Gearing, tires, and panhard bar

Croatan_Kid

Croatan_Kid

How's your hammer hangin'?
Joined
Nov 4, 2007
Location
New Bern
Just wanted to hear some thoughts and opinions on my next move.


I finally bit the bullet and bought some 37x12.50-17 Cooper STTs and they're simply awesome so far. I love them! They're quiet (for now), balanced out GREAT for a 37" tire, they look great, and they run surprisingly true. The most weight in one spot was 5 oz and I think that's great for a tire that's about 85 lbs. Anyway, I can definitely feel a tire under the truck now compared to the slick 315/70-17 BFG ATs I was running since I did the SAS on this truck.

Currently, the truck has 4.10s. It does alright, but I can tell it takes longer to get up to speed and I certainly have to drop back to 4th gear more than I used to. I'm thinking 4.56s will get me right where I want to be, plus I already bought a used set from @Jody Treadway a while ago for the front and got a killer deal on them.

The front is a 79 Ford hi pinion 60, the rear is an AAM 11.5. I'll probably do the front myself, I've already done it once when I went from 3.55 to 4.10, the same shims got me right where I needed to be, maybe I can get lucky again.


Anyway, here's some math and hard numbers. I usually base my gearing needs on 65mph in 5th gear as that is my most common speed when I'm running up and down the highways. Also, my cam starts to make torque right at 2000 rpm and that's its' happy spot.

The Coopers measure about 36.25 when mounted and with weight on them. The old BFGs measured 33.125. The 336 is a constant, the next number is gear ratio, 65 is the speed, and the .73 is my 5th gear ratio.

Old tires: 336 x 4.10 x 65 = 89,544 /33.125 = 2703 x .73 = 1973 rpm @ 65mph
New tires: 336 x 4.10 x 65 = 89,544 /36.25 = 2470 x .73 = 1803 rpm @ 65 mph

New tires and new gears: 336 x 4.56 x 65 = 99,590 /36.25 = 2747 x .73 = 2005 rpm @ 65 mph

85 mph would put me at 2622 rpm.


Now then, I know re-gearing to 4.56 to gain right at 200 rpm might not seem worth it...which is what makes me think maybe I should try 4.88s. A few companies make a 4.63 for the AAM rear, but I haven't found any for the Dana 60. At least, if I did, I can't remember.

Here's 4.88s:

336 x 4.88 x 65 = 106,579 /36.26 = 2940 x .73 = 2146 rpm @ 65 mph

85 mph would put me at 2806 rpm.


With all that laid out, I never plan to go larger than 37s....ever. Not with this truck and not with the price of tires! I think the 4.56s would suffice and since I already have a set for the front, that's why I'm leaning towards them. Also, if I ever make a long trip, this would be the vehicle I use and interstate speeds are higher which would lead to higher RPMs. I added those in for consideration. Wheeling isn't as big of a concern since first gear is 4.02 and low range is 2.72 and that crawls fairly decent with such a torquey cam. This is also my "nice" truck, so I try not to beat it up too bad.



Sorry for the long post, but let me hear what yall think! Also, since Jody is booked solid for a while...who else does gears? I'm thinking of just rolling up to the guys at ECGS and letting them do it since I need the inner Cs cut off my front axle to get the camber straightened out anyway.
 
4.56 will be a nice overall gear
But 4.88 will be stout in strength

You have your cucv for pullin duties if i remember right
So id put 4.56 in it for every day and light wheelin/towing if it was my rig

sent by telegraph from my k30
 
My thoughts exactly.
 
Anybody else? I guess it's a pretty cut and dry situation that doesn't leave a lot of room for discussion..
 
I'm also fairly certain I need to add a panhard bar setup in this mix. The front axle has plenty of lateral movement available when I'm turning and I'd like to keep it as tight as possible. I've been looking at the kit that Ruff Stuff sells, but it'd be pretty cool to have one built for it. It's mostly a price thing, but I'd also have a problem matching the angle of the draglink without a bent panhard bar since I have a bent draglink.

The front uses Off Road Direct brackets and 73-87 Chevy style springs. Basically, they're 47" long and 2.5" wide with 3 or 3.5" wide bushings, however the springs are Alcan packs. I know most setups don't usually run a panhard on a leaf spring setup, but then again, this truck was never meant to have a solid axle and leaf springs under it. BTW, this is my 99 Silverado.

Any of the "local" NC shops want to take a crack at it? It'd be cool to meet some people and get some sweet work done as long as the price is right!
 
Running a track bar on a leaf set up will cause a lot of binding

Are you running polyurethane bushings at all points up front ?

sent by telegraph from my k30
 
Yeah, poly bushings. A panhard on a leaf spring setup won't cause much bind as long as the drag link and panhard are in line. Powerstrokes come with them from the factory.
 
A large number of leaf spring vehicles have panhards from the factory. They do bind some when looking at higher travel amounts but by fully constraining the suspension it would provide a much more predictable setup on the street.

I would suggest building an adjustable bar with poly bushings at atleast one end.

ideally you want the panhard to be the same angle and add long as the drag link but its not critical to follow completely. Measure the horizontal & vertical distance between the ends of the drag link with the tires strait. Find the slope and build a panhard with the same slope.

While its a haul, metalwerx could take care of both for you. ECGS likely could also.
 
I agree. I'd like to put a bushing on one end of it. It would help calm it down and absorb some of the feedback it would get. I think it may be a little more forgiving on a leaf spring setup than a link suspension since they depend on a panhard bar way more than the leaves would.
 
Forgot to mention this...


Call me a cheap ass if you want, but I got on Randy's R&P website to see what gears were available for the 60 front. Just like a thought, normal ratios. 4.10, 4.56, 4.88. The AAM has 4.10, 4.30, 4.44, 4.56, 4.63, 4.88....I guess they finally realized they can make more optimal gearing for all the different tire sizes out there now.

Anyway, little did I know that they sell used R&P sets. How could I say no to a set of 4.56s for just over 100 bucks?!
 
I dont know how much of a rush you are in but I would be more than happy to help you out on the the cut and turn and I can do the gear installs.
you have my number if you want to get up with me next week to discuss it.

Buckeye Performance Inc.
828-779-2242
 
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