Loss of brake assist

[domesticpower]

It started towards the end of the last season but I didn't have a chance to troubleshoot. I'd like to figure it out before this season. I'd go on the brakes and find the pedal to be VERY stiff. After about 1.5 seconds, it gets back to normal or I can just lift off early before the braking zone to have full assist. It's wasting a lot of time and doesn't inspire confidence. To eliminate a vacuum leak, I turned off the car, left it for about half an hour, pumped the brakes (without starting the car) and got 2-3 pumps with assist. I repeated the test a couple of times with no issues. I'm thinking it might be the check valve. Any thoughts? How easy is the check valve to replace and is it the same as the GT or it's different?

 

[TMSBOSS]

Letting the car sit will only identify a vacuum leak in the booster itself. The check valve at the booster is likely OK. If not, the vacuum would have belay down.
Still, changing the check valve should be cheap and relatively easy to do.

 

[domesticpower]

Letting the car sit will only identify a vacuum leak in the booster itself. The check valve at the booster is likely OK. If not, the vacuum would have belay down.
Still, changing the check valve should be cheap and relatively easy to do.

Thanks TMSBOSS. Any suggestion as to what it could be? The problem seems to be worse the longer I stay in WOT before braking, thus suspecting it's the check valve. Do you know the part number for the check valve?

 

[TMSBOSS]

$19.85 list. Should take 5 minutes to change.

XW4Z-2365-AA

https://levittownfordsupercenter.com/levittown-parts/#parts

 

[ArizonaBOSS]

Agreed on investigating/replacing the check valve. I carry a spare with me just in-case. @modernbeat and the Vorshlag guys had some experience with this issue and may be able to elaborate.

 

[domesticpower]

Thank you for the link and part number TMSBOSS.

Thank you ArizoneBOSS, I PM'ed @modernbeat . Did you start bringing spares as a precaution or had an issue with them?

 

[modernbeat]

No elaboration necessary. We had multiple check valves fail, causing a hard pedal. I don't recall if we found the cause of the valve failure, but it's a cheap part. We consider it a wear item and kept a spare in the trailer.

This might be hard to diagnose separately from the booster. When you have good vacuum, you have assist. But once the vacuum dies, your assist goes away.

 

[ArizonaBOSS]

Thank you for the link and part number TMSBOSS.

Did you start bringing spares as a precaution or had an issue with them?

I have not had an issue (yet) with this but I decided it was better to carry a $12 spare than lose a weekend of track time (especially if I were to have an issue in California where I am typically 5-600 miles from home).

 

[domesticpower]

Well, I bought the valve and hope to get a chance to replace it this weekend. I won't find out if it fixes the problem, though, until the first track day which is in the end of May. Thanks for all the responses.

No elaboration necessary. We had multiple check valves fail, causing a hard pedal. I don't recall if we found the cause of the valve failure, but it's a cheap part. We consider it a wear item and kept a spare in the trailer.

This might be hard to diagnose separately from the booster. When you have good vacuum, you have assist. But once the vacuum dies, your assist goes away.

Oh okay, thanks. At least you narrowed down the failure, even if you haven't figured out the cause. I hope it's the same with mine and it'll be fixed with the new valve. I'll try to cut open the old one and see if I can figure out what went wrong.

I have not had an issue (yet) with this but I decided it was better to carry a $12 spare than lose a weekend of track time (especially if I were to have an issue in California where I am typically 5-600 miles from home).

Makes a lot of sense. The cost sucks here though. The valve costs $43 from the dealer.. track day costs $80 so the valve is more than half! I tried ordering it online but it turns out it isn't made in the US so there are duty charges (calculated to be about $8-10 on different sites), another $10 to ship and $19 for the valve itself, comes to at least $37. That's USD, which works out to $49 CAD based on yesterday's rates.. still worth it IMO, but expensive.

 

[k98dave]

If you order on line from a US dealer how does anyone know where the part was actually manufactured? That's nuts....figures.

Sounds like on your next visit you should buy one and just stick it the glove box, or change it out.

 

[domesticpower]

I've just had a chance to take the car on the track this week and the problem is gone! Thanks for all who recommended the fix.

 

[domesticpower]

If you order on line from a US dealer how does anyone know where the part was actually manufactured? That's nuts....figures.

Sounds like on your next visit you should buy one and just stick it the glove box, or change it out.

Yea, I'm going to get a second one as a spare.