grob main wheel and brake disk

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

Well,
to the best of my knowledge, and the Grob 103 twin II manual, and service bulletin OSB 315-17, .
the master cylinder was a modified Magura motorcycle part, which might have been original equipment on BMWs, maybe a R100? which uses dot 3 fluid.
The original equipment caliper is a Cleveland/Parker Hannifin 30-63A, which has a Buna-N O ring( MS28775-224) for use with petroleum based aircraft hydraulic fluid,
I think it was easier and cheaper to change the caliper O ring than to change the master cylinder seals.
The "O ring swap" I mentioned was intended to ensure caliper O ring compatibility with the Brake fluid indicated in the flight manual.( dot 3)
If someone simply replaced either the caliper or just the O ring with the Cleveland called out part number, this would result in the Cleveland O ring swelling over time. That is something you don't want in a caliper.
The ID label on our Grob 103 caliper should be labeled "DOT 3" but is not (Yet).
Larry Suter, on rec aviation Jan. 6th 2015 started a thread that covered it better than I.
If I'm incorrect, please post.
Thanks,
Scott

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

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