The Stovebolt Site Forums The Parking Lot Big Bolts 2-speed rearend strength

Anybody happen to know how much input torque the Timken 2-speed rears (1953 vintage) can handle? The Chevy truck specs give input torque capacity for trannies, but not the rears. I'm looking into swapping in an engine that would have at least 2.5 times the torque of the original.

What is the weak point in these rears? All the gears seem really beefy, but the spurs on the reduction pinions and the corresponding shifter sleeve don't seem too great. Mine has lots of slop in that area (about 1/10 of a driveshaft rotation). That's to be expected, I guess, given its age. But the ring gear key seems like it could be the weakest part. I'd think splines would have been better.

I'm also a little worried about my rearend (well..not so much mine, but my truck's ) because when I drained the gear oil to remove the cover to check things out, it only contained about a third of the quantity that was supposed to be in it (some of which ended up all over the brakes). I have no idea how long it may have been driven with low oil.

Where did you find that kind of spec sheet? I have seen postings with certain claims for HP and Torque but other than engine output I haven't been able to find running gear capacity.

The Chevrolet truck specifications, as reproduced in the Chevrolet truck restoration packs, show transmission input torque capacities, at least for 1953 and 1954, which are the years for which I have the resto packs.

I doubt you will be breaking one of these rears. They put all sizes and types of engines in these trucks, deisels too, with higher torque. If you're gonna put in a big block or such, you won't get enough speed to hurt anything either.

ON the low oil, most I buy have been neglected there, and sounds like you'll need new seals on hubs and brakes now with leak mess. This is another area many old ones I dragged home were needing attention. Parking and setting does more harm than using on these trucks. Some people use synthetic lube now, wonder if you could do that? I have trouble believing that light stuff will lube safely compared to 90 wt. myself??

Gary!

Good to see you around! How have you been?

Regards,
John

well i'll be damned---------IT'S ALIIIIVE-HAHAHAHAHAHAHAHAHA!
HOW THEW HELL YA BEEN GRUMPY?'
and now--the question.

the weak point in the driveline is usually the u-joints and carrier bearing. the diff is pretty well bulletproof. consider the abuse those things get. guys who ain't got a clue grinding the things from 40 mph to an eventual stop, or near stop before they bang like hell into gear, then go flyin' down the road (50 mph) like nothin' happened. and still, after 50 plus years, they still will.

tighten the pinion to take some of the slop out, and yeah-synthetic lubes 10 times better, but is expensive.

i wish i could find a taller set of gears for mine!

Supposedly, the place where these break is out in the corn field; across the rows. The repeated windup and unwind of the axles breaks them. I've never broken one.

These things are very tough. The only thing that breaks them are drivers that dont know how to shift the 2 speed. The pinion bearing is a large double row boll brg. that is very expensive. It can,t be adjusted but Ithink you can replace it with the later roller bearings.

How do you shift it? I have a two speed but have never moved the lever to change gears.

wind it out in gear, and as you do, move the selector. let off the gas and it ought to shift (that's a big ought to).
to downshift, move the selcetor into low, let off the gas and it should downshift.

YOU DON'T SHIFT IN REVERSE OR IN BETWEEN GEARS (NEUTRAL)

it's easy when ya get used to it.

Some one can correct me if I'm wrong. I believe you select the position then when you feel the rpm is right just let off the gas briefly(maybe tap clutch)then hit gas pedal again. The two speed should shift at point of no load when you let off gas. My experience with the 2 speed rears was with electric shift models. The vacuum shifts may reqire a little more time. (The air shifts between Direct and overdrive on modern transmissions is quick.) You will immediately know if you've missed the shift as a 2 speed between gears makes a heck of a racket then you have to play with gas pedal and clutch to get things lined back up. Many people used to just wait until they got into top gear and then shift to the high side. It's all developing an ear for the rpm and the timing of the shift. Have fun.The down shifts are a little tricky as you have to bring the engine rpm up to sycrhonize the drive shaft speed to the lower rear gear.

KoolKar you nailed it in a lot fewer words than my answer

Thanks. I'll try it in the morning.

well if ya screw up ,the truck will let ya know instantly. remember you are matching unsyncronized gears, so the rpm of the driveshaft has to match axle speeds to get the thing into gear right. practice on a deserted stretch of road or a parking lot. most always you will have to come to a stop and start over.

the local fire dept has 1 ford with a gas engine and a 2 speed electric shift. the other day they went busting by my house with lights going, sirens blaring, and the rear end grinding. he had to come to a stop at the intersection just up the road and start over. since i know alot of them guys i had to go by the house and make fun of the guy.

oh yeah, you don't know my backround do ya? spent alot of years in a house down south texas way. we had a b model mack nobody would drive because of the unsync'ed trans. it would pump like no tomorrow, and with a aerial with a 2 stage pump, the mack made a helluva tender. that was most of the time koolkars ride when he worked the red truck and not the bus.

here's good advise for ya. take yer time. don't be too hard on yerself or the truck. patience is a great virtue, and unsync'ed gears are not very forgiving. practice(alot) and the old truck will go like a bat out of hell-----to 50 mph. it's also alot of fun to actually work the truck the way it was intended. that would be basically an 6 speed. (i'm ready for the argument, but honestly, nobody used granny gear)

Ahh...unsynchronized transmissions. I love driving my dad's '30 Fjord AA - that thing will go like a badly wounded bat out of Hades until you hit about 43. Then everyone behind you starts getting ticked off.

I was not expecting it to actually work but it did. It worked first try. It was in low gear. I did what you all suggested and it shifted into high gear. It seems to run less stressed or better on the road that way. Thanks.

When I got my 42 going I told my Dad about the Timken two-speed in it. He worked on many trucks with this differential and said as a rule they were pretty trouble-free. He told that the Kansas Dept. of Transportation once spec'd this rear end in a Dodge truck that had a hemi. They had one operator assigned to this truck who figured out that if he didn't like what he was doing with that truck one particular day, he would put the tranny in second gear, wind the hemi up, and sidestep the clutch. Usually he would smoke the driveshaft, but one time he got the rear end. That was the only one Dad saw broken. In this instance he said the covers that hold the ring gear carrier bearings in broke, which in turn destroyed the ring rear and pinion. The bull gears in the back were OK , though. The low gear bull gear in my truck has a chipped tooth, but has not given me any problems under some VERY big loads.

I drove a big truck for a living and am quite used to an unsynchronized tranny. I still like to use the clutch when shifting the two-speed just to be as easy on the gears as possible. My truck has a mechanical linkage connected to a shift lever inside the cab. It used to have shift cable that ran from the rear end to the rest of the linkage. The cable was very stiff and finally froze up entirely one day. I rigged up a linkage with ball joints on both ends and it works SO much better than the cable.