Jaguar Engines & transmissions Discuss performance / modifications / upgrades etc here..

Limited slip differential REVISITED

 
  #41  
Old 02-22-2010, 05:20 AM
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Originally Posted by avos View Post
Changing tires will not make the difference; it will be the output shaft speed ratio to the speed of the wheels. Putting on smaller wheels does not change that ratio, only the rear end ratio will create a difference here.

Best would be to contact ZF themselves, they should know where the trigger is (in %). Chances are this could be around 10%/15%, leaving not much room for a major ratio change. Another route is to search for Audi/BMW tuners, they might also know more about teh ZF box, and if it is possible to alter the software.

Please PM me for the off topic part, but in short I did make everything myself.

Everything fits under the hood, no major changes there, and surprisingly the ECU offers a tremendous range and fuel supply. So far that hasn't been the border...
Sent you a PM...

If it's measuring wheel rotation, the smaller circumference wouldn't trigger the TCM/ECU sensing a change. Only so much could be done in that regards without seriously harming appearance - possibly ground clearance too. The '10 XKR 3.30 gear might be allowable, but I don't even know if they otherwise used the same housing etc.

What, if anything, did you do LSD wise to yours?
 
  #42  
Old 02-22-2010, 06:08 AM
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Wheel diameter has nothing to do with it I think, as when you change the wheel diameter the it doesn't change the speed the car is thinking your are going, so it is basicaly only the RPM that counts.

If the output speed shaft sensor measure 2000 RPM, then the wheels will rotate with a 3.06 diff 2000/3.06 654 RPM regardless of size. Now if you change the diff ratio to 3.30, then the wheel will rotate at 601 RPM (again regardless of wheel diameter), so now the TCM will measure a difference of 7%.

All academic as I do not know the thresholds/TCM program, would suggest writing a mail to ZF/check with Audi/BMW tuners.

I have kept the 3.06, though would have loved to go to 2.87, but custom made gearing would be too expensive, including reprogramming the TCM.
 
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Old 02-22-2010, 10:28 AM
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I think I am going to white flag this mod in my head and move onto something else
 
  #44  
Old 02-22-2010, 02:17 PM
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It's in the software, though that doesn't mean anyone but factory guys know how to re-write it:

(about the ZF 6 speed)
"OEMs can tailor the behavior of the transmission to each individual brand through software modifications. Each upgraded 6-speed will feature the same gear sets and kinematics, although how the transmission performs will be decided on by the OEMs engineering department. "Fundamentally, BMW will have the same gearbox as, say, Jaguar would, but each will calibrate and setup the transmission based on how they want it to act. The hardware is basically the same," Miskotten said."
 
  #45  
Old 02-22-2010, 06:26 PM
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Are you telling me out of all the people in the world running around in jaguars, and all the people just in this forum we can't find one software engineer to take care of this problem? Some get their *** down to silicon valley and offer one of the (many) unemployed software engineers a 6 pack and some work.
 
  #46  
Old 02-23-2010, 12:49 AM
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I have a MB box, so am not inclined to start searching for software engineers. The best chance would be to speak to the "better" tuners fro Audi/BMW or even maybe VW. The ECU will be programmed differently, but when one of these guys can do it for their 6HP26 boxes, they might also do it for the Jaguars. This is how I found at least 4 places where you could re-tune the Mercedes Box.

Anyhow, just found another clue that TCM reprogramming is needed when changing the rear end ratio. In one of the trouble shooting guides from Jaguar it states that the gear box would give several errors P0720/P0730 when a wrong rear end would have been fitted. Cause, the V6 Stype rear ends are using a 3.31 ratio and the V8 a 2.87 and sometimes a dealer puts in the wrong one, as they look alike and there is only a small difference in partno.
 
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  #47  
Old 02-23-2010, 02:31 AM
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Originally Posted by avos View Post
I have a MB box, so am not inclined to start searching for software engineers. The best chance would be to speak to the "better" tuners fro Audi/BMW or even maybe VW. The ECU will be programmed differently, but when one of these guys can do it for their 6HP26 boxes, they might also do it for the Jaguars. This is how I found at least 4 places where you could re-tune the Mercedes Box.

Anyhow, just found another clue that TCM reprogramming is needed when changing the rear end ratio. In one of the trouble shooting guides from Jaguar it states that the gear box would give several errors P0720/P0730 when a wrong rear end would have been fitted. Cause, the V6 Stype rear ends are using a 3.31 ratio and the V8 a 2.87 and sometimes a dealer puts in the wrong one, as they look alike and there is only a small difference in partno.
That is Damn interesting...
 
  #48  
Old 02-25-2010, 02:36 PM
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That is VERY interesting. It sounds like the Jaguar recommended solution to putting in the wrong rear gear is not redoing it correctly, but instead to reprogram the computer and hope the customer can't tell the difference. (LOL)

What it suggests is that the TCM is reprogrammable. But who? Am armless man could count on his fingers how many BMW or AUDI techs I even have a clue how to find.

This rear gear issue is getting me down, candidly. Building up a car is like putting together a puzzle. Frustrating if a piece is missing.

Any Jag mechanics out there know if the 2010 3.30 gear set is a bolt in replacement to the 3.03? That's a compromise, but could fall into the tolerable range. I "want" a 3.73, could fully live with 3.50, and would prefer it in the aftermarket gear-controlled LSD differential. So far I'm getting no responses to inquiries of how, if at all, this can be done in relation to the TCM.

SERIOUS QUESTIONS?
Shop manual for an 05? On CD or hard copy. Anyone know where I can find one?

2nd - where is the TCM located? If not on the transmission, does it read the speed mechanically or by electronic sensor/signal? Possibly the TCM can be tricked by reducing the rpm info it's receiving in various ways. If mechanical, it's just a reduction gear. If it's reading some rotation, possibly some fashion of PTU could be made that is reduced and let it read it. Or an electronic manipulation of the digital output. Rather than reprogram the computer, just trick it.
 

Last edited by dfwx; 02-25-2010 at 02:42 PM.
  #49  
Old 02-25-2010, 02:49 PM
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Wait a minute...does the Aston have a limited slip diff? And whats the gearing in the aston?

Furhtermore: -----> http://www.ajsengineering.com/Services.html

notice the "powerlock upgrade"
 
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Old 02-25-2010, 02:51 PM
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To answer my own question....

http://www.remarkablecars.com/main/a...artin-db7.html

"A limited slip differential and new rear axle mountings ensure optimum traction."

Now to find out if the trans is the same, and if it where we can get the software....


And some more...... from http://www.astonmartin.com/eng/herit...ars/db7vantage

"Transmission:
Six speed manual with optional five speed automatic. Limited slip differential. Ratio 3.77:1 (man) 3.06:1 (auto)"

Anyone want to foot a guess as to whether or not that's the same trans as in the jag but with a limited slip?
 
  #51  
Old 02-25-2010, 06:53 PM
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The extreme difference between the ratio for an auto versus manual transmission is interesting.
 
  #52  
Old 02-26-2010, 04:21 PM
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In 1999, the more powerful DB7 V12 Vantage was available with either a TREMEC T-56 six speed manual or a ZF 5HP30 five speed automatic gearbox
 
  #53  
Old 02-26-2010, 04:25 PM
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[edit] 6HP26

Two-wheel drive version:[edit] 6HP26A

Four-wheel drive version used in Audi, Volkswagen Passenger Cars and Bentley marques of the Volkswagen Group:
 
  #54  
Old 02-26-2010, 05:40 PM
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By that Logic we could potentially fit a tremec....yummy.

Additionally it would appear that the auto used the same gearing as our jags, 3.07. Meaning that to get a limited slip diff, all we need to do is get a hold of the guts from the Aston's rear end.
 
  #55  
Old 02-27-2010, 05:36 AM
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The DB7 is basically a dressed up XJS, same chassis, suspension and even a Jaguar engine.
Ponder on that, then find an XJS 3.6 with a 3:07 LSD, you have your diff. It would mean swopping the plates out of yours for the XJS.
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Last edited by Sean B; 01-21-2011 at 06:17 AM.
  #56  
Old 02-27-2010, 07:22 AM
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The diff from an XJS will no way bolt into an XK8/XKR if all you want is LSD in your stock 3.07 ratio diff just buy the Quafe unit, it will give you what you want. If you are trying to change ratios on XK8 Jag sell a 3.27 ratio that is used for the Mexican market this is a straight bolt in but is also not pozi. If you want other ratios up to 4.09 just buy a diff thru Jag for an X300 or XJ40, it requires a few mods but is a great bolt on update. The cheapest way to do this is thru someone who sells rebuilt difss such as Coventry West here in the US, as they can customize it for you ie pozi, jurid coupler.
 
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Old 02-27-2010, 08:39 PM
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Originally Posted by JAXKR View Post
The diff from an XJS will no way bolt into an XK8/XKR if all you want is LSD in your stock 3.07 ratio diff just buy the Quafe unit, it will give you what you want. If you are trying to change ratios on XK8 Jag sell a 3.27 ratio that is used for the Mexican market this is a straight bolt in but is also not pozi. If you want other ratios up to 4.09 just buy a diff thru Jag for an X300 or XJ40, it requires a few mods but is a great bolt on update. The cheapest way to do this is thru someone who sells rebuilt difss such as Coventry West here in the US, as they can customize it for you ie pozi, jurid coupler.
The opinion here is that the ECU/TCM will put later model XK8/Rs with the Mercedes 6 speed into limp mode if you change the rear ratio.
 
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Old 02-28-2010, 09:27 AM
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Originally Posted by JAXKR View Post
The diff from an XJS will no way bolt into an XK8/XKR if all you want is LSD in your stock 3.07 ratio diff just buy the Quafe unit, it will give you what you want. If you are trying to change ratios on XK8 Jag sell a 3.27 ratio that is used for the Mexican market this is a straight bolt in but is also not pozi. If you want other ratios up to 4.09 just buy a diff thru Jag for an X300 or XJ40, it requires a few mods but is a great bolt on update. The cheapest way to do this is thru someone who sells rebuilt difss such as Coventry West here in the US, as they can customize it for you ie pozi, jurid coupler.
I'm saying swap the internals out, not the diff casing, that's all! ;-)
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Last edited by Sean B; 01-21-2011 at 06:17 AM.
  #59  
Old 02-28-2010, 01:19 PM
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Originally Posted by dfwx View Post
The opinion here is that the ECU/TCM will put later model XK8/Rs with the Mercedes 6 speed into limp mode if you change the rear ratio.
The later model XK8/Rs (2003+) with the 6 speed transmissions are NOT Mercedes transmissions. They are made by ZF. The Mercedes transmissions came in only the supercharged 5 speed cars, pre 2003 XKRs and pre 2004 XJRs.
 
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Old 02-28-2010, 09:11 PM
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I stand corrected.
 

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