HELP! Brakes-NO BRAKES!-Brakes again

[Tahoe]

Went for a drive today and had a scary surprise. Been driving the car everyday for several weeks now with a solid brake pedal but today was scary. Coming up on stopped traffic in the right lane, pedal goes to the floor, traffic to the left, and a space to the right about 12 inches wider than the Elan so I swerved unto a driveway that luckily had no pedestrians or traffic. Slowly pumped a couple times with nothing then a full pedal. Everything was fine as I started back home and 10 miles away when it happened again after several firm pedal stops. I made it home into the garage with a firm pedal and the reservoirs were full and no fluid leaking anywhere.

So here's what the car came with. In the 70's I believe the owner converted to a Datsun tandem master cylinder (7/8" bore). Pedal is always a little hard, but I figured some day I'd put a different master in. It has 2 remote reservoirs that have very clean fluid and the level hasn't dropped in the 2 1/2 years I've had it. When I had the failures the pedal went right to the floor, no spongy feeling at all, it was just like there was no fluid period. Then when they came back the pedal was hard. No in between, hard, nothing, hard again! Obviously t can't be driven until this is fixed so does anyone have an explaination? Is there a by-pass in the master that has failed and would allow this to happen?

So, I'm I need a new Master, what do you suggest? I know the original duals are hard to find but noticed that WIlwood has some new small masters with the correct bore that would require me going back to a single circuit system.

[billwill]

Does it have brake servo(s) too?

Is it losing fluid?

The only thing I can think of that matches your symptoms is that the fluid is getting past the seal of the master cylinder(s) on the occasions when it goes to the floor, possibly due to some hard object like a shard of metal inside, but if that is so I would not expect it to be able to be sucked back on the return stroke, instead it would come out of the rubber cap that the actuating rod goes through. So you would find a fair amount of brake fluid in that vicinity.

The same sort of thing could happen to one of the calliper pistons, I guess.

If you can't find any fluid, but if the system has servos, the lost fluid may be inside the case of the servo.

[billwill]

Fluid boiled to vapour or water which had been absorbed into the fliud and then boiled to vapour might cause something like that I guess, but you would have to be using the brakes hard a lot to get them that hot, I expect.

[Tahoe]

No Servo. Been all over and under car and there is no leaks. Sitting in the car the brakes are hard as rock but I'm afraid to drive it. Weird because it's a tandem master and I can't think of reason why both circuits are doing this. Maybe with a fresh mind in the morning I'll find something.

[AlfaLofa]

I once had brakes - then no brakes - and then brakes.

But the no-brakes phase ended in an accident.

The cause was the earlier expulsion of one of the brake pads from a rear caliper (after somehow losing one of the retaining pins)

The no-brakes phase occurred when the piston took up the extra space left by the missing pad.

Once the piston was touching the disc the pedal was solid again.

[PeterK]

If it's the dual circuit type of tandem cylinder, maybe the secondary piston seal is failing.
If the primary seal failed, then I would expect to see fluid leaks by the actuating rod as mentioned above, but would the secondary cylinder seal just leak into the primary circuit ?

Peter

[david g]

Russ On the Datsun master cylinder ther are spring loaded inlet valves If thease don't seat properly fluid will push up into the reservoirs Corrosion of the valve seats may have taken place due to water absorbed in the fluid .I do hope you sort it out as I have a Datsun tandem cylinder on my Elan.
David

[alaric]

Hi. As suggested above it sounds like dirt in the master cylinder. A little bit of grit near the non return seal at the outlet from the reservoir will allow the fluid back into the reservoir rather than out to the wheels. The valve opens each time you lift your foot off the brake pedal, hence it can be intermittent. You need to strip the master cylinder, replace all the seals, and any corroded springs etc. Alternatively buy a new cylinder. Also flush new brake fluid through the system so be sure all the 'crud' is out. The same can occur with the clutch master cylinder and the original brake cylinder, so I don't think it's just the datsun. A dual reservoir solution may be the only way to avoid complete brake failure with this problem. Regular replacement of the brake fluid should prevent it happening, in theory. I think you had a lucky escape.

Sean.

[oldelanman]

As it's a tandem master cylinder with separate reservoirs you would need simultaneous failure of the valves in both halves to suffer a complete brake failure which I guess is possible but seems unlikely. Maybe if the primary piston (nearest the pushrod) is sticking in the bore it would prevent both pistons from returning and then neither circuit would recover leading to complete loss of brakes on the next application. Can you reproduce the problem by repeated application of the brakes with the vehicle stationary ?

Either way I would agree that the master cylinder is the most likely cause of your problem. Failure in any other part of the system would only result in the loss of one half of the system - not complete brake failure.

[worzel]

Hi

This is not going to help- much - but I used to experience something very similar years ago with a Scimitar GTE. On the rollers braking was excellent- and on the road too BUT- occasionally after applying full lock the pedal would almost sink to the floor.

I tried every possible cure I could think of- the conclusion was that somehow the pads were being knocked back on full lock. The wheel bearings (pretty much identical to the elan) were definitely correctly adjusted and there was no slop anywhere in the suspension or in the actual caliper mounts. There was no fluid loss either. Quite unsettling on the road- I eventually got into the habit of dabbing the brakes every time I turned a sharp corner.

Never managed to cure it. Other Scimitar owners reported similar problems.

Regards

John

[alaric]

Ooh. Hadn't realised the Datsun unit is a dual reservoir master cylinder. Apologies for that. I would be interested in getting one myself though.

Sean.

[Tahoe]

I though about the pads being knocked back but the rotors and calipers, and hoses were new when I bought the car as was fresh brake fluid. That doesn't mean that the master didn't have some crude or corrosion though. It's the oldest part of the system and the most likely culprit.

While sitting in the car in the garage I can't replicate the event. Probably tried 100 times and the pedal was firm and brake lights were coming on.

I've looked for replacement masters for the Datsun and they are both expensive and the typically a 1 inch bore. That won't work, so I think I'll replace the master with a new one, but it will probably be a single circuit. Other than the stock master, and single master from Wilwood or similar, what are my choices. A quick search found no suitable tandems with the correct bore.

3 different possible Wilwood solutions

http://wilwood.com/MasterCylinders/MasterCylinderList.aspx?minorname=Integral%20Reservoir%20Compact%20Master%20Cylinder

http://wilwood.com/MasterCylinders/MasterCylinderList.aspx?minorname=Compact%20Master%20Cylinder

http://wilwood.com/MasterCylinders/MasterCylinderList.aspx?minorname=Compact%20Remote%20Combination%20Master%20Cylinder

[lesesq]

I had a similar problem with an S4 with the original dual system. The M/C was rebuilt with new seals and worked fine for awhile but recently and intermittently the pedal would go to the floor. I was advised to have the M/C resleeved because pitting can cause the internal seals to fail. I'm waiting to see if resleeving and rebuilding with new seals solves the problem, but I'm optimistic. Have to be with this car.

[Galwaylotus]

My S3 did exactly the same last year. Turned out to be a dragging front caliper. The pad had jammed in the caliper and the resultant overheating boiled the fluid. When I stopped for a while the pedal came back very firm - as normal. Next long(ish) run and the pedal went to the floor again. I've since had the front calipers rebuilt but haven't had the chance to install them yet. The new pads slide freely in the rebuilt calipers so I don't anticipate a repeat of the issue. I'm taking the opportunity to replace the perished front damper bushings with poly bushings and to clean and re-grease the hub bearings (assuming one hasn't overheated in which case it will be replaced). The car has been on jack stands over the winter and we haven't had enough warm dry weather that I have been able to work on it.

[Tahoe]

Still can't duplicate the events, but decided to install a Tilton .70 master cylinder. Ordered today so won't see it for a week. I think I said the Datsun was a .75 bore, but it's actually a .875 bore which accounts for the harder pedal. I'll be going back to a single circuit but that's okay. Decided on the Tilton because of the bore size and it has a remote reservoir which works better for me on a RHD car. It will require adapting to the existing brake lines which I believe have M10x1.0 fittings. Hopefully I can do that easily so I don't have to replace the lines already in place.