copb8 97 Report post Posted December 20, 2021 Almost 2 years ago I had a reputable shop in Dallas rebuild my FMX transmission. At the time it was leaking badly and shifting was erratic and rough. They did a great job at resolving those two issues however when I drove the car a VERY noticeable vibration had been introduced. After many times going back and forth to the shop and trying to diagnose the problem it is still there and killing my enjoyment of the car. At first they were looking for all kinds of reasons that it was drivetrain related such as the 9" rear-end or the driveshaft being out of balance. I never understood this considering that those items hadn't changed at all during the transmission rebuild. We even replaced the driveshaft and while it seemed to be getting a 'little' better, it was always still there and I kept bring it back and saying there's something wrong with the transmission. So here's were we are now. With the car in neutral I can increase RPM's and at 2150 rpms I get a very obvious vibration. As rpms increases it changes frequency and begins to morph into a increasing and decreasing thrumming. To me this obviously eliminates anything driveline related. So they then took an empty bell-housing with the starter installed and attached it to the motor. The motor ran smooth as silk at all RPM ranges. So motor is eliminated as the source of the issue. To me this almost 100% points to the torque converter being the culprit. What else is spinning when a transmission is in neutral. The shop however tells me they've been rebuilding torque converters for 50 years and have tried 2 in the car and even though they balance-tested both of them the vibration still remains. Question 1: Can it be anything else other than the torque converter? Question 2: Is there such a thing as new remanufactured FMX torque converters that I can buy that aren't hot-rod high stall units? Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted December 20, 2021 Do you believe they tried two additional torque converters? I might try bolting your torque converter up to the flexplate with the bellhousing, but without the transmission again and see if you have the vibration. Shops still rebuild torque converters, nothing special about the fmx that can't be rebuilt. When I was running my fmx I bought a new TC that was only about 500 stall rpm over stock. Quote Share this post Link to post Share on other sites
copb8 97 Report post Posted December 20, 2021 58 minutes ago, RPM said: Do you believe they tried two additional torque converters? I might try bolting your torque converter up to the flexplate with the bellhousing, but without the transmission again and see if you have the vibration. Shops still rebuild torque converters, nothing special about the fmx that can't be rebuilt. When I was running my fmx I bought a new TC that was only about 500 stall rpm over stock. I asked about bolting the TC to the flex plate and giving it a spin but they said you need something to hold the internals in place from the transmission side as well, otherwise the internals will just flop around. This kinda made sense to me. Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted December 20, 2021 1 hour ago, copb8 said: I asked about bolting the TC to the flex plate and giving it a spin but they said you need something to hold the internals in place from the transmission side as well, otherwise the internals will just flop around. This kinda made sense to me. Correct, turbine and stator are held/centered by trans input shaft. Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted December 20, 2021 been a long time since I worked on an FMX but isn't there a bushing in the pump housing that the rear boss on the TC rides in. I would surely be checking all bushings on front of transmission that the input shaft is associated with. If they did rule out the TC that is about the only thing left Quote Share this post Link to post Share on other sites
dcm0123 15 Report post Posted December 26, 2021 Once bought a new flex plate from Ford which came through with the weights missing. Had the same problem you described- vibration while in neutral when engine speed was increased. Depending on the application sometimes the weights are on their to counterbalance the crankshaft, not balance the flex plate. Could be the flex plate is your problem. When I brought it back to Ford they said they sell it with and without the weights. The weights will be obvious if they are there as you can see below. I noticed on the Rock Auto website they also sell the flex plates without the holes drilled for the torque converter. If a shop does not drill the holes properly, the torque converter may not be properly centered with the flex plate and cause a vibration. If it vibrates in neutral with the transmission mounter and did not do it when a bell housing was attached, it is directly related to the transmission. You may want to verify they did not put on a rigid properly balanced flywheel when they ran it with the bell housing. I am not sure you can unbolt the torque converter on a Ford and spin the flex plate with out it. On a GM you can because they use bolts. Ford uses studs on the torque converter which protrude through the flex plate. If you cannot push the torque converter back far enough the studs may not disengage the flex plate so it can spin free. There are many companies who sell rebuilt converters for stock applications. I suggest you do the flex plate at the same time in case it is the issue. Quote Share this post Link to post Share on other sites
dcm0123 15 Report post Posted December 26, 2021 If anyone has changed the flywheel (flex plate) or damper make sure they have used the proper one. Ford changed the way they balanced small block Fords. See link below. The 302 engine is what changed and some of the 302 parts will fit the 351. If someone has changed parts make sure they only applied 351 parts or if 302 parts were used, they use the parts from the proper year (parts designed for the 28-ounce offset balance ). The picture of the flex plate you do NOT want is shown below. The 50 ounce version shown has a large cut out opposite the weight. Since it has bee 2 years since you had the work done, you may want to run a compression check on the engine and verify something else has not gone wrong to make sure the current problem is not related to the engine. Vibration problems are not easy to solve. Hope you succeed. https://www.motortrend.com/how-to/1601-avoid-this-mistake-creating-a-balance-issue-with-the-wrong-flexplate-and-dampener/ Quote Share this post Link to post Share on other sites
copb8 97 Report post Posted December 26, 2021 Thanks for all the suggestions everyone. Flexplate is the same one I've had on the car since purchased and prior to the transmission work there was no vibration at all. Issues were leaking and poor shifting. I'm confident in the motor still being smooth. It was less than a year ago that they did the test with just the bellhousing and there's been less than 800 miles added to the car since then, none of them abusive. It starts easily and idles smoothly. What is the stall speed for a stock torque converter? Everything I find online seems to be higher stall speeds for racing or performance applications. Quote Share this post Link to post Share on other sites
dcm0123 15 Report post Posted December 26, 2021 Here is a couple of links. I will look through the OEM service manual later to see if it is stated.Looks like 1500-1800 RPM for stock. Fords are known to have problems with teeth on the flywheel/flex plate. I suggest you inspect carefully for broken or rounded off teeth on the side the starter engages from. ttps://www.allfordmustangs.com/threads/1969-mustang-torque-converter-stall-speed.156394/ https://www.carid.com/1969-ford-mustang-performance-transmission-parts/jw-performance-mileage-torque-converter-2419441604.html?parentsubmodel[]=TRANSMISSION|Automatic https://www.vintage-mustang.com/threads/torque-converter-stall-speed.532293/ https://www.tciauto.com/stall-speed-chart?SID=n5krg8j2k92moj0le9f2r1b5d0 Quote Share this post Link to post Share on other sites
copb8 97 Report post Posted December 26, 2021 Thank you very much for this! Quote Share this post Link to post Share on other sites
copb8 97 Report post Posted December 26, 2021 23 minutes ago, dcm0123 said: Here is a couple of links. I will look through the OEM service manual later to see if it is stated.Looks like 1500-1800 RPM for stock. Fords are known to have problems with teeth on the flywheel/flex plate. I suggest you inspect carefully for broken or rounded off teeth on the side the starter engages from. ttps://www.allfordmustangs.com/threads/1969-mustang-torque-converter-stall-speed.156394/ https://www.carid.com/1969-ford-mustang-performance-transmission-parts/jw-performance-mileage-torque-converter-2419441604.html?parentsubmodel[]=TRANSMISSION|Automatic https://www.vintage-mustang.com/threads/torque-converter-stall-speed.532293/ https://www.tciauto.com/stall-speed-chart?SID=n5krg8j2k92moj0le9f2r1b5d0 The JW unit looks good but when I went to put it in the cart it asked whether it was for a C4 or C6 transmission. No option for FMX. I'll give them a call Quote Share this post Link to post Share on other sites
dcm0123 15 Report post Posted December 26, 2021 I found a few companies which make new FMX converters for racing applications but could not find any who make new ones with the OEM/stock stall speed. You may have to settle for a rebuilt. These are available through Rock Auto, Advance Auto etc. Ask JW Performance if they know who makes new FMX to OEM stall speed spec. Quote Share this post Link to post Share on other sites
copb8 97 Report post Posted April 12, 2022 FINALLY! After jack with it for just over 2 YEARS I have a smooth running transmission. And like I had been saying over and over again, it was the torque converter. They finally pulled the trans again and rebuilt the converter. Now it runs as smoothly as it did when I first brought it in to fix it shifting and leaking. It'll be nice to go down the road and not be pissed off every time I get above 2150 RPMs. 4 1 BobW70Mach1, dcm0123, bigmal and 2 others reacted to this Quote Share this post Link to post Share on other sites
