grob main wheel and brake disk

On Friday, July 20, 2018 at 4:55:41 PM UTC-4, Charlie M. (UH & 002 owner/pilot) wrote:

DOT 5 "will work", but it is even MORE water hungry than others.

Yes, I made a bold statement, I will do my best to provide GOOD relevant links to prove, not just me stating it. Say, within 24hrs?

Any progress on this question? Every source I've seen
says something like "Unlike polyethylene glycol based fluids,
Dot 5 is hydrophobic." My first reaction was that the stuff
must act like a rabid raccoon, so I had to look the word up,
but I think it means the fluid has no affinity for water.

At least, that's the way I understand it.

Jim Beckman

Quit so, normal brake fluids are hydroscopic, and easily absorb water, which then causes vapour issues in the lines when heated, allowing it to be compressed.
Sounds to me like dot5 is a better option.

Quit so, normal brake fluids are hygroscopic, and easily absorb water, which then causes vapour issues in the lines when heated, allowing it to be compressed.
Sounds to me like dot5 is a better option.

On Tuesday, July 24, 2018 at 11:07:52 AM UTC-4, Charlie Quebec wrote:
Quit so, normal brake fluids are hygroscopic, and easily absorb water, which then causes vapour issues in the lines when heated, allowing it to be compressed.
Sounds to me like dot5 is a better option.

I've forgotten if this was the original problem or not, but I've been through the whole process of rebuilding the hydraulic brake system on a Grob 103.. Complications arise because Grob used an off-the-shelf master cylinder derived from a motorcycle application. That requires a different type of fluid than the usual hydraulic fluid used in aircraft brakes, and expected by the Cleveland wheel cylinder O-ring. One of us went to a mechanic that works on power planes, and he handed us an O-ring based on the Cleveland part number. Then I went to a real glider mechanic, and he threw that one away, because it wasn't going to be compatible. I think we got some help from Robert(?) Mudd, and once you know the material you're looking for, McMaster has them cheap (but you probably have to buy at least 25 to get 1). Unfortunately I've forgotten when that material was, but I could look around in my spare parts box, if it's important to anybody.

I got the master cylinder overhaul parts from a company that supplies parts for old BMW (Oilheads?) motorcycles.

Jim Beckman

On Tuesday, July 17, 2018 at 10:38:55 AM UTC-5, Scott Williams wrote:
does anyone know the Parker/Cleveland part number for the brake Disk
used on a Grob Twin II fixed gear which used a Cleveland caliper? Glider made about 1981.
I'm aware of the Dot 3/4 compatible O-ring used in the caliper.

Thanks,
Scott

if anyone wants a new rubber diaphragm for the round cap, it is BMW motorcycle part number
32 72 1 238 387

good lift,
Scott

James,
Our aircraft mechanic put aviation brake fluid into our Grob brake and all the seals swelled up and are no good. Do you recall which master cylinder rebuild kit you used?
Thanks,
Chris

On Thursday, July 26, 2018 at 9:36:33 AM UTC-4, wrote:
On Tuesday, July 24, 2018 at 11:07:52 AM UTC-4, Charlie Quebec wrote:
Quit so, normal brake fluids are hygroscopic, and easily absorb water, which then causes vapour issues in the lines when heated, allowing it to be compressed.
Sounds to me like dot5 is a better option.

I've forgotten if this was the original problem or not, but I've been through the whole process of rebuilding the hydraulic brake system on a Grob 103. Complications arise because Grob used an off-the-shelf master cylinder derived from a motorcycle application. That requires a different type of fluid than the usual hydraulic fluid used in aircraft brakes, and expected by the Cleveland wheel cylinder O-ring. One of us went to a mechanic that works on power planes, and he handed us an O-ring based on the Cleveland part number. Then I went to a real glider mechanic, and he threw that one away, because it wasn't going to be compatible. I think we got some help from Robert(?) Mudd, and once you know the material you're looking for, McMaster has them cheap (but you probably have to buy at least 25 to get 1). Unfortunately I've forgotten when that material was, but I could look around in my spare parts box, if it's important to anybody.

I got the master cylinder overhaul parts from a company that supplies parts for old BMW (Oilheads?) motorcycles.

Jim Beckman

Originally Posted by Charlie M. (UH & 002 owner/pilot)

Ummmm....yes, I am very happy with my post.
Pretty much ANY DOT fluid is cross compatible EXCEPT DOT 5.
DOT 5 "will work", but it is even MORE water hungry than others. I do not believe it is a seal issue, it is water absorption issue. Thus, race cars is fine, other uses, sucks.

Now, mineral based fluids vs. DOT fluids is a different matter. Thus my question.

Oh, and to accentuate this, if you have an old system that uses DOT 1, using DOT 1-4 AND 5.1 is fine.

Yes, I made a bold statement, I will do my best to provide GOOD relevant links to prove, not just me stating it. Say, within 24hrs?

Warning! General observations maybe present

Dot 5 is a silicone based fluid and is hydrophobic i.e doesn't absorb water. Dot 5.1 is glycol based and is hydroscopic i.e. does absorb water.

It's a PITA having the numbering system this way but it means that it's quick and easy (really?) to distinguish between the 2 types of brake fluid that meet the performance standard for Dot 5. Mix them at your peril

https://www.lubricants.total.com/brake-fluid-types

:-) Colin

On Tuesday, July 17, 2018 at 10:38:55 AM UTC-5, Scott Williams wrote:
does anyone know the Parker/Cleveland part number for the brake Disk
used on a Grob Twin II fixed gear which used a Cleveland caliper? Glider made about 1981.
I'm aware of the Dot 3/4 compatible O-ring used in the caliper.

Thanks,
Scott

Check and measure the master cylinder bore size, compare the pictures to your component piston and spring. try here,
https://www.beemerboneyard.com/mamacykifr3.html
good luck