The Stovebolt Site Forums The Shop Area Driveline 4X4 gears not matching Question

I have searched the internet. I know mismatch front and rear axle ratios is not good. I know that there must be some sort of tolerance to this. I want to use a 3.73 rear with a 3.92 front. Cant find any 3.92 diffs in my area that will work. I do not want to pay for, or know how to, rebuild the present rear. I want to buy a used rear. The net says anywhere from 1% to 10% mix match is OK. Need to know what the Stovebolt community thinks/knows about this. I don't even know how to figure the per cent. Is it 3.92/3.73= 1.05% or is it 3.92-3.73=.19= 5%. ??? If I get a 3.73, I can get a 12 Bolt instead of the present 10 bolt. Truck is a 1960 GMC, 6 lug, 4x4 about 60" WMS-WMS. I believe it is a HO35 (old corporate 10 bolt).

Second question: I believe the HO35 is 55-62. I can find some 55-59 diffs. Most are 3.90/3.92, that's good...BUT why do they have a WWI helmet cover and mine has a ring gear bulge cover??? Did they just change the cover? Do I not have an HO35? Is it a GMC thing? I will check my diff cast numbers, The ring gear is dated 1960.

Chevy used Eaton rears, GMC used Dana, probably D60.

Did you check the blog just to the left, at the top of every single page on this site?
Carl

I have not because I have no idea what you are talking about. Drink something and hit me again.
Also: RE: 1/2 T, the 1960 GMC manual says std rear is HO35.
55-59 GMC manual says std rear is SP45(Spicer). Dana is Spicer, Spicer is Dana.
Anyway I didn't get my answers yet, y'all.

Please do not even try to use gears with that much ratio difference. The factory ratios were only .01 different front to back with the front pulling faster than the back. I know you live in AZ and don't have snow or ice, But I have driven a rig with the gearing difference you want but it was uncontrollable. Too big a difference will cause bind-up and added stress on the driveline, over heated t-case and gear lubes. I would not go as far as 10% difference. Different size tires cause the same issues.

Joe

A difference of say 1% with the taller one in front is common. So a 4.10 front and a 4.11 rear will work. Jeep folks claim that you can go to 4%. I don't know what parts would give you that. The slightly taller gear in the front helps keep steering stable when a lot of slip is involved(mud/snow). Any thing bigger than the 4% limit will put way too much stress on the transfer case, or the axles, and that can't be good.

I am making every effort to see if I can replace the spiders without a dial indicator and a shop press and with no experience.
I really have nothing to loose by taking it apart and if I screw it up, it's pretty cheap for the side gears and spiders kit. I have a friend who is going to advise me via Facebook tutorial. He is in WA state. Good guy. Very knowledgeable. I also don't have a impact or torque wrench that goes to 200-250 for pinion nut. May not mess with that anyway. Thanks for the posts, it's sinking in not to screw around with different ratios even though my sense is that a little is OK, but I can not afford to take a chance on damage to Xfer case. Another good reason is I am finding that another D44(thanks EdPruss) or other with 3.92 that will fit width wise, yoke wise, ebrake wise, with perches in correct place is near impossible. I do not want to spend $900-up for a rebuild. I did a whole nice brake job on that rear! I have been thinking out loud here, all done.
Keep the info and advice coming.

As said before you can't get 3.9 to work with 3.73.You won't even be able to drive it.... If you are having a hard time finding a matching different Assy. Consider a new gear set. In your thinking that a little is okay. ..wrong.On a 4x4 even as much as a 1/4" difference in tire size will destroy a frontend.matching tire brands and sizes are a must. If using mixing brands of tires one needs to measure surface circumference to make sure tires are as close as possible. I'm comfortable being with in 1/8". I say this because if mismatched tires create problems then mismatched gears etc create disasters. Yes some 4x4 setup have a slight ratio difference,as noted before,I'm not arguing that at all. I have repair many 4x4 vehicles that have had failures due to wrong gear set or mismatched tires.I cringe when I hear people who believe they can get away with being somewhat close..Close counts only in horseshoes and hand grenades. In mechanics you do it right or not at all.

That's what I need , an expert's advice. I am going to replace spiders myself. Not that hard. Been viewing/reading pictorials. Thanks Q54. Will not mix ratios or tires. I do know that some factory ratios are SLIGHTLY different, but that is accounted for in other parts of the geartrain.

No problem..just a question though, why are you changing spider gears?

Spiders are chewed up, wanted to just switch to another differential. Can't find a 3.92. Was scared to swap spiders. With help from others I have gained confidence and some knowledge and have parts coming to do it. Will examine other bearings and parts during tear down. I need to do one of these before I die anyway. The spider change out is easy but may find other problems with brgs, backlash, etc.
Found many good 3.73 and was considering the mismatch to front diff (3.92).

Also found out that 1960 GMC has Dana 44, even though my manual seems to indicate HO35 (very different). Mine is a 44-1. It just didn't look like one at first.
Thanks to all of you, I have a plan now.

The Man Card prerequisite has a little known section which requires an applicant to set up at least one set of ring and pinion gears and bearings.
Mine was a 1978 Fiat Spider. Fun finding shims for that one. I will admit that mine worked out more from luck rather than skill.
I still got my Card stamped, never the less.
Good luck to you bart!
Carl

That is just one of several merit badges I am missing. I am a frail thing. Hapless, wondering, wandering......but hey, I do sleep with my socket set and truck magazines. Also like to keep the trouble light on all night. Looking forward to getting that stamp.

Carl, I may get my man card, I've ordered ring and pinion, carrier brgs, pinion brgs, side gears, spyder gears and shim set for my 1960 GMC. I will do it myself. I will do it right. It's show time!!!

I remember at least one GMC 4X4 that had a 3.07 gear at one end and a 3.08 at the other (from the factory). That .01 difference could be tolerated, particularly offroad. I seriously doubt that a greater mismatch would work, unless it was used in a fulltime 4X4 with a front/rear differential built into the transfer case.
Jerry

I absolutely can not find a donor Dana 44 with 3.92 to match front with spring perch and etc. I already did the brakes before realizing the gears were busted. Can not find an honest, reasonable person to install the parts. SO I have studied and studied and bought the parts to do it myself. It mainly takes patients and the desire to be correct. The skill level is medium. Will need to buy 250 LB torque wrench, dial indicator and maybe a press. All that is less than having it done. I've done harder things in my life. It has just always scared me and many others. After reading for weeks, it ain't no thing but a chicken wing. The secret part I did not know was the setup sacrificial bearings that eliminate press on, press off. Dana 44 has no crush sleeve or C clips.

Good call- - - -polishing a few thousandths out of the ID of the old bearings allows you to experiment with shim spacing without taking a chance on damaging your new ones. Once the gear contact pattern looks right, then assemble it with the new bearings. It's also possible to fabricate a "torque doubler" with a piece of 1/4" X 2" flat bar and a sacrificial short 1/2" drive extension. Measure the length of your torque wrench and make a same--length copy of it by cutting the extension in half and welding the pieces into holes drilled in the flat stock. Attach the torque wrench to the female end and put the socket on the square drive of the doubler. 100 Ft/Lbs on the wrench equals 200 at the end of the doubler.
Jerry

Neat trick. Gotta remember that. Ordered a cheapy torque wrench from Amazon. The spec is 200-220 Ft Lb so a cheapy will suffice and be a new tool. I have 4 150 Lb'ers.
Yes, need to grind 3 cone ID's and 1 cup OD.
thanks Jerry, I may PM you if I get "stuck".
Forgot to say I need to round up an Inch Lb wrench. Trying to borrow/rent that locally. Won't need it again. They do have $25 beam types, may do that. The dial is much better but 2much$.

I built a lot of transmissions, rear ends, and steering gears with a deflecting-beam in/lb wrench. You just need to get good at watching the needle, as there's no tattletale indicator on that type of wrench. It would be fairly simple to snug a zip-tie loosely around the indicator bar and get a good guesstimate of the needle deflection, though! Check Ebay for good condition used torque wrenches. When I needed a certified calibration torque wrench for my insurance investigation work, I found a great-condition Snap-On wrench and got it certified for less than half the cost of a new one. Just shop carefully!
Jerry

Roger.

To hotrod Lincoln's point on 3.0 and 3.08...it is common on 4x4 tof have a slight ratio variance...this is so the front different pulls more than the back.makes 4x4 a little more efficient. Also helps to explain why truck hops around while turning sharp corners on dry surfaces,and especially on older trucks why it takes awhile to disengage 4x4.at times the driver would have to back up to get 4x4 to disengage. All this is called gear train wind up.back to the slight ratio difference. ..a lot of the above becomes a lot less of a problem...still there but not so noticeable.

May be true but my Original 1960 GMC had Original dated Ring and Pinions front and back...both 47 12. I now have all the parts to begin rebuild of rear. I was thinking of mismatch a small amount but decided the risk of breaking Xfer case or other components was not worth it. I could not find anything close enough to my 3.92:1 front. Close like 4.10 and 4.11, that's no problem, but no donors close to 3.92. So decided to rebuild it myself. $500 for parts.

I have completed the Dana 44 rebuild by myself. Carl will be proud and give me my man card. I advise him and all others to do it yourself. Do it before you are too old to ever again use all the tools you need to buy. Also it makes you popular. 250 lb torque wrench, inch lb torque wrench, press, bearing separator, pinion yoke holder... It is not hard, it's just mechanical neat stuff and many iterations of shimation. You set backlash, pinion preload, carrier tightness and contact pattern, make setup bearings and read allot. Parts= $500, tools are amortised to future use.(wife story)

Congrats on a job well done!

Enjoy the man card. Remember if your wife wants to SEE it she can. Just don't give it to her.

I'm all "geared" up for it.

Atta boy bart!!!
See you at the next Woman Hater Man Club meeting. (Right next to the AA meeting place, scheduled prior to their meeting, allowing for access for members to attend both meetings.)
Carl

"I'm a man, but I can change, If I have to, I guess."

"Duct Tape Forever!"