm and get as much as you want. But that costs you when you clamp on the brakes and the outside of you tread is a quarter inch off the ground. The key is getting and keeping 1/2 to 1 1/2 or so through the entire range of suspension motion. Impossible to achieve, but relocating pickup points will get you closer. Also, no one makes an adjustable replaceable sliding bush for varying camber in the lower control arm like I want. (Yes, i know there are offset bushes. Another tirade for another thread.) So once again it's off to the lathe, mill, and welder to get what I want.
Some may find the parodox of this interesting, but cars dropped 3-4 inches are no uncommon in SoCal. Considering the fact that we have huge trenches at every third intersection or so to drain rain runoff (swear to God- first time it really rained after I moved here 20 years ago, there was water coming UP OUT the storm drains and flooding the streets). We all slow down for the trenches, but they still feel like they'll rip the suspension right off the car. These lowered ride heights give us problems, but we do it anyway. Some of us have spent a little too much time out in the sun.
Regarding negative camber vis-a-vie braking- not sure I understand what you mean. Too much negative camber is too much negative camber, whether braking of turning or going straight. To much will reduce grip, in braking or turning. That's why you want to keep the camber numbers low. Starting with huge amounts of negative camber is only just OK on cars with suspensions like Mac Struts that get all compromised when you lower and try to get good tire camber when the car is tipping in a turn. So I guess- OK, I guess.
Also unclear where you're going on your comments about front roll center. Tire camber alone should have no impact of roll center height- that's all based on the orientation of the upper and lower arms, where the instant center of the control arms is (I can't believe that's the correct way to say that, but it sounds less wrong than a couple other ways I tried it) and the line between the IC of the contol arms and the center of the contact patch. Generally, lowering the car, or my stupid kingpin trick, will lower roll center, which compells the use of a bigger front bar because of the greater lever arm between RC and CofG. So again, uh OK.
All my jawboning so far has been addressing the front suspension. A well thought ou panhard or watts will work OK on the rear, but if you use a mumford I'd anticiplate the need for a larger rear swaybar as they (mumfords) are generally used to stick the RC beneath the ground. I personally like mumfords, a more complex but but gearhead cool approach to rear RC location. Like em but don't use em. For race cars, i generally have the axle housing bent to stick in 1/2 degree negative camber, on a street car I'd just check it to make sure it wasn't too far out of zero and maybe add a little toe to keep the rear on the straight and narrow. But only if I was putting some stickies on it- for most tires i'd probably blow it off unless there was a real problem.
But hey, remember I'm the one who sits out in the sun too long. Enough for now. Time to hit the tanning studio.
The Frontline front set up includes adjustable camber, I believe at bottom inner wishbone (midget on top trunnion). They also sell a rear traction control link (Mumford link) which will drop rear roll centre approx 4ins, all being used on 5.0l road going V8 about 350+bhp.
Hoyle can supply a rear IRS system based around Cossie, to match front set up.
From your description of top and bottom wishbones the roll centre would be higher and certainly lowering car reduces front roll centre but not rear.
At the moment with a large bore exhaust, I have max ground clearance of 2.5ins using Mikalor clamps as the standard were being ripped apart by speed bumps.
|My last post on this topic|
Looked at frontline's website, didn't see what you described regarding adjustable camber lower control arms. No information, no comment.
Also not particularly interested in IRS's, in addition to them being OT (and I know I've drifted and apologise for same.)
I'm not going to argue about roll center height- My drawing using my custom 1-off pieces shows a lower roll center- If you can produce drawings that show my front suspension layout is in error, fine.
Generally, the rear roll center height is at the axle location on a line drawn between the spring pivots- installing a spring with a lower rate or less arc WILL lower rear roll center height as the height variation between the front and rear pivots is reduced. But again I'm going OT....
What constitutes adequate ground clearance for a car is up to the end user. I am unfamiliar with Mikalor clamps, so again no opinion or comment.
Unfortunately Frontline site has not been updated for a while, and has no information on BV8 products which are sold as Frontline Costello. Adverts appear in Safety Fast mag, but Tim is always working on new bits such as K conversion kit for B and a redesign of rear.
|Can I come back briefly to the two gents who have offered solutions to rotating the rack when doing a chrome bumper conversion.|
Al - I understand your method more or less. I believe Chris Betson from Octarine Services has used this technique. I know the steering shaft has to be shortened. What I'm not clear about is which half you are shortening - the upper or lower. If you leave the upper alone and shorten the lower, doesn't the U/J foul the cylinder head or manifold nut?
Jim Stuart - your method is to alter the rack itself. The way I read what you wrote is that the first thing you do is to slice the rack mounting off at a steep angle. You then elongate the holes a little, remount the rack "so you can measure how much to cut off". How much to cut off what? You've already cut the rack mounts. With this method, doesn't it matter that the contact face on the rack will no longer be parallel to the crossmember mounting points?
I would be glad if these two guys can clear this up for me. By the way, is Al in the UK or the US?
|This all started obout lowering you rubber bumper car.If I am on a 180 degree freeway ramp how fast would I have to go to roll a crome bumper car and a stock height rubber bumper car. Is there really that much difference in the two. Sorry for my ignorance in this matter but I have heard for ever lower is better. I just want to know how much better. If I can go around that curve doing 50 in one car an 70 in another then I am ok with the stock rubber bumper. DBW.|
What needs to be cut off is the steering shaft, as you are now using the rubber bumper rack in what is, essentially, a chrome bumper car. Since the suspension has been lowered by the crossmember swap, the rack is now closer to the steering column by about 2". The short leg of a right triangle has been shortened, changing the length of the diagonal.
Not sure what you mean by the contact face of the rack, but if you mean that the rack has been rolled a bit, remember that the rack is still parallel to the crossmember, the tie rod ends rotate so there is no change in that area, & the rack is not moved forward or back, or up or down except by the smallest fraction, say 1/4". The angle of the steering shaft has changed, but that does not affect the suspension in any way.
|Check this out, lowering A arms for RB cars with camber adjustment|
Can you elaborate? The pic doesn't say much. BTW, I saw you guys in Tallahassee and you were great. I'm a huge James Gang fan, too. When's the next tour?
|Those arms were design to lower the RB cars, at the moment we are testing them all over the US on different cars. The Arms lowers the car 11/2 inches and also incorporates camber adjustment.|
Once we tally all of the inputs from several people who have install them on their cars or customer cars, we will then be able to implement their inputs into the product.
We are just testing the waters. thanks for the plug.
This thread was discussed between 28/03/2004 and 08/04/2004
This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.