clutch or tranny?

[eric58]

I have a 1989 silverado with a 305, AT, 4 wheel drive. The problem I'm having is that after about 3 miles of driving it starts losing power, as if it's not shifting into the next gear. The truck starts revving hi but gets no great power or speed, as if something is turning but not engaging. Once I find a consistant speed( say 50 miles an hour) it will stop and just drive fine....If anyone has any help or suggestions I'd be greatful....Thanks

[MagicRat]

So at very light throttle, the transmission will shift through the gears, but as soon as you give it some gas the revs go up, and you don't accelerate much, right?

I suspect your transmission is shifting normally, but its also slipping. This might be bad (aka: expensive) news.

A transmission like yours uses will slip for a number of different reasons, mostly related to low fluid pressure, or worn clutch packs.

First of all, check the transmission fluid level, and top it up if its low.

Otherwise, when this has happened to me, I have fixed the problem about a third of the time by doing a transmission fluid and filter change (not a flush).

If that does not help, a mechanic can easily check the "line pressure" to see if the trans has low fluid pressure when running. If yes, you might have a bad fluid pump or a problem in the valve body. If the line pressure is good, you may have worn clutches, bad seals, or an internal leak caused by cracked parts. Its also possible you might have a bad converter.

The problem is definitely heat-related... some part expands/loosens up when it starts to warm up, creating the problem. This is why only the first 3 miles produces normal operation.

Generally speaking, if the fluid and filter change does not fix this, you are looking at rebuilding or replacing the transmission. :-( . The fluid-and-filter change is cheap to do, a rebuild is expensive. Imho the change is worth doing, even if it only solves the problem 1/3 of the time.

BTW your transmission will not last long at all in this condition and will most likely get worse fast since the slipping will wear-out whats left of the clutch packs pretty fast.

[eric58]

Thanks alot, I try the "cheaper fix" first, I hope you're right about the fluid and filter.

[j cAT]

Originally Posted by eric58

Thanks alot, I try the "cheaper fix" first, I hope you're right about the fluid and filter.

I very much doubt replacing the fluid/filter will help. when you drop the tranny pan you will see much debris and if these particles are larger than dust your in need of much transmission work.

this problem will occur with overfilling [slippage] once this is noticable to the operator the transmission is usually very much done.

line pressures will drop as the fluid heats up. replacing the fluid / filter may for a very short time correct this slippage...very short...


if your very low on fluid the slippage would be on first starting out ..this is because the fluid has cooled and shrunk..hot fluid expands but thats when the line pressure drops...

overfilling creates air bubbles. when this occurs the fluid does not compress very much , this then creates slippage and rapid failure.

if the clutches are worn the torque converter must be replaced. the transmission and radiator fluid lines must be washed out. any old clutch debris will kill the repaired tranny..torque converters can not be cleaned !

[eric58]

Thanks, my luck being what it is you are probably right, I appreciate the help. (Mass huh!/ I use to live in CT and would go up to riverside on the weekend, also spent time at the cape and in holyoke, Thanks again.

[j cAT]

Originally Posted by eric58

Thanks, my luck being what it is you are probably right, I appreciate the help. (Mass huh!/ I use to live in CT and would go up to riverside on the weekend, also spent time at the cape and in holyoke, Thanks again.

post back how you made out. cost of repair/what was the actual component failure.

I have lived around the country/including europe for a time. new england is a safe place to live. summer is the best/ winter is bad....

[eric58]

Well, I figured out what was wrong with the truck...I was a dumb-ass!!! I drive it back and forth from work (5 miles each way) everyday, the other day I was forced to drive about 40 miles, most of it on the hi-way and it ran fine, so when I got home I checked the fluid....and notice that it said on the dip stick, "To check hot ensure vehicle is idling and on level surface....I had been checking it hot after driving but with the engine off and it read right in the croos hairs for hot, when I did it while idling I couldn't even see fluid on the stick, Sooooooo.....2 quarts of ATF later and feeling a little stupid...Long story short it runs fine now and I'm thankful that my "Lesson" wasn't a more expensive one, thanks to all who responded

[j cAT]

Originally Posted by eric58

Well, I figured out what was wrong with the truck...I was a dumb-ass!!! I drive it back and forth from work (5 miles each way) everyday, the other day I was forced to drive about 40 miles, most of it on the hi-way and it ran fine, so when I got home I checked the fluid....and notice that it said on the dip stick, "To check hot ensure vehicle is idling and on level surface....I had been checking it hot after driving but with the engine off and it read right in the croos hairs for hot, when I did it while idling I couldn't even see fluid on the stick, Sooooooo.....2 quarts of ATF later and feeling a little stupid...Long story short it runs fine now and I'm thankful that my "Lesson" wasn't a more expensive one, thanks to all who responded

thanks for the report.

since you have been driving around with that much fluid lost you must have a leak. also the fluid is now damaged from all the slippage and being low also causes the fluid to run hot.

replacing the fluid/filter would be a good idea.

adding fluid use dexronVI and when checking after fill add till at the full cold line on stick ..then get the engine / tranny hot driving 10-20 mi and recheck on the same level spot as before...

never overfill. overfilling is very destructive/no fluid bubbles !

I have used transmedic in the past with the dexron III old transmissions. this seems to help reduce leaks. also helps to clean up the tranny somewhat.