Jump to content
Prowrench

R model multi leaf steer axle

Recommended Posts

does anyone know what year the R model went from a multi leaf spring on the steering axle to the 3 leaf spring?

Share this post


Link to post
Share on other sites

Mid 70s ?

Share this post


Link to post
Share on other sites
3 hours ago, blackdog2 said:

Mid 70s ?

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

Share this post


Link to post
Share on other sites

They are interchangeable buy taking out spacer block but leaving the wedge .

Share this post


Link to post
Share on other sites
Posted (edited)

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

Share this post


Link to post
Share on other sites
Posted (edited)

And to add, I have a retired 1980 DM686SX with a 20k steer axle, I would guess 12-16 leaves but I never counted that truck.

Edited by JoeH

Share this post


Link to post
Share on other sites

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             

leaf-spring-13.jpg

Leaf-Springs-Front-Mack-R600-12865715-thumb.jpg

Share this post


Link to post
Share on other sites

IIRC the taper leafs first appeared in the 70s, but most heavy trucks were still available with a conventional spring pack well into the 80s and beyond.

Share this post


Link to post
Share on other sites

That's a more accurate phrasing of what you're trying to find out. My 79 is shackled. I have an old U model and a steel dash R Ill look at today and see how they're set up.

Share this post


Link to post
Share on other sites

My 1980 DM is a slipper style rated at 20k, 12 leaf.

Share this post


Link to post
Share on other sites
32 minutes ago, JoeH said:

My 1980 DM is a slipper style rated at 20k, 12 leaf.

A DM is different than an R I'm just trying to figure out what year the change took place, I'm willing to bet it was when square fuel tanks changed to round.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites
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

Share this post


Link to post
Share on other sites

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!

Share this post


Link to post
Share on other sites

Not sure what you mean by bounce the throttle; my 79 gets a hop in the chassis around 45 mph or so, it has the shackle style steering springs. Gotta plant your heel.

Share this post


Link to post
Share on other sites
6 hours ago, JoeH said:

Not sure what you mean by bounce the throttle; my 79 gets a hop in the chassis around 45 mph or so, it has the shackle style steering springs. Gotta plant your heel.

that's exactly what I mean but I never experienced that on the newer springs

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites
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

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...