Testing Brake Servo

[DBrands]

My brake servo seems to have failed.

Symptoms:
1. No pedal drop when starting the struck with the brakes applied.
2. Reasonable effort required to stop the truck under heaving braking. It must have been a gradual failure as I can't say there was a specific day I noticed more effort required on the pedal.
3. Excess crankcase pressure, which decreases noticeably when I pull the vacuum hose off at the servo end and plug the end of it (rules out a leaking hose).

Do these symptoms point directly to the servo as the only culprit? I did have a leaking master cylinder, which I replaced. Is there a possibility brake fluid made its way into the servo diaphragm and caused issues?

Should I still pressure test the servo first? Is an inability to hold vacuum the tell-all for its failure?

Is a rebuild kit worth it, or do I just buy new? It appears my servo (NRC4772) is no longer widely available in genuine or TRW fashion. What do you guys make of Britpart/Bearmach/Allmakes for this item?

[Red90]

If it does not hold vacuum it has failed. I'd replace it.

Make sure you know whether or not you have the earlier or later one as they changed at around the time of your truck. They are quite different.  Mine has the later style.

[DBrands]

My setup is the earlier one, NRC4772 (type 80). Serial #HA4
I've got NRC9529 for a master cylinder.

I'm not sure whether to chance a blue bag servo, or try one of the TRW items off ebay Europe.

[Red90]

Maybe Bill can comment on experiences with aftermarket boosters.

[binch]

To be honest I can't remember having ordered one in the past couple of years.    But they come with a two year warranty now.   I'd give it a try if I were in your shoes.

[DBrands]

I did find a few suppliers that said they stocked genuine Servos. I couldn't get a response that they were in fact genuine, as the price was comparable to aftermarket...

I'll test out a pattern part and see how it goes.

[binch]

The genuine version of the servo should be 4 to 5 times the price of an aftermarket.    If it's close to and aftermarket price for a new genuine then something isn't right in Norway ;-)