MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Rear Spring Measurements

Does anyone have the original rear spring arc dimensions? It appears that I am going to have to have my (new) rear springs re-arced to get the proper ride height. My car is a C but I figure that the geometry should be the same as the B and thus the dimensions should also be the same. What will be different is the spring rate, and possibly the number of spring leaves.

Based on some research, and I believe a link from another thread somewhere on this BBS, I found “The Only Way to Measure Leaf Springs” at the site www.eatonsprings.com/measuring.htm.

Anyone have an OEM rear spring that they can measure?

Thanks

Larry
72 BGT
69 C in restoration
Larry Hallanger

Larry

Not knowing too much about Cs I hesitate to make that assumption.

There were 2 rear axles used during the B production - the banjo type and the semi-floating. Even assuming the C has the same rear axle as the B (again I would suggest checking a reference book such as Clausager Original MG MGB, MGB GT and MGC to find that out) I would doubt the springs would be similar even between an MGB and and MGB GT, let alone an MGC and a MGB GT.

My original workshop manual for my MGB unusually (compared to the Magnette ZA shop manual or the Y shop manual) does not give any dimensions for the rear springs either.

Good luck, and sorry I cannot help you.

Paul
Paul Barrow

Roadster and GT rear springs weren't that different, in fact they were the same on the first few RB roadsters, but then the roadster did revert to a slightly lighter spring.

V8 springs were heavier than 4-cylinder GT springs to cope with the extra power. I wouldn't be surprised if C springs were harder also, but then I wouldn't be surprised if they were the same as the C didn't have as much torque as the V8 although it had a lot more than the 4-cylinder.

The springs should be nearly flat under normal loading (rear shackles just short of vertical), but today's occupants are frequently far heavier than Abingdon originally allowed for at 150lb per person. If you are significantly more than that you will need a higher spring rate to stop it bottoming too much on bumps. That may mean you will need *less* free arch than originally. I have a pair of little-used RB Roadster rear springs which measure as follows:

Between eye centres - 41 1/4".
Inverted on floor - 8 5/8" from floor to top of top plate.
Front eye centre to locating pin top centre - 19 1/8".
Paul Hunt 2

Larry,

Another alternative you might like to try is the 'parabolic' spring offered by the MGOC. I've just fitted a pair to my '78 GT with Rover V8. These were to replace a set of 'lowering kit' springs that caused me to take off part of the exhaust on a 'sleeping policeman' (Speed-control bump) outside my son's house.

These kits are available in various spring specifications and the stores people at the MGOC are very good at sorting out exactly what you might need.

One of the reasons that I'm suggesting this approach is that the kits are for a pair of springs on each side and sets of spacer-plates are supplied to make up the overall spring-pack to the same thickness as the original springs, thus easing production. One side benefit is that the spacer-plates can be fitted either between the spring and the axle or below the spring. Thus ride height can be adjusted.

The other reason is that they do give a vast improvement in ride comfort.

Details are in the March 1998 issue of Enjoying MG and it is on the website for members to access. Once logged in select the 'Publications' then scroll down and select 'View extracts from the magazine', then scroll right down the page to March 1998 and 'Spring Replacement'.

Roger Parker will allways help with problems such as these.

Hope this thoughts help.

Regardfs

Peter
P L Hills

Paul B

Rear section of the B and C are identical. Ride height is the same. I think my assumption that the unloaded dimensions on the springs, as measured using the Eaton Springs definitions, should be very close to the same. Number of leaves, and thickness of the leaves, will vary to provide the proper spring rate. An aside, the C uses the same (later) rear axle housing as the B.


Paul H

I assume that your "Between eye centres" measurement is along a straight line and not along the curved surface of the spring. If this is the case then any change in the "Inverted on floor" measurement will have a corresponding change in the first measurement. I had found your data in the earlier thread but am not sure how much value these will have to a spring shop when re-arcing. Any chance you could measure one of the springs using the Eaton definitions?

Thanks

Larry
Larry Hallanger

Larry - I can understand Eaton wanting A and B measurements if they are making a spring for you, but for re-arching your spring they are a given in the spring you hand over to them, and not particularly easy to measure. C also has question marks - they show A and B as being virtually equal, and the line of the centre-bolt is at right-angles to the line between the eyes. However on the B spring the centre-bolt is offset to the front, which means the centre-line of the centre-bolt isn't at right-angles to the eye-to-eye line. And while the differences are small it isn't clear whether one measures along the centre-line of the centre-bolt to where it bisects the eye-to-eye line, or along the line from the base of the centre-bolt where it joins the top leaf to where it crosses the eye-to-eye line at a right-angle. I've assumed the former i.e. along the centre-line of the centre-bolt, and that on mine is 6.5".

But the result of any re-arching will depend very much on the number and stiffness of each leaf. Clausager states 7-leaf springs were used on both roadster and GT, but with an increased 'free camber' (arch?) and load rating for the GT.
Paul Hunt 2

Paul

In looking again at the Eaton site they do acknowledge that the A and B dimensions are probably NOT the same and that it is VERY important to get them right. They also state that these measurements should be made as if the spring was flat (e.g. along the curve of the spring).

Given all of that I realized that I have a set of older GT springs that came out of a parts car that I could measure. However, your Clausager quote throws this out of the window. I think I will just live with what I have until I get the car completely back together and then determine how high it actually is and how hight it should be and give this info to the spring shop.

Thanks

Larry
Larry Hallanger

This thread was discussed between 19/07/2007 and 24/07/2007

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now