No power steering on a Terramite

[BirdmanColorado]

I have owned my Terramite T5C since 1999 having bought it at a rental surplus auction with about 1100 hours on it. Now (June 2020) it has over 2500 hours! I vaguely recall the steering always being hard, but in recent years (maybe it just me getting older??), I noticed the stiff steering as more of an annoyance, so I decided to investigate.

It appears that MANY Terramite T5C owners have issues with power steering. Apparently, power steering is a major weakness…if not the MOST significant failure point of older T5C loader/backhoes. Through forums like this one, I learned that the PS problem is either due to a failure in the steering column valve box, or the adaptor plate on the Eaton hydrostatic transmission.

Whatever the steering column valve box problem is apparently has to do with water freezing in the column tube, upsetting a seal near the steering box, and bingo….problems Galore erupt and show their ugly head. In my case, I did NOT suspect the steering column box because; 1. I could still steer the tractor (albeit hard), and; 2. My tractor is/was always garaged. The steering box still looks new. I REALLY suspected the problem was low/or no boost pressure.

I came upon this thread on TBN which REALLY helped tremendously to drill down to the problem. Posts by bd53bz2 were a gold mine and was the first one to nail the problem I had with my T5C. Subsequent posts from: Wdchyd, cstamm81, and ChippyMcGee provided FANTASTIC information on this forum.

I was so impressed and so grateful for this information, that I decided that I too should register on TBN and take the time to share what I learn and what I experience. THANK YOU bd53bz2, cstamm81, Wdchyd, and ChippMcgee for your information. Now allow me to pay-back some myself with much gratitude for this forum and the kind people who contribute.

More to follow.

 

[BirdmanColorado]

Given the post from ChippMcgee with the Eaton pdf on the hdyrostatic transmission (HST), I determined my HST was an Eaton, P/N 70142-LCL-02. You will find this mechanism also referred to as a “pump.” Consider “pump” and “Transmission” synonymous. Decoding this P/N means my unit had the Gerotor Charge Pump, Lefthand rotation, and incorporated the design code 02 configuration.

This “Gerotor Charge Pump” is the source of the power steering problem folks. This is also referred to in various places as the “Adaptor Plate,” or the “Charge Pump Adaptor.” This sub-assembly is find number 36 on the pdf manual that ChippMcgee kindly provided earlier in this thread (or just Google “Eaton 70142 repair manual”). Another good pdf source of information is called “Eaton Medium Duty Piston Pump, Parts Information” dated August 1995. Google this as well and download for your reference.

Whatever it might be called, this sub-assembly is where the pressure for power steering on the T5C originates. Follow the hose from your steering box to the HST. You will find it attaches at the bottom of this adaptor plate. The Eaton manuals above show this port as being plugged and used for a pressure test point with a gauge. Apparently, Terramite thought it was a good source of boost pressure to use for power steering. It is supposed to generate anywhere from 100 to 300 psi output depending on which HST configuration you have. My configuration was supposed to output 250-300psi (which was pressure to the power steering input hose). How do I know this? Well, you really have to tear-down your unit to find out. I’ll tell you why later, but you have to tear it down anyway, so accept that fate and read on…..

 

[BirdmanColorado]

First, I pressure washed as best I could all around the hydrostatic transmission (HST), hydraulic oil tank, and main pump.. Then, I situated the tractor where I wanted to work on it for a few days. I lifted the back-hoe boom, crowd-dipper, and bucket to farthest up and out position as it will go and propped them up with boards for safety. The tractor in this configuration sends the most oil back to the hydraulic tank which is what you want. See the photo of my tractor in the garage where I did this work.

My first task was to 鍍ee-in a 0-600psi hydraulic pressure gauge in the power steering pressure hose and measure the pressure (sorry, I did not get photo of this setup). I was supposed to have at least 100psi, but the best I got with engine full throttle was 40psi. This confirmed to me that like the others I had read on this forum, my adaptor plate had failed to generate adequate pressure and was the source of my power steering problem.

Given the 都tack of this HST (housing-to-back plate-to-adaptor plate-to-main pump?.I considered just pulling off just the main hydraulic pump to get at the adaptor plate. But doing so would mean the back plate would drop with the adaptor plate as well, things would fall out, and it would be a much bigger mess. So I proceeded to disconnect all hoses, the forward/reverse foot-pedal device, and I pulled the entire HST out of the tractor. Make sure you plug/cap ALL hydraulic open hoses/ports with metal or plastic plugs/caps (I purchased metal caps and plugs of proper thread to accomplish this. Have a large capture pan underneath because you will be catching 3-4 gallons of oil (remember, it is motor oil, NOT hydraulic fluid).

More to follow?

 

[BirdmanColorado]

The first and second slides below show the failure of the adaptor plate pressure relief valve. There was no way to repair the obliterated seat thread in the adaptor plate.

The third slide describes the function of the gerotor/adaptor plate and how the pressure relief valve worked to control desired pressure.

I mentioned earlier you have to read the Eaton manual (the second pdf I mentioned) and then disassemble your HST to learn what charge pressure your machine was intended to produce. The manual says if the adaptor plate relief valve assembly has a tapered spring, the charge relief setting is 100-150 psi. If the spring is cylindrical and has a light green color marking on it, the charge pressure is 200 – 250 psi. If the pressure relief valve spring is cylindrical and has a pink color marking, the charge pressure is 250-300 psi. So you MUST inspect the spring to figure out what pressure your system was designed to have. Mine was pink, so I knew that I should have 250-300 psi in the system.

As the third slide describes, I decided to establish an external oil pressure relief valve that would maintain somewhere on the low end of 200-250 psi (reduced pressure a little bit to reduce stresses).

First, I had a local machinist bore out the pressure relief valve bore in the adaptor plate, then thread the wall between the high and low pressure cavities. He then installed a brass plug (with Loctite) to establish a new barrier in the adaptor plate, totally separating and sealing off the high/low pressure cavities. Although it is hard to photograph given its location deep inside the aluminum adaptor plate, the fourth slide shows the new plug that was installed.

I purchased online a hydraulic relief valve that I could adjust 150 to 300 psi. This was a McMaster-Carr part no. 4704K32.

More later.

 

[the old grind]

....More later....

On behalf of 'the guys' .. "thank you in advance!!!" :drink:

 

[BirdmanColorado]

So I’ll wrap up with this last post and also try to give you some cost perspective (I did this June 2020).

First….the best news of all is that my repair scheme here worked beautifully!! I feel like I died and went to Heaven given that I now have a tractor with power steering (that I did not have for 20+ years!).

The two slides below show my installation. The first slide shows the pressure test setup that I installed to check pressure. I had a healthy 200-225psi reading up to full throttle!! The second slide shows the final installation. All works perfectly, no leaks, and power steering works great!

Now, a bit about cost.

First, I initially explored what it would take to find and buy a new adaptor plate and/or a new (rebuilt??) HST. Suffice it to say I found you CANNOT purchase a new adaptor plate anymore. It appeared that maybe I could buy a whole new HST to the tune of $1,700! Obviously, I quickly ran from that option. I basically concluded that parts for this Eaton unit are just HARD to get or non-existent. I was worried that I was going to have to re-use some of the old o-rings and a crush gasket that was in the HST, but I was elated to learn that I could still buy a “seal kit” for the unit, albeit for a mere $96 after shipping (ouch!). I’m sure this seal kit will probably be history too in just a few more years?

So what did I spend to fix the power steering? Total was about $617. Biggest chunks were the pressure relief valve, seal kit, machine shop cost, two new hoses, and lots of new fittings/gauge that I did not have laying around.

This sounds high, but given that I feel I have a “Like New” tractor now, I think it was well worth every penny. This is especially true with the hard-to-find nature of finding parts for these old Terramites.

Finally, I’ll close by mentioning that I did lie a little bit up front. When I took the adaptor plate to the machine shop, the fantastic machinist I worked with did mention to me another approach to fix my problem. He said that he could thread the bore like he did for the plug, but then go in and machine out the plug to basically serve as a new seat for the original pressure relief valve parts to work in. This probably would have been a little cheaper approach too since I would have saved a new pressure relief valve and the new hoses.

However, my 30 year mechanical engineer experience served me well here to understand the failure mode of this part. That is, the gerotor pump creates a high frequency pressure pulse. This pulse was at or near a first or second order critical natural resonant frequency of the aluminum thread/steel seat combination. Over time (and with different coefficients of thermal expansion going on), the steel threads of the seat just beat to smithereens the aluminum threads. It was an unfortunate bad design.

With that conclusion and not about to repeat the same mistake, I elected to just plug with a similar material (brass) having similar thermal characteristics and move on.

Again, I REALLY appreciate all those who posted before me that helped me tremendously. I’m probably a little late, but I hope my information here will help some other person down the road. Thanks for reading and Good Luck!