CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Suburban tranny problem?

my 1995 chevy suburban slowes way down when going up hill and has a hard time gaining rpm motor seems to run fine i was wondering if it is a torque converter problem

That sounds like a drivability problem, not a transmission problem. I would let a drivability man look at it.

transman

Possibly a partially clogged catalytic converter. This could be easily tested with a vacuum gauge; if you can find a tech who has one and knows how to use it.
(The gauges are cheap, real lifesavers, and only takes a few minutes to use. Shame more techs don’t use them.)

thank you i was thinking it might be that too but forgot to check if converter was gloeing red how do you check with a vacum gauge?

Guessing. Some of them can test pressure too.

I used to remove the 02 sensor, screw in an adaptor that had a nipple on it for a vacuum line, attach the vacuum guage to the nipple then start engine and read the positive pressure going into the guage. What you are measuring is the back pressure. The higher the reading, the more stopped up the converter is. I havnt done this in a long time so I dont remember what the reading should be. ok4450 would know this better than I would. He’ll probably check back in shortly.

transman

Here is the plugged exaust test with vacuum gague (from “Gears” magazine,a transmission trade mag, May 08)

Disable the EGR

Connect a vacuum gague to a manifold vacuum port. Avoid using the MAP sensor port.

Start engine,bring to temp. Record vacuum level at idle.

Raise engine speed to about 2000 rpm record value

“In general, manifold vacuum at 2000 rpm should remain fairly close to where it was at idle. If the vacuum drops by more than about 2”, suspect a plugged exaust."

“Gears” troubleshoot quiz likes to say your problem is “likely a clogged fuel filter”

I kinda like this mag.

Well, I never tie into the exhaust at all. It’s much easier to plug into a manifold vacuum line or tee.
Anyhoo, here’s what I look for and you really have to keep your eye on the needle because some of this is very subtle.

The manifold vacuum will vary at idle based on altitude, barometric pressure, humidity, etc. Normally you will see around 16"-20" at idle and the needle should be steady; no fluctuating, etc.

Assume you have a 17" reading (common at my altitude) Blip the throttle quickly and the gauge needle should drop to zero instantly.
When the throttle is released the needle will do one of two things.
It will drop instantly back to the original 17" reading (normal, no clog).
It will be a bit hesitant about dropping (pretty significant clog) or the needle will return to a slightly higher than normal position before dropping back to zero (less evere clog).

With the latter, the needle will jump from zero to say 19" before the needle settles back to 17".
That’s how I do it anyway and hope this helps.

Oh, that makes a lot of sense and a heck of a lot easier than tieing into the exhaust. The last time I did this was back in the 80’s. It was time consuming and of course you couldnt check it when it was hot or you’d melt things. You would have to check cold and check it fast. Thanks for the info.

transman