occasional slipping transmission

JerryP · October 11, 2015, 09:53 PM

Took the 89 chieftain 23' out to camp this weekend.
It did great overall, for the 200 mile round trip, except for 3 instances of what seemed like the tranny slipping..,
Each time it was just as we topped a hill, it seemed sort of like a downshift, but was not, and spun up, I had some grip on the gears though.
I was going around 55-60 each time, not in any particular hurry.
I dropped it into neutral, and then to 2nd gear, then back to drive, and it straightened out.
I remember some of the old GM torque converters had a slip, and lock issue around 35-40 mph, but do not remember anything at 55mph.

Thoughts

?

Froggy1936 · October 11, 2015, 11:38 PM

First things first, Check the fluid "Hot" & on the level , If ok and no burnt smell , Try an additive like Lucas Not cheap but will extend a worn (but not worn out ) set of clutch,s Would need more info trans type and miles would help ! Frank

JerryP · October 12, 2015, 01:31 AM

Quote from: Froggy1936 on October 11, 2015, 11:38 PM
First things first, Check the fluid "Hot" & on the level , If ok and no burnt smell , Try an additive like Lucas Not cheap but will extend a worn (but not worn out ) set of clutch,s Would need more info trans type and miles would help ! Frank

89 Cheiftain, 454 chevy engine, and I assume the TH400 transmission.
50,600 miles.
Checked the Fluid, seems OK, not sure of the age if the fluid though, as I bought it in February.
Has been running perfect, ran good this weekend except for that weird slipping feel 3 times as I finished climbing a hill
Think I will change the transmission fluid this week.

Rickf1985 · October 12, 2015, 07:16 AM

Drooped to second at 55 with 4:56 gears!

Ouch! Check the vacuum line to the modulator to make sure it is not loose or cracked.

JerryP · October 12, 2015, 01:52 PM

Heading outside to check that out.
Not sure if was dropping down, or slipping. Felt like both slipping and dropping down. It was for such a short time, I could not be sure.

JerryP · October 12, 2015, 02:16 PM

Could this be the culprit??
It is cracked, and may have come off while I was looking for it, or could have been off a while.
It is cracked, and needs to be recut, and put back on
The red tube runs into a steel line, that goes to the transmission lower right side.
Tranmissions are not my expertise.

Rickf1985 · October 12, 2015, 05:26 PM

It could very well be. That will cause any number of problems including eliminating all vacuum advance on your timing. That will make it fall flat. It would cause problems with the upshift if it caused enough vacuum loss in the red line which is the modulator line. It should not cause a a slip. It may cause a forced downshift due to sensing a low vacuum signal but should not do so at that speed. The line to the left is bad also, and so are the lines coming from under the carb into the Y connector. You have a LOT of vacuum leaks going on there.

M & J · October 12, 2015, 05:55 PM

Follow that steel line down to the transmission. There should be a rubber line connected to a small round can. Thats the vacuum modulator and helps the trans sense load so it knows when to up shift. Make sure its not cracked and leaking.

JerryP · October 12, 2015, 08:08 PM

Will do.
Thanks

JerryP · October 12, 2015, 08:11 PM

Quote from: Rickf1985 on October 12, 2015, 05:26 PM
It could very well be. That will cause any number of problems including eliminating all vacuum advance on your timing. That will make it fall flat. It would cause problems with the upshift if it caused enough vacuum loss in the red line which is the modulator line. It should not cause a a slip. It may cause a forced downshift due to sensing a low vacuum signal but should not do so at that speed. The line to the left is bad also, and so are the lines coming from under the carb into the Y connector. You have a LOT of vacuum leaks going on there.

Plan is to eliminate all but the necessary vacuum line, AIR pumps are gone, and plugged.
I eventually plan to rip it all out except for the distributor, Transmission, and whatever else is require to make it run, and put new line in those parts

Rickf1985 · October 12, 2015, 09:21 PM

Just a thought here, I was just reading your post in the travel section and the way you described the sensation of the slippage sounds just like maybe a clutch fan engaging. Did the engine get a lot louder? Maybe it was not slipping or speeding up but just the fan clutch engaging and the fan roaring. That will happen after a long pull like that.

lngfish · October 14, 2015, 05:40 AM

Rick has a good point here,

Your radiator cooling fan might be "Engaging"- fooling you, making you think, "with the Louder noise", your Trannie is "slipping". Use to fool me but I got used to it.

Or Your trannie might be slipping.

I hope it is the Fan.

lol

JerryP · October 16, 2015, 12:09 AM

Thanks guys
Several people have mentioned the fan as the likely culprit, and I think you guys are right. I did not lose power, or speed, but I sure thought something was slipping and wrong
Warm day, long hill, makes sense.
Out of curiosity, I checked the fan today, and that thing is huge, and the pitch is really angled, so it would have to make a lot of noise, especially with the engine cover not bolted down tight.

lngfish · October 16, 2015, 08:23 AM

Like a 747

lngfish · October 16, 2015, 08:29 AM

BTW I have my fan clutch seize up one time, so it did not un clutch, that was really loud! f-14?

I had to replace clutch in an Advance parking lot.

JerryP · October 16, 2015, 02:59 PM

I wonder how many people, heard it, and ended up buying a torque converter, or transmission...
I feel pretty car savvy, and it never occurred to me.
Makes me feel stupid for not realizing what it was, and I can take apart a motor, and even put it back together with only a couple of pieces left over ;-)

Rickf1985 · October 16, 2015, 03:36 PM

Don't get too confident until you are sure that is the problem, I suggested it because the conditions were right for the fan clutch to kick in but if you are not hearing the fan at first start up of the day then this may not be the problem. Just leep it in mind for the next time you are on a long hard pull and be listening for that sound.

And fix all those vacuum lines. Remember that if you pull all of them off you will be changing a lot of things with how the engine runs. No EGR means you may start to have a pinging issue and have to retard timing a bit.

legomybago · October 16, 2015, 05:26 PM

Sounds like your clutch fan engaging.

My in-laws had our P30 out of town, then came the call, "The motorhome is stuck in second gear!" they said. They drove the RV 40 miles to a tranny shop, had a new governor put in the TH400, well it did the same thing, the engine would scream. So I asked them to drive it with the engine cover off and manually shift the gears 1st, 2nd, 3rd, well, it shifted into all three speeds, then he noticed that the fan was making all the noise....frozen clutch. He changed it at a Napa parking lot. And he got some new tools out of it too, he bought ratchet wrenches to do the job, way easier.
So your not the only person who thinks tranny problems when could be cooling fan related.

dickcarl · October 19, 2015, 10:38 AM

Hearing that fan engage (with the doghouse a little loose) is a TERRIFYING noise. I'm still not used to it after over 1,000 miles.

lngfish · October 24, 2015, 06:23 AM

That is funnie only a few parts after taking an engine apart and putting it together.

Keep doing that and you end up with a new used spare engine.

Let us know what you find out when you find out.

Curious to know.

lngfish · October 24, 2015, 06:39 AM

One thing I never figured out is even though I know it is normal since my Fan Clutch is relatively new:

"Why is it engaged when engine is just started ?, then when engine warms up a bit, Dis-engages, then as engines warms up MORE from here it En-gages again?

ENGAGED, DIS-ENGAGED, ENGAGED

This is what mine does say with it 60 degrees out:

1. Start up and engine on FAST IDLE FAN PRETTY LOUD-NOT SCREAMING BUT LOUD- Medium Loud

2.1 MIN later; Kick DOWN fast Idle, engine drop in speed to 800 RPM or whatever it is. NO TACH.

3. "IF" LEFT AT FAST IDLE , in about 4-5 Minutes, never timed it, guessing, FAN Dis-engages and get QUIET' Smooths-Out

4. FAN RUNS QUIET from then on and you just hear engine at fast idle, then Kick it Down.

5. SO, GET in and Start Driving it.

Fan not engaged for like 2-3 miles. Then, this is funnie, believe it or not, but I'd say 90% of the time, it engages exactly at the same location MOST TIMES like clock work. Sort of funny.

This is how I test my fan clutch.

Well sort of.

Anyway I'd love to know what makes it engage cold I guess is the question.

Rickf1985 · October 24, 2015, 08:42 AM

The clutch works off of a viscous silicone oil. After it has been sitting the oil settles and will lock the clutch until the centrifugal force redistributes it around the hub. I put a new heavy duty clutch on mine a couple years ago and it engages way too early. I have left it on since they do sometimes have to break in but as soon as my thermostat opens the clutch kicks in. You talk about noisy rides! I will be changing it out this winter.

Bnova · October 24, 2015, 08:49 AM

That actually sounds about right, the fan has a viscous (silicon like) fluid inside the hub and a thermostat that opens and closes a valve that causes the fan to either free wheel or lockup and turn at water pump speed.

So when you first start up, the liquid is cold and not quite so fluid yet, but after a few minutes of turning with the valve still in free wheel mode it would begin to free wheel. Then as the radiator heats up and begins to warm the thermostat in the fan clutch it the thermostat in the clutch changes the valve to make the fan turn faster. Radiator cools and the fan slows down.

Rickf1985 · October 24, 2015, 09:06 AM

Yes, but it is not supposed to start kicking in until about 200 degrees. Mine kicks in as soon as the thermostat opens. Under normal circumstances the regular airflow would cool it down long before the fan is needed. This thing kicking in all the time is rough on mileage. I had it up to 10 MPG at one point and now I am back down to 7.

Bnova · October 24, 2015, 09:15 AM

My brief and basic explanation was in ref to the OPs question, just how a fan clutch works and his operation sounds pretty close to normal. If in doubt, just put a new one on, they're not terribly expensive.

Your post got there while I was typing mine.