thoughts on replacing front air springs on an MCI

[bevans6]

Well, I just finished changing out the springs, and a long and dirty job it was!  Actual working time was probably about 8 hours, spread over three days.  I thought I would post some thoughts, so that the next guy who uses the search function and needs some tips can start where I finished off...  

Get the bus on level hard surface and air it up.  Jack up the front by both of the axle jacking points, take off both front wheels and block the body jacking points fairly high.  Leave the jacks in under the axle so you can adjust the height of the axle.  

Drain the air from the dry tank, the wet tank and the accessory tank.  Lower the axle so that it causes the levelling valve to think the bus is too high at the front, and this will exhaust all of the air from the front springs.

Soak the 16 ring clamp nuts with penetrating oil of your choice.  It won't really work, but it makes you feel better.  Wire brush the nuts and studs, that won't do much either, but you can do that while you let the penetrating oil soak for a bit.  The challenge with these nuts is the studs are loose in the clamping rings, kept from rotating by two little tabs.  As soon as you start to loosen them, they come out of the holes, the tabs disengage and they start to spin.  You have a couple of options.  You could cut them off with the flame wrench, but there isn't much room and my bus has undercoating that would start to burn, plus they are so rusty they pop and spit all over you (yes, I tried this).  You could cut them off with an air hammer and chisel bit.  That is loud, obnoxious and surprisingly slow (yup, tried this too).  You could make up a cunning tool from a set of those welding clamp vice-grips that have two fingers on each jaw.  Weld a piece of 1/8" strap between the fingers on one jaw, clamp the affair on so that the strap holds the stud into it's hole so the tabs keep it from turning, and access the nut on the other side between the fingers.  Should work a treat.  What I did, not having such a set of vice-grips and it being a holiday up here and the stores closed, is hammer a screwdriver between the ring and the flange, opening up the gap and likewise forcing the stud to engage the hole with it's two tiny tabs.  Eventually all the  nuts come off.  Don't forget the one on the bottom flange that is hidden up inside a hole in the axle  carrier housing.  Drop the axle down so the spring comes free easy, take it out and over to your workbench.

The rings come off the spring with the leverage of a couple of screwdrivers, kind of like dismounting a tire from a rim, just don't poke yourself with the screwdriver when it slips.  Lever them off, wire-brush, glass-bead, sand-blast, and otherwise clean up and paint, since they are all rusty and their original cad plating has all worn off.  Likewise inspect and clean, maybe paint the flanges where the springs seat.  Mine were in very good condition, so I didn't need to do much here.  Install the rings onto the springs then slip the new studs that came with your new springs into place, but first go out to the bus and take a careful look at the relative positions of the holes on the top and bottom mounting flanges for each spring.  None of mine lined up, none of mine matched any other, so they may well be kind of random.  Or they weren't paying attention when they made my bus.  The point is it's a lot easier to get them to line up if they are really close in the first place, because it is hard like the blazes to rotate the rings once they are on the springs.  You could use slippy lube, I chose not to thinking I wanted all the grip I could have once they were on the bus and attempting to hold air.

I installed the lower nuts first.  Wiggle the studs through the holes, which they don't line up for because the spring rubber is pushing them out too far, get two nuts on diametrically opposed studs, crank it down, and you will now be able to get the spring washers and nuts on all the other studs.  Crank them all down, go back and put spring washers under the first two nuts, and don't forget the nut and washer inside the hole in the axle arm.  You have to crank the steering to one lock so the radius rod doesn't block access to the hidden stud-in-a-hole on the rear spring.

Crank the axle up to squash the spring against the top flange a bit.  This makes it easier to line up the holes and get the studs started.  Wiggle, curse, push, prod, and eventually all the studs will line up with and enter the holes.  It helps to get a couple of nuts on a few studs and pull things into place.  Eventually they are all on, double check that none of the studs rotated in the hole and they are all sitting flush with the ring, or they will eventually cut he air bag.  Torque the nuts.  

Repeat on the other three springs.  When they are all in and tight and you have checked you torqued all the nuts and all your tools are out from under the bus,  jack the axle up so that the leveler valve is calling for air (arm angled up towards the back of the bus).  Air up the bus, with the engine or shop air, whatever your choice.  The air system is empty, so it needs to fill entirely and it will take a while for the air springs to come up to pressure.  Eventually the bus will rise up off the blocking, inspect your work, look for leaks, etc.  You could use the time while you are waiting to lube all the  front suspension and steering joints.  When you are happy, take the blocks out, lower the axle so you can install the wheels, torque the wheel nuts, and go have a cool libation of your choice.

And that's how I spent my long weekend in may...

Brian

[zubzub]

Good Post seems to explain everything clearly,....but I'm a little thick these days....you don't live far, maybe you could come by for the weekend and do  the air bags on my '04 so I could learn by watching your technique.   You'll have to do all the bags as the left side and right side will require a mirrored technique and like I said....I'm a little thick these days. 

[Melbo]

I found it easier to use a dremmel and angle grinder to just cut down the center of the studs and split the nuts off --- I used a mirror to see what I was doing on the back side ( got better at it as I went) but you did a very accurate description of what to do and how to do it. If others need help let them supply the beer and you can just point at what they need to do next.

Melbo

[Chopper Scott]

My 7 had brass nuts on all but 2 bags in the rear when I changed them. It didn't take much heat on a brass nut and then I hit them with an impact and off they came. The 2 bags that had steel nuts were another issue however and were on the rear. The fronts are a lot easier than the rears as the rears have 12 versus the 8 bolts in the fronts (? crs). There also are several bolts in the front if I remember right (crs again) that are hidden and you can't get to them with a torch. I was lucky and they came right out. I had a leaky beam that I had repaired but figured that it was only a matter of time so I went with the Mohawk kits and eliminated the beams. Just what I did.

[bevans6]

Ah, brass nuts...     The British cars from the '50's and 60's that I work on from time to time would all come with brass nuts on the exhaust manifolds.  They just wouldn't stick and you could always count on being able to undo them.  Ham-fisted mechanic's hated them, they were only good for about half the torque of the typical grade 2 steel nut.  You would be snugging them up, and just a little bit more and they would strip...  Lotus 18's came with brass nuts for the lug nuts on the wheels, I think due to corrosion issues with the magnesium wheels.  Again not a place for a ham fisted mechanic!

Actually a really good application for brass nuts holding down the spring rings.  If I had any intention of being the guy who, 30 years from now, changes the springs on my bus for the second time in it's life, maybe I would go out and get some!   

thanks for the kind words on my story, I appreciate it.

[Chopper Scott]

There was no reusing them. I'm thinking the brass nuts are a one time deal Brian. Actually they were kind of a pain because the bolts themselves were so corroded on the threads beyond the nut that getting them off was the hard part.

[robertglines1]

Good post..maybe save someone skinned knuckles and a melt down...Scott the newer prevost I have has small 10inch by 6 inch tanks at each air bag to act as the air beam did...the 89 has no tanks or air beam..FYI....Bob

[Chopper Scott]

I thought about doing something like that Robert. It wouldn't be all that hard. After changing to the rolling lobes and eliminating the beams I thought about doing such if the ride had gotten worse. Luckily I can tell no difference. On hindsight I wish I had planned ahead and replaced all the shocks while I was at it but they all seemed to be still in good shape visually.

[roadrunnertex]

Many years ago I had to do the same thing to a PD4104.
Went back together with stainless steel lock washers and nut's also anti-seeze on the special little bolts.
Next person will have it easy on that PD4104
jlv