The rear subframe brace from a c70 convertible fits the front wheel drive 850/70 series cars, so I decided to install one and see how it affects the handling and ride of the 850R. Aftermarket companies makw chassis braces that work in a similar way but why not have the one Volvo made to reinforce the car once they cut the roof off? Unfortunately they are low on the car and most junkyard forklifts will damage them lifting the car so finding a good one can be tough. And they are heavy. These are not lightly built.
The brace connects both of the engine subframe rear mounts to each other and the body. It is the large U-shaped oval tube in the photo below, as seen from the front of the car.
Installation is a fairly easy job once the car is in the air. Unclip the rear O2 sensor wiring retainer from the under exhaust cross-panel and remove the four 12mm bolts to remove the panel. You will re-use these bolts to install the brace. Support the rear of the engine subframe and remove the big 18mm subframe bolts on each side as well as the two 14mm nuts that attach the brackets. You won’t re-use the brackets. You will need to replace all 6 of these bolts with c70 convertible ones, which are longer. The subframe brackets and under-exhaust cross-piece are not re-used, the brace takes their place.
Installation is the reverse of removal and not too hard. I found it easiest to thread the big subframe bolts on enough to hold and then attach the rear cross-piece under the exhaust before coming back up to install the 14mm bolts. Torque the subframe bolts down and remember to angle torque the two big ones. 77ft-lbs plus 120 degrees for the big ones and 37 ft-lbs for the small 14mm headed ones.
These is a chance the subframe will shift during install so an alignment may be needed.
C70 convertibles also got a reinforced engine subframe and aluminum subframe bushings but since those are much more difficult to install they will sit until I happen to have the engine out for some reason.
Driving impressions and a report on how often the brace scrapes speedbumps to follow. It is low on a normal car and very low on a lowered car like mine.
o k cool so you put it on…but you don’t mention if this is actually a good idea?!? any improvement?
Do you know the part number?
thanks!
There is a very small but noticeable increase in stiffness of the car itself and it feels a little more solid under hard cornering. There is a very noticeable increase in vibration and harshness on old or rough roads. That is on my lowered car with an OMP brace and XC90 subframe mounts with ipd poly inserts. I’m curious how it would feel on a stock car.
Despite torquing everything properly and using all new hardware, the brace moves around enough to make some noise and require re-torquing every few thousand miles.
Would I do it again? No. Not enough improvement to be worth the effort to install it and keep torquing it and having to reach around it when doing maintenance under there. I would spend my cash on ipd bars or better springs/shocks instead.
I do not know the part number for the brace itself. The long subframe bolts are 977509 and the longer bolts on the front are 982821