3rd member options?
#2836369
10/23/20 07:13 AM
10/23/20 07:13 AM
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Joined: Jul 2013
Posts: 84 Norway
cudaerik
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OP
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Joined: Jul 2013
Posts: 84
Norway
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I'm in the process of ordering a new complete 3rd member for my 30spline 8 3/4" and my question is what should I order? The vehicle is a 69 Roadrunner with a 500hp 440 backed up by a 5 speed manual transmission. This is a street car with 275 60 R15 BFG's and it will see no tracktime. In my other cars I have always used a Detroit Locker and I'm happy with that but I'm curious about the Eaton true track and Doctor Diff's Helical Gear Sure-Grip ("Sure-trac II") Please advise me.
1970 Plymouth Cuda, 512cid on 230 400 block, 5 speed manual.(TKO 600) 1970 Dodge Charger 500, 446cid, 5speed manual.(TKO 600) 1969 Plymouth Roadrunner, 383cid, 5speed manual (Tremec TKX)
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Re: 3rd member options?
[Re: AndyF]
#2836831
10/24/20 08:46 AM
10/24/20 08:46 AM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Talk to Cass at Doctor Diff. I'm pretty sure the helical is the way to go these days. They are much smoother than a locker and much more reliable than the old clutch pack design. Not sure I agree with the reliability comment, other the then clutch style by design does/ was intended to wear over time, and that time I suspect does vary, other then that I'd also lean for street to the helical style.
Last edited by jcc; 10/24/20 08:47 AM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: 3rd member options?
[Re: AndyF]
#2837318
10/25/20 03:23 PM
10/25/20 03:23 PM
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Joined: Jan 2006
Posts: 704 USA
rftroy
super stock
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super stock
Joined: Jan 2006
Posts: 704
USA
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Talk to Cass at Doctor Diff. I'm pretty sure the helical is the way to go these days. They are much smoother than a locker and much more reliable than the old clutch pack design. Yes. Call Cass. Avoid the Eaton Detroit Truetrac. They have quality issues with the Chrysler 8-3/4 version. I got one and had to send it back. It had a tremendous amount of side play on one of the output worm gears that engage the axle splines. Many reports on Mopar sites about this problem. The play causes the axle splined end to move side to side, in two dimensions, and therefore the wheel to wobble. People have also reported clunking noises. Robert
AAR 4-speed 3.91, Tor-Red; 70 440 6 pack Roadrunner 4-speed 3.54, Plum Crazy; 68 Formula S conv 383 4-speed 3.23, Electric Blue; 69 Barracuda conv Slant 6 OD4 2.94, 71 B5 Blue; 78 Lil' Red Truck, Red; 70 Challenger S/E. 505 6 pack, Passon 5-speed, 3.55, B7 Blue
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Re: 3rd member options?
[Re: rftroy]
#2837385
10/25/20 07:12 PM
10/25/20 07:12 PM
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Joined: Dec 2004
Posts: 10,552 Rittman Ohio
fourgearsavoy
I Live Here
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I Live Here
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Posts: 10,552
Rittman Ohio
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I really don't know what could be more "reliable" than the clutch style sure-grip unit. I have had them in Dana rears and 8 3/4 rears on the track and street with zero issues. If they do happen to wear out you can rebuild it No downside at all IMHO Gus
64 Plymouth Savoy 493 Indy EZ's by Nick at Compu-Flow 5-Speed Richmond faceplate Liberty box Dana 60
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Re: 3rd member options?
[Re: chargerbr549]
#2837472
10/26/20 05:03 AM
10/26/20 05:03 AM
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Joined: Jul 2013
Posts: 84 Norway
cudaerik
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Thanks a lot for the information. I will give Cass a call.
1970 Plymouth Cuda, 512cid on 230 400 block, 5 speed manual.(TKO 600) 1970 Dodge Charger 500, 446cid, 5speed manual.(TKO 600) 1969 Plymouth Roadrunner, 383cid, 5speed manual (Tremec TKX)
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Re: 3rd member options?
[Re: rftroy]
#2837515
10/26/20 11:09 AM
10/26/20 11:09 AM
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Joined: Mar 2007
Posts: 3,277 West Coast, USA
jbc426
master
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West Coast, USA
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Talk to Cass at Doctor Diff. I'm pretty sure the helical is the way to go these days. They are much smoother than a locker and much more reliable than the old clutch pack design. Yes. Call Cass. Avoid the Eaton Detroit Truetrac. They have quality issues with the Chrysler 8-3/4 version. I got one and had to send it back. It had a tremendous amount of side play on one of the output worm gears that engage the axle splines. Many reports on Mopar sites about this problem. The play causes the axle splined end to move side to side, in two dimensions, and therefore the wheel to wobble. People have also reported clunking noises. Robert These are good info. Cass build my A-body 8 3/4 and I had the issue with the play mentioned above. Cass then built me a 489 case 3rd member with the helical Eaton. The only thing I can add is to make sure you use the gear oil without the friction modifier in it. I used the dinosaur oil initially, but now I'm going to use the Redline synthetic without the friction modifier in it. The issue is how hard the wheels lock together which changes with the various gear oils.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: 3rd member options?
[Re: moparx]
#2837608
10/26/20 03:20 PM
10/26/20 03:20 PM
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Joined: Mar 2007
Posts: 3,277 West Coast, USA
jbc426
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West Coast, USA
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Eaton says they use conventional oil when they test/design the units.They state that using friction modifier, in any gear oil whether it be conventional or synthetic will reduce the amount of bias the helical gear set-up will have. In other words it won't lock as hard. They even say that different weights of gear oil have a subtle effect.
Friction modifier is used to reduce potential and actual clutch chatter in the clutch style units.
I am going to use a synthetic without a friction modifier added, which may or may not alter the bias. I have 3.91 gears with a .67 overdrive, so I am looking to reduce heat at modern freeway speeds with the synthetic.If it affects the bias too much, I'll drain the synthetic and go back to conventional gear oil. I just had a drain plug welded into my 8 3/4 to make gear oil changes easier.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: 3rd member options?
[Re: AndyF]
#2837658
10/26/20 05:12 PM
10/26/20 05:12 PM
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Joined: Aug 2003
Posts: 43,127 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,127
Bend,OR USA
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I had a customer who I furnish a new , from Cass , clutch type 8 3/4 posi unit that he had a local shop assemble and installed. I furnish 2 quarts of the non synthetic Valvoline 75/90 WT gear oil along with a bottle of friction additive for the clutches, the shop guy who installed it in the Lawyers car(my customer) use their synthetic gear oil with no modifier. The owner called me very upset that he had almost wreck his 1967 Plymouth GTX on the way home foromm the shop when he started to turn right up his road to his home and the posi unit locked up and almost made him go straight forward into the ditch instead of letting his car go around the corner like normal. I replaced the unit and he had the same experience again so I ended up providing him a helical gear type posi before I found out what that shop was doing to make those posi units act that way My message is to make SURE you use the correct gear lube for your type unit
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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