Technical X1/9 Rear Differential What fluid type?

[vincex19]

Hello,
I recently purchased a 1980 X1/9. I am doing the struts today and want to drain the differential fluid. I suspect the other owner used the wrong fluid and I want to drain it. (He told me not to drive it far so I am concerned and apparently if you use the wrong fluid you can ruin the differential). I have conflicting specs on the fluid. Some state SAE 90 (conventional) and other state straight 50 Weight. Can you please let me know what is the fluid type for the differential and also where the drain is or the best procedure to empty and refill it. I have the car on the road and once I check the fluids and finish the struts I want to drive it around and I really want to make sure I use the correct fluids..... also any thoughts on synthetic oil for the engine? Thank you for your help. Take care.

 

[bludvl_x19]

Use a regular 80W90 gear oil as a basic preference (as is in my car) Jimbro will recommend Redline MT90 as his choice, I have had no personal experience with it though.

DO NOT use any EP oil, it will destroy the gearbox.

 

[vincex19]

Thank you. Just changed one strut and I needed a brake line. I am also changing the brake shoes... do you know how the piston compresses on the caliper? Does it press in or do you have to rotate it? And if you have to rotate it is it clockwise or counter? I cant seem to compress it with a clamp and it does not seem to move counter or clockwise. I do not want to push too hard in case there is a different way of compressing it. Thank you once again.

 

[sledgehammer]

It should really turn clockwise with a big screw driver in the slot. Failing that a large pair of mole grips has worked for me in the past. If they dont turn freely you would be better to over haul the calipers and replace the rubber seals, available from eurosport pretty cheaply.

 

[Lucio]

I took Jimbros advice a couple years ago and used the MT90 oil. My x19 only had 8k on the clock but still crunched occasionally in low gear change and reverse. Totally cured it..quality oil, expensive (bout £50 for a full change) but worth every penny.

 

[vincex19]

Thank you for your inputs. I want to drain the differential. But I was wondering if the differential and the transmission are the same. Do they have separate drains? Does the manual trans and differential take SAE 80. I found the drain and the fill plug for the transmission which uses a 12MM Allen key to remove but I did not find one for the Differential which is why I am asking the question. Any input will be greatly apprecaited. Thank you.

 

[bludvl_x19]

You have it in one, the gearbox and transmission use the same fluid, the holes should be on the front of the gearbox, left hand side of the car. It sounds like you have found them alright

 

[vincex19]

Red Line 50304 Synthetic MT-90

Is the the fluid you used??

 

[digger58]

I used that oil in a car with only 10,000 miles and can say it seems to work very well, expensive but...........

 

[jimbro1000]

That is the stuff - the SCCA autocrossers prefer the lighter MTL fluid but for road use the MT-90 is better. It is expensive but when you compare how good it can made a gearbox feel, even one that is worn and a bit clunky it has to be cheaper than getting the gearbox rebuilt to feel the same way.

I've used both the above and the lightweight shockproof oil (about 140 grade equivalent) and all of them work significantly better than regular mineral and synthetic oils and I don't hesitate to keep using it despite it being very pricey here in the UK. I suspect the price difference in the USA would make it a bit more favourable still.

One thing worth noting, these oils are also suitable for replacement of EP oils and are listed as such but don't have the destructive characteristics of those oils so are safe to use in older gearboxes as well.

If in doubt contact Redline directly - they are a pretty approachable bunch - and they can advise on what you need exactly. I had a chat with one of their head chemists a couple of years ago at the Autosport show and he was more than just a bit helpful which is more than can be said for a lot of the exhibitors where most people get treated like trash unless they are waving fat wallets around.

 

[bludvl_x19]

Jimbro: for those unaware (like myself) what sort of price should enough MT-90 oil cost?

 

[vincex19]

Hi,
Looks like it takes about 3.x quarts. I am buying 4 quarts at 13.49 each.
If you buy it from Amazon.com (like me) you can get shipping for free.
(Prices from Amazon are in US Dollars and free shipping is within the US).
Take care.

 

[vincex19]

Any thoughts on Motor Oil. I know it calls for 20/50 but I was hoping to use Valvoline Durablend which is a synthetic blend but at 10/40. Do you think this can cause any problems or would you use 20/50. Please let me know. Thank you.

 

[jimbro1000]

You can get MT90 for about £14+vat from places like Demon Tweeks and don't forget delivery on top of that. Some places sell it by the gallon too (about £60).

There isn't a lot of saving to be had, just keep in mind that a gallon of decent synthetic engine oil costs about that much, just to put it in perspective!

Engine oil isn't so critical on the grade, it is the quality that really counts. My personal preference used to be for a 15w50 oil but they keep messing with the weights as new standards are introduced. The latest grades are not necessarily the best as the metallic (phosphorus) content has been reduced for the newest api standards and this is bad news for old engines. Not entirely sure what the latest is but anything past the SJ standard may be pushing your luck for engine longevity. The new SM standard is supposed resolve this but it is largely unproven.

Equally, low grade oils tend to be cheap and nasty so you need to be careful there too. You can buy some really nasty 20w50 oils here in the UK but I wouldn't put them in anything as they lack all of the additives that make modern oils so good and long lasting.

 

[81Strada]

I bought a 5 gallon bucket of GL1 straight 90w from Walley Mart for 30 bucks a few years ago. Down to my last 3 quarts now and have run it in my old Yugos/Strada with no problems. Of course, I'm pretty easy on my gearbox, skipping 2 gear in upshifts and generally easy shifting til it warms up.