I have a drivetrain setup issue

[garydan]

So... I have what looks to be a totally stock 85 blazer front and rear with 3.08's and 35" tires matched to a NP208 transfer case and a 700r4 transmission. This from what I've been reading is a recipe for transmission disaster.

So clearly I need to get some gears. My plan for the truck is a weekend road cruiser, and with infrequent trips off the pavement. It's also important that the truck will be able to tow a boat from the ramp to my driveway every once in a while. I plan on getting a smaller boat (less than 20ft).

Should I go with just a gear swap in the stock 10 bolt. What other options do I have to meet my needs at a reasonable cost? I see all of these 14 bolt FF, SF....etc... I'm still trying to find out what all that means (FF vs SF).. but I see that people are getting great deals out there. What do you suggest. Right now I'm thinking I should get 4.88's in the stock front and rear.

Thank you for your time and suggestions.

 

[Merv]

FF have center hubs that stick out. SF have drum like the 10 bolt flat no hub.

 

[Stomis]

Ok 4.88s since your gonna be towing is a VERY good idea. Your transmission will love you for it. Also get a big cooler on that bitch asap.

Now on the down note I would ditch the 10b rear. You will doubtfully have any trouble with the front 10b occasionally wheeling 35's BUT it wouldnt be a bad idea to keep a small tool kit and spare set of shafts just in case. Like I said ditch the rear 10bolt for a semi or full floating 14b. They're both plenty strong for 35's and towing.

Heres the skinny on SF vs FF.

Full floater: A full floating axle has a hub much like a front axle with a separate bearing system that the wheel rotates on. That hub that you see sticking out is basically a lockout (a term for a locking hub that keeps them locked 24/7) that connects the differential to the hub and drives the wheel. This is a very safe system because if by some freak chance you should pop and axle you wheel wont go anywhere.

Semi floater: A semi floating axle contains an axle shaft with a bearing pressed on the end of it. This axle has the flange and studs that the wheels mount on built into it in once piece. While it is not as clunky and completed of a design it has a few weak points. The first being that most semi floating axles like the 10b (i'm unsure on the 14b) are retained with c-clips. These are clips inside the pumpkin on the axle shafts that stop the shafts from walking out. Another downfall is if you break a shaft your tire is gonna depart from your vehicle . And the final thing I can think of which isnt even major is that the shaft and flange are a welded piece.

Both 14bs are very strong and will suit your needs. The upside to the semi floater is that you can find it in a 6lug to retain your wheels and not change the front axle. The down side is they are hard to find.

Good luck my friend it sounds like your on the right track.

 

[4X4HIGH]

I wouldn't go 4.88's in the stock 10 bolt axles as the pinion gear gets very small and very weak and will break. The best choice for a rear axle would be the 14ff but that would mean you'll need some 8 lug wheels. For what you're wanting to use the vehicle for i would go with 4.56's especially is you keep the front 10 bolt in the rig.

 

[garydan]

Stomis, Thank you that was helpful, things are getting clearer by the day. Where should I be looking to get a 14 bolt rear?

 

[Stomis]

I wouldn't go 4.88's in the stock 10 bolt axles as the pinion gear gets very small and very weak and will break. The best choice for a rear axle would be the 14ff but that would mean you'll need some 8 lug wheels. For what you're wanting to use the vehicle for i would go with 4.56's especially is you keep the front 10 bolt in the rig.

Ah see I always forget about the thin pinion with low gearing... You may get away with it though since the ten bolt has a tiny bit bigger of a pinion stock than the typical axle with a ring its size.

Always here to help though man. Source what you can for your axle. Craigslist, ebay, local junkyards. I believe the semi floater in a 6lug comes from an 88-90 something truck.

 

[Chaddy]

I would get a 14boltFF with 4.56 gears. You will also need an 8 lug front end with wheels to match. Install the biggest trans cooler that you can find.

 

[garydan]

So getting a upgraded ring and pinion in the stock 10-bolt is generally considered a waste of money? As far as 14 bolt FF, What years of GM trucks are interchangeable with a 1985 K5 Blazer? What should I be looking for on ebay or a junk yard?

 

[Stomis]

So getting a upgraded ring and pinion in the stock 10-bolt is generally considered a waste of money? As far as 14 bolt FF, What years of GM trucks are interchangeable with a 1985 K5 Blazer? What should I be looking for on ebay or a junk yard?

In the rear yes, in the front no.

 

[Happyjohn]

Not sure I agree with Stomis. I ran 4.88s in a ten bolt till
I grenaded the gov-bomb, never had an issue with pinion.
Put an Auburn limited in there, was still going when I fell into
a free 14 bolt.
'course, that could be the exception........

 

[Hogback Fabrication]

I wouldn't go 4.88's in the stock 10 bolt axles as the pinion gear gets very small and very weak and will break.

I've heard many rumors alluding to this (and yes, I understand that the pinion gets smaller with higher ratio gears) but do you have any personal experience or proof of this?

I don't really think the 10 bolt pinion is going to be a weak link, but that's partially because I've never seen one break.

 

[4X4HIGH]

I've heard many rumors alluding to this (and yes, I understand that the pinion gets smaller with higher ratio gears) but do you have any personal experience or proof of this?

I don't really think the 10 bolt pinion is going to be a weak link, but that's partially because I've never seen one break.

I had seen enough pics on here of broken pinion gears that were running deep gears but never any personal experience with such.

 

[Hogback Fabrication]

I had seen enough pics on here of broken pinion gears that were running deep gears but never any personal experience with such.

Not trying to be confrontational so don't take it that way

I searched a bit, couldn't find any broken 10 bolt ring/pinion pics on this site (regardless of ratio).

I searched pirate too, not much there.


I know that people occasionally break 10 bolt ring and pinions but they are rarely the weak point, regardless of ratio.

That's my experience, including plenty of people running alloy shafts and joints.

 

[4X4HIGH]

I haven't taken anything as confrontational.

It has been a while since i last seen those pics and i think it was before this site was hacked pretty good so they're probably not searchable anymore. Regardless usually a u-joint is the weakest point but people do stupid things when they get stuck and things break in those instances. Who knows, maybe every broken pinion pic i seen was from driver error in such a situation.

 

[Stomis]

Not sure I agree with Stomis. I ran 4.88s in a ten bolt till
I grenaded the gov-bomb, never had an issue with pinion.
Put an Auburn limited in there, was still going when I fell into
a free 14 bolt.
'course, that could be the exception........

Yeah theres always the exceptions of people who drive right or just get lucky

Theres a few more factors here though. You've got towing which is a huge deal and a money investment issue.

 

[69TowRig]

Good Lord, 4.56s and 4.88s? The guy started with a truck on 30" tires and 3.08s. Just doing the math (which says 35/30*3.08 = ~3.60) he only really needs 3.73s to get slightly better performance than stock, 4.10s would probably be ideal for his towing uses (without completely going out of the RPM range of the engine). Anything more than that would be ridiculous for a DD.

 

[USSkoval]

Good Lord, 4.56s and 4.88s? The guy started with a truck on 30" tires and 3.08s. Just doing the math (which says 35/30*3.08 = ~3.60) he only really needs 3.73s to get slightly better performance than stock, 4.10s would probably be ideal for his towing uses (without completely going out of the RPM range of the engine). Anything more than that would be ridiculous for a DD.

I disagree. 3.08 gearing is crap to begin with, even with little tires. 4.56 or 4.88 will do a much better job of keeping the engine in it's powerband and will also keep the converter locked up easier at higher cruising speeds.

 

[Happyjohn]

Good Lord, 4.56s and 4.88s? The guy started with a truck on 30" tires and 3.08s. Just doing the math (which says 35/30*3.08 = ~3.60) he only really needs 3.73s to get slightly better performance than stock, 4.10s would probably be ideal for his towing uses (without completely going out of the RPM range of the engine). Anything more than that would be ridiculous for a DD.

possibly true in a vacuum. However, 35s are usually wider and heavier,
plus they also raise the truck, increasing aerodynamic drag. this all
puts more of a load on the drivetrain. Minimum for regaining O.E.
performance would be 4.10s, better for towing would be 4.56......

 

[Thunder]

4.88s??....1ton runing gear??? In a weekend warrior road truck that will see little offroad and towing a light boat?
Come on guys. He is not running the Rubicon or towing a house.

4.88 will put the guy over 3000 RPM in drive @65mph Not exactly great for a "Weekend road truck" Plus it will suck fuel like crazy.
1 ton running gear is way over kill.
Keep the 10 bolts and run 4.10 or 4.56 max. either one will be fine for his uses.
If the truck is more road use and fuel milage is a concern go with 4.10
4.10 will put him a little over 1900 RPM @65 in overdrive which will keep the 700r4 happy. In drive 2500rpm @ 65 which is in the middle of the powerband for towing.

 

[blueblazes44]

I agree Thunder. Just use some of the $$ you save on a good trans cooler and you should be fine.