Hi,
Quick replies and ideas would be greatly appreciated, because I'm in some remote area of northern canada -Baie Comeau to Labrador highway.. (somewhere only the foolish would take a car with 275,000 miles, unless it was a Volvo 240!)

Yesterday on some back roads and gravel, driving carefully at low speeds 20mph , not pushing it like it was a pickup or anything, but still washboard gravel and decent size potholes..

When I get back on the pavement there is a hugely noticeable vibration, I dare say drivetrain because I've been wrong about diagnosing these vibrations before. It happens only when braking from about 35 mph right down to zero at a complete stop, and seems to chatter most as it's nearing a stop from 10-0mph. If I feather the brakes lightly and coast to a stop it wot do it but under normal to heavy braking there's a definite rumble .. It starts up in the gear selector (automatic) and then as I complete the braking, the vibration seems to transfer further down the line to the differential and rear wheels.

I'd like to think it's a warped rear rotor, which wouldn't be impossible given their age, but the suspension workout on the back roads and the fact that the vibration also occurs when in reverse backing up without the brakes applied has me thinking it's not the brakes ... Trans mount ?



Any ideas ?

Edit/update
Just had a look underneath with a flashlight. Visually all the bushing seem good, none of them are collapsed or off centre or have any clunking when I rock the car back and forth in park. TABs, front trailing arm bushings, pan hard rod, torque rods, even the suspension shocks are aligned and in place where they should be. The tranny mount looks within spec, it's not pancaked out and the tranny isn't resting on the cross frame.

Edit 2
one of the lug-nuts on the back wheel is seized and I don't want to break it for the sale of an inspection or just to have a better look at the brake rotors..
But I did another test and from a stop if I accelerate hard ( that's relative in a Volvo but as hard as this girl will go) I can replicate the drive train chatter or vibration in the first few seconds of take off. Again another clue that it's not the brakes...