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Author Topic: Power Brake Booster Check Valve  (Read 1640 times)
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greekz
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« on: October 25, 2017, 12:51:23 PM »

I am experiencing shifting problems with my 1967 GT-350.  It does not shift into drive until I reach about 60 miles an hour.  This is happening if I shift manually through the gears or in drive.  I plan on changing the vacuum hoses and modulator valve if necessary, but just wondering if the brake booster check valve could be the culprit.  As far as I know, it is the original.  Has anyone experienced this problem and the culprit was the check valve?  The modulator valve and its rubber hose are 27 years old, I changed the rubber manifold vacuum hose a few years ago, and the small rubber vacuum hose that is at the check valve outlet is at least 30 years old.

Thanks in advance for any insight.

Greek



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6S1134 - '67 GT-350 #2339
Rodney T
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« Reply #1 on: October 25, 2017, 02:23:36 PM »

  Hoses can get weak .  Then the vacuum sucks the hose closed.  Another item to check is the short length back by the modulator.  Might be cracked where you cannot see.

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greekz
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« Reply #2 on: October 25, 2017, 02:54:20 PM »

Thanks Rodney, I will add that to the list.

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6S1134 - '67 GT-350 #2339
greekz
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« Reply #3 on: November 06, 2017, 05:09:03 PM »

After changing both vacuum hoses, modulator valve, and brake booster check valve I still have the same problem.  Looks like it is transmission pulling time.  After 27 years it might just be time anyway.  I forgot to mention I hate automatics!

Greek

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6S1134 - '67 GT-350 #2339
BigBlock
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« Reply #4 on: November 07, 2017, 11:03:47 AM »

I've had 3 C6s over the years that had the same issue you have, won't shift into D until higher speed or backing off the accelerator. After taking them apart two had dried cracked rubber gasket around the side servo piston. The third had gunked up governor. On the governor the radiator cooler had a leak and water got into the fluid. Since they were out I had them rebuilt. The re-builder said he has seen many autos with water damage from an old radiator.

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greekz
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« Reply #5 on: November 15, 2017, 01:32:57 PM »

After consulting with my transmission guy, and telling him what I had done,  he suggested isolating the brake booster and see if the transmission will shift.  Good news, after isolating the brake booster I took the car out for a test drive.  The transmission shifted perfectly in Drive, or shifting manually through the gears.  Makes sense if the booster is leaking vacuum there would not be enough to actuate the modulator valve.

Now I need to have my booster rebuilt.  Does anyone have a recommended shop that can rebuild my booster? 

Greek

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6S1134 - '67 GT-350 #2339
car 26-JD
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« Reply #6 on: November 15, 2017, 01:37:30 PM »

Booster Dewey's
http://www.boosterdeweyexchange.com/
503-238-8882

« Last Edit: November 15, 2017, 01:40:15 PM by car 26-JD » Logged
greekz
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« Reply #7 on: November 15, 2017, 01:45:27 PM »

Booster Dewey's
http://www.boosterdeweyexchange.com/
503-238-8882

JD,

Have they done work for you before?  Do you know they will rebuild mine, or just exchange?

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6S1134 - '67 GT-350 #2339
car 26-JD
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« Reply #8 on: November 15, 2017, 01:52:20 PM »

Yes they did one for me - I sent mine in for rebuild and got mine back - they do that just discuss and make sure your paper work covers that.  Many others in the SAAC community have used them and have also required they get theirs back.  (maybe they will chime-in too)

I've never heard of any issues.

As a side note the booster, master cylinder, cap and bail were all painted semi-gloss black as a unit - so before reinstallation do that it's much easier to do out of the car.



« Last Edit: November 15, 2017, 02:26:21 PM by car 26-JD » Logged
greekz
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« Reply #9 on: November 15, 2017, 01:57:14 PM »

JD, thanks. I will give them a call, and for the heads up on painting.

Greek

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6S1134 - '67 GT-350 #2339
car 26-JD
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« Reply #10 on: November 15, 2017, 02:05:14 PM »

Another note, there were two versions of stickers on the master cylinder lid for '67's.  I would think your car would have the later version (others will know better) link:
https://www.npdlink.com/store/products/decal_brake_master_cylinder_cap_locate-125971-1.html

... since this topic is up here is the other "earlier" version (the lettering looks a bit "thick" in the example);
https://www.npdlink.com/store/products/decal_disc_brake_master_cylinder_exaggerated-125870-1.html

There are others that may offer these, but these were quick to find...





* LaterVersionD-mc1410.jpg (30.64 KB, 500x500 - viewed 18 times.)

* earlierVersionD-95.jpg (30.09 KB, 500x500 - viewed 16 times.)
« Last Edit: November 15, 2017, 02:27:35 PM by car 26-JD » Logged
greekz
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« Reply #11 on: November 15, 2017, 02:14:55 PM »

Another note, there were two versions of stickers on the master cylinder lid for '67's.  I would think your car would have the later version (others will know better) link:
https://www.npdlink.com/store/products/decal_brake_master_cylinder_cap_locate-125971-1.html

... since this topic is up here is the other (earlier version);
https://www.npdlink.com/store/products/decal_disc_brake_master_cylinder_exaggerated-125870-1.html

There are others that may offer these, but these were quick to find...



Thanks for the information.

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6S1134 - '67 GT-350 #2339
Bob Gaines
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« Reply #12 on: November 15, 2017, 03:57:48 PM »

Another note, there were two versions of stickers on the master cylinder lid for '67's.  I would think your car would have the later version (others will know better) link:
https://www.npdlink.com/store/products/decal_brake_master_cylinder_cap_locate-125971-1.html

... since this topic is up here is the other "earlier" version (the lettering looks a bit "thick" in the example);
https://www.npdlink.com/store/products/decal_disc_brake_master_cylinder_exaggerated-125870-1.html

There are others that may offer these, but these were quick to find...


Yes the early repro sticker is a poor replica . It was closer to the "ESA" style sticker in lettering and border.  Yes The ESA would be appropriate on a greekz's car. Be sure that you use the correct plain(no raise letters) top cap without the small post 1970 vent made into the cap.

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Shelby Car Enthusiast, Collector, Shelby Concours Judge
greekz
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« Reply #13 on: November 15, 2017, 05:22:20 PM »

Yes the early repro sticker is a poor replica . It was closer to the "ESA" style sticker in lettering and border.  Yes The ESA would be appropriate on a greekz's car. Be sure that you use the correct plain(no raise letters) top cap without the small post 1970 vent made into the cap.

Thanks for the info Bob.  I do have the "ESA" sticker, and fairly sure the correct non raised letters and non vented cap.  Will check the cap to be sure.

Booster on its way to Booster Dewey. I really appreciate the help!

Greek

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6S1134 - '67 GT-350 #2339
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