I have a 66 deluxe, this is my first hydro mini and I need some help diagnosing an issue.

The background is the car was laid up for many (many) yrs on stands, I recently started the process of getting it back onto the road. Initially when the engine went back in and it was taken off stands it sat on the bump stops. I rigged up a grease gun pump with gauge and pumped up to regulation height wheel centres to guard, rocked the car to settle etc. I used penrite green radiator premix which is a suggested replacement (only minus alcohol I believe). Psi was around 280/290, it was off the bump stops. All good I thought.

It held fine, and did so for around 6-7 weeks. During that time it wasn’t driven, but was transported on and off trailers, jacked up numerous times, moved on the driveway etc.

The the passenger side lost pressure, seemingly over night after moving off the driveway. It was sitting on grass at the time, I couldn’t see any fluid around or obvious signs of why. Have now re-pumped on driveway. It started off around 100psi, put it back to 290psi, front was about a finger width off the bump stop, 3 finger off guard and rear 4 fingers.

No obvious leaks. No drips or any fluid I can see or feel and it has held overnight. Confused.

Any ideas on why or suggestions for next steps ?

(yes I know dry is an option, but don’t want to spend time and cash on that right now, only after diagnosing/fixing hydro )

Check the obvious, Schrader valves. You may have to take off the hydro pipe protector plates that run full length under the body. Gets a lot of dirt and crud over the years. If it is a leaking pipe, they can be silver soldered. Cheers, Alan.

I would be parking it on a cement floor to see where it drips. Open the passenger door and stand on the sill and bounce the car a few times. It could take while for the drips to reach the floor.

The common leak points are the fittings, hoses and connections. Could also be the bags or steel pipes. The flare fittings can corrode on the seating area causing a small weap that can drop the pressure with very little evidence of a leak.

The drips can travel along the pipework or drip onto the subframe and move along to a spot that is nowhere near the original leak.

You mentioned about going dry. You can always keep the hydro but add competition bump stops. They can take a bit of weight off the bags extending their life. You will get a bit harsher ride. Like a cross between wet and dry. But you would want to get the leak issue fixed. If my bags were fine and it is just a leaking fitting thats what i would do.

It may have a LF hose leak, this won't be obvious until it fills up the top of the bag and overflows.
This leak happens if water got in there for years and the steel crimping rusted. And/or the old hose rotted.
Hydro hoses can be replaced, PM me for more info.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

"this won't be obvious until it fills up the top of the bag and overflows."

my thoughts too Kev

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

Thanks for the tips, very useful. It’s now kept pressure for 10 days, and I haven’t seen a hint of any fluid on the ground, pipes etc

I have fitted the rear comp bump stops now which were already on my list. I know some people also fit shocks to the front, I will consider that at some point.

The only thing I found was that the valve cap had black baked-on crud in it, when I first took it off to re-pump there was a little fluid in the cap. I thought it was from when I first pumped. Perhaps the crud had depressed the valve enough to create a slow leak, or the valve is dodgy. (Or maybe I just dug out a petrified rubber seal ?)

It’s my only theory at the moment. I guess I wait and see how long it holds and if I need to follow my theory and renew the valve.

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

They are just Schrader tyre valves, I would replace with new from a local tyre shop. Mine didn't charge me..
Replace the cap seals too.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi, I will just add a little safety comment on working with hydro. One of the business owners of an early successful mini businesses nearly lost an eye when he was checking a front hydro hose, and had his face above the area, while he fiddled with hose. Being at 300psi odd pressure and corroded it shot off the bag, hit him in the eye and knocked his eyeball right out, creating merry hell and a lot of anxst. He is fine now, but often we forget that motor cars are inherently DANGEROUS... Think , be safety conscious .... I suspect most home mechanics are not trained and will not have had training to point out potential dangers
Batteries can explode fuel fumes can ignite jacks can collapse Petrol can burn the skin boiling radiators can burn loose clothing or hair can get caught in moving objects. Brakes can fail i am sure everyone has had a moment
Cheers Lindsay Siebler

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1967 EX works rally mini restoration virtually complete OBL45F
1965 Mk1 Cooper S
1970 Colt 1100F SS
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project

I visited the said successful mini business owner in the eye & ear hospital after the hydro hose hit him in the eye and worked with him for a few years afterwards. He still has a scar on his Cornea to this day. Treat Hydrolastic components with great respect, they are operating under high pressure and are now 50+ years old. Bags with 300psi in them are hand grenades these days.

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Have a Nice Day.
If already having a nice day please disregard.

with metal types, tightened (nipped up) with pliers etc...

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"Show me the Mini!"

You want metal caps not plastic. They are the 2nd line of defence if a valve leaks.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yikes! I’m normally pretty good at thinking about risks before acting. But definitely had not considered that outcome when i stuck my head over the top of the front hose to inspect - exactly as you described. Thanks for sharing

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

My hydros act the same no signs of a leak but it drops after a long time

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1973 Clubman GT - YG2S8 1637

They do drop with age.
Also I find they ride higher in summer and lower in winter.
I adjust pressure accordingly to give me 2-1/2 fingers clearance at front tyres.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.