Stupid Question

[Jon Bradbury]

Here's a couple of stupid questions

 

What's the ratio of the diff on a DOHC Sierra? It's H reg and has rear discs.

 

On the ratio, if the ratio is higher (as in 4:1 vs 3:1) would I expect the wheels to go faster for a given propshaft speed or slower?

 

In other words, if I want higher acceleration should I go for a higher ratio or lower?

 

Sorry, these are pretty elementary questions, but I'd like to be sure.

 

I'll be looking for a new diff soon...

 

One other thing, is it worth trying to get a LSD from the XR4?

[geoff shep]

With a diff ratio of 4:1 back axle goes round once for every 4 turns of prop shaft. So 4:1 is lower gearing than 3:1, ie wheels go slower.

 

Check here for VIN information VIN Decoder

[niduncan]

There is a Speed Calculator on the Rhocar website that you can download. This allows you to change wheel and gearing details and shows the results in a variety of graphs.

 

Down load from Here

[Jon Bradbury]

With a diff ratio of 4:1 back axle goes round once for every 4 turns of prop shaft. So 4:1 is lower gearing than 3:1, ie wheels go slower.

 

Check here for VIN information VIN Decoder

Thanks for that Geoff.

 

The VIN decoder doesn't list my axle which is coded U

 

[Shandylegs]

Ford axle codes

A=3.36 B=3.77 D=3.92 F=3.842 J=4.056 K=3.31 M=3.14 N=4.29 P=3.58 J=3.62 V=3.33 Z=3.59 2=4.27 3=3.62 4=3.82 5=3.26 6=3.12 8=3.56

 

3,14 CW47-Pin15

3,38 CW44-Pin13

3,62 CW47-Pin13

3,92 CW51-Pin13

3,77 CW49-Pin13 6.5 inch diff

 

3,38 fitted to 1,6 OHC ECO 5 speed

3,38 fitted to 2,0 OHC HC

3,38 fitted to 2.3 v6 ESTATE

3,14 fitted to 1,6 OHC ECO 4 speed

3,14 fitted to 2.3 v6 SALOON

3.14 fitted to 2.3 Diesel

 

85GG 4006 DC --- 3.97

85GG 4006 BC --- 3.62

85GG 4006 AC --- 3.38

85GG 4006 FB --- 3.36

87BG 4006 GB --- 3.14

 

86GG 4006 AAA --- 3.92 LSD

V87BB 4006 BAA --- 3.62 LSD

V87BG 4006 CAA --- 3.38 LSD

85GG 4006 AAA --- 3.36 LSD

 

Vin plate codes for Diff ratio

 

Ratio Code

3.14 M

3.36 A

3.38 U

3.62 V

3.64 3

3.92 D

[Snapperpaul]

BEWARE......the diff ratio confusion issue still reigns... I have a diff tag that says 3.38 and the Vin plate says V

 

This is info from Nigel and so far matches what i have found

 

M=3.14

A=3.36

V=3.38

U=3.62

3=3.64

D=3.92

 

There seems to be a continual assumption that V = 3.62 when really it is 3.38 this incorrect info i think comes from the Granada Vin plate info, a site i found when looking for ford bits, or at least it is where my confusion started. I think that it is only the diff tag that can be trully trusted.

According to fords own info sheet

( thanks again Nigel) my 2.0L saloon should only have a 3.38 if it was an auto and it wasn't !

[Jon Bradbury]

I guess it's a 3.62, then

 

Is there such a thing as a 3.62 LSD? I don't want to knacker the speedo accuracy for a LSD.

[Snapperpaul]

See Shandylegs post..its only the diff code i dispute.

[Guest Robin Allison]

XR4x4 lsd diff should be 3.62 for the V6 the 4 cylinder version is a 3.92 (i think)

 

Also don't forget the diffs can be 7" or 7 1/2".

Xr4x4's are 7". I have a 1990 Xr4i and that is fitted with a 7 1/2" non lsd.

[Jon Bradbury]

Oh God.

 

So I suppose it's not such a stoopid question after all!

 

I *think* mine's a 7 incher, but how do I tell? What is the measurement referring to? I imagine they are not interchangable...?

[Guest Robin Allison]

Its all to do with the width of the top mounting. If you measure across the top in line with the mounting bolt (top one) it will be either 7" or 7 1/2".

 

If you have a 7" the you can only refit a 7"diff

 

If you have a 7 1/2" diff fitted then either will fit. The 7" one will need some washers to pack out the 1/2" gap at the top mounting.

 

Or change the rear cross beam for a V6 Granada one which should be 7 1/2".

 

The diff's to go for are the 7" lsd from an XR4x4 or 4x4 Sierra Cosworth. Either of these will go in even if you just need to fit some extra spacers at the top bolt.

 

The 7 1/2" lsd diff's are found in 2wd Sierra Cosworths and the early Granada Cosworths (pre shape change)

 

One more thing check the size of the output drive flange from the diff. They should all be the same size. 2wd Sierra Cosworths have a larger flange size and will not fit other drive shafts.

[Guest salty_monk]

The 7.5" has blind bolts either side whilst the 7" has a through bolt with a nyloc the other end.. that's the easiest way to tell..

 

On a Pinto engine I believe the best ratio to go for is 3.92 as it gives you the best acceleration & the best top speed but does mean you'll run at higher revs when "cruising" on the motorway & consequently a slightly higher mpg...

 

Every LSD from Ford I've heard of or found is 3.62 so if the 3.92's exist they must be pretty rare...

 

You can buy a Quaife style 3.92 LSD rebuilt into your casing with new seals & bearings for around £200 (that's what he quoted me last year) from Phil @ road & race in Orpington Kent.

If you want anything higher like a 4.1, 4.3 or something you can get them but the price goes through the roof as just the custom pinion is £400+

 

Dan

 

P.s. if you want a 7.5" non LSD with standard push in shafts I have one in a 3.92 with new seals fitted.

[Jon Bradbury]

Ah, well, I'll measure the width but I can say it has a through bolt so should be a 7" jobbie. Thanks for the offer Salty but it looks as if it won't fit. Mine has flanges & lobros in any case (it's discs on the back).

 

Cheers

 

JonB

[Guest salty_monk]

Orpington is not so far from you... let me know if you need the number of the guy there. Should have it somewhere.

 

He races a Caterham with a 240bhp xe engine so he knows what he's talking about with this sort of car.

 

Dan