Tech Tips

Rear Drive Axle

The Rear Drive Axle (AKA - Rear-end) needs little maintenance other than a periodic check. But, as most you know it is the most overlooked part of an RV as far as maintenance. With standard 80W-90 GL-5 gear lube you should see 100,000 miles before changing assuming it does get contaminated with dirt or moisture. But, with 75W-90 synthetic gear lube you can go 200,000 miles before changing.

The bottle on the left is NEW Mobil 1 75-90W. The bottle on the right has about 30,000 miles on the fluid and is going on 5 years old. Is it to early to change? Maybe, but considering that a coach can sit for days, week's or even months between trips and the trips can be anywhere from a 10 miles to 3,000 miles it's a wonder that it doesn't look like a milk shake due to condensation that gets in via the vent tube.

The Dana 130/150's used on the W22/24 holds 24.5 pints of fluid/gear lube. Yes, that is 12 quarts or 3+ gallons. The price of Mobil 1 75W-90 Synthetic Gear Lubricant is $9 a quart. Products like Royal Purple and Redline cost about $15 a quart.

To drain the rear axle you need a 1/2" drive ratchet to remove the drain plug at the bottom of the rear axle housing. You will also need something the will hold 3 gallons of fluid. I would also suggest that you drain the fluid shortly after you pull in off the road while the fluid is warm.

Once the fluid/gear lube is completely drained replace the drain plug and tighten. You may want to add a little "thread sealant" for insurance against a leak.

Now remove the fill plug on the back to the rear end housing and add 12 quarts of 75W-90 Synthetic Gear Lube or until the fluid start to run out of the fill hole. Be sure that you drain the bottles completely as you can lose as much as a 1-quart if you don't. I used the first bottle and drained each succeeding bottle into it. Once you have all the fluid/gear lube in the rear end replace and tighten the fill plug.

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Oemy's "Utra" Glass Cleaner

I got real tired of water spots on the widows and I tried dang near every product and home remedy known to man to correct it. Some worked a little while others did nothing. But, one day I was working in the bath room cleaning the shower stall and was trying to get rid of some rust stains. I was using a product called Wink. It worked pretty good and cleaned some hard water deposits up. So, I said what the heck and I tried it on the shower glass. Wa La no more water spots. Since then I use a rubber squeegee to remove the water after we are done with showers and only need to do the water spot treatment occasionally.

Next I decided to test it on the windshield and side windows by adding Wink to windshield washer fluid. But, I modified the formula slightly by adding some RainX. This worked really great but there was still something missing. I realized that the paper towel I was using just didn't cut it. So, I switched to a micro fiber cloth and that was the answer. The key is to get the water spots off with the spray and a micro fiber cloth. Then polish the glass with a dry micro fiber cloth.

The basic formula is - 1 oz of Wink and 1 oz of RainX to a spray bottle topped off with windshield washer fluid. You may have to add a touch more of each depending on the size of the spray bottle. It may take as many as 4 or 5 applications get the the water spots off.

One word of Caution - DO NOT use this spray on anything but glass. This is not a general purpose cleaner.

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Evans Tempcon Heater Control Valve

The Evans Tempcon heater control valve has been issue with many RV owners that have it installed. One of the IRV2 contributers found out that the valve has been revised and/or updated. The new valve has a 4 wire connector versus a 3 wire connector.

So,I called Evans Tempcon about the new valve and spoke to their Tech person. She said it is the same design just a different vendor and a different pin configuration and that's why the pig tail adapter is supplied to convert the old 3 pin wiring to a 4 wire version.

The design of the Evans system is called a "stacked" HVAC with the heater core sitting in front of the evaporator. The control valve is not designed to be a "blend" type valve per si. So, if you adjust it to change the heat level it could take as much as a 1.5 mins to see the complete change, according to their tech support rep.

The replacement valve (RV218999) can be ordered from Comfort Air 616-454-2200 and ask for Dave.

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ABS Bypass

The following was provided by John-D an IRV2 contributor.

As a temporary measure you can totally disable ABS on most vehicles and do so very simply.. The only tool you need is... YOUR FOOT.. Yes, your foot.

Simply press the brake pedal and hold it while starting the vehicle and for 30 seconds after the releasing the start switch (key) The ABS light will stay on, alarms will sound, but the ABS will be disabled till the vehicle is re-started.

This does no harm, and will not void warranty

To re-enable ABS.. Shut off and re-start w/o touching the brake pedal

Note - You can press the brakes immediately after the engine catches too.. That's when the ABS is testing the switch.

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Bad Starter Solenoid

Copied with permisson from Max Hubrich

There have been a few reports on a "no start" issue with no previous warnings. After trouble shooting the problem by checking the chassis battery, checking electrical connections, etc the starter is usually replaced. But, when Max Hubrich had this problem he dropped the starter so he could bypass the solenoid to see if the starter would spin and it did. So, he went to the local auto parts store to see if he could get a solenoid. The parts guy indicated that they didn't sell many solenoids anymore just complete starters. He did not have a solenoid for a 8.1L but he had one for a 5.7L. What do you know, an exact match.

Now all he had to do was R&R the solenoid. But, thre is a small problem. It takes a #6 Deep Torx Socket to remove the heat shield and solenoid. Max had to buy a 1/4" drive socket and grind it down for clearence to make it work. Max, was able to fix his stater for about $75 instead of $175 for remanuactured starter or who knows how much for new starter. Here is a photo, supplied by Max Hubrich, that shows the old and new solenoid. It also shows the modified #6 Torx socket and extension Max used.

I have added the above parts numbers plus an AC Delco number to the RV Chassis Parts Xref. I checked my local Autozone store and they had the Wells SS906 in stock.

I have also done some searching for the #6 Torx Socket and found any number of them for $3 and up depending where you buy them. But, the shipping cost is high. So, I thought I would check good old Harbor Frieght and you can get a complete set for $7.

NOTE - I got an Email indicating the a #5 Torx Socket may be a better fit on SOME starters.

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A/C Evaprorator Cleaning

It has been usually warm here in Texas this spring (2009). So, we have had to use the A/C before I had a chance to check out A/C and clean things up. This year it was obvious that the evaporator needed to be cleaned, as there was a musty odor when the A/C was on. It dawned on me that I had NOT cleaned the evaporator coils since it was new, almost 5 years in April. Shame on me.

The first thing you need to do is remove the A/C cover. Mine is held on with 4 screws, 2 on the front and 2 on sides at the rear of the cover.

Next you need to remove the cover over the evaporator. It is held on with 9 screws. 6 are in plain sight, but 3 are under the foam seal at the rear of the evaporator cover. There is foil-backed piece of insulation covering the bottom side of the evaporator cover that you may have release as you remove the cover.

Now don't be surprised when you take the cover off and see the NASTY looking evaporator coil.

The first thing you need to know is the coil fins are VERY THIN and FRAGILE! Almost any side movement will bend the fins. So, be very careful.

So how do you clean that mess? You can get some commercial spray but I do not recommend it as is a mild acid and would probably ruin you roof when you rinse it off. I used VOOM RV Cleaner. You could also use Simple Green, 409 or any other household cleaner. Just be aware that what ever you use the smell will linger on the evaporator coils for a while.

Next you will need a stiff brush with bristles that will get between the coil fins and not damage them. I used a parts cleaner brush.

Lastly you will need a spray bottle to rinse the coils as you brush them in an up and down motion.

The How To:

  1. Put an old towel under the evaporator to collect the dirt and water.
  2. Spray a generous amount of cleaner on the coils and let it soak for 10 to 15 minutes.
  3. Brush a small section of the coils in an up/down motion to loosen the dirt, mold or what ever and rinse with water from the spray bottle. Use plenty of water to flush the junk out the drains on each end of the coil pan. If they get plugged they are a real PITA to unplug. Take your time....

The end result.............

Now just reverse the disassembly process and proceed to the next phase. What you mean I am not done? Yep, You need to clean the air filters inside the coach.

Newmar has a balanced A/C system. When either the front or rear A/C is running alone it will feed the whole coach. But, the majority of the air will flow to area where the A/C unit is located. But, when both are running you get the maximum in each area. On my coach there are 8 Supply/Return air vents.

Although the outside temp was between 75 & 80 the supply air temp was 38 at the vent directly below the A/C unit and 42 at the furthest vent from the A/C unit. The temps were measured with a infra-red thermometer.

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A/C Fan Speed Change

While you are up on the roof cleaning your evaporator coils you might want to consider swapping the LOW and HIGH speed blower motor wires. Why? Assuming you have a Dometic System the Auto cool mode works as follows:

In the AUTO COOL mode, which is the air conditioning mode, the fan will automatically select the speed depending upon the difference between the temperature SET-POINT and the room temperature. When that difference is:

8 or more- The fan will operate on HIGH
4 to 8 - The fan will operate on MED
4 or below - The fan will operate on LOW

If you have a Heat Pump unit there is no MED speed and the temperature difference is 8. Below 8 the fan runs on LOW.

Why is this important? Well, very seldom will you ever see an 8 swing. So, I decided to swap the HIGH and LOW speed wires so my A/C fan runs on HIGH when the temperature is 4 or less.

There is one other option, you can set the FAN to HIGH. But, then the fan runs continuously even after the A/C compressor shuts off.


Remove The Fan Shroud

Next locate and remove the cover to the circut board and fan wires. This cover is held on with 2 mchine screws. One of them may be under the foam seal.

Once you have the cover off you can swap T1 (Black wire) with T3 (Red Wire). Remember, these 2 wires are hot (120 volts) unless you have removed the shore power.

Once the wires are swapped replace the cover, reconnect the shore power and test the system. If everything checks out reinstall the A/C shroud.

Note - I did the swap on both A/C units before I reconnected the shore power for testing.

Now when the A/C kicks in the fan will run on HIGH speed.

But, be aware that if you have the coach setting in the heat with no A/C running and you start the A/C it will probably start in LOW speed and switch to HIGH speed once the temperature drops below 4 below the set point.

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Cooling Fan Switch

Those of us with the twin cooling fans it has been have suggested that they be run for about 2 to 3 mins after engine shut down. The easy answer is to add a SPST switch to turn the fans on & off. But, most switches can't handle a high current draw. Be sides you probably would have a fair amount of heavy wire to run for the power and switch. A better way is to use a relay. This way you only need to run a light 12v signal wire and the heavy stuff is only needed at the relay. I decided to design

I was curious as to how OEM powered the fans and started digging around in the schematics. Take a guess? Yep, a 30 amp Relay that is signaled by the ECM via the A/C. The relay is located in the big fuse box on the firewall.

On my Newmar I had an empty switch location on the dash called Aux 1 that I decided to use. I called the dealer & picked up a lighted switch that fit in the empty spot. The light was not hooked to the switch so I had to wire it in such a manner that the light comes on when the switch is in the on position.

Now I had to find a place to mount the relay. I decided to mount it next to the 20-amp fuse relay that powers my US Gear Aux Tow Brake. This is the perfect spot as I have access to fused 12v power, a short ground wire, an existing hole through the firewall to run the 12v signal wire and a short wire run to the fans.

Switch in the Off Position

Switch in the ON Position

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R & R OEM Fuel Filter


  • 20 mm wrench fuel filter nuts
  • 5/8" Flare wrench fuel tubing nuts
  • inch wrench/socket  - fuel line/filter hold down clamps
  • Open Emd or Adjustable (Crescent) wrenches - Use if you don't have flare wrenches.
  • A container to hold about a cup of fuel (what is in the filter).
  • Disposable rags to wipe up any spilled fuel.

Filter Location:

  • W series - Drivers side frame rail behind the rear duals.
  • P32 series Passengers side


  1. Bleed off the fuel rail pressure. Generally letting the motorhome set for few days will do this.
  2. Using the 20 mm & 5/8" wrench loosen fuel line nuts.
  3. With the wrench/socket remove the bolts from the hold down clamps. Leave fuel filter hold down clamp bolt tight until you are ready to remove the filter.
  4. Using the 20 mm & 5/8" wrench remove fuel line nuts.
  5. With the wrench/socket remove the bolt from the fuel filter hold down clamp.
  6. Put a rag under the fuel filter to catch the fuel the remains in the filter. Remove the fuel filter.
  7. Remove the clamp from the old filter and install it on the new filter.
  8. Check the O rings on the fuel fittings for damage and replace if necessary.
  9. Install the new filter and just get the fuel fittings started, do not tighten at this time.
  10. Install the bolts in the hold down clamps. Just get the bolts started, do not tighten at this time.
  11. Tighten the fuel fitting nuts and then the hold down clamps.
  12. Recharge the fuel rail by turning on the key. Now check for leaks. If there are no leaks start the engine. Again check for leaks.
  13. The install is complete.

Note - If you have to use the Crescents or open end wrenches becareful not let them slip and round off the fuel line nuts.

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