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MG Midget and Sprite Technical - Racer help - brakes, clearance, turning radius

Hi All:

If you remember I am the chap that is building the midget based racer. I wonder if there is someone who can help me with a few points.

1. What is the original clearance - distance from ground to bottom of the front cross member?

2. Can anyone supply me with pictures of the brake hose setup for disk brakes? I need the mounting point for the brake-line to hose, the mounting of the bracket that protects the brake hose and the angle that the hose bolts to the calliper.

3. Also what limits the turning radius on an original car? In other words what stops the wheels at full lock left or right?

Any help greatly appreciated.
Godspeed in Safety Fast
Jc



John Crawley

John,

I'll make some picture for you for the brake hose setup and check what limits the turning radius. About the original clearance, I can only measure what the actual clearance is of my Midget MK I with diskbrakes.

Bas
Bas Timmermans

John,

The limit of the radius is a puzzle. Its the steering rack or 2 notches at the botom of the kingpin assy.

I hope picture will upload correctly

Bas


Bas Timmermans

Bas has the earlier version of the brake hose/pipe connection. Later cars had the hose bolted through the inner wing, just to the rear of the damper.

The amount that the stub axle can turn is controlled by two ears on the bottom of the kingpin and lugs on the bottom of the stub axle.
Dave O'Neill 2

Thanks guys . . .

Bas: I think that I can see my problem. I think that the brake-hose that was supplied by a local shop is too short. I used the cross-member from a wrecked early Sprite - the disk brakes are from a later midget. Perhaps they sold me hoses for an early car. Did you get a chance to mesure the clearance of your MkI? Because the monoposto body is so light, as compaired to the original, my car looked like it was on tip-toes when I rolled it out into the day light. I lowered the front end by dropping the spring pan 1 @ 3/5 inches. I am curious as to original height to know if my stearing geometry is now off. I have set it so that the shock arm is level with the ground when the weight of the car is on it.

Dave: I asked the radius guestion because the bracket that bolts to the caliper to protect the brake-line, limits the turning radius by hittting the tab that the brake-line and brake-hose connect through and I was sure that this was not correct. I now remember the ears on the stub axel from when I rebuilt them.

Godspeed in Safety Fast
Jc


John Crawley

John, Mine is an early car the first series with diskbrakes. Its the same set up as yours. I checked the parts calalogue and there are only differences between drumbraked cars and diskbrake cars. There is also a special braided hose set as I have mounted. There is no difference in hoselenght between early and later diskbrake cars.

As for the height I measured about 19 cm (a little less then 7,5 inches) between garage floor and frontcrossmember. I did some suspension work and measured afterwards so this could be a cm to high because the suspension should settle after work.
Bas Timmermans

John,
I've not measured it recently but from memory I think ground clearance on a Mark II is 5 inches (or about 125 millimetres).

Trev
T Mason

Trev is spot on. I dug up a tech spec sheet and it stated 5 inch or 12,7 cm. Mine sits a bit proud I guess.

I dont know where they measure this. Could be the lip at the back of the trans tunnel. I dont know if thats lower then the front cross member.
Bas Timmermans

Jc, I made up my own braided stainless lines for my car, but copied the length of the original rubber lines plus about an inch for some slack. My car is a 73 with original disc brakes so the hose mounting is what I think you're wanting to see. The support bracket bolts on with the same bolts that hold the caliper to the spindle and position the hose almost straight upwards from the port on the caliper. As far as I can tell the steering stops are built into the king pin at the bottom of the swivel axle assembly. Should be two projections on the lower bit of the king pin and two stops on either side of the swivel axle that would engage those to limit travel.
Can't help you with the original turning radius though.



Bill Young

Stupid me. Off course the lowest point on a normal Midget is the exhaust. I went out to measure again. After the suspension settled I measure 17.5 cm between ground and front crossmember and the lowest point of my exhaust is 9 cm but that would be of no use looking at the pictures of your car. The sump is a bit lower than the front crossmember.

I dont know if you want to know but the turning circle is at left lock 9.79 meters and on right lock 9.51 meters. And yes the little tabs at the botom of the kingpin assy will stop the from turning any further.
Bas Timmermans

My car is on 155/80/13 tyres. They are a bit taller than original so the 17,5 still is a bit too much.
Bas Timmermans

Hi:
I am getting there. I think that I will move the connecting point for the brake-line to brake-hose to closer match Bill's '73 I forgot that I have 14 in. wheels on the racer so the clearance will be a bit more for the suspension to be at the correct angle. I now have lowered the front until the shock arm is level with the ground and it seems about right . . . the height is at 5 7/8 in. I lowered the rear to match and the result is that the car looks just right sitting in the driveway – we will see what it is like when it eventually gets on the track. I find it amazing that such small changes in height make such a difference in the way the car sits.

Thanks again guys for all the help . . . I’ll keep you posted on progress.
Jc
John Crawley

Are you going to 'corner weight' the car?
Dave O'Neill 2

Dave:
Set-up of the car will be a bit of a problem because of the antiquated design. As a Monoposto it is inherently cross-weight balanced but front-to-rear is another matter. Since I used the Sprites exact wheel base and track measurements I hoped its front-to-rear would be similar but it will be light in the rear-end. I have placed the battery and on-board fire-suppression as far back in the tail as I can but these do not compensate for the lost body weight. My rear suspension is: 1/4 elliptical springs (cut down MK II) with helper leaves reversed to the bottom; Adjustable trailing upper links; watts linkage with the off-set arm attached to the frame and unequal/non-parallel links; and external tube-type shocks. With this set-up I do not have much adjustment except for pinion angle but will have no body lean and no wheel-hop. I will add long leading links if necessary but I think the back end will be pretty stable. The front suspension is currently stock but I am working on a Lotus style in-board tube-shock set-up that I previously used on my first Sprite race car.
I purchased the first Sprite new in 1963 when I was 19 and drove it hard for 4 years. I rolled it, crashed it, and raced it before it was sold to finance a new MGB. Twenty years later I found it in a pile of junk– bought it and put it back on the autocross track. It now has a Capri 2.6 V6, top-loader trany, narrowed Ford rear-end. It runs a Holly 400 cfm carb, offenhouser intake, crane cam and is ported, polished, and balanced. It also has a Lotus style front suspension, disk brakes and many other mods. The body has been changed to Bug-eye by swapping a nose for front fenders & bonnet and a rear bustle for the trunk etc. The last time it ran in anger it was 2/10ths of a second behind a formula Atlantic and 1/10 of a second ahead of a Corvette.
It is very much like George Washington’s hatchet – you remember the very one that chopped down the cherry tree; it has just had 3 new heads and 5 new handles. The Sprite has changed over the 47 years since it rolled out of the show room but it is my original car and I still love it just as much as I did on the first day. My son now owns the Sprite and is restoring it to run on the street.
For the front shock setup I use the original shock as a pivot point only, weld a spare shock arm on the original arm and then run tube-shocks inboard meeting on the rack mounting square tube behind the radiator. Of course with this you have to run an electric fan.

Jc



John Crawley

This thread was discussed between 14/08/2010 and 20/08/2010

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