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Newly rebuilt 727 overheat issue

Micah Toler

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I just had a 727 bult for my 74 charger 400ci, it has a 292dur 509lift Mopar purple cam, Harland Sharp roller rocker, trick flow 270 heads, Chrysler 8 3/4 rear with 3.55 GR, hays twister full race 10" converter @ 3200 stall, and a deep pan, I am running atf+4 in it.

So here is the low down, when I installed the transmission a month or so ago with a broken wrist it seemed to be in a bind and would not let the torque converter slide forward to meet the flex plate. So, I decided to remove it again and see what the issue was. As I loosened the bell housing bolts the converter freed up and slid forward to meet the plate, so I snugged the bell housing bolts again. I checked the end play of the converter travel; it was over tolerances by 1/16. So, I added four grade 8 washers between the flex plate and converter to make the difference. Remeasured, and it came just into tolerances. Finished the installation and added 4qts fluid warmed the engine to normal operating temperature and added 5 qts more fluid after cycling through all gears to bring the level full.

Test drove apx 1 mile and parked the car because the transmission cooler line was leaking where i had installed a compression t-fitting on the exit line of the trans for a temp sensor. I repaired the leak and dove the car to my local exhaust shop, and then to a local body shop to make an appt for alignment, apx 10 miles. I did run it a little bit to explore any issues that I might have with the car, but not too much seeing as how the front end was all out of alignment. I got a plastic/rubber melt smell at a stop light which i assumed was all of the new stuff installed on the car and when i pulled into the driveway i looked at my trans temp gauge and was shocked to see it at 230f degrees. I pulled in the shop killed the engine and put a drum fan on it to cool it down quick. FYI i did prime the converter before instillation.

Now my first thought was that during the instillation when I couldn't move the converter forward was that I may not have gotten the pump ears lined up and broke them off destroying the pump. I've heard of it happening to others and I thought for sure even though I was careful to seat the converter, i had messed up and broken them off. My wrist still being broken I decided to have a friend remove it for me so we could replace the pump flush it out and start over. When we got it out, I looked inside, and the pump ears appeared to have no damage there and there were no odd wear marks on the converter. I took a section of hose and with lung pressure blew through the cooler line to be sure it was clear, I blew fluid from the line which suggests a functional pump. No problems there. I blew into the entrance port of the trans, again clear. I blew through exit port of the trans coming from the pump, there was some resistance, and I could hear it make a little clicking noise, but that would be expected as I was blowing the pump around a little which further suggests with no obvious visual damage that the pump is not damaged.

The converter did suggest the use of a trans cooler that i did not think was necessary because I am running a giant four core radiator. I have since purchased a 19 core, stacked core cooler from Earls auto plumbing and an oil thermostat that I will install. I plan to pull the pan and check the pickup for blockages. I checked my tire size because I've read that under 22" diameter tires can cause overheat issues, but my 14" tires measure 25" diameter, so I don't think that that is the problem, but I did order some 15s for it. My trans builder suggested that I use type F fluid but with what I think I know about f, that it swells bands for a tighter shift and is used by racers who rebuild their trans often, I decided to use a full synthetic for longevity with it being a new rebuild with newer materials being used in the bands etc. Hence my decision for atf+4. So back to my original question, what could be causing overheat? What other tests can I perform? Should I take it back to the builder? That could be a problem and story in itself that i can explain if needed. Any thoughts/suggestions please?
 
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Did you check your fluid level hot and in neutral, does the fluid smell burnt? Typically, high stall converters produce more heat. I usually bypass the radiator and just use a good trans cooler. Place it in an area of good airflow. 440'
 
You're going in a lot of directions.
Tires overheating the Trans? No.
Put the cooler in, without going through the rad, and see how it does.
 
Break this up into a couple paragraphs to make it easier to read! Goo

Did you check your fluid level hot and in neutral, does the fluid smell burnt? Typically, high stall converters produce more heat. I usually bypass the radiator and just use a good trans cooler. Place it in an area of good airflow. 440'
Yes, hot in neutral after cycling through gears. I don't know the temp of the transmission because I had not yet wired the temp gauge, but the engine had reached normal operating temp ie. thermostat had opened. No burnt smell or color.
I had decided to piggyback off of the radiator into the cooler. I figured I would just mount it in front of my radiator. Do they typically run that much hotter? 230 seems awfully high to me. I wouldn't think it would run that kind of temp, medium duty driving at such a short distance. But I am somewhat new to high performance parts.
Did you check your fluid level hot and in neutral, does the fluid smell burnt? Typically, high stall converters produce more heat. I usually bypass the radiator and just use a good trans cooler. Place it in an area of good airflow. 440'
 
You're going in a lot of directions.
Tires overheating the Trans? No.
Put the cooler in, without going through the rad, and see how it does.
Yes, a lot. It's very perplexing to me.

Seems perfectly logical to me though. Too small diameter wheel could cause an issue, over working the stall converter with consideration of my cam and gear ratio. But I'm probably over thinking all of it, my tires are 25" diameter and I only drove it 10 miles @ medium intensity.

My thought was that maybe there are a few simple issues that each has caused a slight increase in temps that have added up to 230+. Ie. tires, fluid (levels or types), improper ratios between equipment etc.
 
You're going in a lot of directions.
Tires overheating the Trans? No.
Put the cooler in, without going through the rad, and see how it does.
Why not plumb through the rad too? I already have the fittings on hand without having to buy another -6an to -5an union. Wouldn't you think it would just add cooling capacity?
 
Just wondering why a 10" full race convertor ? Drag races only last 1/4 mile. Not really intended for daily driving.
No point in a high stall except for power braking take offs.
Put a larger diameter, lower stall convertor in it.
Heat is always a factor with high stall convertors in normal driving. Like a big cam. They like RPM's.
There are street cars and there are race cars. Race cars don't make good street cars and vice versa.
Add fluid capacity to also help with cooler temps. Try to block as little of the radiator as possible with the cooler or you will just add the engine running at a higher temp as well. Might add an electric fan to the cooler as well.

When you’re looking at buying a torque converter for street/strip use, there are some tradeoffs that you will need to consider when it comes to stall speed. If you go into a higher stall speed range, the car has the ability to produce better elapsed times, however, it will start to generate a lot more heat on the street and lose some drivability. If your car has a bigger camshaft and rearend gear, that will only amplify the drivability issues for street use.

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The billet-faced ATI StreetMaster converter was the perfect choice for the Red Dragon due to its dual purpose use of street driving and track duty.

Caine further explains what can happen with too big of a stall speed on the street for a torque converter.

“Heat is the biggest issue. Too much stall and people tend to short shift, leaving them in high gear at 20 mph and making the converter do all the work; this is a bad scenario. If you choose to run a loose converter on the street, you must wind up each gear and let the converter couple before shifting. This can make a world of difference on the temperature gauge.”
 
First, I would wonder if your dowel pins installed in the back of the block are really locating
the transmission radially? Second, A ten inch "FULL Race" convertor is a heat machine for a
street car. Third, There is nothing wrong with running the fluid through the radiator first, and
then through the cooler. The factory did that on the automatic Hemi cars. Most of the heat
gets removed by going through the radiator, and then a bigger temperature drop through the
cooler. Remember that the front fitting on the transmission pushes the fluid to the radiator,
and the rear fitting always needs a supply of oil to lubricate the rear bearing!
 
Just wondering why a 10" full race convertor ? Drag races only last 1/4 mile. Not really intended for daily driving.
No point in a high stall except for power braking take offs.
Put a larger diameter, lower stall convertor in it.

Heat is always a factor with high stall convertors in normal driving. Like a big cam. They like RPM's.
There are street cars and there are race cars. Race cars don't make good street cars and vice versa.
Add fluid capacity to also help with cooler temps. Try to block as little of the radiator as possible with the cooler or you will just add the engine running at a higher temp as well. Might add an electric fan to the cooler as well.

When you’re looking at buying a torque converter for street/strip use, there are some tradeoffs that you will need to consider when it comes to stall speed. If you go into a higher stall speed range, the car has the ability to produce better elapsed times, however, it will start to generate a lot more heat on the street and lose some drivability. If your car has a bigger camshaft and rearend gear, that will only amplify the drivability issues for street use.

The billet-faced ATI StreetMaster converter was the perfect choice for the Red Dragon due to its dual purpose use of street driving and track duty.

Caine further explains what can happen with too big of a stall speed on the street for a torque converter.

“Heat is the biggest issue. Too much stall and people tend to short shift, leaving them in high gear at 20 mph and making the converter do all the work; this is a bad scenario. If you choose to run a loose converter on the street, you must wind up each gear and let the converter couple before shifting. This can make a world of difference on the temperature gauge.”
I chose the Hays because I preferred the manufacturing process by which they were made. When I ordered the 3/4 race converter from Holley they were and still are on back order. I asked the technician what the difference in the full and 3/4 race were. His reply was "price and horsepower rating". They were available now for around fifty more. They suggested with my cam and rear dif set up that I use 3600-4200. I asked if a 3200 would make it a little more streetable, they said yes, and I bought it. My friend ran basically the same set up in a 68 Plymouth wagon and I loved it. In fact, the differential is the same 8 3/4 from that wagon that was given to me as a weeding present. At any rate, it was basically the same. The only difference is that he ran a stock 440, and Im running a 400 with trick heads. So do you suggest stall speed too high with this combo? I hate to think i heed a different converter when i just invested 700.00 in this one.
 
My two cents. (and thats all its worth)..... You are thinking too hard...that type of converter makes heat, period. Get an add-on cooler, maybe even a fan forced style. Also, you should have never tried it without an in-line block for a temperature gauge so you can tell whats going on when. Good luck with it.
 
First, I would wonder if your dowel pins installed in the back of the block are really locating
the transmission radially? Second, A ten inch "FULL Race" convertor is a heat machine for a
street car. Third, There is nothing wrong with running the fluid through the radiator first, and
then through the cooler. The factory did that on the automatic Hemi cars. Most of the heat
gets removed by going through the radiator, and then a bigger temperature drop through the
cooler. Remember that the front fitting on the transmission pushes the fluid to the radiator,
and the rear fitting always needs a supply of oil to lubricate the rear bearing!
This is sounding more and more like my full race converter is the culprit. I sure don't want to have to drop another 700 on a converter. Hopefully the cooler will take care of it. I think the dowls are ok. But please elaborate, what do you mean by "locating the trans radially"? I think the pilot baring was in a bind causing it to not slide forward. I did grease the baring before hand and i have never had this happen before, but I've only installed a hand full of transmissions.
 
My two cents. (and thats all its worth)..... You are thinking too hard...that type of converter makes heat, period. Get an add-on cooler, maybe even a fan forced style. Also, you should have never tried it without an in-line block for a temperature gauge so you can tell whats going on when. Good luck with it.
Exactly. You will see when the converter starts building heat, if there is an issue.
 
If you are running at under stall speed you are always going to get a lot of heat no matter what you do.
It is similar to driving a manual transmission with your foot 25% on the clutch pedal.
The manufacturer has no way of really knowing what the actual stall speed is - in the car 3200 could be higher or lower depending on the engines torque output.
A lot of heat in the transmission will dramatically shorten its life.
A trans cooler with a fan on it may get you some leeway- but overheated oil is bad news.
 
A loose converter with mild gears can build heat. 25" tires are pretty short. So by all rights it should be OK with a decent cooler. From what I can see there is no trans issue. Build wise or mounting to the block. You have covered the bases on that. Not My sons turbo charged car ran a pretty loose converter with a 3.54 gear and a trans blanket. He ended up running two coolers in series. It worked very well. I think you are on the right track.
Doug
 
If you are running at under stall speed you are always going to get a lot of heat no matter what you do.
It is similar to driving a manual transmission with your foot 25% on the clutch pedal.
The manufacturer has no way of really knowing what the actual stall speed is - in the car 3200 could be higher or lower depending on the engines torque output.
A lot of heat in the transmission will dramatically shorten its life.
A trans cooler with a fan on it may get you some leeway- but overheated oil is bad news.
So running under 3k, which is the apx stall speed of a 292/509 cam, in stop and go traffic will always produce more heat because the converter is over working, correct?
 
Correct as the converter has not reached lock up/stall speed it will "slip" generating excess heat.
 
Another thought; take a good look at the cooler lines for any kinks.
 
Another thought; take a good look at the cooler lines for any kinks
I did have one 90 @ the front right before the rad that had collapsed a little when I bent it. I formed a whole new stainless line because I wasn't happy with the way it looked (it probably would have performed ok). All of my plumbing is stainless. All of my plumbing is good. Thats why I used my breath to blow out the lines. That way I would know if there were an obstruction. But thank you, every thought helps.
 
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The high stall was in fact the problem. Installed a cooler from Earls. Problem solved! Thanks everyone!
 
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