MG Sports Cars

With the rear jacked up there may not be much tension left on the spring.
Need to a pic with the car on a lift or jackstands with the suspension at full droop.

Steve

I suggested to Dave that with the car on jackstands he might put a little pressure on the lower end with his floor jack and safely remove the lower bolt. Spring pressure then should be no more than 350 lbs at the most, I would think. I agree Rick, that the big nut could be backed off as well.

Jim

Rick:

Hope these help? Rear suspension in "full droop".

M

Addendum:

Maybe it's just me and I'm looking for smoke, but I took the hi-resolution digital image of the second picture and ZOOMED in on the shock-- and it looks like it might already have been bending the rod! A straight line between the bolts shows the rod has a slight swag in the diff direction.

Could just be the camera angle, surely. But...?

M

Here's the damage. Apparently some brake line damage as well.

The failure appears to be from metal fatigue progressing from the root of the threads. Note the crack propagation towards the center from both sides prior to complete failure by tensile stress on the remaining intact area. This indicates that the rod was flexing and induced the metal fatigue. So the obvious question is, why would the rod flex? Provided the rod and the rod ends are on center it should not. The fact that it obviously did indicates that perhaps the rod end was machined slightly off center, meaning this indicates a manufacturing defect. I would suggest contacting QA1 for a replacement under warranty. (Implied or required by statute if not actual, being a manufacturing defect it should be replaced) The springs should not be binding but longer replacements are probably a good idea The bent one should be replaced of course and I think they are about $50 a set.

Can anyone come up with any other reason the shock could have failed in this manner? Careful measuring of the rod end would determine if it was machined incorrectly. Note the angle of the failure line in relation to the rod end's orientation. This should correspond to the offset, and this should be confirmed before replacement with a similar part if possible. If the mode of failure cannot be confirmed the next step would be to look for a coil-over with a larger diameter shock rod.

Jim

Guys ,I have an extra steering wheel with the 6 bolt hub. It looks just like the one that broke. I'll throw it in the trunk this weekend for the Dayton show if anyone can get it to Dave's. If not, I'll mail it next week. Capt'n

Mike....are you coming to Twists? If so, just bring it up to Michigan.

Rick, Yes, coming to Twisty's. Have reservations at Barney's playland! Abby has to valve cover race. I'll leave the wheel in the trunk. Mike

Cool!

I think things are getting a little clearer on the shock failure. Apparently the units we have are a racing part and a street part is available from the same manufacturer as well as others. The following is guesswork on my part but it seems that the race shocks are made lighter than the street units in order to save weight where the street units are built for durability. So where our units have a 1/2" shock rod the street unit has a 5/8" rod which gives 50% more cross sectional area and makes for a much, much stiffer rod. With the 5/8" rod the rate of flex on the rod would drop to infinitesimal levels, well below the threshold required to cause metal fatigue. In our case, the rod flexed very slightly over an extended period, causing cracks to propagate from the thread roots of the shock rod. Eliminate flex, eliminate the cracks.

Put simply, the coil-over unit failed because it was too light for the application. But who knew?

QA1 made our shocks. Jim Nichols says they make a street shock (silver body) that has a 5/8" diameter shock rod. I suggest we buy those and put them on the car.

I suggest we go to the 12" springs as well and up the spring rate by 25 lbs to slightly stiffen the rear end as it can use it.

I suggest we get adjuster nuts that will accept a wrench so we aren't buggering up the nuts with pliers and pipe wrenches.

I suggest we include a bump stop in the unit like the one we have now, I think it is the shortest one available for these.

The good shock can be measured for length both compressed and extended.

The rate is printed on the spring coils.

Probably the part number in on the shocks.

We do not have to use QA1, or the original supplier.

If I can do anything more to help figure this out please let me know.

Jim

Jim, I replied on the other board and Jim Stabe provided a picture of the silver QA1 Promo-Star. They come with the spanner nuts. The article I attached may be helpful too.

As I recall, QA1 says not to use their shocks for rebound travel limiting,(use a strap/etc). Anyone verify this with instructions ? Good Luck, roverman.

It's interesting that the cross weight ( RF to LR ) and right side weight are exactly the same.

Are these weights with or without driver weight? In a car this small, that makes a big difference in left side and forward weight bias. And, of course, it would put cross through the roof if you're adding ~200lbs to the left side seat.


Annoying that the scale didn't break out individual wheel weights.



Edited 1 time(s). Last edit at 08/10/2013 12:37PM by Todd McCreary.

That weight was without the driver. It was also the first car we weighed, so Jim & I were figuring out the scale and failed to get the other readings.

I think maybe we did get the other weights later didn't we Dan? Maybe my memory is faulty but I thought we put the car back on the scale but didn't bother to empty out the trunk the last time around. The weights are tabulated on this site somewhere.

Regardless, when considering the engine in this car I think it's safe to say that the results are nothing short of amazing. The long preconcieved notion that the car would be hopelessly nose heavy was definitively put to rest. Much of this result can be laid at the feet of the ballast added by the Jag IRS, but also is due to the light weight of the BBB engine.

Too, we see the same kind of numbers with most of the cars just lower in overall weight. Considering we made no conscious effort to keep the weight down the overall weight comes as no surprise, a few hundred pounds heavier than a similarly equipped unmodified car. For exact numbers see the weight tabulations posted on this site:
[www.britishv8.org]
[www.britishv8.org]
[www.britishv8.org]

The other thing we saw is that adding the driver typically adds near equal weight to the front and rear and some to the passenger's side as well, so it would be mistaken to see this as loading another 200 lbs to the left front tire as that is not what happens by any means. And too, as a proportion of overall weight it is clear that the Roadmaster would fare better in this regard than a light weight conversion such as for instance, Curtis' car, and I would challenge anybody to demonstrate that his car handles turns better in one direction than in the other.

Jim

--->so it would be mistaken to see this as loading another 200 lbs to the left front tire as that is not what happens by any means.

Indeed. In the racecar, our 240lb driver would add about the following:

LF 85
RF 15
LR 130
RR 10

Granted, a lightened roadster (only 1900 w/o driver), but it certainly doesn't go all to the LF...

M



Edited 1 time(s). Last edit at 08/10/2013 06:24PM by madmax.

I don't think you can count the Roadmaster's weight as taken at BritishV8 2008 in Winsconsin. That was with the "Swiss cheese" green bodyshell.....that was for all practical purposes a rolling chassis at the time.

Very true Rick. No glass (heavy stuff that) no interior, etc, etc, etc. It is interesting to see where the added weight went and how much was there with only the rolling chassis and drivetrain (stock MGB axle).

Jim

It was also the first car we weighed, so Jim & I were figuring out the scale and failed to get the other readings.


Yeah, I assume you just push the 'Wheel Weights' button to toggle the display between individual corner weights and the analytic screen you're showing in your pic.



Jim
The other thing we saw is that adding the driver typically adds near equal weight to the front and rear and some to the passenger's side as well, so it would be mistaken to see this as loading another 200 lbs to the left front tire as that is not what happens by any means.


madmax
Indeed. In the racecar, our 240lb driver would add about the following:
LF 85
RF 15
LR 130
RR 10


Remember, I said the *cross weight* would go through the roof? Your example demonstrates that ... maybe I exaggerated a little bit, max. It would provide a 1.7% bump ( 50 / 3019 ) to the cross weight number and make the car tighter in left hand turns. Think of it this way; cross is an indication of how firmly the LR is planted in the turn, *when turning left*. If you add weight to the LR the rear grips better ( tighter or understeer ). If you take weight away from the LR ( and consequently add it to the LF ) then it doesn't grip so good ( looser or oversteer ) in relation to the front end.

Regardless, I wouldn't worry too much about it unless you're going to set the car up for a track day. And in that case, the car needs to be scaled in the 'as raced' condition. That is, stripped of accessories as much as feasible but with a driver and helmet and a full ( or however much you want to race with ) fuel tank.

For now, I'd just keep the car as balanced as possible for the street. But you shouldn't really be near the limits on the street anywho so it probably doesn't really matter ... except for curiousity.