cossie51

Went out in the car tonight to see if replacing the ECT sensor had cured the over fueling issue I had on Monday night and it's fine now but when driving it came on boost quit hard and I hit a bump in the road and then heard a bang from the rear and lost all drive

Got the car home and jacked it up to see the prop turning but no driver to the rear wheels so I'm guessing that would be the diff gone.

It was on a standard diff but it seems like a good time to upgrade but just wanted some advice on what other people are using and would recommend?

Adam-M

I wonder what's broken, either the little planet gears or crown wheel and pinion? If planet gears I'd go for a gripper diff I love mines. If crown wheel you'll need a bigger diff tbh or a supra diff but I'm not into that idea myself.

What power are you running? Iirc the standard for cwp is good for upto 500bhp

cossie51

My car is just about making 400 bhp. I thought it might be the planet gears, it happened as the car loaded and unloaded the weight of the car over the bump so thought it might have been planet gears snatched and just let go. Will have a look once removed.

ajamesc

Problem with the 7.5 inch diff when you get good grip and torque the c.w.p is simply not up to the job. I done this flooring it from already moving in 2nd coming off a roundabout

R4N SS

iTrader: (6)

go for a Jag diff like Rod has if you dont to go the Supra route

Caddyshack

I have got the MK 6 degree beam with Supra diff conversion so it accepts the diff without a Supra diff fitting kit needed.

The supra diff benefits from having a weir kit fitted and mine had new seals and bearings, it made a bit of noise for about 150 miles then settled and is totally quiet now...I love it.

If you go 6 degree you get so much more traction, they handle really well. Also ask fr the bladed anti roll bar mounts to be fitted...just in case you upgrade later. The standard 7.5 can still be fitted as he doesn't remove any of those fitting parts. The Supra diff needs a rear cover replacement too but I believe MK is making these again.

Jag option is also proven to never break.

OR go big time and fit a 9 inch but I would rather spend that money on the 6 degree beam and one of the above as you get the traction and handling benefits of the beam.

Caddyshack

Here is mine

cossie51

Spoke to someone this morning who said he had Bara's uprated viscous unit and uprated planet gears fitted and set up by bara and it put the power down very well at 500 hp in his car but was told it probably wouldn't stand up to running semi slicks or full slicks if driven hard. Mine is a road car and will never have semi slicks on so this could be an option for me.

Anyone else run one of these ?

Caddyshack

Are you 4wd? If the wheels can spin then it can protect the diff.


I guess it is one of those things that if you spend X on the 7.5 with Bara work done that could be Łx towards the setup that you know will not break but if it does work you save all the extra expense and hassle. Bara built my Weir kit Supra Diff for me as well as my Oppliger gear box and my front Quaife diff. Bara tends to tell it as it is, when he built my front diff he explained it was the best we could do under Ł1500 and explained where the weak links were...he also gave me the more expensive R&D option and said that would be bullet proof. I trust his word.

cossie51

No my car is 2WD and at 400 ish bhp the standard diff has been ok for the last few years and it gets quit a hard life. I'm not in to launching it off the line which is what breaks most diffs so do I need a top of the range diff that bullet prove or is that just over kill.

Adam-M

Gripper diff would be perfect for your power level and they put power down very well. Probably cost half what a good supra set up would cost, ideal world 9" diff but that's overkill.

Caddyshack

Yeah, doubt a 2wd needs to go too mad as you can spin away the excess torque.

I would be inclined to use the Bara option or the Gripper. The beam is a good option even with those.

Marc sierra

iTrader: (1)

A 2wd will need a stronger diff than a 4x4 as only 66% of the torque is going to the rear on a 4x4. That is also the reason why a 2wd has a 7.5" and a 4x4 has 7" as standard. The tyres will spin at the same torque, as that is just the grip limit of the tyres, for which it doesn't make a difference whether it's 2wd or 4x4.

Caddyshack

Good explanation, like that.

Why don't 2wd break boxes like 4wd though? Is the 2wd box stronger as same sized housing contains more strength as doesn't need room for transfer?

Tyres will spin at same torque, yes but if a 400 bhp / 400 ftlb car was 4wd the rear diff only sees 66% of the gross power / torque. 2 wd gets all the torque so the gross engine output on a 4wd can be higher before rears spin. Plus a 2wd has 2 tyres contact patch, a good 4wd with lsd (front and rear) has 4 contact patches to distribute the power.

Putting it another way the 2wd has more torque to deal with on 2 tyres, the 4wd rear only has 66% of the same torque therefore a 2wd will be more willing to spin the rear wheels than an exactly the same powered 4wd twin lsd car will spin the rears. So a 400 bhp car will spinnthe power away where a 4wd is more likely to have 100% traction; albeit spread across 4 tyres.

I am not arguing with you by the way, I am here to learn.

turbotrev

Imo I've seen many a 2wd car in all sorts of power variants break standard or slightly modded T5 boxes.
They are shite.
And rear beams for handling seem to work awesome but I don't think they necessarily majorly improve grip.
There are other small mods you can do and with a decent tyre in a 2wd you can get ample power down

Cheers Paul

Caddyshack

I may have different experience but as my Pug was running a lot of camber on the rear on the standard beam, this could be an anomoly due to how it was fitted to the Pug 205 shell? (but don't think it could affect it much) I think it was due to the fact that my car ran quite low to the ground which made it sit in more of a squat position, It used to spin the rears in second on a dry road, now you would have to heavily provoke it to spin in any gear. I think others have reported improved traction.

I was able to dial in bob on geo that was recommended to me so I think the traction benefit was due to the fact that the tyre contact patch is now optimised....

I understand that the handling improves by a fair margin too with the beam.

Sierrasideways

iTrader: (1)

I broke my T5 on a launch about a year ago. May be a quaife diff in mine but not 100%. Was told by my mechanic it's not standard but don't really know how I'd know for sure without opening it.

Philip.

Caddyshack

I didn't realise that the 2WDs broke stuff like the 4WD cars do...wow.

Tremec and Jag diff or Supra diff could be the way to go then on big power cars or if you break something and need to upgrade?

Modern tyres don't help as they are so much better than when the car was designed let alone twice the power and more that we put through them.

Back in the day 205's had a reputation for lift off oversteer...it was blown out of proportion a bit like 911's being tail happy....You have to try VERY hard now to get any movement from the back end of a 205 as the standard tyres are just so good....I used to get my old 205 stepping out with a good lift back in the day...now I cannot get anything even on a wet and greasy roundabout, barrel in, big lift...it just tightens the line a little....all this is the enemy of Cossie diffs and boxes.

Adam-M

Borg warner upgraded the t5 that came out of the mustang to cope with the extra torque but probably still "only" good for 450ish depending on how hard you drive. Tabetha used to always say the t5 was only rated to 180lbft but that's bull shit, maybe he's confused with the mt75 that I can believe being only capable of that torque as it's basically a 4x4 version of what comes in a dohc 8v sierra.

I don't get any wheel spin but I have a de-cambered back end and without this hardly any of the tyre touches the road, I want to get a good beam next more for handling than anything else as it's all very twisty roads round my way.

Marc sierra

iTrader: (1)

With the tyres spinning at the same torque I meant at the same wheel torque. Obviously a 4x4 can have more engine torque before the wheels starts spinning. Due to that the gearbox on a 4x4 has a harder life than a 2wd gearbox, at least in the lower gears.


Diffs will break quickest in lowest gears (first, second) as the torque to the diff is than the highest (engine torque amplified by the gearbox). The torque to the gearbox and clutch is always the same (just engine torque), so for the gearbox it matters less in which gear it is. Clutches will start to slip mostly in high gears as the 'resistance' from the car accelerating is then highest. For a 2wd this 'resistance' in low gears is quite low as it will simply spin the wheels, for a 4x4 it is much higher as will will not so easily spin the wheels. I guess it can be quite easy to kill a clutch when launching a 4x4, as you will need to let it slip to prevent the engine bogging down. For that reason I don't launch my 4x4, but I have no problems doing that on my 2wd V6.


I believe the T5 is breaking above 400 bhp, while the MT75 is breaking above 300-350 bhp. Officially the MT75 is rated at 300 Nm. But the 4x4 Sapph already has 290 Nm as standard and the Escort 305 Nm. In practice I believe the 4x4 box can take about 350 lb.ft / 475 Nm.

cossie51

Will pull my diff out tomorrow and find out what broke !

Been looking at having a gripper diff put in but would like some advice on if there are any other upgrades I should be looking at having done and who is best to use for supply and build up.

Also is there different specs and which is bet for a 2WD road car.
Never used on track

ajamesc

I had a gripper I fitted it myself I had to grind some off the casing and lift the diff in with in with the crown wheel not bolted on to get it to fit in the case. Then bolt the crown wheel on and fit the bearings good strong diffs but again the crown wheel and pinion are rubbish. Mine had a hewland shoot peened one

Adam-M

Wasn't yours running over 500 brake when it broke your cwp Andy? Never heard of the casing needing ground unless your crown wheel was bigger?

One thing to remember about the gripper is it's quite a noisey diff but I love the noise and associate it with my car, it always locks both wheels together like expected. Think a quaife diff is only really suited to a fwd.

ajamesc

Mine was 500bhp and yep the gripper dose need case mods too get in. It is a noisy diff definitely at low speeds

markk

iTrader: (2)

Slight case mods yes, i didn't have to build the crownwheel on separate though, all in in one go.

They are not noisy anymore, new plate design has eliminated almost all noise.
Mines about 6 months old, even solid mounted its pretty quiet.

ajamesc

Got mine years ago off tom gripper I went to his house lol the diff don't tapper at the end it certainly don't fit in built up. Only way mine would fit in was with the crown wheel loose on the diff.

markk

iTrader: (2)

Yes, when i had my first one in 2004 i went to Tom Seals house in Coventry too.

The diff unit goes in parallel to the case. I mill either side of the case by 10mm, they just slide in, and I'm on a bigger crownwheel being a 4.3:1

cossie51

After being advised against having a plated diff put in my 2wd cosworth by 3 well known transmission company's and being told a Quaife ATB is the way to go as it's only fast road use. I am now having a Gripper plated unit installed after the ATB unit was fitted but 6 weeks on Quaife have said they don't have the 108mm flanges need to finish the diff and don't expect to have stock until Nov/Dec at the earliest.

Hope I am making the right choice as I don't fancy waiting till the end of the year just to get the diff back so I can get some use out of the car this year.

markk

iTrader: (2)

As long as its a road use it will be awesome. Mine is obviously setup for rally, so prrload and ramp angles are higher.

cossie51

They said they would set it up with the correct preload and ramp for road use as I said I don't want something that wants to push on in roundabouts but I want it to do its job when exiting whilst winding the power on.

Should be fine if they deliver what they have promised

markk

iTrader: (2)

ATBs are shite, honestly, they have done you a favor at Quaife, they are good at that.

Adam-M

Only way I can imagine them not recommending a gripper on a cossie is by them not actually driving one.

Had a go in a mk1 rs with a quaife and it was pants

cossie51

I've driven a focus Rs mk1 and every time it tried to spin up it dragged you towards the kerb but they were known for that. Never driven a RWD with the ATB fitted so couldn't comment on what they are like. Guess I will ever find out now.

4x4sapphire24v

Hi guys, was wondering does anyone know of anyone know of a company that does a conversion to the jag diff for the Sierra rear beam?
I’m currently using an MT75 Dohc Sierra box converted to fit my BOA v6 with the Granada cosworth 7.5 inch diff. The car is currently making 407hp and 443lb/ft torque and is surviving ok but I will be mapping the car over the winter and it will have in excess of 500lb/ft of torque so can imagine something will break and want to be prepared to upgrade.
Any help or suggestions would be appreciated. This will at least let everyone know that the MT75 can handle well over 400lb/ft with completely standard internals.

Caddyshack

You could speak to Mark at MK Motorsport (Flat Track on here) and see if he has already got the jig for one or if he will do a conversion. I expect he would fabricate one for you, especially if you went for one of his 6 degree beams and that would also allow you to use the bladed rear adjustable anti roll bar if you had the lugs welded on at the same time. (there is a picture of my beam at the top of this thread that he made for my supra diff)

Mark V8

iTrader: (2)

MK Jag beam

4x4sapphire24v

Thanks for the info guys. Much appreciated

DAN400

iTrader: (3)

going the supra route would be more straight forward tbh
where you from ? ive a supra diff in my car

4x4sapphire24v

DAN400 im from near Dungiven in northern ireland. I got a supra diff last night but my one has an oil cooler built onto the side of it. Not sure if thats the right one but looks right apart from that. Did you make up your kit for fitting it yourself?

DAN400

iTrader: (3)

im in aghadowey, i bought an mk motorsport fitting kit
think the cooler can be screwed off and a blanking plate made to close it off again, ive 2 supra diffs laying here with no cooler