MK5: No MOT/TÜV pass due to rust film on brake booster

[Colibri]

Hello,
During the last MOT/HU/TüV the examiner suddenly reached to the second metal foil stripe on the brake booster, tore it down and said:”the brake booster is corroded. Here you can not only use rust converter, it has to be replaced completely.” I did not get the MOT/HU/Tüv pass certificate.

Background: When we bought our used MK5 (Ford Nugget, BY 96, 2.5 TD, 63 kW) in 2014, one of the five metal foil stripes on the brake booster was already gone and there was a rust film at this spot. Since then we passed the MOT/HU/TüV control three times (2014, 2016, 2018) and no examiner ever cared about this rust film spot which did not get worse.

Since the brake booster (with brake assistant/ABS) works fine I am therefore reluctant to get it replaced for material costs of around 400€ (new) or used for 80€ (with probably rust film underneath, too) - plus the repair shop costs will be much higher.
I am thinking about removing the rust on the spots, using rust converter and either paint it black or get some of those metal foil stripes if available and then going to another MOT/HU/TüV station for the re-examination.

Am I too naïve?
What would you do?
Did anyone have the same issue?
Is it possible to buy this kind of metal foil somewhere?

Many thanks for your feedback in advance!

[MinorMatt]

That would not be a fail in the UK.

I would be inclined to remove the booster completely, remove the strips, sand the rust and use a converter, then repaint the whole thing in satin black, refit without the strips and claim you have fitted a reconditioned one (its partially true!)

[Mislaid]

Not familiar with your test but would do as minormatt suggests and have nice looking "reconditioned" black paint on unit and forget the tape

[Colibri]

Hello Mislaid, hello MinorMatt,
Thank you for your recommendation. "remove the strips, sand the rust and use a converter, then repaint the whole thing in satin black" sounds good. Also detaching the master cylinder from the brake booster, I am cofident to do that. But I have absoluetly no info on how to remove and refit the brake booster correctly. Have you done it before? Have you any further info, I could refer to?

[Chug]

This might help, the pin going to the brake pedal can be a pain if you have big hands/fat fingers, or if it's rusted, otherwise a simple 10 min job.

http://www.catcar.info/ford/?lang=en&l= ... OTIwKzA%3D

[Colibri]

Hello,

Due to the holiday season, my feedback is unfortunately a little late: I had successfully removed, overhauled and reinstalled the brake booster. With this, I changed the brake fluid, too.
The inspection of the revised brake booster at the second date of the main inspection was carried out by the same inspector (!) without any complaints. HU badge issued for the next two years. YES! : d

The only problem and frustration occurred with bleeding due to a rusted-up bleeder screw (for more on this, see viewtopic.php?f=5&t=200526&start=15.)
Through this work I have learned a lot again. We also saved a lot of money, because the brake booster installed in our Transit has an ABS sensor. Unfortunately, this model is not available in good, used condition for a reseanable price, but for a relatively high price in a condition which does not differ significantly from my complained brake booster, namely with rust. A new one is out of question due to its ridiculous price.

A big thank you at this point for your constructive and encouraging tips and hints!

Below are photos and notes that may help others:
• For the removal (two nuts) you need a slightly longer nut for the ratchet (approx. 65mm total length), the working position is a bit uncomfortable but it goes quickly
• The two brake light switches can be easily separated and the cables can be laid out of the work area
• The split pin on the brake pedal can be easily removed with two flat-nose pliers and reinserted when installing. During the installation, I needed a helper who would direct me from the footwell so that the brake booster was repositioned at the specific point on the brake pedal
• The ABS sensor connection cable can be easily removed with a plug
• The vacuum hose must be pulled off with a little force and patience; some Vaseline spray will help here - especially when reinserting
• The lines of the two brake circuits must be detached from the brake fluid reservoir so that there is space to remove the brake booster from the engine compartment
• The plugs of the brake cylinders fit into the two openings of the brake fluid reservoir and the covers of the venting screws fit on the ends of the brake line, in addition I had fixed the cut fingers of latex gloves with painter's tape to seal even better - however, I had completely emptied the system and used fresh brake fluid
• You also need a container that is not too high and is positioned with a rag under the open brake circuit so that no brake fluid drips onto elements in the engine compartment, a flat plastic box worked great, but had to be emptied in between.
• To rework the brake booster, I protected all openings of the brake booster from dirt. For this purpose, cut fingers of latex gloves were fixed with painter's tape and the main opening was perfectly closed with a lid of a liquid detergent.
• Revision: Removal of the specification sticker with a hair dryer - careful puttying of the heat foil - rust removal and removal of loose paint with a cordless screwdriver and wire brush attachments - rust converter - primer with rust protection including surface compensation - black matt paint spray - sticking of the specification sticker (I had some double-sided carpet tape).
• Installation in reverse order
• Topping up with brake fluid
• Bleeding the brake was basically ok. Unfortunately, I had an unexpected and real problem here with a rusted-up bleeder screw. Only bouncing and long, long, long, long exposure to graphite solution helped. It took most of the time of everything.

TS_brake-booster.jpg

Colibri