shanemc

my 91 sapphire was originally a 4x4 but it was converted to rwd before i bought it,but it still has the 4x4 7" diff etc.got the diff reconditioned a few weeks ago when it started getting noisy,but now its given up the ghost again,this time its lost all drive.just wondering should i get the diff repaired again or should i go for the 7.5" 2wd rear diff and beam,are they a big job to fit?it looks straightforward,but a total pain in the arse?!
plus my beam is polybushed,is it possible to reuse these in the 2wd beam?
any opinions appreciated,
thanks.

Shane

tabetha

The beam bushes will be fine for either beam.
If you have just paid good money to have your diff fixed get back there and complain, unless you are happy with 2 weeks use for the money ?
It is down to them to correct THEIR mistake.
I would not go to the bother of changing the beam just get your diff fixed they are the same strength in 4x4 as 2wd rear diffs.
The change though is straightforward, from 7" to 7.5" beam.
tabetha

foreigneRS

tabetha you are mistaken. i am not surprised that a 7" diff didn't last long in 2wd configuration. if it would handle the torque, why was a 7.5" fitted in the first place to 2wd's (and even scorpio's)?

shanemc don't bother with another 7" diff. put the 7.5" 2wd beam in. straightforward swap. swap the 4x4 vented discs over first though

polybushes can be used for beam mounting, but not semi-trailing arms on 2wd. they should have a special bush in them

tabetha

Yes I must admit I have never heard of 500bhp + being put through 4wd ?
As 2wd has more propensity to spin this would relieve the strain also on the diff!!
tabetha

foreigneRS

tabetha so you're trying to tell me that a 7" diff can handle as much torque as a 7.5" one?

tabetha

The dimension is the OUTSIDE casing, it bears no relationship to the guts of it, I am not trying to tell you anything this is my opinion which is what the author asked for.
ANY diff is going to have an easier time where the wheel can spin as this offloads the strain, ie 2wd as it is more likely to spin, all else being equal.
I can't see FORD commisioning another diff to save 1/2" of clearance where it is not necessary, ie I can't see it being different internally, but I could be wrong as I don't know for sure having never taken a 4wd one appart.
tabetha

foreigneRS

i think you are wrong. the insides of a 7.5" are bigger and can handle more torque than a 7". the external dimensions of 7" and 7.5" happen to correspond to the crownwheel diameter iirc

if the diffs are the same, why have 4x4 and 2wd rear diffs got different ratios?

opinions are all well and good, but surely facts are better?

tabetha

Facts are of course better if you know them as a fact.
The slight difference of ratio, can easilt be attributed to two different person working out the ratio, and one rounds UP while the other rounds DOWN 3.63:1 is in the middle.
As I said I have not taken a 4x4 one apart so could not say for sure, WHICH IS WHAT I SAID.
If I bothered to count the teeth on the input and crown wheel I would do a little math and work it out, but it would work out to an infinte amount of places as crown wheel unlikely to be a multiple of the input EXACTLY so ?
I still am not convinced that the 4x4 will be significantly weaker than the 2wd diff.
tabetha

foreigneRS

even if you shout at me mate, i still can't see where you said that in your first post as quoted below?

maybe in the future you'll get the chance. then you can come back on here and tell me i'm right

shanemc

i was didnt think this thread would turn into an arguement!cheers for the input anyways lads.
ive been offered a 7.5" diff at a fairly good price so i think im gonna take it,ill have more peace of mind with it in place,im convinced the 7" diff isnt up to the job on its own.

will a granada beam fit?got offered one for free yest off a mate.

@tabetha
ive given him back the diff to see what went wrong,i honestly dont think its failure was any fault of his,i'd say the viscous coupling just collapsed or sheared,he's fairly well known as regards fixing diffs,i wouldnt have much reason to doubt his workmanship.ill try and get a free check over of the 7.5" diff off him before i fit it thou...

Shane[/quote]

foreigneRS

shanemc no argument here, just discussion

the 7.5" beam on 2wd sierra's originally came from the scorpio in the first place, and was chosen so that a 7.5" lsd could be used that would be capable of handling the torque output of the YB as the standard sierra 7" lsd from the xr4x4 isn't

shanemc

got the 7" beam out on the ground today,surprisingly straightforward and easy,even when severely hungover!
cant get the handbrake cables off the calipers thou,cant seem to pull em forward enough to unhook em off the lug on the caliper,and the adjusters are slackened off.any idea what im doing wrong?theyre 4x4 calipers

foreigneRS

they can be a bugger. if you don't have enough slack even with the adjusters right off, it can sometimes help to take the cable of the handbrake lever. above the propshaft there is a pin that goes through the lever and the cable with a little c-clip on it

shanemc

got the cables off,was pressing out the polybushes on a hydraulic bench press out of the 7in beam to fit to the 7.5,and one of em split!!fcuking ba5tard!!!
the fun never stops with these cossies it seems!wonder can poly's be bought seperatly?i think i might just go down to the ford dealers tomorrow and just buy two new standard ones to fcuk!

Remko GT

That's normal. Polybushes go into the beam (or semi-trailing arms, or where-ever) but hardly go out in one piece. Maybe the new ones are easier because they are 2-piece items since, well I don't really know.
AFAIK polybushes are only sold per pair. At least, all the Powerflex items I've bought for my project car were packed per pair.

The pin Nick is referring to can appear to be stuck. Don't hit too hard because you might lose it. I almost lost mine last night when I was fitting the cable. Also take care not to molest the c-clip. It's very puny and fragile. The problem reaching that pin is that the prop is in the way so could be tricky to reach. Maybe if you have really small hands.

shanemc

we got the second bush out ok,just used a big flat plate between the bush and the hydraulic ram,looked like it was just going flatten the top of the bush at first,but then it popped out with plenty of force!used loads of washing up liquid aswell around the lip of the bush.that pin can be tricky to get out alright but managed to drift it out ok,used plenty wd40