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1998 Haas VF4 rebuild


Feb 25, 2016
Hi guys, I am starting the rebuild of this 1998 Haas VF4. It has been mistreated in the past and would like to fix most issues with your help and learn from your experiences.
This is my first milling machine :) I would like to share what I have gone through with future Haas users.


I need some advice on how to:
1) Replace the Y axis linear guides. What would be the right procedure to replace and align the linear guides and trucks?
I was quoted $695 from Haas for one linear guide with 2 trucks (PN# 50-9011). The SN# on the runner block: 1651-432-10
It seems that I would need to change both guides and all trucks.

2) Purge way lube system and fix lines. There is no oil pressure (0 psi at the oil gauge). How can I purge the way lube lines? What would be a good warm up program to lube the bearing blocks and ball screws?

3) Replace way wipers (I have replacement wipers)

4) Fix low gear fault in transmission. I will get a low gear fault alarm 118 When homing all axes (air pressure 90 psi at main regulator, Secondary pressure reg at 20 psi when spindle is running). I can still home each axis individually and run the spindle at 1300 rpm, (any lower rpm, I will get a gear fault). UPDATE: I now get a 126 gear fault.

5) Flush transmission oil with Mobile DTE 25. (how to remove the old oil first, not just the over flow)

6) Fix the solenoid. If I remove the red clamp connector wire (purchased as is) I would get a Low Air Pressure Fault

7) replace the "removed" drive sprocket, the drive belt, and drive sprocket
Items# 72, 73, 74 pg 345 from the service manual http://diy.haascnc.com/sites/defaul..._Service_Manual_96-8100_English_June_1998.pdf

8) Fix the chip aggar

9) Fix the coolant pump switch. It does not work from the panel. A separate switch is hardwired to the coolant pump for now. I believe the circuit in the main board is burnt.

10) Fix the door rail. I have to turn the Door hold override on when turning the machine on.

THE VF4 REBUILD TIMELINE (What I have done so far)

powering the machine and installing air compressor

Removed, clean way covers and guards

Cleaned up the machine from old grease and chips
06.jpg 06b.jpg


Feb 25, 2016
Damaged teeth on the "removed" drive sprocket, the drive belt and drive sprocket

Gear fault alarms 118. Update: I now get 126 gear fault

I would love to hear everyone's opinion. Thank your for all your help!!



Aug 3, 2009
I would call it maintenance not rebuild. But ... well the little cam screws can be a challenge if you don't get the gunk out of them. Spray them down and let them soak and blow each allen head out. To do a proper job your going to need to clean the bottom of the table where the truck mounts and the saddle. So you should pull them both off with a forklift and be ready to clean clean clean. You will need to re-establish square as your going. Haas should have a write-up on all this and you should ask them for it. Knowing what your getting is the difference between cleaning a VMC and putting it back together fixed.


Hot Rolled
Sep 14, 2010
Maryland, USA
Welcome to this old Haas. It looks like your starting out right.

With rails neglected like that I can only imagine what the spindle and z axis rails look like. I would suggest you go ahead and remove all the enclosure and Z axis covers for easy access.I would Finish basic cleaning and then go through each system and make a punch list.

Haas is not the manufacturer of the rails or ball screws, you may find better pricing through other sources for most all the industry standard parts, micro switches, solenoids etc.

Good luck and keep us posted!