Sunday, March 20, 2011

Building a tractor cab.

Having completed the second tractor cab for my 2003 Kubota L3000DT, the first being a miserable failure, I thought I would touch on some of what I learned in the hopes of saving others from my mistakes.

As mentioned the first cab was a train wreck born out of desperation. For starters I began the project well into a tough winter following a subzero ride to scoop out my daughters acreage. Under pressure and looking for quick results I used 1/8 thick angle iron. I did finally manage to fashion a frame with a half- arsed working door, a plexi-glass windshield and piece of plywood for a roof.

The angle iron had too much flex and my haste resulted in a cab which not only was an embarrassment to myself but my entire family both living and dead. With spring breaking I pushed it off into the scrap pile where it rests as we speak.

Rule number one, don't build a cab with angle iron.

Rule number two, don't wait until winter is upon you.

Rule number three, do use square tubing. It holds it's shape and is relatively easy to work with..

Tools recommended, Chop saw, large and small squares, welder, preferably mig, a protractor or angle finder of some sort. An assortment of clamps and vise grips, die grinder with cut off wheel is handy as is a ninety degree die grinder with 2 inch 3M Rol-Loc 36 grit sanding discs

Overview of problems to resolve.

Mounting the cab.

I decided to keep contact between the cab and the tractor itself to a minimum. The lower front of the cab mounts to the loader frame down low. The only other point of contact is the rear mounts which are GM rear wheel drive transmission tail-shaft mounts, PartsMaster Part # 2378.

By limiting the cab to tractor contact points to four I hoped to keep the cab isolated from picking up and amplifying vibrations. No through a very hard winter this seems to have worked well. I figure if the rear mounts settle I can easily put some steel shims under them to regain the proper height.

The door.

Although two doors would be nice with only a door on the left side I was able to make the right side, and the cab itself, much stiffer then had a second door been added.

The door is the most challenging part of the build as it's opening must hold it's shape and space is very limited in particular at the bottom between the frt. of the rear tire/fender and the loader mount. The odd shape dictated by the limited space makes getting a good stiff door opening difficult.

How Wide

Another design issue is how wide to make the cab. The fenders on the L 3000 DT flare in towards the front. It is tempting to narrow the cab up so that you can follow the line of the fender all the way down By moving the cab outboard the cab runs out of fender to follow as it drops down towards the bottom of the door.

I decided to make the cab wide and by using good weatherstripping was able to fill the gap between fender and cab. I am very glad I chose the extra width as it is hard to find room for everything inside as it is. For sure mounting the heater and leaving room for my small dog would have been tough had I narrowed it up.


I chose tinted automotive glass which has a film of plastic between two pieces of glass. This can be glued in or mounted with rubber molding as used in older cars and trucks. The glass shop had the molding in bulk rolls. As my cab was constructed of square tubing I used 1/8 by ½ flat steel spot welded inside the window openings to slip the window molding into. Most of the tack welds on the ½x1/8th inch flat steel were kept on the inside.

The outside seam where the ½ flat attaches to the square tubing needs to be sealed so it does not leak air and water into the cab.

For this I used a epoxy body sealer, Evercoat Maxim, 710822. This fits into a caulk gun. There are two chambers in the tube each holding one part of the epoxy, when you squirt it out it goes though a special end where the two parts are mixed together before they hit the end of the nozzle. I put rubber gloves on using a finger to spread the sealant into the seam. This did work although if doing it again I would try a Popsicle stick

When dried I sanded some and am happy with the way it turned out. You do get two of the special nozzles with a tube of the sealer they being one shot deals due to the epoxy quickly setting up in them. Plan your work accordingly.

I did not make the rear window as large as the opening instead tacking in some pieces of 7 inch wide 1/8 steel in on both the top and bottom to shorten it up. Having been is use for a winter I will report I am happy with this small rear window. I did cut out for lights on the top seven inch piece. Had I to do it over again I would have left the lights off and simply relied on the factory lights which I moved from the fenders to a light bar.

Fitting the windows was more complicated then I thought. For starters I had assumed cardboard would be the perfect material to make the patterns. The glass shop asked I make the patterns the exact size of the opening they then would deduct the margins required to compensate for the width the molding. I tried this on the first window a small fixed side one and it came ¼ inch short. Frustrated but early in the build I simply replaced the piece of ½ inch flat steel with ¾ inch to allow it to work.

In preparing the next pattern, a much larger one, I noticed the cardboard was hard to hold and keep straight. Afraid of getting more glass which didn't fit I chose instead to use some light,and cheap, luan wood floor under-layment. . This I could rough cut then slip into place and mark with a pen. Cutting it closer yet I then used a hand plane to get a perfect fit. I asked the glass company to keep the patterns for me.

Now, if a window did not fit, we would have the pattern to verify it was not I that screwed up.(-:

Of course my windshield was next back from the glass shop and did not fit. Turns out the cutter had forgot he was to allow for the margin and had cut to the exact size of the pattern.

I will add that even the floor underlayment was wobbly, on a couple of the larger windows I screwed some two by twos to the back of them as stiffeners. This all sounds like a big deal but is not, the wood cuts and planes very easily and time spent getting good patterns is invaluable.

This windshield molding is nice stuff to work with and pretty forgiving. I had last worked with this style of window retention in the beginning of my carrier as a mechanic when installing windshields in old Ford pickups.

The one difference between then and now is the moldings I used on the cab have a flap on the back side which when the glass is in place you roll into place to lock the molding into the glass and opening. This works well but takes a knack to roll in and get properly seated. I used a short cotter key puller. If you get everything just right it goes in pretty slick. Certainly helped to use soap water in a spray bottle to lube it up. All I can say is it takes some dinking around to catch on to. The whole time I did it I was thinking there should be a neat little special tool which rolls it in with less effort. Completed I asked the people I got the glass from and found they too use a cotter key puller.

Typically this molding runs the entire distance around the glass with only one butt seam. Normally the corners are curved and you can scoot right around them. I also saw on some cabs they put 45 degree angles on the corners and are still able to use but one piece of molding resulting in a single seam or butt end.

I choose to make the front and back window openings with 45 degree corners and on the side glass went with straight corners which dictated four separate pieces molding for each glass. The front side windows are rather hybrids due to there odd shapes using some of each.

I will note on the lower side windows I chose to use ¼ thick poly carbonate due to some inside corners. I figured cutting the inside corners would be too much of a challenge for my glass shop and that any scratching from use would not be terribly noticeable so far down the belt line. The poly I was able to cut with a jig saw without problem.

As far as cutting the rubber molding I had the best results using a fine toothed hack saw. I made a point to engage the back flap of the molding into it's little groove then lay the molding flat on a wood bench and saw thru it. I found a hacksaw to work just fine. I had much better luck with this method then using a razor knife.

The frame

Back to the square tubing frame. I used 1&¾ by 1/8 inch thick square tubing for the main frame and 1&¼ by 14 gauge for the door and window frames. I considered using 14 gauge for the main frame as most of us, myself included go to thick when using square tubing. Concerns about the integrity of my door opening holding up caused me to opt for the 1/8 inch. No regrets at this time.

The heart of this build, and most likely yours is the front of the cab and how it ties in with the tractor cowl and dash. In my case I was able to come straight up from my perch on the loader brackets then angle the tubing forward and then angle it back this combination let the lower bar which supports the bottom the windshield run straight across the top of the dash panel.

Neat trick.

Setting this front corner up is tricky, mine comes up 22 inches, then angles forward and then angles back. Here I stumbled on a trick I found to be of great aid.

To make a pattern for you corner post grab a piece of scrap square tubing, mine happened to be a length of rusty 1.5 inch 14 gauge. Now do some eyeballing and determine just how far you want to go up to your first angle. . Now take your pattern piece and put in the the chop saw and cut it clear thru with the exception of the very back side. You can now easily bend this to the angle of your choice. Do the same for the next angle joint, being careful you cut on the proper side so you can bend it the direction it needs to go..

Now you have a nice pattern stick you can bend as you please. I was able to clamp mine to the lower leg of the loader brackets and then see just how close I was to being able to cross the dash panel where I wanted and tweak it as needed.

Also now I could stand back and visualize how the cab would look. Once bent you are able to cut the pieces of your corner post out and then laying the pattern right on top of it tack it together, the second corner is made by simply using the first as a pattern.

Two frt. corner posts made you can position them then add the two frt. cross pieces to form your front windshield opening.

A note about chop saws. I recently got a new DeWalt. On this saw I am able to move the back stop forward. This allows one to center the square tubing up exactly under the blade so when you cut thru it comes straight down making it very easy to cut thru the entire tubing without cutting into any of the bottom wall. Without this feature it would have been harder to make the pattern piece as my old saw would have came in at an angle.

A tip on the door and and any opening windows, build the openings first keeping them as square as possible. It is important to keep the margin between the door or window frame and the opening the same all around. I would suggest clamping or tacking into the inside of the opening some 3/16 or ¼ inch , as you see fit,steel plates to act as temporary aids. Now you can fit the individual pieces of the door or window into the frame clamping them to the shims you just installed. Pieces all fitted and clamped you can tack weld them together and when firmly tacked on all corners you can pull it out on the bench for finish welding.

For what it is worth when I built the window and door I did not miter my corners instead simply butting them together. I did cut small pieces of steel and close off the holes left by the open ends of the steel tubing.

For dressing the welds I used a small 90degree die grinder with two inch 3M Roloc 36 grit sanding discs. These work well. They are flexible, fit into tight spaces and give a nice finish to the welds.

With the front end formed up you can start adding the rest of the cab being careful to keep everything as square as possible. One word of caution. I made a simple perch on the ROPS to mount the aforementioned transmission mounts. On my tractor the ROPS is not square with the world. Looks square but is not. I found it best to ignore the slightly out of kilter, 5/8 inch off, ROPS and keep the cab square.

Cab built you will want to fill in all the gaps left between the cab, tractor cowl and fenders.

I used 16 gauge steel to build panels which were then bolted to the cab to fill in between the cab frame and the cowl and pedals ect. This is not so hard as it may seem. Use cardboard to make your pattern. A friend allowed me the use of his plasma cutter, this made short of work of making the cuts. Had the plasma cutter not been available I would have used the die grinder with a cut off wheel.


While making the cab I spent a good deal of time Googling about trying to find a source for weatherstripping which would work well. I came up empty.

However, while taking the wiper motor and transmission out of a friends junked 93 Dodge Dakota I noted a piece of nice four foot weatherstripping between the hood and the cowl. This worked perfectly to fill the gap between the frt. panels and the cowl. Searching for more I visited the local junk yard and found a variety of different styles. Some worked perfectly to seal the door and window openings, others worked well for sealing the cab to fender gap. Most of what I used came from the hood to cowl . Also noted some of the trunks had nice pieces.

You should be able to see in the pictures how you can lay a piece of 1/8 by ½ flat steel on the inside of the door or window, tack it into place and then slip the weatherstripping onto it This worked far better then I could have imagined. On the hinge side of the door and window a simple household adhesive backed weatherstrip worked fine.

Door latch

Looking for a door latch I thought to try a storm door handle. I thought this would be rather chinzy but for lack of something better gave it a try. Very happy with it so far. Also used storm door closer to dampen the door. This also worked out better then expected also.The rubber weatherstripping used has a cushion effect so that with the latch adjusted the door stays nice and tight and the combination of the stripping cushion and the dampener give it a nice vault like feel.


The hardware store was also tapped for the simple steel screen door hinges. These were welded on and have removable pins so both the door and window can be removed.


Now to the roof, I had originally planned on purchasing a formed plastic cab top built by Westendorf Manf. called the Cool Cap. However my son got involved in building canoes which got him involved with fiberglass resins and cloth. As the cost would be much less I opted to simply build the roof from wood, when done we lay two layers of glass cloth across the top to seal the roof and then coated the sides, front and back with fiberglass resin. The underside I coated with polyurethane varnish to seal it up and finally coated the top and sides with a poly-urethane white paint.

Where the wood top contacts the top bars we used the same weatherstripping used to seal up pickup truck camper shells.

I also welded in 45 degree angle braces in the corners of the top roof cage to stiffen it up. These are about a foot long.


A friend had a junked out 93 Dakota pickup which had just what the Doctor called for. As you can see in the pictures the motor mounted nicely into the upper corner the wiper arm fitting into the right lower corner.

Some points on the wipers, be sure to use a motor without the hideaway park feature. On the Dakota one wiper pivot had a long drive arm, one had a short arm. You want one with the long arm. Use the short arm and the lever will go past center. To clarify, the wiper arm off the motor is going to go around in a circle. If the arm on the wiper pivot is as short or shorter then the wiper motor arm it wont go up and down but around and around,or, get pulled to the top and stall at top center.

Also, pay attention to the length of the rod between the motor and the wiper pivot. I cut mine long and then overlapped it playing around with the length clamping the two together with a vise grip to fine tune my wipers down position ect.

Careful on locating your motor . See where the motor parks, when parked you want the motors arm pointing straight away from you wiper arm pivot, if not your wiper will not park at the bottom of the windshield but part way up and then duck down when started before sweeping back up.

There is a lot of geometry in wipers. Rome was not built in a day, study it out before welding anything permanently.

I also swiped the Dakota's wiper switch which mounted nicely onto the Kubota's steering column and also borrowed the washer tank and the delay wiper module.

One other modification to the wipers was the wiper arm itself. As with most arms it is bent to allow the wiper to lay flat along the windshield when parked. My wiper arm originally was mounted on the left side and then swept to the right. This left my angle backwards so when at rest the wiper stuck up at a sharp angle. To fix this I had to pull the bent arm out of the arms base and flip it around. There was rivet holding this outer arm into the base section. I found a short screw to take the place of the rivet and all was well.

Another wiper tweak I went from an 18 inch blade to a 22. Trouble was the holes the arm snaps into are different from 18 to 22 inch blades. This was resolved by snapping the plastic insert from the 18 to the 22.

Yet another wiper tip, pay attention to where you mount the lower pivot arm, play around with how the blade lays against the bottom when at rest and how square it is when at full up and against the right cab corner. By moving the blade pivot location right or left you can find the sweet spot where it works and looks the best.

As for wiring the wipers, I suggest whatever you use go to a friendly auto repair shop and beg, borrow or steal the correct wiper wiring diagrams.

To recap, the TOP six reasons I liked the 93 Dakota wipers.

#1 Park is park, they are not hideaway park where the wipers drop under the cowl out of sight.

#2 The shafts the wiper arms slip onto are not indexed, you can put the arms on any position you want.

#3 The rod which runs between the motor and pivot is easily cut then overlapped, clamped into place, and played with till the length is perfect.

#4 The wiper switch/TS stalk is easy to take off and remount on your tractors column.

#5 Both the motor and the pivot are easy to mount.

#6 You can't beat free. (-:

The point is, certainly there are many used wiper setups that will work. Just make note these are the features you are looking for. If you don't have access to some other used ones and are going to call a junk yard to get one the Dakotas should be plentiful and you know they will work.

I should also note if you are spooked by the wiring and don't wish to wire in the factory switch and have the park feature and intermittent you can simply wire the motor up as on and off.


I inherited a little fleet store heater from my father, a Maradyne Model 8000.The pictures pretty much tell the story here. I will note it is drawing outside air from the underside which keeps the air much drier and less likely to fog

On the Kubota there were no taps for hot water instead you take off the bypass hose which is just a short loop and hook the hoses up to those nipples. Important to note you can not put a shut of valve in this line, the bypass circuit has to have water flowing at all time or your in danger of overheating.

You can install a H valve which will prevent it from being blocked off when shut off. I won't go into the details of how an H valve works but if your going to use one some research is in order. At this time I am not using a water valve of any kind.


As you can see in the pictures 1&1/2 PVC was used to fashion defrosters. I am not saying they don't work but believe they should be larger to really get significant air to the glass, this being said I have had absolutely no trouble with the windows fogging, which I credit more to using outside air, and the dryness of our winter air, then to the defrosters themselves.

Blower speeds.

Searching for the easiest way to control the speeds of my heater fan I found a place on line listing a simple three speed switch with the blower resistor required to give multiple speeds hooked right to the back of the switch. Part number for this unit is 119-9910. Believe it was originally used on early Mustang after market AC units. Quizzing some AC friends on the internet Glenn from La. had one in stock and was kind enough to donate it to the build.

Several storms into this winter I have found the heater to work very well. I have had no problem with the windows fogging up. Coming in from my daughters acreage the other day I had the heater turned to low fan speed with the outside temps about 5 to 10 degrees and was comfortable in shirt sleeves.


For a headliner I simply used a square of ½ inch chipboard which I was just barely able to slip in place around the wiper mount and door closer bracket. A trip to the carpet store yielded a piece of light gray outdoor carpet which is easily glued and stapled onto the chipboard .

The headliner did quiet the interior up somewhat. I had planned on a car radio but instead chose a simple set of ear muffs with the radio built into them. This makes the long trips to my daughters much more bearable. With a regular radio and speaker setup I think the thing would have to be turned up so high to overcome the interior noise it would be annoying.

Sealing it up.

A cold wind will certainly highlight any shortcomings you have in sealing up your cab. I am including pictures of rubber matting I used to seal the area under the seat, around the side levers and also the floorboards. This has been both cheap, easy and effective. The matting is the stuff they use to protect pickup boxes. Got mine at the fleet store for 50.00.

Planning ahead for this matting I welded a1/8 by 1 inch flat bar across the back inside of the cab to bolt the rubber to. This allowed me to attach the matting to the bar and then drape it under the seat and down to the floorboards. This was easier done with the seat out of the way. In the process I built some extensions and raised the seat 2&7/8 inch. This made it much easier to fit the rubber under the seat and also at 6 ft. tall I like the higher seat better. I should note it is still low enough my 5-8 daughter has no trouble working the pedals.

You will note the rubber matting is also used around the clutch pedal and steering arm on the left lower side of the cab. This was a problem area. When pushed in the clutch pedal breaks the plane of the 16 gauge steel panel, when the steering arm, which is right beside the clutch pedal is full back it also breaks the plane but in the other direction. I tried a couple different methods to seal this up finding the rubber matting attached on two sides and loose on two sides was by far the simplest and most effective.


I had planned on using aerosol cans of Kubota orange available from the dealer but at the last minute decided to take to the body shop and have done professionally. As is so often the case, with time running short everything promptly went straight to hell.

Although only one Kubota orange the body shops supplier booted it mixing the paint five shades to light. With storms approaching and glass to put in I choose to go with what we had and if it bothers me I can strip it back down next spring and put it right. As it was the last piece of glass was put in on a Friday night and the first big storm hit that Saturday.

How doe's it work​?

I love it. The door opening and frame, a big concern, are holding up well. I like the way the door feels with the damper and and might add the little locking collar on the door dampener is handy for holding the door open at times. At the end of the dampeners travel the door is open 90 degrees.

Getting out with snow boots on is a little awkward due to the narrowness of the the door opening down low but certainly manageable. Once in plenty of room. The heater does a fine job. The last storm I was driving around in my shirtsleeves with the fan on low, outside temp. was 5 degrees.

The cab is a little noisy as I earlier mentioned, lots of transmission noise and engine noise comes in, the radio headset resolves this. The cab itself is very quiet, no rattles, hums or buzzes.

The cab is perhaps a couple inches higher then it would have to be but with the raised seat I am very happy with it, visibility is good. I had thought I might want to install a small window above the clutch in the 16 gauge steel panel but having put some hours on it do not feel it is needed.

The wiper works very well. Couple days I used them to good effect.


What did it cost to build? I made no effort to keep track of the steel costs. The glass, poly and rubber molding came in at about 700.00, which was less then I expected. The body shop bill was 350.00 This could have been cut had I painted it myself. The wood for the roof, fiberglass resin and ect. I don't think would be over 150.00. The heater, wipers, odds and ends were freebies but I think 250.00 would be fair. With steel maybe 1750.00 or 1800.00 total.


No effort made to keep track, I would guess 150 hours although I am certain a second one could be done much faster.

What is it worth?

I looked up a new cab and believe the Simco was 2500.00 and then you start adding the options, wipers, heater, extra for hard sides ect. When we priced a Kubota cab for Dad's old 520 articulated loader I recall it being well north of 5K.

For me, it was a very enjoyable project which gave me a good deal of satisfaction during the build and once completed and in use I just love it. No comparison to moving snow without a cab as opposed to with one. I actually find myself looking forward to foul weather.

I will list some of the dimensions below.

Main frame square tubing, 1&3/4 by 1/8 inch

Door and window frames 1&1/4 by 14 gauge

Door at narrowest point, 8”

Door at widest point, 26”

Height of door opening, 65”

Front to back at longest point,50”

Seat to headliner, 31”

Height of windshield, 31” width 37”

Height rear window, 22” Width, 37”

Overall height of cab from ground, 91”

Height from ground to floor of cab 22”

About welding on that ROPS.

I believe on my tractor there is a warning to not weld or alter your ROPS. I did. It is as simple as that. You do not have to and I am not telling you to. You can bring up a frame independent of the ROPS to attach your cab to.

For me it seemed like make work to ignore a nice stiff mounting area and I could not see where my welding would weaken the ROPS. You need to be aware of the risks and make your own choices when it comes to safety though. My cab is a one off design, I have done no safety testing of it. I make no claims about it's safety. I am not selling plans, I am simply showing what I built and how I built it. You are in charge of you.

I thank you for listening, Copyright, Roy Gage 2/10/11


  1. This is great! You did an awesome job. I have been planning on building my own cab for 2 winters now and have been stealing the best ideas from all over. You seem to have summed them all up here. The only thing I would change would be to try and use the square tube of the frame as my ducting for the heater.

    Thanks for the great write up,

  2. A wonderful job!! I plan on making one on my tractor sometime in the spring! you got some great ideas , like the window defrost a lot!!!

  3. Best homemade cab on the web, I plan on building my own next year and have read this half a dozen times.

  4. We are managing New Japanese Truck Spare Parts for cab mounts, Mitsubishi Trucks, Toyota Dyna, Hino Trucks and Nissan UD Trucks in Australia.

  5. Great article, wonderful idea to made a homemade cab. Thanks for sharing the idea. Agricultural machinery.