'79 - '85 THM 325 & 325-4L Information...
Posted: Tue Sep 22, 2009 3:34 pm
Hello Everyone:
While we're on the subject of Toronado transmissions, I'd like to share a personal experience.
The 3 speed THM 325 ('79 - '81) & 4 speed THM 325-4L ('82 - '85) were based on the downsized THM 200 & THM 200-4R. IMHO, both the 200 & 325 had a weak link: the intermediate band. This 'friction element' (along with other components) creates 2nd 'gear' when it stops the rotation of the direct clutch drum. GM engineered smooth shifts which resulted in extra heat & wear on this band. The original band in my '84 wore out @ 77,000 miles. The 1-2 shift became very long and ended with an abrupt bump (called a slide-bump). Under moderate to heavy acceleration, the 1-2 shift became a slide-bang...
There is good news... If you are in need of a trans rebuild or your trans still shifts without slipping, I would highly recommend that you have a 'shift kit' (also known as a 'shift reprogramming kit') installed. This can be done without removing the trans from the car. The trans oil pan & valve body are removed and most of the modifications are made there. The shift kit will make the shifts a bit more firm but will not make them harsh. The shifts will still occur at the same speed points but will feel quicker & sharper. Less slippage & less heat will now occur @ the shift points making the band & clutch frictions last much longer.
I installed a Trans-go shift kit http://www.transgo.com/sk_generalmtrs.php in 1992 when the trans was rebuilt @ 77,000 miles. I was totally pleased with the improvement. 100,000 miles later when the trans needed a rebuild for other reasons, the shifts (especially that pesky 1-2) were as good as they were @ 77,000 miles. BTW, the rebuild @ 177,000 miles was due a worn drive chain (slack) & sprocket bearings.
Since heat is the real enemy of automatic transmissions, I would also recommend the installation of an auxiliary trans oil cooler. This can easily be mounted at the bottom right side of the A/C condenser. It should be 'plumbed' in series with the existing radiator trans oil cooler and be 'ahead' of it. In other words, oil leaving the trans should pass through the aux cooler first, then through the existing radiator cooler before returning to the trans. In cold weather, it's important to allow the trans oil to maintain proper operating temperature.
The THM 325 units are not as bullet proof as the THM 425 ('66 - '78 Toronados). The THM 425 was based on the highly regarded THM 400. However, since we hopefully don't race our '79 - '85 Toronados, a non-abused THM 325 (especially with a shift kit & aux cooler) will last a good many miles... My '84 is about to turn over to 188,000...!
Paul
While we're on the subject of Toronado transmissions, I'd like to share a personal experience.
The 3 speed THM 325 ('79 - '81) & 4 speed THM 325-4L ('82 - '85) were based on the downsized THM 200 & THM 200-4R. IMHO, both the 200 & 325 had a weak link: the intermediate band. This 'friction element' (along with other components) creates 2nd 'gear' when it stops the rotation of the direct clutch drum. GM engineered smooth shifts which resulted in extra heat & wear on this band. The original band in my '84 wore out @ 77,000 miles. The 1-2 shift became very long and ended with an abrupt bump (called a slide-bump). Under moderate to heavy acceleration, the 1-2 shift became a slide-bang...
There is good news... If you are in need of a trans rebuild or your trans still shifts without slipping, I would highly recommend that you have a 'shift kit' (also known as a 'shift reprogramming kit') installed. This can be done without removing the trans from the car. The trans oil pan & valve body are removed and most of the modifications are made there. The shift kit will make the shifts a bit more firm but will not make them harsh. The shifts will still occur at the same speed points but will feel quicker & sharper. Less slippage & less heat will now occur @ the shift points making the band & clutch frictions last much longer.
I installed a Trans-go shift kit http://www.transgo.com/sk_generalmtrs.php in 1992 when the trans was rebuilt @ 77,000 miles. I was totally pleased with the improvement. 100,000 miles later when the trans needed a rebuild for other reasons, the shifts (especially that pesky 1-2) were as good as they were @ 77,000 miles. BTW, the rebuild @ 177,000 miles was due a worn drive chain (slack) & sprocket bearings.
Since heat is the real enemy of automatic transmissions, I would also recommend the installation of an auxiliary trans oil cooler. This can easily be mounted at the bottom right side of the A/C condenser. It should be 'plumbed' in series with the existing radiator trans oil cooler and be 'ahead' of it. In other words, oil leaving the trans should pass through the aux cooler first, then through the existing radiator cooler before returning to the trans. In cold weather, it's important to allow the trans oil to maintain proper operating temperature.
The THM 325 units are not as bullet proof as the THM 425 ('66 - '78 Toronados). The THM 425 was based on the highly regarded THM 400. However, since we hopefully don't race our '79 - '85 Toronados, a non-abused THM 325 (especially with a shift kit & aux cooler) will last a good many miles... My '84 is about to turn over to 188,000...!
Paul