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Discussion Starter #1
Hey everyone, looking for info on medium duty steerable front drive axle for a build I'm planning. Its gonna be for a 91-93 gmc topkick with a detroit 6v53. The only one I have come across is a rockwell fds-75, they have hydraulic brakes (post '84 have disc brakes), came with a 4.88 ratio but doesnt seem like a popular one. so my questions are 1. how available are parts for this axle ( replacement ring and pinon to get the 4.88 ratio if I cant find one)?, 2. Is there any other axle that I should be on the look out for? I have tried searching in google and forums but not much success, keep running into the same walls everytime. Looking at the newer topicks with the pickup conversion they seem to run a dana 70 most likely beefed up a bit. the only downside i see to that setup is instead of running a duramax (not sure of the weight) and light duty bumper I will be running a 1600+ lbs detroit, and hanging a heavy bumper (homebuilt roadarmour style) with a hydraulic winch and running 46-53" load spec military tires. and dont think the dana 70 will be up to the task. any info or advice will be great

Howie

oh btw the 2 1/2 ton top load rockwell will not work for me, the 6.72 gears are just too much and 1200 bucks each for replacement ring and pinion to bring it down to a 4.60 ratio is way outta my price range and trying not to use custom parts in the drive line.
 

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Rockwells,52" Michelins and an OD 6sp Eaton would put you at [email protected] rpms and 74mph at 2500rpms. How much faster do you want to go? If money isnt a problem use a double OD Fuller or an aux. Spicer unit. No point in a 4.60 axle ratio with those tires. Other routes will run into more money. Ford F600/700/800 4WD front axles are hard to come by and pricey and they are the 2nd cheapest to M35A axles. My 2 cents.
 

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Discussion Starter #3
Thanx for reminding me of the fuller 6 speeds, they have a deeper overdrive than the spicer 3053a I was thinking of using in this truck, might just work with the military rockwells. Ran the numbers on a ratio calculator with those and the 5.29 that is commonly found in the fds-75 axles and the numbers look good at least on paper so it gives me options.

As for how fast I want to go, well want to be able to keep up with traffic on the thruway. Have to go on alot of road calls in the winter for work and also its a 60 mile round trip to work on the thruway, mostly 55 mph speed limit and a stretch of 65mph toll road. I will be driving this truck mainly in the winter to and from work so when the weather is too bad I wont be going that fast, maybe 45 mph in a bad snow storm.

Howie
 

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Good luck with finding info on the FDS75. There's not much out there.
Still don't know if the 4.88 are definite. Or what spline count they were available for. Only see 5.29 sets listed.
The rears seem fairly common, under old Ford F600's, Uhaul trucks and such. Around the '69 year.
Have to rebuild the king pins on mine, haven't taken it apart to find out if it's bearings or bushings.
Have to regear, but that means I have to get a F106 rear, since the existing Spicer axle only has one ratio
compatible with the Rockwell, 6.14 that's in it now. Will go with 5.29 at the very least, but really would like 4.88.
Then I can use 46" tires, don't want to go bigger. Non-OD tranny.
There is some scattered info on Pirate 4x4.
As an aside, spent some time driving a military FMTV couple of weeks ago. If you can, fit LOOONG leaf springs. That thing was really nice, the long springs just soak up the bumps. Like a Caddy compared to an old duece. Not marvelously impressed by the CAT 3126, decent but nothing special. The governor is set too low, 60 on a flat and 62 downhill, not safe. The Allison 7 speed was wonderful. Fun on fire roads. They have Merritor axles, deep ratios.
 

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Discussion Starter #5
Ya seems like any front drive axle for a medium duty is hard to find info on. Was hoping some of the companies would have archive info on stuff from the late 70's to early 90's but when they switch holding companies or come out with a new design the old info just goes away. But part of the fun of this hobby is finding the info that you need.

Howie
 

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Discussion Starter #6
So been searching for a while now and picked up info on various gear sets that were offered in the fds-75 or mx-10-120 rockwell (now meritor) axles. 4.88 were an option and would work great (50-53 in tires are gonna make the truck to big if a lift is needed, I'm assuming it will be). Figure if it was offered by the manufacturer then ring and pinion sets have to be out there somewhere. If I find some I will post the link to make it easier for the next person looking for the same info. If anyone has any info I would be happy to hear it. Still getting the money together and looking fir the right truck to start with so plenty of time to figure this out, just a bit frustrating sometimes,lol.

Howie
 

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check out goodys truck parts in ohio they have parts for fds 75. from what I've learned 5.29 is the "highest" new gear you can get others are available used or reman.

micah
 

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Hey rr, I know this is an old post long dead and you might not be around anymore. But did you ever figure anything out on your front axle problem? I'm hunting for info on a 6v53t 4x4 project too but for a toy hauler. The Axle area seem to be a problem.
 

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If you are looking for a front medium duty drive axle I'd thing Marmon Herrington would be the primary source. They've been building them about forever. Their current line ranges from their light duty unit MT10 rated at 12,000 lb which comes in 8 or 10 lugs and has regular disc brakes. I believe most of the units after that all use air brakes. They have heavier units rated up to 32,000 lbs. What you won't find about them is cheap. They are expensive. Ford offered the model CT8 in a dealer installed kit for the F Superduty (F450) trucks in the late '80's and early '90's. That one is rated at 8000 lbs. Never saw a vehicle with one installed. That kit probably cost half as much as the truck.
 

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Ed, I suspect a Dana 60 would be a bit light for a 1-1/2 ton truck. A Dana 70HD front axle isn't the most common thing around either. You also have the issue of matching lug patterns to the rear axle. Seems the Top Kick used a Fabco SDA-1200 front axle. That company also had an SDA-1400 and SDA-1600
 

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Pricey option is a DANA 80 front diff.
 

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Does Dana make a front 80, or someone weld 60 or 70 axles into an 80 diff?

Ed
DANA 80 front is popular custom aftermarket followed by the GM 14 FF front.......can be built with quad calipers too.
 
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