Sure-Grip gear/tire size change?

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matthon

matthon

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I have a 67 Barracuda with a 742 3.23 Sure-Grip and 245/60R14 on 14x7 wheels on the rear.

It's a healthy 383 with a tunnel ram and 4 speed.

I'm converting it to a 5 speed, and have set of sbp 15x7 wheels.

A friend suggested 255/60R15 tires with 3.73 gears would be a noticable improvement.

Thoughts?

And forgive my stupidity:

Is it just a matter of buying the gears and a gasket, or are there other parts/items to consider?

Is there a certain brand of gears that is of better quaility?

I never swapped gears in a Sure-Grip, is this best left to an experienced mechanic?
 
Going to the 255/60/15, wont gain you much in tire width, (maybe 3/8") but you will gain about 1.5" in dia and a much greater choice of tires. With the 5 speed that sounds like a winning combo.

You will need: Gears, Carrier gasket, Axle gaskets/seals, New SG gear lube..since your in there anyway, may want to check axle bearings, U-joint, etc.

Ive changed many a complete/built carriers, but never installed my own gears &/or SG into an actual carrier. I have seen more than a few blow up due to DIY swapping of a gear set. I think its best left to a professional who have the tools, know how, etc. jmho.
 
I am using a Tremec TKO 5 speed with 3:91 gears and 255/60-15 rear tires. It is a good setup
 
matthon said:
A friend suggested 255/60R15 tires with 3.73 gears would be a noticable improvement.
Click to expand...
Improvement in what?
What are you expecting from the extra gear?
TKO 500 ratios
3.27 1.98 1.34 1.00 .68
The 3.27 low gear is already 23% more TM,(Torque-Multiplication) than the 2.66 box making your starter gear go from 8.89 to 10.56 a very nice street starter gear. The rest of the spreads look pretty good too. Whereas the 3.27x3.73=12.2 starter gear is for a weakazz smogger-318 .
But in contrast the 1.98x3.73 is a very nice 7.39 second gear that will get you 60mph@5640 rpm.
And the 3.73x.68=2.536 final drive will pull down the cruise rpm to 65=2050 almost too low for any performance street cam to be fuel-efficient at. Bumping the cruise-rpm to 65=2250, would require 4.10s, but this makes the starter gear 13.41, and that is pretty steep requiring a very-early 1-2 shift. And second will now hit 60@6050..

So Ima thinking, the other TKO ratios;
2.87 1.89 1.28 1.00 .64 ,might be a better choice, now with 3.91s. Now the starter gear is 11.22 just barely-liveable, and 60 in second comes to 5510, and 65 cruise is 2020 , Yeah that cruiser gear is down there again, so yur gonna have to cruise faster,lol. or if economy matters to you then chose your cam carefully.
But there is a second overdrive ratio available namely .82, that will cruise at; 65=2590 with 3.91s or 2350 with 3.73s. This set-up with 3.73s will get you a slightly more relaxed starter of 10.78, and a slightly more relaxed 60=5255. But with 3.73s and at 32 mph, the Rs are only 2800 in second/4230 in first so what are you gonna do to accelerate briskly?
I like cruising at 2800 in second because my engine is purring sweetly. And it has enough power to easily initiate tirespin at 32 mph with the BFG 295s back there. Ima guessing your 383TR will do the same with 255s.

If you don't need the overdrive, the A833Commando box is a good alternative. The ratios are 3.09-1.92-1.40-1.00; and with 3.23s the starter is a nice 9.98, while 60 in second is 4620, and 65=2610, easy to tune for economy, and 32mph is 2470 in second/3970 in first; yessiree; we're outta here!
 
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I would prefer to swap the entire carrier, as mine isn't broke so why 'fix' it, and changing back would be easy.

Greater tire selection would be awesome.

AJ, I wasn't even thinking TKO, my apologies I definitely should have posted the trans. It is an A-855.

Ratios are 2.64, 1.92, 1.40, 1.00, 0.70.

My understanding is the 15s with 255s would essentially lower my rear end gear ratio.
 
matthon said:
I would prefer to swap the entire carrier, as mine isn't broke so why 'fix' it, and changing back would be easy.

Greater tire selection would be awesome.

AJ, I wasn't even thinking TKO, my apologies I definitely should have posted the trans. It is an A-855.

Ratios are 2.64, 1.92, 1.40, 1.00, 0.70.

My understanding is the 15s with 255s would essentially lower my rear end gear ratio.
Click to expand...


Wheel size doesn't affect anything. It's tire diameter. If you have a 28" tire it doesn't matter if it's on a 10 inch wheel or a 20 inch wheel. The OD is still the same.
 
matthon said:
I would prefer to swap the entire carrier, as mine isn't broke so why 'fix' it, and changing back would be easy.Greater tire selection would be awesome.AJ, I wasn't even thinking TKO, my apologies I definitely should have posted the trans. It is an A-855.
Ratios are 2.64, 1.92, 1.40, 1.00, 0.70.
My understanding is the 15s with 255s would essentially lower my rear end gear ratio.
Click to expand...

Yeah that 2.64 low gear was a deal-breaker for me. The A855box has almost identical ratios to the standard
A833(2.66-1.91-1.39-1.00) except of course for the added overdrive. Nothing wrong with that if you also convert the rear end to plus 20% over say 3.23s. That would be 3.91s.
That will get you a starter of 10.40/perfect; a second that will get you 60=5600, and a very nice 32@2990; and 65=2210 also very nice.. All math done with 27" tires. Where it counts; those numbers are very similar to the numbers I now run, and IMO, with a 223 to 230 cam, they are perfect,lol..
This 60mph=5600 likes a cam to peak at ~5400 so Ima thinking a [email protected].
The cruiser gear will like a [email protected]
First gear don't much care unless your cylinder pressure is in the basement.
So Ima thinking a [email protected] cam is up the middle, peaking at around 5300. Good headwork will easily carry that to 5600.
A 230/237FTH on110cam cruising at 2210 will suck gas pretty bad. I'd close it up to 108.
A 223/230/110 cam can make great fuel economy@2210.
A 228/110 is in the middle somewhere, but for street, I would close it up some anyway. And with headers,I would ask for no more than a5* split on the intake to exhaust; so 228/233/107. I would make that a fastrate(42* ramps maximum) and install it at 105, for an Ica of 60*, This will give you enough extraction to not go broke filling it up on gas every few hours. At 900 or so ft elevation; this 60* Ica will work pretty good with 9.6 Scr or so. This would make an excellent street combo............. except for one thing; It will roast those 255s to smithereens in no time.

Of course if you have some other cam, then you might wish to run some other than 3.91 gears. I'm just suggesting the above as a good match.

Those 255/60-15s are about 27" tall,
about same as 295/50-15s, same as 275/55-15s, about same as 225/75-14s..
A common tire grouping for our A-bodies is 25.5 to 27, with 28s being about the tallest. From the tallest (28) to the smallest (80) is a 10% difference, equal to the difference from 3.23s to 3.55s, or 3.55s to 3.91s. So yeah you can play that tire-swapping-game if you don't mind mega-tirespin with the 80s, and no sideways traction at all; if the car starts to rotate on you, you will have only milliseconds to correct it, then around you go; forget skinny 80" tires. Forget 80s period.
For straightline work, the taller the better; 275/60-15s are at about the height limit of 28 inches. After that you will have to move the rear axle back or start cutting on the body. I ran that size at one time, and for straightline work it did pretty good. I only moved to the 295s (27 tall) to get the width I needed, to keep from spinning-out all the time.
 
Cam specs below.
383 is fairly stout, aluminum heads, headers. I don't recall the specs on the heads or pistons.
I have been driving it with this combo for many years.
First with 390 Holleys, it made 440/461. After a few seasons I switched to 600s and there was a noticable difference.
This past year I upgraded to efi, and after sorting out a fuel pressure issue, it is definitely a different animal.

Also, the slight hesitation at times with the tunnel ram and 390s was evident, different with the 600s, non-existent with the efi.

So, plenty of info above to read thru and digest.

If I understand what I'm learning here, it appears a taller tire with 3.91s is a good option.

I'm still unclear on the effects of just bolting on a taller tire and not changing anything else?
Or, how to measure, maybe not the best word, where I'm at currently, if that makes sense?

20190506_195022.jpg
 
matthon said:
Cam specs below.
383 is fairly stout, aluminum heads, headers. I don't recall the specs on the heads or pistons.
I have been driving it with this combo for many years.
First with 390 Holleys, it made 440/461. After a few seasons I switched to 600s and there was a noticable difference.
This past year I upgraded to efi, and after sorting out a fuel pressure issue, it is definitely a different animal.

Also, the slight hesitation at times with the tunnel ram and 390s was evident, different with the 600s, non-existent with the efi.

So, plenty of info above to read thru and digest.

If I understand what I'm learning here, it appears a taller tire with 3.91s is a good option.

I'm still unclear on the effects of just bolting on a taller tire and not changing anything else?
Or, how to measure, maybe not the best word, where I'm at currently, if that makes sense?

View attachment 1715331432
Click to expand...


Honestly, if you like to see things graphically you can order a Moroso Power/Speed calculator. They are cheap and you can sit there and change tire size and gear ratio and see the difference at whatever RPM you want.

Or, you can go old school and do the math. I use the Moroso deal all the time.
 
your cam is on the money to make a nice streeter with 3.91s and 27/28 inch tires.
Here's how the tire thing works;
say you had 2000 ftlbs coming out the rear end and 24" tall tires. Those 24s have a radius of 12" and so are a torque arm of 12 inches. And so that 2000 ftlbs makes it to the pavement unchanged.
Now swap on 28s and that torque-arm changes to 14". And so the torque is reduced to 12/14 =.857 and so .857x2000=1714 ftlbs to the pavement. So now if you need the 2000, then you have to increase your rear gear by that same .857 number. If you had 3.23s to start with, then you will need 3.77s just to get it back; 3.23\.857=3.77
Tall tires increase footprint faster than going wider, and so the theory is that they will provide more traction quicker; but there is more science to it than just footprint. Street tires suck because they have short,hard, sidewalls and long-lasting rubber compounds, that are designed to get even harder as they wear out.
So for straightline work,your best bet with them is to go tall.
And for a streeter, I like to gear it to hit the power peak plus about 200 rpm at 60mph, in second gear.. That will make her about as quick as may be expected in any zero to 60 contest, and still have gear enough to cruise with. Overdrive is icing on the cake.
 
I'll look into that Moroso Power/Speed calculator, sounds interesting. Thank you.

AJ, thank you for the explanation, understood.

So, I have an open 8 3/4 with a 741 case in a 62 Dart parts car. Open meaning non Sure-Grip if I have that term correct.

It has the tapered axles, and iirc a spacer between the axles, but none of that matters as I won't be using those parts.

I should be able to put 3.91 gears and new bearings in the 741 and swap that in place of my 742, yes?

Need to make sure the u-joint matches up too.

I'm forgetting the Sure-Grip part though.
Not sure if that is purchased separately, or can be added to the existing 741?

I've read up on the different cases, but it was info overload, but iirc the 741 is on par with the 742.
 
Any factory period SG (SureGrip) will fit in any carrier. Allbeit the TracLoc clutch type takes it's own bearings, and has it's own center spacer.
On the street, I haven't been able to break any of them, there is just not enough traction. The center spacer does have to be transferred into the SG... if it is not already in there.
If you ever solve your traction issues, it would be a good idea to swap to 7290 or even the larger 1350series joints but I don't see 7260s having a problem with the combination of 3.91s, a 2.64 low, and those 255s, all on the street.

Altho I blew up a 7260, going around a slow corner with 295s once......... After that I went straight to 1350s except at the rear yoke; that is now a 7290,with an adapter-joint . After I installed a CenterForce clutch and Type II disc, it shifted so hard,I had the bright idea of making the rearmost joint, a fuse in the system. Bad idea. It was a fuse allright. I got rid of that CFII disc and made the factory 340 disc the fuse instead; much better,and safer, idea. But now that 340 disc regularly spits out springs. So I reduced the clamping force of the CF pressure plate,by spacing it away from the flywheel about .020 IIRC. Now it is both streetable, and the disc lasts waaaay longer. The flyweights seem to be doing their job. I guess I couldda just bought a lesser clutch, or installed skinnier tires, or dropped the cylinder pressure, or installed a 318......lol.
 
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How about a 318 poly?
One for sale near me for $10k with apparently all the available go fast goodies.

Traction issues? I don't have no stinking traction issues! But seriously, it gets up and goes darn good, with the 3.23 though.

I've been running a Centerforce all these years, love it.
Recently replaced the front and rear 7260s, just with new 7260s, when the rear one started clanking away. Glad that's all it did.
I recall quite the discussion regarding the u-joint sizes, since it is an original big block car, but that's what it came with.

A member hinted at selling a new Dr Diff with 3.73s, but I hate taking things 90% of the way to save a few.

I see a new Dr Diff with green bearings, I take it those are best, 3.91, and a 1350 yoke, assuming there is a 7260 to 1350 adapter joint, is $1,375.

Expensive, yes, but seems reasonable.

They only offer the 489 case, my understanding is that is the strongest.

I like their disclaimer, please allow several days turnaround.
Several days?! That's way too long!
 
My advice is to just buy the new Dr. Diff pumpkin with whatever gears you decide in it and the Sure-Grip. "Green bearings" are the wheel/axle bearings. You might as well stick with your original tapered, adjustable, outer wheel/axle bearings if they are in good condition. Just tell Dr. Diff you need the spacer in the differential for those adjustable axle bearings if you decide to keep them. And yes, there is no problem adapting 1350 yoke to 7260 driveshaft, it's done all the time with a conversion U-joint.
 
I misread the website, they are asking for which bearings you have, not what you want.
I was not aware of the different bearings, stock vs green, on the axles.
My guess is a change of bearings requires a press.

I don't see a 1350 to 7260 u-joint on their website, only 1350-7290 or 7260-7290.
I would of course call them first.

Add a gasket kit and let the good times roll.

Mopar 8 3/4" (8.75) 489 Case Third Member
 
I believe the u-joint is a Dana-Spicer DP72601350.

And you're correct, changing the bearings is not a DYI project for the majority of us. As long as the originals are in good shape, there is really no good reason to change them.
 
If you order from Dr D you can specify what rear yoke you want it to come with.

If your bearings are reuseable, a good idea is to repack them. I use a Moly Grease. If the seals are good and the grease doesn't get contaminated, Moly-grease is good to over 20 years. Just reset the end-play now and then.
If you install new tapered bearings, wash out whatever grease is in them, and Moly them.
 
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