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MG MGB Technical - rear end sagging

my mgb roadster 1965 model has a height of 25 inches from the floor to the mid point of the front fender, and 23 1/2 inches at the rear with the spare tyre and a full tank of petrol.

where do i start and what do i look for.
the rear shocks were replaced with a pair from world wide auto parts, 2 years ago.

thanks for the help

vignes
vignes pillai

A couple of things to mention. The usual measurement is from the centre of the wheel up to the bottom of the chrome strip. This eliminates any variation due to tyre size. If you look here http://www.mgb-stuff.org.uk/suspensiontext.htm#rideheight you will find lots of stuff on ride height including measurements taken on various cars around the world.

Second thing is that the dampers (shock absorbers) have nothing to do with the ride height. Ride height is purely a function of the springs.
Mike Howlett

"dampers (shock absorbers) have nothing to do with the ride height."

Assuming they are not siezed. :o)

Other than that as said low ride height is down to the springs themselves, assuming the attachment points have not collapsed. Springs can be very variable, including replacements. Many complain that they result in too high a ride height, which is because they are either too hard or over arched. I've had the opposite problem, and have had to extend the shackles by an inch or so to stop bottoming and grounding on country roads, but the rear still looks lower than a lot of other chrome bumper cars.
Paul Hunt

thank you Howlett, the measurements from the centre of the wheel to the bottom of the chrome strip are the following.

left front 13.5cm
rear 14.5cm

right front 12.75cm
rear 14 cm

vignes pillai

sorry , it is inches and not cm as stated .
vignes pillai

From your numbers it seems that your rear springs are fine and that something on the front is amis to cause almost 1 inch variation.

If your rear is higher than the front, it certainly isn't sagging.
Roadwarrior

i have read through Paul Hunts very informative article,and i see my readings to be withen the normal range, but what could be causing the 1 inch variation between the front and rear.
the readings were made because i wanted to change my tyres from 165R/14 to 185-70-14, due to unavailability of the 165 R tyres
vignes pillai

One inch variation between front and rear is nothing to be concerned about, I doubt they were dead level even when new as severl different spruing specs both front and year were used at different times. And as Roadwarrior says it isn't sagging at the rear anyway but higher than the front, and 14 to 14.5 inches is higher than average for a chrome bumper.

It's the almost 1" variation between the left front and the right front that is worthy of more investigation. That could well be causing the 1/2" variation between sides at the rear, as a problem at one corner will usually be visible at the diagonally opposite corner.

As for the tyres, 185s are pretty wide, you could get them rubbing on the arches at the rear when cornering. Can't you get 175s? Even those rub a bit on mine.

You don't need to measure ride-height characteristics when contemplating a change of tyre size. Roadsters originally had 155/80s, GTs 165/80s, which made the GTs have a rolling circumference 2.7% greater which made the speedo read 2/7% lower for the same speed. Even with 185/70s it's only 1.7% greater, and they were standard on the LEs with alloy wheels. 175/70s would be 0.3% smaller i.e. insignificant.
Paul Hunt

thanks for the input everyone
vignes
vignes pillai

This thread was discussed between 14/04/2015 and 16/04/2015

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