How do I know if I have exceded the rating?

[rockrat]

So I have the truck in for its 140k overall and the brakes are shot. So after a new master cylinder, booster hard and soft lines, I'm just about done. The front rotors were just replaced 2 years ago. Knowing this, I decided to remove the rotors and take them in for a little truing up.

This is a 4x4 and the front is a bit different than other trucks. The rotor slips into (notice that I didnt say out of) a hub with a sealed bearing. This assembly is bolted to the truck and a drive shaft is allowed to go through the hub. The hub diameter is about .050 smaller than the id of the rotor that it fits into.

This little distance leaves room for the rust to build up and expand between the hub and the rotor. So when the book tells me to remove the hub by pulling it off by hand and it does not work, I normally will burn the book and just try to get it apart myself.

So I have the hub and bearing in my little harbor freight 12 ton press. This press has more than paid for itself over the years that I have owned it. I have run the press till it is tight. So I run the jack a bit more and the press gets tighter. Nothing happens and the press is really tight. I'm trying to decide if I will pump the jack again and then I notice on the side of the bottle jack a little note to the user.

Do not exceed the rating of this press

We had a die tryout press at the old shop that had a gage on it so you knew when something might be in a state of shear. It was a good method of not trashing a new die. This has nothing.

How the $&*% would I know if the press was being over run until a catastrophic failure happened? Yes, I can feel the press get tight and grunt. And I know that I should not hang on the bar that I am using to operate the jack. But there is no gage on this thing to show me that the jack is at its maximum "operating pressure".

Maybe I'll get Peter to ship me one of those £700 load cells and I'll make this $50 press into a computerized can crusher or something.

I had thought about locating a place on the jack that I might drill a hole for a pressure gage but that is a project down the road.

I did get the bearing out by using a hammer while the thing was in the press for a little instantaneous tonnage. It finally gave up and I went in to have a victory beer.

What are your thoughts? Run the jack till the frame bends? Hate to destroy a good piece of equipment. Drill a hole that I can put a pre-loaded shear bolt into that would break and fall out at 10 tons?

rock~

[J Tiers]

Dunno ......... the rating is where something breaks, even if that is at 4 tons, I guess...

Watch out too....... I have a JET arbor press, the size which is called "1 ton" for some reason.......

Anyway, the revolving "platen" on it was cast iron..... it broke one day, which is how I found out. I don't know who thought THAT was a good idea.

I don't think I want to see what happens if the blocks that come with the frame presses break due to being cast iron..... probably spray pieces like a grenade at 7 or 8 tons.

[x39]

When it starts to make you nervous, you have exceeded the rating.

[flutedchamber]

I have used my HF 20 ton press quite a lot. I have pumped the jack until it internally bypassed. Whether or not it was above the rating on the jack I don't know.

Put a good amount of pressure on your hub, then tap the disc assembly with a small brass hammer around it's interior circumference. It will pop loose with the vibration from the taps.

[wierdscience]

When you hear the paint cracking that's about max.

Only way to know for sure will be a pressure gauge.Either gun drill the ram,or find a place to tap in a test port in the base.Don't be suprised if you end up needing a 10,000 psi gauge though.

[Willy]

What Flutedchamber said.
Without a gage you really have no way of knowing what the pressure really is. I, like you, have always flown by the seat of my pants as well. And like you I haven't screwed anything up...yet.
But as Flutedchamber suggested get it as tight as you feel comfy with and either strike the bottom of your support plate a good solid smack with a 16-24 oz. hammer or let a good air hammer with a large faced punch rattle the area in question. Usually works for me.
If that doesn't cut it for me then I will either use heat, if possible depending on the part, or I'll take it to somebody with a real press.

[oldtiffie]

Hydraulics safety

The maximum pressure rating and working pressure should be stamped onto the pressure vessel (the hydraulic jack/cylinder).

The maximum rated working pressure is typically half or less of the maximum test pressure.

The best or only way to know what pressure you have in your pressure vessel is to insert a good pressure guage into the pressurised component (cylinder or pressure lines).

The pressure applied is the "pressurised" surface area of the cylinder ram in square inches by the pressure applied in pounds per square inch. This pressure will be in pounds.

To convert pounds pressure applied to tons applied by the ram/cylinder, 2,240. This will ordinarily apply at the pressure guage.

Here is my 20 tonne (pretty well same as 20 ton) hydraulic press with a pressure guage calibrated in psi and tons applied.







My press has a detachable "EnerPac" type portable cylinder for use with the rest of my hydraulic stuff. Some cylinders/rams are rated at 2 tonne, and others at 5 and 10 tonne.



http://i200.photobucket.com/albums/a...ydraulics6.jpg

[saltmine]

What brand/model truck is it Rockrat? The reason I'm asking is because some trucks the hub and rotor are one piece. GM and Ford trucks have removable rotors. Some '80's and '90's Dodges the hubs & rotors can't be separated from the wheel bearing, without destroying the bearing. (I know this after watching my boss try to press apart the rotor & bearing assembly on a 1/2 ton Dodge 4 X 4, and ended up having to buy a new rotor /wheel bearing assembly, $750)

If it's just rust holding the rotor on, a 12 ton HF press should easily handle separating it. I have a 12 ton HF press, and while removing a pinion bearing on a 9" Ford rear end, I bent the crossbeams and the pins, before I got the bearing off. Usually, a hydraulic jack press will bypass if you overload it, and Chinese jacks will fail long before they get anywhere near their MAX rating.
From experience, I usually saturate the hub/rotor area with a good quality penetrating oil before I try to knock them apart. Makes the job go so much easier.

Oh, BTW, if the rotor is that stubborn, chances are, you won't be able to reuse it.

If it is a Dodge, you have to turn the rotor with the bearing assembly on it...if the rotor is salvageable.

[Ken_Shea]

Rock, a bit of heat in the right place won't hurt either.


OT, I like that EnerPak , much better then those short stroke pumps incorporated in many of the bottle jacks.
I just picked up a foot operated pump, 3 pedals, quick pump, a sensitive pump pedal and I don't know what the 3rd pedal does yet

[Willy]

Rock, a bit of heat in the right place won't hurt either.


OT, I like that EnerPak , much better then those short stroke pumps incorporated in many of the bottle jacks.
I just picked up a foot operated pump, 3 pedals, quick pump, a sensitive pump pedal and I don't know what the 3rd pedal does yet

Release the pressure perhaps.

[Ken_Shea]

Release the pressure perhaps.

That was my guess too Willy, I've barely looked at it, should be more obvious when I do.



EDIT:

Yep, just checked, pressure release.

[rockrat]

When it starts to make you nervous, you have exceeded the rating.

Ha! Should have stopped a long time ago if thats the case.

I did get it apart last night and I do have room for turning. Both have good looking outside surfaces but the insides will need touched up. Yes, I'll cut them both.

The truck is a '98 Ford F150. Its been a good truck but I just cant keep the rust under control. My '92 mustang has less rust on it and I drove it through a few winters. The wife had a '95 t-bird that she drove year around and it had less rust on it when we traded it in last year than the truck.

All I can figure is that since I dont know where the truck was for the first 4 years of its life, it must have either been flooded and not reported or came from farther north where the salt seeds were planted long before I go it.

What is even more strange; I replaced some brake line on it a few years back at the same time I had to replace a line on the t-bird. I bought a 20' roll of brake line, bent them up, flared the ends and installed them both on the same weekend. The one on the truck rusted faster than the one on the t-bird. Makes me wonder if the whole truck is electrically charged to rust faster.

rock~

[A.K. Boomer]

I have used my HF 20 ton press quite a lot. I have pumped the jack until it internally bypassed. Whether or not it was above the rating on the jack I don't know.

Put a good amount of pressure on your hub, then tap the disc assembly with a small brass hammer around it's interior circumference. It will pop loose with the vibration from the taps.

Iv got the identical press that Rockrat has - an HF 12 ton - If it has an internal bleed valve I wouldnt count on ever going there, Iv hid behind my 2' by 3' piece of 1/8" aluminum and pushed my press further than I ever should have and even broke one of the cast plates,
What I generally do now is take it to a safe "limit" ( A limit iv tested before many times -- A "limit" thats below the other "maximum limits" that iv verified -- anotherwords -- get to know your press --- and it doesnt take a piece of aluminum to do this -- but a nice chunk of 1/2" thick plywood might help )

Anyways -- take the press there and do what flutedchamber suggested --- first start tapping ----- its amazing what a little frequency can do --- I start with a small little hammer, I also use some liquid wrench, If that dont cut it I start upping the ante -------- its not uncommon to find me a half hour later using heat and the air hammer ( this is by far the greatest tool for setting up frequency's ) and even using the hand sledge to pop the bottom rail upward against the press, Be very careful with the last suggestion as you can build up incredible forces due to the press taking allot of the elasticity out of itself and the materials and then you applying kinetic energies ---- this is how I broke a plate, ---- but its also how Iv removed many of parts over the years that were most likely surpassing the rating of my little 100 dollar press,
I was also standing behind one of the side beams and still had my shield,
I feel it was safe for me but not for the press.
I dont use my press enough to justify putting on a gauge or buying a better one -- sometimes an entire year will go bye without use (actually kinda rare but its happend )
Other than that its like my HF floor jack -- they owe me nothing and have been working for about 2 decades without any real problems (I paid 49 bucks for my floor jack )
I know I'll probably catch hell for this post but Iv actually seen guys with all the bells and whistle's scare the crap out of me so bad that Iv had to leave the room because they dont even align an elongated part correctly and are too focused on their gauges and crap and have their face right in front of the part as its cocked directly towards them ----- so if I sound "irresponsible" for hanging out behind a protective barrier "Well excuuuuuuuuuse me"

[aboard_epsilon]

Here's my 30 ton press ..
i don't know how you would add a gauge to this as it has no lines .

yup, some wheel bearings when pressed out are destroyed...it's that way and is meant to happen.

so best, get a new wheel bearing before...toohand, if you have that type of hub

the hubs on mine defied all effort with a sledge hammer.........yet came out easily with the press that i ended up buying because of this..so i cant see you making and more progress with a hammer ....just damage.





all the best.markj

[Willy]

the hubs on mine defied all effort with a sledge hammer.........yet came out easily with the press that i ended up buying because of this..so i cant see you making and more progress with a hammer ....just damage.

all the best.markj

Mark, much like a bearing puller, proper application of a press does not so much rely on brute force alone, but technique.

While pressure from a puller or press will often move the impossible, it is usually more easily accomplished with a combination of pressure or tension, and the frequency imparted by a hammer blow. More or less along the same principle of an impact gun being more effective at loosening a nut or bolt than a lot of torque with a wrench alone.

The next time you have something in the press and it has nut budged yet, give it a tap with the hammer in the right spot and I'd be surprised if it does not move. And usually with a lot less force being applied.
This technique makes you press or puller think it's a bigger one.