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MG MGB GT V8 Factory Originals Technical - Antitramp bars

Gents
I'am in the process of building V8 conversion and considering the rear suspension. I have done a lot of research and considering antitramp bars/improved axle location. My leafs have lower profile and standard dampers.
The design of antitramp (type) bars, that are available, in my opinion, would tend to stop the front section of the leaf from functioning properly,, causing the axle to tend to rotate, as the rear shackle swung forward or back. The same would be true of radius rods. 'Perhaps I know enough to be dangerous'... can anybody explain the functionallity.
Cheers
b bourne

The basic function of anti-tramp bars is to keep the front section of a leaf spring from bending into a "s" shape as the pinion tries to rotate upwards. I think the best design is one where the bar is of the same length as the front half of the spring from the center bolt to the front mounting eye, and is parallel to the a line drawn between the front spring mounting bolt and the center of the axle housing. This basically makes two parallel bars that will move together without causing any rotation of the axle, yet the lower bar will keep the bottom of the axle from moving forward, and the spring length will keep the axle from moving rearward, so no effective rotation can happen and the spring doesn't bend upwards. Effective bars for a street car are pretty easy to fabricate. Weld tabs from the spring mountings and drill for bolts (same size as the rear shackle bolts), making sure that the holes are directly under the front bolt and the center of the axle. With the car at rest and normal ride height, measure the distance from the front bolt to the rear bolt and build a bar from around 1" heavy wall tube with sections of larger tube on each end to take either rubber or poly rear shackle bushings. The bushings allow for some compliance to reduce any ride harshness but will still eliminate and axle rotation.
Bill Young

The function of the antitramp bars is not primarily to prevent spring compression (which it does), but to stop the axle rotating opposite to the wheel, bending the spring upwards, and pulling the axle forward. In a series of jarring jolts. A sensation I am all too familiar with. Ironically the best car for V8 conversion is the rubber bumper, which usually needs to be lowered to chrome bumper height, via the use of blocks, which exacerbate this problem because of the increased leverage!
I initially thought the antitramp bars would act like high field levers (if you are into sailing you'll know and love these) loading huge forces (tons) into the spring mounts. It took me a while to work out, but because the antitramp bars are located below the bottom of the spring, as the spring moves up, the antitramp mounting point (below the center of max' curvature of the spring) rotates/moves away, just a bit, enough. Draw some diagrams and it becomes clear (like all obscure things)
However, I will not fit antitramp bars. I am thinking that is you allready have coil over shocks and two antitramp bars in place then if you fit a third bar (centre, on top of the diff') you have a trailing arm suspension. Much superior.
peter

Anti tranp bras or traction bars in the US.
Keep in mind that traction bars will also stiffen the rear and thus creating a loose handling car when corner.
Traction bars are for stright line and lots of torque, more torque than we have in our B's
A mcuh better way and one that we use on all of our road racing cars, where you need traction out of the apex on a turn.

Find an old set of MG leaf springs, removed the first or second leaf from the master leaf (master leaf the one with the bushings) cut the rear section just pass the center hole and enough to cover the spring pad.
Removed the spacer leaf (the smallest) and install the cut down leaf in place of the spacer leaf. This leaf will not increase the spring rate, but it will keep the front of the spring from flexing and increase traction, if more is needed add a leaf.

No welding or fabricating. See the V8 news letter archives for photos, I sumbmitted them at the last year V8 meet.

I gladly send you the pictures via e-mail if you would like.
Bill Guzman

Bill.

Like you, I do not like the design of the anti tramp bar kits that are on the market. The fact that you have a leaf spring that lenghtens in bump that is restrained by a fixed length radius arm, imputs a conflict into the suspension which as you say, will produce undesirable effects.

I have seen an alternative to the fixed radius arm situation whereby the front of the bar is attached to the bottom of a pair of trangular bell cranks, the pivot point is the front leaf spring support bolt with a further bush resting on the top of the leaf spring so as the spring compresses the the bush on the spring is raised the bell crank rotates to the rear effectively lengthening the radius rod. The radius rod can be tuned by having a rod end installed at the chassis end.

Your solution sounds much simpler and would be pleased if you could e-mail me a copy of your design

To kevin477jackson@btinternet.com

Thanks again,

Kevin.
Kevin Jackson

Hi Bill,
Can you send me a copy as well
tony@batesfamily.net
Thanks
Tony
Tony Bates

Can I get in on that Bill? I can't find it in the archives. I've never really liked the antitramp bars. Your idea sounds like the goods.
petern.sherman1@bigpond.com
Peter

Bill,

ME TOO..

mgfish@comcast.net

thanks,
Bob
BOB FISHER

Send the e-mails as a group. Can someone psot them so that others can view the photos.

thanks.
Bill Guzman


like this?
http://www.britishv8.org/Articles/Easy-Traction.htm

I think what Kevin described isn't too far from what Robert Milks has on his car:
http://www.britishv8.org/MG/RobertMilks.htm
(four photos about halfway down the page)
Curtis

Great Idea, I was procrastinating how to address the traction bars. No need to any more.

thanks.

Mark.
M Mallaby

Can someone comment on the effectiveness of the rear sway bar('77-80) as an anti-tramp/spring windup device - it seems to be mounted in a position that would prevent axle rotation.
Graham Creswick

As Kevin described above, I used this set-up on my MGC - see British V8 under MGC - 3rd picture down. As the axle rolls rearward when the wheels start turning, the anti-tramp bar pushes forward rotating the bellcranks so that the upper bolt presses downward on the spring preventing it kinking upwards. Works well but I think the geometry might be improved if the front lower anti-tramp pivot was brought forward so the overall length was the same as the front half of the spring.
I found I had to use the Nylatron material for spring pads as the stock rubber items or the red polyurethane pads are too soft and allow the axle to twist excessively before the spring itself starts to twist.
I would reccomend this to anyone with a higher torque engine as the spring pad and plate sizes seem pretty minimal as fitted. Bob Elwin.
Bob Elwin

Bob,

Thats exactly what I was describing, could you let me have the dimensions of the bellcrank and also what type of bush did you use to sit on top of the spring?

I agree with with your comment regarding the length of the radius rod, I was intending to use the bellcrank facing the other way round which would achieve this anyway.

To keep things simple I was going to buy the kit from Moss cut off the the bush at the spring end, cut a thread and fit an appropriate size rod end so the bar can be tensioned, with the top bush sitting on the spring.

Effectively this allows the suspension to work as intended, but under hard acceleration prevents the dreaded tramp setting in and doing untold damage to springs and axle.

Kevin.
Kevin Jackson


Graham asked: "Can someone comment on the effectiveness of the rear sway bar('77-80) as an anti-tramp/spring windup device"

I can't answer the question from personal experience, but it's a question I'll be putting to Mikel Moor because I understand he's done something tricky in that area. He reportedly cut the sway bar in half and clamped it such that it functions as a de facto pair of anti-tramp bars (but with some spring effect built in.)

---

As for using cut down leaf springs as Bill recommends. I'm still trying to understand the claim that they don't increase spring rate. Don't they?

Carol Smith was no big fan of anti-tramp bars... but his preferred approach (in race classes where leafs were required) was to clamp the front half of the spring leaf pack REALLY tight to aide axle location, and to rely on the back half of the springs for most of the displacement.
Curtis

The added half spring is not conected to the leaf spring, it's only attached by via the center bolt and spring pad. During accelaration the spring makes contact with the attached half spring, thus keeping the spring from wrapping and create wheel hop.

There is not physical way that it would add spring rate.
Bill Guzman

Kevin, I'll measure the bellcrank pivot dimensions o/c tonight. You're right in thinking you could just turn the bellcranks over to arrange for the overall length of the anti-tramp bar to match the front portion of the spring as it moves up and down. Won't help me as my bars would now be too short! I tried to buy a set from Moss but found I could make much stronger items in a few nights once I had the dimensions from a buddys' car! The top bolt has a sleeve on it so it spreads the load slightly as it contacts the upper spring leaf. Don't let the axle tramp as it will destroy the springs, clamps and other attachments pretty quickly. Some sort of trailing arm system with coil springs is probably the best bet but this has worked OK on my car for several years. Bob.
Bob Elwin

Graham, to hear from you!!!
The late MGB's did have a sway bar that was attached to the top of the rear end and forward to the balkhead.

Yes, this is a very good idea, if you could change the angle of the arm going forward to aim down, this would create a dwon force and actually push the axle down into the ground thus creating traction.


Bill Guzman

Kevin, I measured the bellcrank dimensions - as follows - between bolt centers. The upper sleeved bolt that presses on the spring is 3.25" horizontally rearward from the front spring shackle bolt while the attachment for the front end of the anti-tramp bar is 2.75" o/c vertically below that point. (Don't forget you are going to reverse the bellcranks which will require longer a/t bars.)
The center of the rear pivot for the a/t bar is 1.75" below the lower face of the heavy spring clamping plate. You will need to weld a "U" shaped bracket to support the rear of the a/t bar to the plate and bolt it through.
If you can make the a/t bar the same length as the forward part of the spring, I doubt that there will be enough length change as the forward part of the spring flexes to make much difference as the length change is virtually all taken up by the rear swinging shackle. You can make the a/t bar adjustable for length by using left and right hand threads in each end so you can turn it with a wrench on a flatted area for fine-tuning. The pivots are available with left and right threads for that purpose. Good luck. Bob Elwin.
Bob Elwin

Bob,
Thats a beautiful car you have there.

Thanks for the the very helpful additional information ,and on second thoughts I would put the rod ends on the axle mounts with the bushed end on the chassis end to provide some insulation against vibation and harshness.

I would use the Moss Kit because it would provide 90% of whats required and would just need to cut off one end of each tramp bar and fit the rod ends and use the cut off parts with internal bush for the ones that bear on top of the springs, and then have four bellcranks cut and drilled and thats it.

I'm changing the rear axle for a 3.07 and fitting new springs in about a month so might try Bill's ingenious and cheap solution first and see how well it works.

Thanks again,

Kevin.
Kevin Jackson

Graham, on my 78 "B" . i have the rear sway bar fitted with the Energy Suspension Poly bushing kit. also we have added a set of sub-frame connectors from the center X-member to the front spring hangers. the rear housing & pinion attempts to rise on acceleration so we pre-loaded the sway bar ends to remove any rearward play. the poly mounts on the R/E housing and the ones mounting to the uni-body do very well. i "dropped the hammer" at 3k and then bumped rev limiter at 6k w/o wheel hop, both rear wheels left marks.
T/w bill G. who advised my set up should be adequate since i thought about the 1/2 spring leaf system after the summer meet. the sub-frame connectors we made were make of 1"X3"X 1/8" rect. tubing. will share plans if you request. have a great day and SAFETY FASTER!
kelly stevenson

Kelly,
Thanks for your comments. Interesting that I have just replaced my rear sway bar rubbers with urethane ones but have not put them to the test yet - we'll see if that makes any difference in performance.
Generally, my '76B wheel hop is minimal on typical city asphalt roads and tire adhesion is more of a issue. I do, however, remember having a lot of wheel hop and no traction at Wabash Valley drag strip while attending the 2005 V8 meet in Terre Haute...must have been the wet tar!
Kelly, I'll be sure to look under your car in Cleveland and take notes.
Graham Creswick

Graham, i will share some pics of the connectors and info if you send a private message to my e-mail. do not have your address. TRACTION or lack of it is only problem i experience! What dif. ratio do you have?
kelly stevenson

This thread was discussed between 27/03/2007 and 30/03/2007

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