Hopefully going to pick up a complete sierra cosworth 2wd rear beam tommorow. What part number should the diff have? I want to make sure its a genuine cosworth 2wd unit not a cheaper open diff.

Thanks matty

 

If it's 2wd it'll be a 7.5" diff with 110mm lobro's, afaik all other Sierra's used a 7" diff & 100mm lobro's

 

Yes, you should check on the 108 mm flanges for the driveshaft. All other Sierras/Granadas had 100 mm flanges, but some also had the 7.5" diff, mostly open diffs but also some lsd.

 

and roll bar pick up points on the trailing arms ,although im not sure if some of the better models came with rear roll bar too

 

should i just measure across the width of the lobro where the drive shaft bolts too,

also should i check that both hubs spin the same way to check its an lsd?

is there no cosworth part numbers? i dont want to buy it to find its of a pinto.

 

Even on an open diff both driveshafts can spin the same way, it's no proof that it's an lsd. The way to check whether it's an lsd (and also the condition of the lsd) is to try to turn the driveshafts opposite ways. If it's an open diff it will be very easy, if it's an lsd it will be difficult (or still relatively easy if the lsd is worn out).

Regarding the rest of the rear beam, the 3dr had the arb pickup points outside the spring area. The 2wd sapph had them fixed to the brake pipe bracket on the inner side of the arm. Also something to check is whether the ball joints connecting the arms to the subframe are not worn. Any play will be too much! New ones are about 80 pounds each, so you wouldn't want to replace all 4. (And replacing them by poly bushes is not the best idea)

 

The 2wd shafts where they come out of the did are 108 pcd on the bolts so simply measure the out put flange of a non 2wd version and see if they are bigger or not
The LSD as mention could be shafted but without removing the cover you can't tell for sure