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Tranny slipping in hot weather

 
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Old 23 May 2011, 09:25 pm
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Join Date: May 2011
Location: Savannah, GA
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Unhappy Tranny slipping in hot weather

I have a 2005 PT with manual transmission. Been driving stickshift for more years than I care to tell and have never had this problem - my transmission slips when the weather reaches close to 80 degrees and above. As I live in the southeast and the weather is getting warmer - well you get the idea. At cooler temps it doesn't slip. I've had 2 mechanics tell me it's NOT slipping - but I can hear and feel it slip. Any suggestions?
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Old 23 May 2011, 09:32 pm
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Location: Savannah, GA
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Default Re: Tranny slipping in hot weather

Quote:
Originally Posted by dragmom View Post
I have a 2005 PT with manual transmission. Been driving stickshift for more years than I care to tell and have never had this problem - my transmission slips when the weather reaches close to 80 degrees and above. As I live in the southeast and the weather is getting warmer - well you get the idea. At cooler temps it doesn't slip. I've had 2 mechanics tell me it's NOT slipping - but I can hear and feel it slip. Any suggestions?
PS I have 57,000 miles on it.
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Old 23 May 2011, 11:32 pm
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Location: Mooresville, NC
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Default Re: Tranny slipping in hot weather

Need to know, do you have the Getrag G288 or the NV T350 manual tranny? Big differences in the make up and connection to the engines.

Two different shift patterns, you don't need to go look at the tranny to tell which one you have. G288 Reverse is top left, T350 Reverse is opposite, bottom right. Here's the shift patterns:


Basically, there are a few different things that can make your tranny slip like you are talking about, and while it can be compounded by use of improper tranny fluid/lubrication/oil, dirty/old same, but that is not normally enough to cause slippage.

There is a huge difference between clutch slippage and transmission gear slippage, but both are realistically tied together. I've had myself armpit deep pulling manual trannys for similar complaints and they all ended up one of four things: 1) bad pressure plate, 2) warped flywheel, 3) clutch glazing and starting to go bad, or 4) bad/defective/going bad throw out bearing, or as known by the Engineers, "Clutch Release Bearing".

All of these can be affected by clutch, engine and or tranny temperatures. The amount of slippage can help tell where to look. There are also some very basic tests that can be done to tell which it might be. So, here I go... at the end of this diatribe I'll tell you what I think it is....

1). Bad pressure plate - as the springs on the pressure plate wear and age, they do become somewhat sensitive to temperature. Logically, when it's cold out, the springs are stiffer, when it heats up, they relax a bit, if they relax too much, the clutch face starts pulling away from the flywheel, causing slippage. This is normally a "late in life" event with a clutch. If you are running a G288 and have been zooming around, driving it like you stole it (for shame, that's how I drive...lol) then it can be this issue. Sadly, with both trannys, these are modular clutches so to replace the pressure plate you'd have to replace the entire clutch assembly.

2). Warped flywheel - again age, use/mileage, and temperature have an affect on this. Also, someone who shifts hard all the time slamming the clutch onto the face of the flywheel can cause the flywheel to heat up dramatically and cause warpage. Also if the car has been raced at the track, without proper cool down times between runs, the flywheel can most definitely be warped. If the engine has been overheated a few times, to the point where it's really hot, as in you are driving a volcano hot, then the engine's heat can warp the flywheel. It bolts right to the back of the crankshaft, so heat transfer can be a problem. If the flywheel is warped, you have to remove the tranny to get to it, but replacing a flywheel is a pretty simple task once the tranny is removed.

3.) Clutch glazing - people who drive and tend to have a foot resting on the clutch pedal don't understand that all they have to do is pull that clutch away from the flywheel by less than a millimeter to cause the clutch to glaze on the face of the flywheel. I've seen many times where someone had a slipping clutch, brought it in and all we had to do was sand down the face of the flywheel then deglaze the clutch, problem solved. If you constantly have your foot on the clutch pedal, you're glazing your clutch. It takes VERY LITTLE pressure to do this, and it's a total aggravation but an easy fix, on some cars...

4.) Bad or defective throw out bearing - also know as clutch release bearing, or even clutch pressure bearing. Not going into a long dissertation on what it does but it is critical to your transmission shifting properly. The clutch release bearing separates the flywheel from the clutch disc. If the bearing is defective, it can cause two main problems:
a) The clutch disc will not be able to separate from the flywheel, enabling usage of only a single gear.
b) The clutch disc will disengage at random points while driving, cause the transmission to "slip".
As the bearing wears, it becomes more and more affected by heat. My take is that your clutch release bearing, or throw out bearing, is going bad. People who hold their clutch pedal depressed while sitting at stop lights, or sitting in traffic, shorten the life dramatically of the throw out bearing. It's only engaged when you have your foot on that pedal.

The release bearing is what presses down on the rotating spring plate or "pressure plate" to release the clutch disk. Levers and springs in the pressure plate release the clutch from the engine's flywheel separating the power of the engine from the transmission. The Release or "throw-out" bearing, is only engaged when your foot is on the clutch pedal, this means that the bearing is pressing down on the levered springs of the pressure plate and holding them there while rotating at the speed of the engine. When this bearing goes bad you could hear a squealing or screeching noise whenever the clutch pedal is depressed. This bearing is not engaged when your foot is off the clutch pedal.

Now, how to test for these issues? Not that difficult, but be SURE YOUR TCS IS TURNED OFF FOR THIS!!! 1) Bad pressure plate - stomp on it! Get a quick shift into second and hold it into WOT (wide open throttle), like you're racing on the track. When you near redline on the tach, and the clutch starts to slip, it could be either 1 or 3, above. 2) Warped flywheel - get on the highway and get up to cruising speed, then drop down into 4th and hammer it. If the clutch goes slip, slip, slip, slip at what seems like regular intervals, or grab, grab, grab, grab at regular intervals, then it's likely your flywheel is warped. 3) Clutch glazing, same as the test for 1 above, hammer it and at WOT if it's slipping it's a good chance it's glazed. Lastly, 4) Bad TOB - get the car hot, find a section of road with a big uphill pull, go up that hill in 5th, then drop to 4th like you're pulling a trailer, get it really wrapped out in 4th, if it's bad you'll feel this kind of nudge in your butt, not a total slippage, but a feeling like it's about to slip, then go back to 5th, still laying into and see if you feel the same.

My take, it's the TOB that's bad.

If you want, here's an article on the PT Cruiser Manual Transmissions. It's about 3 meg so I can't post it here, but click on the link and you can save it to your computer. It has some great info on the clutch and tranny.

Now - how do you fix this problem? Personally, I'd not suggest anyone tackle these who don't already have experience in working on transmissions. If you have the proper tools, a floor lift, a tranny jack, and room to work on it, then go for it. I've rented a service bay to do a tranny pull before, was great, and they provided me the tranny lift so all I had to provide were my power tools and hand tools. In all cases, the tranny has to come away from the flywheel to ascertain the problem. You can pull the two apart, if the car's on a lift, drop the tranny, and right away look to see if the flywheel is warped. Then pull the clutch assembly off and you can tell if it's the TOB or pressure plates or clutch itself.

Here's a shot of the TOB, item 1 in this drawing:


Don't know if I was any help, but hope so. I'd say have a shop drop the tranny and take a look at the release bearing. They can tell in less than a minute if it's bad, that or they are idiots.

Oh, and this issue is hard to find unless you are looking for it specifically, that is until you drop the tranny, so they are probably thinking it's not slipping.
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Old 24 May 2011, 04:58 pm
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Join Date: May 2011
Location: Savannah, GA
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Smile Re: Tranny slipping in hot weather

chromenut, Thanks so much for your excellent help. After reading your response (I have the NV T350) I also think it may be the TOB; I'm in an area where everyday I am in bumper-to-bumper traffic for an hour (not good to constantly have to downshift) because otherwise I know not to ride the clutch.

Can no longer work on my own cars - too old! Wish mechanics took women more seriously though, I know what I feel and what I hear when I drive. Thanks again for your help.
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Old 24 May 2011, 06:28 pm
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Join Date: Nov 2007
Location: Mooresville, NC
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Default Re: Tranny slipping in hot weather

Remember, when you hold in the clutch pedal, the TOB is engaged and spinning at the speed of the motor. I spend a LOT of time in neutral when taking my daughter to skewl because of the wear and tear on the TOB if I'm constantly holding in the clutch.

Based on what you have stated, I'm willing to bet it's the TOB. The problem is getting it on a rack with a tranny lift. I can tell you that it's two hours work, but really only about 10 minutes of actual work to replace the TOB. All the other time is pulling the tranny then reconnecting it. Generally you can use a special pulling tool or small screwdriver and have the TOB off in a minute or so.

You should still be good to go on that TOB until it really starts to slip. The one problem with them is when they go, they go with you in one gear only. Meaning either you're in neutral, or stuck in one gear and can not shift.

Good luck!!!
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