Zf5 swap or ring and pinion change.

[Dillonn]

My truck is an 86 with a 6.9, auto with a 5:13 rear end as far as i can tell. It is screeming at 65mph. So...
Trans swap or rear end work? The tag on the rear end shows 5:13 if i read it correctly??? I work the truck so i dont want to loose the towing power, this truck runs stong! Any suggestions?

 

[WhiskeyBottle2]

I vote for a zf-5 speed...and 4.10 rear

 

[riotwarrior]

Hi,

Well one thing...YOU DIDN"T mention what transmission you currently have....Auto...which one......I am going with a 3sp meaning C6 then, if that's the case, a Gear vendors OD unit would probably be simplest...just requires shortened drive shaft...

I don't think gear change in diff is good idea...as that would likely be very very very expensive!

If you don't want to go the GV OD then maybe an E40OD swap? Get a built one!

Lastly the Std trans swap as then you have more stuff to add...pedals, master/slave setup etc...

JM2CW

Al

 

[The Warden]

I would vote in favor of the ZF swap...yes, it's a bit more involved than adding a GV or switching to an E4DOA, but IMHO the efficiency gains would be worth it ESPECIALLY compared to keeping the C6 (with no torque converter lockup). Also, I would either pull the rear cover off the differential or do a "spin" test...the F-450 "Superduty" trucks weren't sold until 1987, and were pretty much all equipped with either 4.88 or 5.13 gears IIRC, but 5.13 gears in an F-250 or F-350 weren't very common. More to the point, at 65 mph with 5.13 gears, stock tires, and a C6, you'd be spinning between 3700 and 3800 RPM...which is higher than the stock 3400 RPM governor

FWIW 4.10 gears are usually perfect for these trucks if you're working them...and yes, a R&P swap would be expensive; you might do better to just swap axles. 4.10 axles are pretty common...

 

[dgr]

You are running an F450? With 19.5" wheels? If not, something isn't stock under that truck. You have different tire size choices available to you so you might want to provide more detail or else someone might suggest dropping your gear ratio to something appropriate for a 3/4 or 1 ton truck.

A ZF5 will drop you about 700 RPMs at 65.
4.88 gears will drop you 165 RPMs
4.56 gears will drop you 370 RPMs
a gear vendor will drop you about the same as a ZF5

Gear changes are "cheap" in comparison but you will loose as much low end grunt as you gain in highway speed. An extra gear, either with the ZF5 or a gear vendor will allow you to keep both.

JM2CW

 

[Black dawg]

are you sure it is 5.13?

My vote would be zf swap, but gear change really isnt that expensive if you can do the work yourself. If you have been living with 5.13s, I would keep them and add overdrive. Gearing it taller will take alot of the pull out of it.

t-19 with a gear vendor and 5.13 gears would be a towing machine.

 

[ocnorb]

are you sure it is 5.13?

I second this question?? My '86 with 3.54 gears and the C-6 screamed for mercy at any speed over 60 MPH. The guy I bought it from told me it had 4.11 gears, but when I pulled the cover they were indeed 3.54s.

I love the ZF-5 swap. Made the truck much, much more enjoyable to drive and tow with. (I left the 3.54s in.)

 

[Dillonn]

Many thanks for the replys I will double check the rear end, can anyone point me to the place to look for zf5 parts...

 

[Hydro-idi]

I second this question?? My '86 with 3.54 gears and the C-6 screamed for mercy at any speed over 60 MPH. The guy I bought it from told me it had 4.11 gears, but when I pulled the cover they were indeed 3.54s.

I love the ZF-5 swap. Made the truck much, much more enjoyable to drive and tow with. (I left the 3.54s in.)

My PO told me the exact same thing with my truck. He said it had 4.11 gears in it but it really has 3.55. I had truck at the gear shop getting ready to put 3.55 gears in when he pulled the rear diff pan off and told me....hey, looks like you won't be giving me any money today lol. But yeah my rig is screaming plugging on down the highway too haha. At 60 mph, I'm turning about 2600 rpm. That's also with 235/85/16 towing tires. Other members here say that's about the right rpm/mph ratio.

 

[dgr]

Stock tires are 235/85R16. With the governor at 3300 RPM, your maximum speed is under 61 miles/hour. Go back and reread the whole tag. IIRC, on my tag (4L10) for 4.10 limited slip, the 4 was right next to the bolt head and barely readable. What does the door sticker say for the axle code?
http://www.drivetrain.com/parts_cat...d_ratio_do_i_have_in_my_ford__is_it_posi.html

 

[icanfixall]

An easy way to determine what gears you have is to mark the driveshaft and the inside tire. Jack up the rear of the truck... Some say both wheels need to be off the ground but I did this with just one wheel off the ground. Make sure you block both the front and back of a tire so the truck does not roll away with you under it. Now put the trans in neutral and turn the driveshaft with you hands. Count how many times it turns when the tire mark has made one full rotation. Thats your rear end ratioo. 3/12 turns is 3.55/ 4 and just a little more turns is 4.10 or 11 gears. And 5 turns of the shaft is 5.13 gears. All you need is chaulk and a jack.

 

[Black dawg]

if you only jack up and turn one tire, you have to turn the tire 2 complete turns.