Arknsparc Posted May 5 Share Posted May 5 My new to me project car, a barn find 1941 olds hydramatic now starts and runs like it just came off the lot. Couple of brakes are sticking so I raised the rear end off the ground to see what the transmission is doing and at idle, in neutral, left rear is spinning like crazy and the right wants to rotate but brake sticking on that side. When I tried putting in gear, when on the ground, the old girl didn't even try to move. If I tried reverse it just made a good nasty grinding gears noise. I'm interested in thoughts on what's happening... 1 1 Link to comment Share on other sites More sharing options...
Oldtech Posted May 6 Share Posted May 6 First thing is crawl under there and turn the driveshaft by hand to make sure the rear diff is working - though it sounds like it if it's spinning in neutral. Second is check the fluid level in the transmission. Now my thoughts. There isn't likely any gear noise from the transmission, what you are hearing is the reverse "dog" trying to engage with a spinning reverse drum. Why it isn't engaging could be several things including that the driveshaft is spinning when it shouldn't be. hence the first suggestion. Low fluid can cause all sorts of things to not work. Of course you are likely looking at a tranny rebuild at some point but these things are built. Usually they have some ability to move. 3 Link to comment Share on other sites More sharing options...
Arknsparc Posted May 6 Author Share Posted May 6 Oldtech, Thank you for responding... I found the dipstick for the transmission fluid and the level is right on the mark and looks nice and red. The reverse grinding noise actually first occurred when the rear end was still on the floor and there was no tire rotation. (I wasn't clear about that in my post) With the tires in the air whether the transmission is in neutral hi or low the wheels spin and the brakes will stop the spinning smoothly and quietly. The rear diff seem to be working, is quiet and I can probably live with the leak at the seal for now until I establish more of a working car and how much we decide to drive it. I wasn't sure which tire would be the drive wheel or if these were posi rear ends? Are you saying the transmission is rebuildable? I haven't called around yet but you would not hesitate to have the unit rebuilt? Link to comment Share on other sites More sharing options...
rocketraider Posted May 6 Share Posted May 6 Driveshaft and rear wheels should not turn with HydraMatic in Neutral. Either the external shift linkage is out of adjustment or something isn't right inside the transmission. Could be related to engine idle speed. HydraMatic can be torn down, cleaned and rebuilt. Companies like FATSCO in New Jersey should be able to supply a rebuild kit. The issue will be finding someone willing to do it but I believe FATSCO has a list of reputable transmission rebuilders they supply parts to. As Oldtech points out, these things were overbuilt. They were used in tanks during WW2 and the original 1940-55 Slant Pan design was popular with drag racers for its durability. It was the basis for the B&M Hydro racing transmission. 3 Link to comment Share on other sites More sharing options...
Oldtech Posted May 6 Share Posted May 6 The transmission is essentially the same until 55. There were some upgrades, but a good trans shop should have no problem rebuilding one. If you want the complete story and have the time here's a link. 1 Link to comment Share on other sites More sharing options...
Matt Harwood Posted May 6 Share Posted May 6 I'm not sure the grinding going into reverse is something wrong. The early Hydra-Matics had a problem going directly from neutral to reverse. Even the manual says to put it in drive first, let it drop into gear, then slowly move it to reverse. That should prevent the grinding. You should determine how much it's driving the rear wheels with them in the air. I bet with the car on the ground, nothing happens. It might be some slight residual torque being transmitted, but not much at all. The only real way to determine the transmission is healthy or broken is to drive it. So get everything else in order and take a gentle road test and evaluate it then. Torque converters (fluid couplings to be specific) are a little weird, especially in these early automatics. They work really well and are quite durable but they are primitive. Test it and report back! 6 Link to comment Share on other sites More sharing options...
rocketraider Posted May 7 Share Posted May 7 Now that Matt mentioned it, I remember a friend's 1942 Oldsmobile would grind and carry on going into reverse. He always called it the HydraMatic dance... At one time he had two of the remaining 1942 Oldsmobiles. Not that there were many to begin with. Link to comment Share on other sites More sharing options...
Oldtech Posted May 7 Share Posted May 7 Up until 1950 reverse was a lock pawl like a park pawl. no gentleness there, which is why it helped to have the trans "stopped" to shift into reverse. They added a clutch in 51 to fix the problem. There is a "Park" on this trans. It is moving the lever to the reverse position. The reverse pawl, combined with a spring loaded band on the rear clutch locks things up. Only problem is you can't start the engine in Park. 2 Link to comment Share on other sites More sharing options...
Pfeil Posted May 10 Share Posted May 10 Just a small correction on the years. This trans (slant pan) was used in 860 and 870 Pontiac and Olds 88 & super88 through the 56-model year. 1956 Pontiac Star Chief and Olds 98 and all Cadillac get the new "Controlled Coupling 4 speed HydraMatic". Link to comment Share on other sites More sharing options...
Arknsparc Posted June 14 Author Share Posted June 14 Well there's progress today. After freeing the brake drums and setting her back down I tried putting her in gear and she wouldn't go forward even with a rev of the engine. Grinded real bad still going into reverse. I adjusted the carb to slow the rpms and tried again and she ground much much less, and the car jumped a little. Let off the brakes and she moved! I actually couldn't help myself and drive her backwards around the yard and back into the shop. So it appears I have a transmission that'll go backwards but not forward... Thoughts again much appreciated... 🤔 2 Link to comment Share on other sites More sharing options...
61polara Posted June 17 Share Posted June 17 As far as grinding going into reverse, the factory manual say to pause in Drive before going into reverse. Then pull it into reverse. Also there is a park feature on these transmissions. Have it in Drive or Neutral and turn the engine off. Then shift into reverse and the transmission is locked. Reverse is the lowest gear ratio and may pull stuck brakes. Are you sure your brakes aren't locked up? Free the brakes and then try the transmission in Low. 1 Link to comment Share on other sites More sharing options...
Oldtech Posted June 17 Share Posted June 17 It sounds like your front band may not be applying which would cause no first gear This would also allow - i think- the trans to spin freely when it shoud stop when placed in gear on the way to reverse, causing the grinding . so I'm afraid you may have an issue, But could be just a sticky valve too. Who knows what kind of whale oil is in there!. If twas mine... I would pull the trans pan and see whats in there. If you don't find anything suspicious change the oil to some nice Dexron and see if it works. https://youtu.be/GL6s2DwqH_0?si=5PtUPQMeRTRaydo4 1 Link to comment Share on other sites More sharing options...
Grimy Posted June 17 Share Posted June 17 (edited) On 5/6/2024 at 2:51 PM, Matt Harwood said: Even the manual says to put it in drive first, let it drop into gear, then slowly move it to reverse. That should prevent the grinding. YES, YES, 1000 times YES! And Reverse is also "Park" but only when engine off. Edited June 17 by Grimy added 2nd sentence (see edit history) Link to comment Share on other sites More sharing options...
Arknsparc Posted Friday at 03:14 PM Author Share Posted Friday at 03:14 PM My rpm's at idle, when going into reverse, were to high creating the majority of the grinding issue. The manual I have says "firmly" put into reverse and with the low idle the grinding into reverse is reduced to acceptable. (My artic cat 4 wheeler had a similar problem...) When I look at the tranny fluid, via the dipstick access through the floor, the color of the fluid is a very colorful ruby color suggesting the fluid is relatively new. My new angle of attack is to make sure all the right parts are moving in the proper direction linkage wise under the cover on the side of the transmission. I watched the entire video the amazing wheelchair mechanic recorded and hope to see something obvious. If I eventually end up pulling the transmission how easily does another GM transmission bolt up to this engine? All input appreciated!!! Link to comment Share on other sites More sharing options...
Oldtech Posted Friday at 04:03 PM Share Posted Friday at 04:03 PM Your existing transmission is quite repairable and would be much easier than a swap. Yes, you can put anything in anything if you have enough determination. Other than an overdrive type, there isn't a lot to be gained. Link to comment Share on other sites More sharing options...
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