Vacuum Modulator help...

[Row]

Im new to this forum and have been looking for info on how to tell if my vac. mod. is bad...I'm having issues like others have described with the shifting...any info would be great! Also, this is my first truck ever...I'm new to this world of trucks!

This is my mod...

[fine69]

So whats your question?

If you think its bad, replace it. They are only like $12 bucks.

[Wrenchbender Ret]

First pull the vacuum hose off of it. If there is any sign of fluid at the hole it is a sure sign its bad. Start the engine & make sure you have vacuum at the hose. If so do as Fine69 says & just replace it. There is a screw in side the hole that you turn with an allen wrench to taylor it but it doesn't change very much.

[Row]

Can I just take it off? Links on info about how to change one out?

[Row]

Sweet!!! I'll do that...thanx a lot!

[Longhorn Man]

whats the problem... why do you think it's bad?
This issn't actually a part that goes out often.

[Row]

My truck is showing signs of a bad vac mod...I jus wanted to see if there were ways to test the vac mod to rule it out...

[ChevLoRay]

Somebody correct me if I am wrong...but the vacuum modulators that I have seen that have gone bad are evident because the diaphragm allows the engine to suck transmission fluid into the intake through the vacuum line.

[mr48chev]

They are easy to change and inexpensive as the guys said. I'd be and sure to check the whole vacuum line first though as that is usually where the problem is.
If you do see trans fluid in the tube that the vacuum hose connects to the modulator is bad and needs to be replaced.

[Row]

I checked the hose and there wasn't any fluid...I have another question, is the vacuum line supposed to be one piece of rubber or a metal vacuum line with 2 pieces of rubber on each end? Mine is the second example. I'm gonna replace it all tomorrow but I've called a few auto parts stores and they don't carry the metal vacuum line that my truck has on it.

[Wrenchbender Ret]

The original comes with a metal line & short rubber hose on each end. They seldom go bad. You can buy them at LMC. but you could make one with a brake tube of the appropriate size from any parts store. Cut it to size & bend it to match the old one. Lots of times guys put the whole thing in rubber hose & it works but is not the recommended way.

[Row]

Thanx a lot...I have still been looking and really needed some help. Can I bent the brake tube by hand or do I need a special tool?

[OrangeCrush1970]

I just went through mine. The metal tube should be fine, just replace the rubber's on each end and throw in the modulator...$15. If your probs persist, you need to investigate the trans.

Here was my thread for the symptoms, etc. Hope this helps.

http://67-72chevytrucks.com/vboard/s...d.php?t=326698

[Row]

can u give me a link on how to replace the vac mod? and what vac mod brands are better?

[OrangeCrush1970]

Take your pick:
http://shop.advanceautoparts.com/Pro...e=1159&PTSet=A

Fram is good, I got the standard equip b/c it was all they had in stock.

It's simple to remove and replace. You need to remove the 1/2" bolt and fork that holds the modulator in place. Modulator should pull out...Be sure to get the old rubber washer out (mine didnt come out w/ the modulator). Install new modulator in the reverse that you took the old one out (w/ rubber gasket)...install your rubber elbo to metal tube (a new one should come in the box w/ the new modulator). Get some new hose for the section up top that connects to your manifold vac (same size hose...I took my old one w/ me to the store).

You can use gasket maker on the metal tube (male ends only) and the exterior nipple on the vac modulator (not the larger end that intalls in the transmission!!!!). Gasket maker isnt nessecary but it helps seal things up.