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R model multi leaf steer axle


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My 79 has 3 leaves on an 11k steer axle, just bought an '88 with 4? Leaves on a 20k steer axle, and I have a 95 with a 16 leaf 18k steer axle.

The 79 is an R686st

88 is an RD690S

95 is an RD688S

It's not really a year thing, it's more of a weight rating thing....

Edited by JoeH
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Well I guess I should have worded my query differently. The older R's had a multi leaf that was pinned in the front and was a slipper at the rear, at some point the R's started using a "taper leaf" which was commonly 3 leaves pinned at front and the rear of that spring pinned to a shackle and the shackle pinned to the hanger drawing is the old style on R's photo is new style What year was the change on R's? the rear spring hanger is very different and maybe the front

On 8/17/2019 at 5:27 AM, blackdog2 said:

Mid 70s ?

That's what I'm guessing wish i could pin down a year             



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10 hours ago, JoeH said:

Probably also around the time they added 3 inches to the back of the R cab too.  

I'm thinking you are correct padded dash, new style suspension and add depth to the cab. I'm guessing the change in the suspension was due to the fact that the old multi leaf would cause your foot to bounce the throttle at 45 mph not 44 not 46 but at 45 and what a pain that was, couldn't give it more throttle unless you shifted to 5th couldn't drop r's otherwise you'd be too low

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ahh, if it were only so simple...

This was back in the age when the customer was always right, even if the customer demanded a Detroit engine, Fuller transmission, Rockwell axles, and about the only thing Mack was the cab and if was a conventional a subcontractor built it. Continental Baking bought 200 odd Mack Western F models with just those specs, they were almost identical to their Freightliners except for the Mack cab. One of the big oilfield service companies bought a fleet of WS models in 1980 with Detroit 6V-92Ts and heavy axles to carry high pressure pumps powered by Detroits. Looking around the new trucks at a Mack dealers lot you'd find similar looking trucks, one with the old style stack of springs and one with taperleaf. And that's just the beginning of the "kid in the candy store" options filling the thick data books... Stuff like "Hotchkiss rear suspension with taper leaf springs", air starters, and a long list of aluminum components up to and including aluminum frame rails... Those were the days!

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My 79 does it, we figure it's just a driveline balance thing or just how the truck is loaded. Started life with a 5tg wheel, but we have a concrete mixer on it with most of the weight sitting on the Camelback.  On a full load I probably have 12.5k on the steer (rated at 11k) and 40k on the Camelback (rated at 38k). My guess if it's not a driveline balance issue is just soft springs on the front with a top heavy load.

Come to think of it, there's a 100 yard section of road near me that would make my 95 rd688s triaxle do it at like 42mph itd get that same hop going. If I went through slower or faster it wouldn't do it. But they repaved the road last year so it doesn't do it any more.

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  • 2 weeks later...
10 hours ago, Dirtymilkman said:

It's all how you order the truck. You can still spec multi leaf front springs. I have had less maintenance with them. It seems the taper leaf eat bushings more often. Multi leafs are stiffer ride though. 

they certainly are, the multi leaf were sandwiched in a slipper pad at the rear which was more forgiving to extreme travel of the spring


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