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MG MGB Technical - Damper problems!!

I have a 1975 Rubber bumper mgb roadster with a Chrome bumper fitted.
When I bought the car it had Spax rear shockers fitted.
During the rebuild of the last 12 months I have fitted new rear leaf springs and Koni shocks.
I have a problem that the suspension travel is greater than the shock absorber travel with the obvious problems. The shockers are from the MGOC and state that they will fit all MGB
D M Tetlow

The springs being 'about level' (if you mean flat) doesn't tie up with a high ride height and the axle straps only being 'slightly bent'. When lowering a rubber bumper you must change the damper drop-links (lever-arm dampers), the axle check straps and the bump rubbers to keep the original amount of axle travel as well as keep the axle centralised in that travel under 'normal' loads. Substituting chrome bumpers for rubber *will* make it ride higher as there is less weight. Fitting chrome bumper springs may or may not correct that, but won't be enough to reduce the ride height to chrome levels, as both the front and rear spring mounting points are different on chrome bumper and rubber bumper cars. Without doing some structural work to change the mounting points the usual way to reduce rubber bumper cars to chrome bumper heights is to fit special *conversion* springs which ride even flatter than the normal springs. Rubber bumper springs are harder i.e. uinder a heavier load they should flex the same amount as chrome bumper springs with the lighter load as the *amount* of axle travel is the same, although the starting and finishing points relative to the body are of course different. As such with chrome bumpers rubber bumper springs will give an even *higher* ride height. The amount of arch will also have an effect. But these days whether any given spring is harder/softer or more/less arched than the originals is a matter of conjecture, there seems to be ever more departure from the correct specs these days, not less. A mismatch between damper mounting plates and axle travel could well cause bottoming at one end of the damper travel or the other. You could also have incorrect dampers for this application, whether everything else is correct or not. To be frank, anything other than the standard lever-arm dampers with leaf springs is a waste of money.
Paul Hunt 2

Thanks Paul.
A lot of the grey areas are not so grey now.
I will keep what I have for the moment until I can afford a IRS.
Regards
Dave
D M Tetlow

Dave
You can get your car down to Chrome bumper height by buying conversion springs, as Paul suggests. You could try doing a swap where you bought them.

Or you can purchase one inch lowering blocks, to begin with. When the blocks are on then you need to redrill the spring hanger holes and move the front eye of the spring up as per your requirement. This is not hard to do, just drill some new holes about 40 or 45 mm higher up in the original chrome bumper spot. This approach means you can get the ride height exact, and over here blocks (plus U bolts) are around $100 while springs are around $450. This is what Iíve done. With my orrigional rubber bumper springs (which have more arch than chrome ones) I moved the holes up about 44mm to get the ride height exactly level. Do use new drill bits and a centre punch if you adopt this approach, itís easy accidentally to drill off centre. With a bit of luck, (because of the chrome bumper springs having less arch than rubber bumper ones) you may not need to drill the hangers at all.

It is well worth pursuing a level chrome bumper ride height because it makes a big improvement in handling.

What ever approach you take, you do need to cut about one inch off the rubber bumpstops, if you are still using the original ones. This is so that you have enough suspension travel. If you have less than 2 inches of potential upward suspension travel (when at ride height), then there is the likelihood of sudden oversteer appearing half way through a corner, due to not enough suspension travel. Ideally you want 2.5 inches of upward and 2.5 inches of downward, i.e. ride height is at the mid point.
P.N. Sherman

Hi P.N.
Thanks for the help.
I have ordered a lowering kit.
My geometry seems to be a bit odd though!!
I have at the moment a 4" clearance between bumpstop and bump rubber and about 2" drop to the check strap limit.
The clearance above the wheel to lower lip of the arch is 2".
The front spring location is 10" above ground and the rear 13"
What do you mean by the ride height exactly level?
If I have got it right though, the spacers will lower the springs so reducing the ground clearence 1" and if I raise the front spring mount point 2" up, the spring will pivot about the rear mount and drop the body say 1".
My check straps are almost tight at the moment so raising the axle will help and my exhausts run under the axle so they will have more clearance too.
I did notice though that to drill the front mount points higher it is not possible to get the drill square. did you drill at an angle?
Regards
Dave
D M Tetlow

Dave,
By level I mean level with the front. You will have bought some up rated, lowered front coil springs to get the ride down at the front.
Two inches sounds about what mine was. I simply undid the bolt and moved the eye up as high as I could get it to go. However I have the original rubber bumper springs so I was looking for all I could get. Car was supported on stands and the diffí on a jack.
You might need to do some geometry. The centre of the radius of the arc is the bottom of the rear shackle. But yes, very approximately it translated to about half of 45mm at the axle. The top couple of cm of tyre now are out of sight behind the guard. Big visual improvement. Big improvement in cornering. Yes I drilled at an angle. I used a cheap battery drill. Slow is good for metal. Iíve noticed since then that hardware shops have started selling right angle drill adaptors for around $20. which might make it a bit easier. Not that itís hard really.
I used a centre punch to mark the hole. I marked it about 2 to 3mm lower than I needed because I expected the hole to creep up a bit because of the angle and thickness of the metal. I then drilled a small pilot hole, then a bit larger etc , in case it wandered. Use new sharp drill bits and itís an easy job. Probably a good idea to have two or three of the thin pilot hole drill bits before you start. I broke one when I got impatient and tried to hurry it along.
On the port side it occurred to me that I could get a drill horizontal if I crawled underneath and drilled from the inside, above the exhaust pipe, which is mostly empty space in rubber bumpers. So that side took about 30 seconds to do! If you use your spring eye as a guide to the other side of the hanger you might want to consider wrapping some tape around a smaller drill bit to protect the spring bush. Once the hole is started then you can drop the spring eye down out of the way. Itís up to you. This very quick and easy approach might be possible on the other side if you take the battery out and drill through the side of the battery box to where the hanger is. One more hole there wonít be noticed. Obvious this didnít occur to me until I had done the drilling at an angle thing on that side so I canít guarantee it will work.
You really will need to wear some safety goggles otherwise I guarantee you will get metal shavings in your eyes. Infact I (eventually, ouch) wore some swimming goggles.

Peter
P.N. Sherman

Hi Pete
My problem is that the car was changed to Chrome Bumpers before I bought it and then has been modded to V8 spec. The front is high too and I am sure it should be lowered. I have rebuilt most of the suspension and if my memory serves me, the height of the front springs before I fillted them was 9", which I think is the std height.The clearance between the top of the front tyre and arch is 3".
When you say level with the front I assume you mean the chassis. At the momemt the sill (chassis) by the front wheel is 9" off the ground and the sill by the back wheel is about 11".
When lowering the front is just a shorter spring fitted?
I have MGC 14" wire wheels with 65 profile tyres so the diameter is approx the same as the std B, and have just fitted a spax front damper conversion.
Thanks again for your help Pete. I am very interested in getting the handling better as I have splashed out on a LSD and power steering, and have just rebuilt the engine with new inlet, carb, and SS twin ceramic coated exhaust.
Regards
Dave.
P.S. Well done in the cricket.
D M Tetlow

The correct way to measure ride height is between the middle of the axle and the bottom of the trim strip, front and rear. This removes any variables coming from wheels, tyres, and tyre pressures. It *does* depend though on reasonably accurate replacement of any wing panels and consequently the trim strips. Dampers make no difference to static ride-height - unless they are siezed! Typical chrome bumper ride heights are around 14.25", front and rear, but there is a *huge* amount of variation, from actual data supplied to me anything from 12.75" to 15.5" on a CB, 13.25" to 16.25" on an RB.
Paul Hunt 2

Thanks Paul
D M Tetlow

The car is 15.5" at the front and 16.5" at the rear.
Dave
D M Tetlow

My car is also a '75 V8 chrome bumper conversion. For the front springs I went to the local MG place
'MG Workshops" and bought a set of "uprated -lower to chrome bumper spec" springs for $110.
I could have saved a little money and gone straight to a spring manufacturer however I figured that the MG place would have trial and error-ed their way to getting it right. Also Andrew at MG workshops will change any gear that is not dead right.
It sounds like you're setting up somthing pretty hot. If you havn't already done it you might consider looking at a thick as possible front antisway bar. I got one slightly less than an inch thick, and would go heavier if possible. The current theory is to control sway/roll at the front of the car with heavy springs and antisway bar and let the back axle move freely to follow the road and maximise rubber on the road and traction , in other words alot of people no longer have a rear antisway bar.
Don't forget to do something about the rear bumpstops or you will get a whole lot of sudden over steer when the bumpstop contacts partway through the corner. Leverage through the outer wheel and axle then lifts the inner wheel a little and you loose traction back there. The traction issue angain.
Like me, you can either simply cut about 1" off the rubber, a 5 minute job. Or go to the trouble of removing the rubber bumper 'add on cresent of metal bumpstop base' and moving the bump stop base back up to the chrome bumper location. I'm going to do this shortly.
best of luck
Peter
P.N. Sherman

I have a similar front anti-roll bar as yourself, mine is 7/8". I cannot increase the diameter unless I buy one with a different profile as it is only about 1/4" infront of my crankshaft pulley.
Were your rear bump stops about 2" high? I will check the clearance is at least 2.5" on mine when I fit the lowering blocks.
What I intend to do is to fit front lowered uprated springs and the rear lowering blocks then, if necessary, move the front eye up to get the ride height as per Paul's instructions, ( i.e. trim strip level to ground front and back)
One very good point you have mentioned is about the rear anti-roll bar. I have a small one fitted!!! It has always been a pain as it seems to be a bit of a bodge and I have had to fit poly bushes to stop it clonking.
In my case though I think it might be a necessary evil as it when it restricts the travel and the load is lifted from one wheel my LSD should compensate. I do not have a big motor, I bet the max power I give out is less than 200BHP so I do not intend to throw the car about too much!
I want a reasonably easy car to drive with a non stressed motor.
Regards
Dave
D M Tetlow

Congratulations, Dave, that puts you highest in my chart :o( (http://www.mgb-stuff.org.uk/wn_suspensionframe.htm click on 'Ride Height' and scroll down a bit)

My factory RB V8 had a rear bar and an uprated front bar fitted by the PO. The crank pulley rubbed on the front bar under braking, and eventually I got an oil leak from the sump where it had been resting on the front cross-member and rubber through! Eventually I discovered the plates between the block and the rubber mounts had been installed on the wrong sides - they are handed but fit either side! The effect was to bring the engine about 1/2" forward of where it should be. Was quite a job to swap them over with the engine in-situ, I can tell you. Another side-effect was the rear cross-member was attached to the front two chassis rail holes one side and the rear two the other. Also had problems with the rear (Hopkinson) bar drop-links breaking. It does seem to give more location to the axle comparing it to a V8 without, but also seems to reduce rear grip in the wet, although tyre choice seems to have a bigger effect.
Paul Hunt 2

Went out for the first run since the 2nd rebulit today. Only a few knocks, not too bad.
I will be fitting the lowered front springs and rear lowering blocks next week and hope for an improvement.
Dave
D M Tetlow

This thread was discussed between 01/12/2006 and 09/12/2006

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