3.8 brake & clutch reservoir leaks.

[rswaffie]

I have just swapped out the round clutch and front brake system reservoirs for the third time in 3 years. The rear brake reservoir was swapped for the second time last year and appear ok. The previous swaps were due to cracking around the spigot and/or sweating hoses. They have all been supplied by SNG and the clutch reservoir was one of the items that comes already fitted with cohline hose. The front brake was slightly older so was fitted with cohline by me when installing it. The currently ok rear brake reservoir is also the more recent pre-fitted hose version.
Both the offending items were very wet with fluid on the underside and around the spigot and this was dripping down via the hose on to my upper bulkhead, frame and vin plate panel paintwork - several hundred pounds to repaint but I’m not doing that yet
On removing the items from the brackets, I noticed that the brake reservoir was wet around the cap and down the sides, as well as under the cap. I had fitted a couple of extra cap seals as there was a gap between the cap and top of reservoir (the threads on the cap didn’t match the reservoir so didn’t screw all the way down). There was also evidence of the same on the clutch reservoir but not as much.
I haven’t checked for cracking yet, but what would cause fluid to be forced out of the lids? I only have fluid to just over half way up each reservoir.

[mtnjag]

Sounds familiar. Just changed my rear reservoir due to cracking around the spigot.

Like you, bit the bullet and I purchased the SNG with the hose installed to avoid the spigot cracking caused by forcing a tight hose on and I bought the cap to go with it.
I bought the cap because in the course of chasing the prior leaks I found, as I think you have, that caps and reservoirs are not necessarily the same thread.
So If the threads don't fit right no matter what seals you install they just may not be doing the job. That was one of my prior leak diagnosis theories anyway.

Also, you are only filled half way up but are you leaving fluid on the inside of the cap or bottle threads when you fill somehow. Then weaping down when reinstalling the cap?

I chased my leak for quite a while until finally getting it, for now. Had a shop towel under them on the bottom splash shield forever it seems whenever I parked back in the garage.

That brake fluid is slippery stuff.

Good Luck

[rswaffie]

Thanks Layne,
I’ve dried all the thread areas and inside around the caps and bottles, but still seems to get wet. The brake masters were stainless sleeved and rebuilt with new seals by Classic Brakes 3 years ago, but I think I read something on the forum about a valve or seal that may fail and cause fluid to be forced back up to the reservoir - but don’t know if this relates to brake/clutch or both. How could I test it?
When I took the car to Project Heaven last week to get a paintwork repair quote, they suggested I applied the brake whilst they looked to see if the level in the reservoir rose, but could see no change in levels. Not sure if this was a valid test?

[mtnjag]

If you have orig style MCs-The valve mentioned is part of the piston assembly. When you push on the brake a seal at the end of the MC piston assembly seals the inlet and allows the MC to pressurize-pushing fluid out to the caliper pistons. If the MC seat at the fluid inlet hole is messed up, or the piston seal is bad you can push fluid back out to the MC.

Watching the inside of the Reservoir when you push on the brakes should be a pretty good test if someone knows what to look for.

Even if that seal is bad. unless your reservoirs are full it is not likely to overflow the reservoir.
Also, if that is happening your brakes will be bad, not function properly and you should notice it because you will not be pressurizing the fluid to the caliper pistons.

When Classic Brakes sleeved them they should have checked the seat face of the MC. That face is NOT helped by the SS sleeve. If it is bad it must be machined (not likely) or the MC tossed.

I use Karps in Southern Cal although I have used Classic Brakes in the past with no problem.

You do Know the Original Front and Rear MCs for the 3.8s are different although they look the same?

[tinworm]

I still find and use original round and square bottles - quite often they are still in useable condition although not as sparkly as new repro .. they spruce up with a good scrub with washing powder and some water though ! They don't leak or crack (so far)

Barrie

[rswaffie]

Thanks all.
The new reservoirs are in place and to confirm if the leak is from the top, I’ve rolled up some kitchen paper and wrapped one ‘tube’ around the top part of each reservoir and held them in place with som tape. If any of them leak from the lid, I’ll be able to tell. If they do, then I’ll have to look at the masters.
Edit: I should have mentioned that there are no obvious issues with the actual braking - no loss of pressure or sticking-on.

[rswaffie]

An update: The two new reservoirs have been in place for the last couple of weeks and I’ve done a couple of hundred miles in it. I added two extra rubber gaskets in the lids and made sure they were tight, as well as keeping the hoses to a length that reduced any horizontal pressure on the spigots to a minimum. So far, no visible leaks from lids, spigots or hoses. I’m not counting the chickens yet, so will continue to monitor before I get the paintwork rectified on the inner bulkhead.

[mgcjag]

You may want to think about silicone fluid....harmless to your paint work. ....Steve

[rswaffie]

Yes Steve, the guys at the Project Heaven bodyshop suggested I should change to silicone. They have done the same to a couple of their track cars without issues. They said to flush it through with plenty of silicone fluid first.
I expect that this suggestion may generate both positive and negative views as to the effects of potentially leaving traces of the dot4 fluid in place, or possible impact on seals in the braking system components?

[paydase]

I have silicone fluid in the brake circuits of 3.8 FHC since I bought it.

The big advantage is that silicone is an hydrophobic fluid, eliminating the risks of internal rust in the pipes and callipers, and very forgiving if you don't change fluid for a while.
Certainly the fluid change from DOT 4 has to be made very carefully with thorough flushing.

[1954Etype]

I would not recommend going over to silicone without replacing all the rubbers in the system. (We wouldn't do it). However, if a,n. other company have done it successfully numerous times.......

[rswaffie]

Thanks Angus. I have read (on here possibly) that the seals would need changing, but it has not been made clear as to why? It’s the same type of rubber isn’t it, regardless of the type of fluid? Or does the old style fluid degrade the rubber over time, so they should be replaced as a matter of course?
I may just fabricate a protective ‘catch tray’ to cover the areas that may be at risk of future leaks.

[paydase]

I would not recommend going over to silicone without replacing all the rubbers in the system. (We wouldn't do it). However, if a,n. other company have done it successfully numerous times.......

Angus, you are certainly right.
In my case the shift was done 20 years ago by a specialised shop. They also changed all the brake hoses.
No issue since then.

[mgcjag]

There is a love or hate it theme with silicone......a decent restoration company would in my opinion only reccomend changeing to it if you replace all the seals in the system....they have to give guarantees on all the work they do........however i can say that iv used it for many years on new rebuilt brake/clutch systems...and just flushed through old systems....iv never seen a problem.....Steve

[Series1 Stu]

Hi

I don't think there is a problem with chemical degradation of seals using either silicone or mineral based brake fluids but I seem to recall that the silicone does not have the lubricating properties that mineral based fluids do. It was suggested to me that, for older cars such as ours, mineral based fluid is better - with DOT 5.1 being the preferred choice.

I suspect either will be fine but definitely flush the fluid as best as you can to avoid mixing them.

Don't ask me who had the bright idea of calling silicone based fluid DOT 5 and then an improved mineral fluid DOT 5.1. Obviously someone that is out to confuse people.

Regards

[mgcjag]

Mineral brake fluid will rot your seals.....stay with DOT rated fluids.......Steve

[Gfhug]

Steve, forgive me for asking, but are you saying that 5.1 despite being DOT 5.1 should not be used because it is mineral?

Thanks

Confused Geoff

According to wiki lies DOT 5.1 is glycol based like 3 and 4 and

“ Lack of acceptance of silicone-based fluids led to the development of DOT 5.1, a fluid giving the performance advantages of silicone, whilst retaining some familiarity and compatibility with the glycol ether fluids. DOT 5.1 is the non-silicone version of DOT 5, defined by FMVSS 116 as being less than 70% silicone. Above that threshold makes it DOT 5. “.

Further research has mineral being the typical aviation hydraulic fluids (DTD585, fluid 4, etc) with Rolls Royce and Citroen also using them. Certainly does rot seals for glycol based brake oils.

[mgcjag]

Hi Geoff...i knew this would happen when i mentioned Silicone.I never mentioned 5.1.......5.1 is Glycol based not mineral...everyone can reasearch and make up their own mind what to use.....Steve

[Gfhug]

Hi Steve, no that’s fine. It was Stuart’s use of the term mineral against 5.1 that lead to my confusion. Thanks as always

Geoff

[Series1 Stu]

Yes, sorry my bad. I meant glycol, not mineral. That's what comes from intensive hydraulic system development.

Regards