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 2Likes
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1
Post By 427sharpe
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1
Post By eschaider
07-24-2016, 04:36 PM
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CC Member
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Join Date: Jun 2016
Cobra Make, Engine:
Posts: 84
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Posi Rear
I was thinking of upgrading to the Posi rear end, I don't track or race the car, but have trouble laying down the power on with only one wheel working.
Thoughts?
Backdraft wants about $2,000 for the unit, any other less costly alternatives?
Thank you.
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07-24-2016, 04:59 PM
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CC Member
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Join Date: Dec 2015
Posts: 1,442
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07-24-2016, 05:07 PM
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Half-Ass Member
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Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 21,896
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Not Ranked
Quote:
Originally Posted by Bill Bulmer
Backdraft wants about $2,000 for the unit, any other less costly alternatives?
Thank you.
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Backdraft Parts - Limited Slip Differential That seems pretty high, considering I could buy a new Powr-Lok on ebay for less than $500. What is it that justifies that kind of cost on a BDR? Or, put another way, why does a BMW rear cost two grand for what seems like a pretty straight forward, common upgrade?
Last edited by patrickt; 07-24-2016 at 05:24 PM..
Reason: Added last sentence for clarity.
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07-24-2016, 08:04 PM
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CC Member
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Join Date: Aug 2013
Location: Haslet,
TX
Cobra Make, Engine: BDR #888, Keith Craft 408
Posts: 344
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Quote:
Originally Posted by Bill Bulmer
I was thinking of upgrading to the Posi rear end, I don't track or race the car, but have trouble laying down the power on with only one wheel working.
Thoughts?
Backdraft wants about $2,000 for the unit, any other less costly alternatives?
Thank you.
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What gear ratio are you looking for? I have a spare 3.91 with 40% lockup that I could sell you.
Kevin |
07-24-2016, 08:05 PM
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CC Member
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Join Date: Aug 2013
Location: Haslet,
TX
Cobra Make, Engine: BDR #888, Keith Craft 408
Posts: 344
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Not Ranked
Quote:
Originally Posted by patrickt
Backdraft Parts - Limited Slip Differential That seems pretty high, considering I could buy a new Powr-Lok on ebay for less than $500. What is it that justifies that kind of cost on a BDR? Or, put another way, why does a BMW rear cost two grand for what seems like a pretty straight forward, common upgrade?
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You answered your own question.. It is a BMW part.....
Kevin.... |
07-24-2016, 08:10 PM
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Senior Club Cobra Member
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Join Date: May 2001
Cobra Make, Engine: A CSX Cobra,1966 GT350 and an '06 Ford Heritage GT
Posts: 1,829
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Quote:
Originally Posted by Grey 65
You answered your own question.. It is a BMW part.....
Kevin....
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True. BMW='Break My Wallet"
__________________
"I think we have more machinery of government than is necessary, too many parasites living on the labor of the industrious." Thomas Jefferson
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07-24-2016, 08:54 PM
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Grey, I think I would actually entertain a 3.91. What is the condition/mileage and price please? Thank you.
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07-27-2016, 08:06 PM
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CC Member
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Join Date: Jun 2006
Location: wellington,
oh
Cobra Make, Engine: BDR #260 w/ 347 stroker, Canfield 195 cc heads, prosystems carb on a VicJr, Comp roller cam
Posts: 221
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You can also pick them up on ebay...just remember that BRD cars require 14mm threads on the front bolt. BMW E36 3 91 LSD Posi Differential Limited 325i M3 40 Lock Up Backdraft Cobra | eBay
BTW...i got the 391 gear in mine...I like it!
__________________
BDR#260...21.6K miles logged as of 4/2018 
www.motorheadsohio.com We are an engine machine shop, specializing in crankshafts!
47 years of doing business an going strong! stop on by for a personal tour of the shop
Last edited by tamanaco; 07-27-2016 at 08:08 PM..
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07-27-2016, 09:51 PM
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Thanks Tamanaco, great to know, as I wasn't sure if it would still cruise comfortable on a fast highway sped of around 75 (my usual hwy speed) with the 3.91. I assume the pickup is even better and with both tires hooking up, it really takes off.
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07-30-2016, 05:46 AM
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CC Member
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Join Date: Jun 2006
Location: wellington,
oh
Cobra Make, Engine: BDR #260 w/ 347 stroker, Canfield 195 cc heads, prosystems carb on a VicJr, Comp roller cam
Posts: 221
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Quote:
Originally Posted by Bill Bulmer
Thanks Tamanaco, great to know, as I wasn't sure if it would still cruise comfortable on a fast highway sped of around 75 (my usual hwy speed) with the 3.91. I assume the pickup is even better and with both tires hooking up, it really takes off.
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One thing I did not mention in my final transmission ratio of 0.062 = about 1800 rpms at 60 MPH...you should have an overdrive (OD) transmission for this diff. gear ratio if you plan on doing any highway driving. I guess I was assuming an OD trans in your car.
__________________
BDR#260...21.6K miles logged as of 4/2018
www.motorheadsohio.com We are an engine machine shop, specializing in crankshafts!
47 years of doing business an going strong! stop on by for a personal tour of the shop
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07-30-2016, 05:55 AM
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Yes, I have a .063 final drive (5th gear). Thank you.
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07-30-2016, 09:06 AM
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CC Member
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Join Date: Jun 2006
Location: wellington,
oh
Cobra Make, Engine: BDR #260 w/ 347 stroker, Canfield 195 cc heads, prosystems carb on a VicJr, Comp roller cam
Posts: 221
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Not Ranked
Quote:
Originally Posted by Bill Bulmer
Yes, I have a .063 final drive (5th gear). Thank you.
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You are all set...
__________________
BDR#260...21.6K miles logged as of 4/2018
www.motorheadsohio.com We are an engine machine shop, specializing in crankshafts!
47 years of doing business an going strong! stop on by for a personal tour of the shop
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08-21-2016, 08:21 AM
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I have been doing a lot of soul searching, but after putting some more local miles on the 3.46 open rear, I am confident that the car will be better for me with a 3.91 LSD (I have the .62 5th gear overdrive). It is almost impossible to drive slow with the 3.46, as the engine hates to be run under 2500 RPM (bucking, burbling, snorting, etc.), and when I bring the RPM"s up for some fun, the traction is very limited.
Grey 65 (Kevin), please contact me about your 3.91 again, I am ready to go. Thank you.
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08-21-2016, 01:51 PM
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CC Member
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Join Date: Feb 2006
Location: Gilroy,
CA
Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4V ModMotor
Posts: 2,645
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Bill,
Check out these torque biasing diffs. Wavetrac makes them for BMW also and they are about half of the price you were looking at. No clutches all 9310 gearing and stunningly smooth through the corners. I have one for the 8.8" Ford and there is absolutely no POSI carrier that even comes close.
Click here => Wavetrac
Almost forgot they come with a transferable lifetime warranty.
Ed
__________________
Help them do what they would have done if they had known what they could do.
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08-21-2016, 03:44 PM
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Thank you Ed, I will look into it, much appreciated.
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