1979 cabover tilt ram

[RS Disposal]

Did a quick search and didn't really find an answer. Hopefully someone here has some hydraulic knowledge.  While doing some major engine work (long story in another thread) my tilt ram stopped working.  It just locked up solid  Would collapse or extend, even with external pressure.  Just figured it had gone bad being the truck is older.  A new pump was installed and it worked for quite awhile before this happened.  My hydraulic guy wanted almost $800 to rebuild and I was able to get a new one thru Mack for $900 so I went that route.   Installed it and it worked for just one cycle and the it also locked up.  My understanding of a hydraulic ram is very limited, but I for the life of me can't figure out why this has happened.  I do know that the ram has a safety feature in case of a hydraulic line rupture so the cab doesn't come crashing down.  What could I have done to of caused this problem again.  I am thinking that for some reason the safety feature has locked it up for what ever reason.  Any pointers as to what I might be able to do to correct the problem.  If I cant figure it out then I guess I need to take back to dealer and see what they will/can do.  Ram is only 1 week since purchase and only worked for one cycle.  Even took it to my hydraulic guy to put on his test bench to eliminate a possible bad pump on my end.  We are both at a loss as to why a new ram would act up unless I just happened to get a bad ram to start.

 

[Geoff Weeks]

Air in the system can cause the safety check to lock. Basically, the cyl is double sided, fluid on both side of the piston, so for the ram to move oil has to go in one port and come out the other. So if there is no pressure (air) coming out, it slams the ports shut, preventing the ram from moving either way.

 There should be a bleed procedure somewhere in the manual.

[RS Disposal]

On 2/26/2024 at 5:07 PM, Geoff Weeks said:

Air in the system can cause the safety check to lock. Basically, the cyl is double sided, fluid on both side of the piston, so for the ram to move oil has to go in one port and come out the other. So if there is no pressure (air) coming out, it slams the ports shut, preventing the ram from moving either way.

 There should be a bleed procedure somewhere in the manual.

I haven't been able to locate a bleed procedure in the factory trk shop manual.  Haven't had alot of time to research on the internet yet.  

[mechohaulic]

after  safely blocking the cab ;; did you try working the cyl  when it was disconnected from the cab?? no weight on the ram, still having both lines to cyl  =move up/down lever to each position = work pump ??  guess it's a P I A at the moment ,  yrs back cly 's didn't have the check system == I know : sub zero day road call for F model which was left partially up outside . I was under cab leaning over driver steer tire cracking hyd lines ; fortunately I was a LOT thinner back then. might not  be here today . that cab came down super fast . does the pump it self have a breather which is clogged /covered ? clean around pump fill port , remove fill plug /vent -cover with clean rag ;; try pump operation.

[mechohaulic]

rewrite =logged me out 

is this system a single cyl  or two ; can't remember that far back. ?  are the hyd lines aero-quipt or premade plastic style ?? did you try disconnecting the lines from cyl attaching a soda bottle  to each line and work the pump ?? 

[RS Disposal]

On 3/3/2024 at 5:26 PM, mechohaulic said:

rewrite =logged me out 

is this system a single cyl  or two ; can't remember that far back. ?  are the hyd lines aero-quipt or premade plastic style ?? did you try disconnecting the lines from cyl attaching a soda bottle  to each line and work the pump ?? 

This is a single cylinder setup.  The pump was replaced a while back and worked quite awhile with the old ram before the same thing happened.  I just assumed the old ram had dies being over 40 yrs old.  I never did try working ram with the ram un installed but still hooked up.  I did take it to my hydraulic guy and he wasn't able to do anything.  Pretty sure there is something that I can do being i'm sure i'm not the only one that has had this problem.  I just need to find the correct solution.

As far a hydraulic oil, i used just regular jack oil. Didn't consult the factory manual.

[RS Disposal]

Ok, after the ram just sitting on the bench for a couple of weeks cause I got frustrated.  I can now by hand move the piston all the way in and out with no problem.  Mu questions is now , how would be the proper way to bleed if there is an other way from the normal of just cracking the respective line and working the pump until all air is expelled.

Should I be using something other than regular jack hydraulic oil?

Edited March 5 by RS Disposal
additional comment

[mechohaulic]

when you state " hyd guy wasn't able to do anything " ;; do anything or FIND  anything is my question.  seems awkward that system has same problem after two main components replaced. that puts my thought back to POSSIBLE internal line failure/ problem. days of old ,your correct on bleed procedure with crack respective line; can't say same today with internal checks, reason I asked regarding piston ram disconnected from truck and work up/ down piston operation. 

[RS Disposal]

2 hours ago, mechohaulic said:

when you state " hyd guy wasn't able to do anything " ;; do anything or FIND  anything is my question.  seems awkward that system has same problem after two main components replaced. that puts my thought back to POSSIBLE internal line failure/ problem. days of old ,your correct on bleed procedure with crack respective line; can't say same today with internal checks, reason I asked regarding piston ram disconnected from truck and work up/ down piston operation. 

The hydraulic guy said he hooked it up to his test bench and wasn't able to get it to move either direction.  There is no debris in the screens that are in the in ports.  His theory was that even though new the internal checks valve malfunctioned.  I know when I first put it on and bleed the lines the fluid came thru nice and clean with no debris to indicate hose failure

I guess I try hooking it back up tomorrow and see if I can work it without the weight of the cab

[mechohaulic]

this hopefully will be a situation where once issue is solved you will scratch your head and say "why didn't I think of that " ! a simple problem will break b=lls on occasion.is there a screw top on that cyl .. spanner wrench =2 pins holes ?? sure would like to see an internal diagram showing check valve. 

[RS Disposal]

44 minutes ago, mechohaulic said:

this hopefully will be a situation where once issue is solved you will scratch your head and say "why didn't I think of that " ! a simple problem will break b=lls on occasion.is there a screw top on that cyl .. spanner wrench =2 pins holes ?? sure would like to see an internal diagram showing check valve. 

This ram has a c clip type on the end

[stutz 712]

I had trouble with cab tilt on a Cruisliner a few years back.  Blowing lines and pumps and no tilt.  Even replaced a cab lock cylinder to no avail.   Finally started pulling cylinders and found broken seals on the end of the cylinder rod causing it to dead lock.  I know you said cylinder is new but may be worth checking 

[RS Disposal]

update on what is happening

Like I stated previously the cylinder got to the point it would move after sitting a couple of weeks on the bench.  Hooked up to the lines and bleed multiple times.  Was able to extend and retract the cylinder with the pump multiple time. hooked up to the truck and locks up with the weight when trying to lower cab.  unhooked from truck and again was able to extend and retract the cylinder. Only thing I can think of is, even though the pump is new, it is a 2 way pump and worked for a while, it is not specifically a cab tilt pump.  So I ordered a cab tilt pump from PAI.  Maybe something specific about a cab tilt pump that this pump isn't compatible with my system pump

[mechohaulic]

1- does the pump have a breather  cab weight is pushing oil back too fast with clogged breather ??  2- pump pushes cab up to center point and cab will tilt fully over with its own weight ?? thinking of older F-models .. 3- cab fully tilts forward and pump brings it back to center with weight bringing cab back to drive mode ?? opposite of raising cab..  4- even if not a specific cab pump , should still pump if it's a two way pump.

[RS Disposal]

On 3/9/2024 at 5:10 PM, mechohaulic said:

1- does the pump have a breather  cab weight is pushing oil back too fast with clogged breather ??  2- pump pushes cab up to center point and cab will tilt fully over with its own weight ?? thinking of older F-models .. 3- cab fully tilts forward and pump brings it back to center with weight bringing cab back to drive mode ?? opposite of raising cab..  4- even if not a specific cab pump , should still pump if it's a two way pump.

Yes. the cab raises to a center point then fully tilts under its own weight.  To lower, the pump tilts cab back to its center point and then it lowers under its own weight.  That was my thinking when I bought the pump.  It was alot cheaper than a true "cab tilt" pump.  But I did get the new pump today so in the next day or so I will get a chance to see it it works.

[RS Disposal]

Ok guys, this one is totally off topic here, but didn't want to start a whole new thread.  Doing rear brakes on this truck and unfortunately this truck requires the drive hub to be removed to replace shoes.  Can't find anywhere in my factory service manual as to what the axle flange nuts need to be torqued to when putting axle back in. Any help as to what I should be torquing them to.

[mechohaulic]

possibly you can't find  a torque  number based on there might not be one written in "stone". I never torque a wheel hub nut. it was more based on feel (experience )? had one  ole martin flat bed (grease bearings) which took a while to figure. inner nut brought to "spec" the bearing way too tight after install/ tightening outer nut. the inner nut had to be so loose , wheel set wobbled. install outer nut and tighten ; wheel set perfect. oil or grease bearings make a difference. bearings are lubed / center hub filled to max without making a mess light lube on seal  -depending on seal type. C/R seals spin within themselves , I always put small amount of oil on the two mating parts of seal and manually spin the seal before install. ; install outer bearing and all nuts/ locks = bring to a reasonable tight then spin the wheel based on wheel set  was on  a wheel dolly not just hub. if the wheel stops spinning and rolls back - it's a tad to loose. stops to sudden = it's too tight. 

[mechohaulic]

for once I didn't go off topic ==PLEASE NOTE for the record. author did !!🤣

[RS Disposal]

1 hour ago, mechohaulic said:

possibly you can't find  a torque  number based on there might not be one written in "stone". I never torque a wheel hub nut. it was more based on feel (experience )? had one  ole martin flat bed (grease bearings) which took a while to figure. inner nut brought to "spec" the bearing way too tight after install/ tightening outer nut. the inner nut had to be so loose , wheel set wobbled. install outer nut and tighten ; wheel set perfect. oil or grease bearings make a difference. bearings are lubed / center hub filled to max without making a mess light lube on seal  -depending on seal type. C/R seals spin within themselves , I always put small amount of oil on the two mating parts of seal and manually spin the seal before install. ; install outer bearing and all nuts/ locks = bring to a reasonable tight then spin the wheel based on wheel set  was on  a wheel dolly not just hub. if the wheel stops spinning and rolls back - it's a tad to loose. stops to sudden = it's too tight. 

I was able to find wheel bearing nut torques on a previous thread here on this site.  Followed that recommendation and I felt comfortable with it.  My question actually deals with the axle flange nuts where the axle is bolted back to the drive hub

[mechohaulic]

that explains things better. . couldn't find  torque. in todays world of  high tech EVERY fastener has a recommended torque. simple fact is most are unnecessary;; common sense takes priority. axle flange nuts (5/8  fine thread --15/16 socket ). with gasket or without ?? even torque with air gun in staggered opposite location around hub. 

[RS Disposal]

14 hours ago, mechohaulic said:

that explains things better. . couldn't find  torque. in todays world of  high tech EVERY fastener has a recommended torque. simple fact is most are unnecessary;; common sense takes priority. axle flange nuts (5/8  fine thread --15/16 socket ). with gasket or without ?? even torque with air gun in staggered opposite location around hub. 

there wasn't a gasket when I took it apart so I didn't use one putting back together.  I went with what the nut and bolt industry google search for grade "C" nuts using a mid range torque of 100 ftlbs.  The studs do have the tapered cone on them anyway.

[mechohaulic]

gaskets of days gone by ; like many applications are replaced by "goop". hopefully you did put some type of sealant on axle/hub.  with goop sealant the tightening process need more care. reasonable layer of goop then evenly tighten bolts . air gun and super torque uneven may thin out the goop in one area resulting in leak. 

[Geoff Weeks]

2 hours ago, RS Disposal said:

there wasn't a gasket when I took it apart so I didn't use one putting back together.  I went with what the nut and bolt industry google search for grade "C" nuts using a mid range torque of 100 ftlbs.  The studs do have the tapered cone on them anyway.

Aurgh, too late now, but NEVER use goop with the taper cones, it make getting them out the next time a real chore. Use a gasket.

 When you remove the nuts, you should just have to give the flange a rap with a hammer and the cones will pop out. When blue goo is used they stick in the hub and don't release.

 Blue goo can be used on axles with straight studs and plain nuts (no cones), but I used to stock the gaskets and changed every time the axle was pulled.

[mechohaulic]

unsure at this age ; I thought the cone axles always had gaskets? neverseize was used on the cones by me==light film. . don't recall goop and neverseize on same axle which would indicate a gasket was there. hub studs kept gasket in place -if needed a small amount of sealant on hub to gasket area .

[RS Disposal]

23 minutes ago, mechohaulic said:

unsure at this age ; I thought the cone axles always had gaskets? neverseize was used on the cones by me==light film. . don't recall goop and neverseize on same axle which would indicate a gasket was there. hub studs kept gasket in place -if needed a small amount of sealant on hub to gasket area .

I was pretty much just going on the previous axle removal and replace where there was just evidence of silicone and no gasket.  I did make sure that the cones were clean.  I do know that the last time the axle was pulled was 30+ years ago due to a pinion gear break.  This truck sees ALOT of salt in the winter being it works up canyon at the local ski resorts.  I had no problem getting axle out.  Two quick hits with a hammer and the axle popped right out. If the axle ends up showing signs of leaking I will just op it back out and make a gasket.

Previous heavy work was all done by my dad who is no longer with us.  I have been keeping up on the lighter pm maintenance work.  But as far as the more intense work I am pretty much a newbie to heavy trucks, as those of you that followed me on my engine breakdown last summer will attest to.  I asked ALOT of questions.  I am a light truck/automotive mechanic so I do understand the basics of mechanic work.

Shop manuals are great for alot of things, but I highly value real world experience. Particularly on older trucks

Edited March 15 by RS Disposal