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Fix 760 Rear Suspension
by Dave Johnson


The old Gold Brick is now re-powered and has a few thousand miles on the PRV6 and all is well in that department. However, the rear end had developed the speedboat look as the Nivomat shocks had finally quit. They had been there since 86 when the car was new, and that says something for their durability.

Having just spent way too much dough on an old car already, I baulked at the replacement cost of Nivomats. These shocks are internally sprung and contribute to the overall ride height. Something I was quite unaware of at the time, but was soon to find out.

I happened to have a pair of serviceable Monroe gas shocks of an old 760 hulk purchased for parts, and proceeded to remove the existing ones. A fairly simple task, until it came to removing the bottom bolt through the trailing arm. These had rusted into the steel grommet through the rubber bottom bush and would not yield to any amount of heating , lubricant or drifting.

I had limited time and failure on the day was not an option. I use the car daily. 
The solution may sound butcherous, but it worked. Using a 100mm angle grinder with a thin steel cutting disc, I was able to cut the bolt on both sides of the bush by reaching up and actually cutting through the eye of the shock, missing the arm. Itís tricky, but can be done carefully, and youíre going to bin the shock anyway. The usual precautions with eye protection and spark direction apply.

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Click to enlarge

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After

After

Dirty but nice


Also, use a full diameter disc, a worn disc will not reach to the offside of the bolt. Once both sides are cut, lift the shock out, and purchase a 12mm high-tensile bolt as a replacement complete with a locknut. And GREASE the bolts lightly before re-installation!! Next time you change shocks will be a pushover.

Anyway, with the Monroes installed, next problem! The back end was even lower!
Thatís when I learned what Nivomats do. The coil springs as fitted were like piano wire, (actually about 9mm wire) and were not ever intended to perform solo. The internal springing contributed largely to the overall ride height. Needless to say the handling and ground clearance was abysmal. Whoops!

Then I remembered the hulk also had a fairly hefty set of rear coils, so I removed these and while there I took the trailing arms and tramp rod as well as the whole torque rod assembly. Turns out that these had been re-bushed not long before the thing died, and the springs are 11mm wire. At the same time the old diff was removed and the urethane bushings around the live axle were in pretty good shape too. 

If you have a shudder on acceleration, these and the trailing arm bushings are likely offenders. And while youíve got its pants down anyway, you should consider replacing these. This was all done in the course of about four hours and was surprisingly easy to accomplish with a good set of axle stands and floor jack. I would recommend a good set of long-reach sockets in 12, 14,17,19mm and ring and open-enders in the same sizes. A small pry-bar, mallet, and some 5x5 timber blocks or assorted timber to support the axle and take the strain off the brake lines.


FCP Groton web site



When replacing the springs (easy) wind on the rubber bottom seats and orient them correctly before tightening the top spring mount fully. Then pop them into the bottom seat in the trailing arms and lift the arm with the jack enough to engage the shock bolts without a struggle.
The Brickboard 760 section has excellent directions for performing this and other maintenance tasks, and is a must-read before attempting any DIY mechanics, and covers this in far greater detail than I intend to. 

Test drive time and itís a whole different car now. The ride is back to what a 760 should be, - smooth a silk even on the rough metal roads up North here, and the handling has tightened up hugely. I have subsequently installed new KYB gas rear shocks and road noise has further diminished. New springs are readily available, but for a sedan, used wagon springs will work just fine, as these are usually a heavier rate.

There are progressive rate springs available which will give a soft ride but still handle towing and extra weight well. The Brickboard has a good discussion of various brands .
Height adjustable air-shocks would also be a good easy fix to rear end droop, and would eliminate the need to replace the springs, as well as allowing scope for ride-tuning.

Suspension bushes, shocks, and labour are cheap in view of what they do and in terms of how much more pleasant and safer your car is to drive.

Next mission,- the front struts.

Dave Johnson


 

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