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1986 Unimog U1700L (435 series)
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405 Posts
Discussion Starter #1
Has anyone tried adding a gearbox oil cooler radiator to their vehicle?

Most performance vehicles will have one of these, especially autos. Its usual to add one when upping the HP.

I see that the engine has an oil pump, but no mention in the literature of a gearbox oil pump. I have had a few vehicles, manual and auto with gearbox oil pumps, but I am guessing the U1700L does not have one.
In this case, I would have to add a special pump (and low pressure warning switch), which is a real hassal.
One issue then, is where to pick up and return oil? The obvious candidates are the oil filler and drain bungs (simply add a Tee piece to each).

Has anyone added an oil intercooler and do you know if any kits might be available? I hate designing bespoke if theres a kit out there which is close to what I want.
 

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Unimog U1250
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1,677 Posts
I've looked at this and one way to do it would be a VDO oil cooler pump and an external cooler. When I fit the temperature sensor to the transmission to record the temps to see if there is even a problem. Even after sustained high speeds, I have never measured the temps to be over 80 deg C on mine using the laser temp gun
 

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1986 Unimog U1700L (435 series)
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405 Posts
Discussion Starter #5
I followed the link to the previous post on the topic. My gearbox does not have the shape casting that houses an oil pump. If it did, I could remove the pipe (part 75) and fit an intercooler.

I vaugly recall measuring 75C on the gearbox on a warm day of about 30C. I thought 75C was high.

I can leave the issue and see how it goes when I get it back on the road in a few years time. I just like to plan ahead.
If the U1700 has an oil pump in the gearbox I suspect the discharge is not accesable, unless there is a pressure switch where I can fit a Tee?
Anyone know if there is an oil pressure switch?
 

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1987 435 U1300L OM366A CLAAS overdrive workgroup gearbox
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63 Posts
I have been following a thread on Unimurr forum thinking of a similar install to UG 3/40 I will post some photos. It seems there is an electric pump solution that can be switched on and controlled in the cab. Oil temps below 90 degrees seem to be ok, I think the temp sensors showing over 75 degrees is when the cooler should kick in.
 

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1987 435 U1300L OM366A CLAAS overdrive workgroup gearbox
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63 Posts
From what I can gather there is maybe an outlet for the internal pump? With boxes without the internal pump outlet MB may have installed a system on the MB Trac using the drive shaft of the rear PTO and a supplementary pulley on the gearbox flange to drive a modified steering pump?
 

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1986 Unimog U1700L (435 series)
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405 Posts
Discussion Starter #8
Hi Bunyipben,

Any info on the electric pump ? looks like they have picked up from the drain and fil holes, which is the easiest solution.
 

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1987 435 U1300L OM366A CLAAS overdrive workgroup gearbox
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63 Posts
all I can find from German translation

"The pump is a construction similar to Mocal, but equipped for oils and hardly m by Schlüter Motorsport."
 

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1987 435 U1300L OM366A CLAAS overdrive workgroup gearbox
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63 Posts
Update from another Unimog Owner who has installed an oil cooler to UG 3/40

Hello forum,
Now I have finally installed my gearbox oil pump and it runs and the temperature goes from 100+ degrees to 70-80 degrees down.
Pump and cooler from Mocal in GB.
Pump is a Flojett # D72X003AR Duplex II Diaphragm pump. The cooler I took the smallest of Mocal. My gear is the UG 3/40. I did not want to complicate it and just installed a power switch to start the pump. We live here in the bush and if I make that too complex, it breaks, yes, who and where can it be repaired.
L. G.
Jochen
 

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1986 Unimog U1700L (435 series)
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405 Posts
Discussion Starter #11 (Edited)
Thanks Bunyipben,

This gives me enough info to determin what I need. Not cheap parts though. Need good quality items, as a leak could be catastrophic or very inconvenient if not fixable in the middle of nowhere. Noticed that a good radiator is about $500, same for pump, then the cost of hoses etc. No change from $1k.

Choices: Change gearbox oil more often, or keep it cool and change less often.
 

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'91 U1250 '02 U500NA
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3,438 Posts
Let me think...Windshield wiper blades are less than that.🤑
 

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1986 Unimog U1700L (435 series)
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405 Posts
Discussion Starter #16
Hi andre_
I fitted a temperature sensor to my gearbox in one of the drain holes and wired it to my Madman EMS-2 engine management module.
 

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Ex ADF UL1700
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3 Posts
Hi andre_
I fitted a temperature sensor to my gearbox in one of the drain holes and wired it to my Madman EMS-2 engine management module.
As for fitting the oil cooler - I see some great pics of plumbing this into the drain plugs and return to the rear filler plug. But just wondering where you get the hardware - has anyone found someone who has made one in Aust or an off the shelf product to allow you to plumb into the drain plugs?
One thing I am concerned about is starving or having the transmission overfull. I am assuming before you install an oil cooler fill it up (and the lines and pump etc with oil to determine the additional oil you need in the transmission over and above standard? This would be a pretty accurate exercise if you were circulating the oil from transfer case sump plug to transmission sump plug - because you could while the vehicle is stopped circulate the oil and continue to add oil to the fill plug until it is full.
 
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