I have a 96 SSEi. I had never driven a SC 4T60 car. MAN THIS TRANS SHIFTS LIKE I WOULD HAVE BUILT IT, NOT GM!!!!! I don't know what the differences are b/t the 4T60E and the 4T60E-HD, but I can guess... I can't wait to tear one down.

This one has 147,000 miles on it, but it was pampered by one older adult male owner. I've been beating on it for a month, but no problems. I swear this thing shifts better than ANY 4T65E, HD or not, that I have driven, and I've driven alot of them. Wtih the exception of the one I built for a customer, which now shifts like an old TH350 with a shift kit, the 4T65E just never has a consistant shift feel, perf shift or not, HD or non.

My opinion, the 4T60 is a better trans for one reason... vacuum modulated line pressure. The PCM controlled PWM PC solenoid in the 4T65E SUCKS!

Anyway, I am in the planning stages of a 4T80E swap into the 96 Bonne. Look for a new thread some time soon.

Oh, the wifes Montana lost 4th gear (4th clutch shaft splines stripped) at 109,000. 2000-model 4T65E.

Pontiacjeff, my thoughts are the same as yours. The 4T60 is a better trans from a reliability standpoint as well as operational at high mileage. And it can be built stronger when the time finally comes.

Your wife'* 65 lasting until 109k is rare.

The difference in the HD unit is the internals. Primarily the Diff. Not just a different ratio, but built stronger. When yours lets go on that 96 SSEi, It'll either be a slipping TC due to losing all the friction material on the 2nd gear clutches, or you'll launch part of your diff through the case.

I like the -65 second gear, I use the -60 low/reverse steels in the -65 when I build them, the -65 has a stronger OD, too, except the shaft splines need to be heat-treated (these splines are the same as the -60, I don't know why they don't fail as often in the -60?) The -60/-65 converters are interchangeable. If I could build a -60 with the second gear parts and OD parts from the -65 (perhaps this is the -60HD???) and a true hydraulic valve body out of the 440, that would be a trans to run!

But I'm still putting my eggs in the 4T80E basket...

Supposedly, this is the origin of the -HD diff, as used in the 4T65E-HD. I will say the tailshaft housing on the 65-HD is different than the -65 non-HD. From what I can see, however, the 60-HD tailshaft housing is identical to the -60 non-HD. This would lead me to believe that if the 60-HD has a stringer diff, it is NOT the same as the beef-cake diff used int he 65-HD which requires a different rs axle, tailshaft housing, and output shaft in the tranny.

Jeff, from what a few experts have told me, there is a big understanding in the 4T60 knowledge in general. Either the tailshaft housing or the trans housing itself is beefed up and not the same as a non-HD 4T60. Many trans shops substitute parts however, not knowing.

The 4T60E(HD) case and/or tailshaft housing may LOOK the same but is supposedly derived from beefier sources, one being mentioned to me often is the 4T60E case used in the Caddy 4.9 liter V8. Note that in the v8 application of the caddy, very few early failures were noted. The advice given to me should your OEM case not be suitable for rebuild is to find a 4T60E from a 4.9 liter V8 application and rebuild that, or another OEM L67-installed trans case donor (park avenue, riviera, SSEi, etc). I've also been TOLD that even AC Delco is distributing factory remanufactured transmissions based on the non-HD 4T60E due to the small numbers of HD units in circulation still.

A possible explanation of the 65E 2nd gear set lasting longer may be the difference in hp/tq curves between the S1 and S2 engines. So in other words, you may not have 2nd gear clutch failure to the extent the Series 1 L67 does, simply because we develop our power down lower.

Nah... second gear drum, clutches, piston, everything is bigger and stronger in the -65E. And when I build the -65e it will bark the tires in second gear with stock pcm tuning. The one i built for a GTP hit so hard at light throttle the customer asked me to put the old accumulator setup back in it. It would squeal the tires at WOT for about 20ft. in a mildly modded GTP. The rear view mirror fell off it hit so hard one time... that'* when he asked me to soften it up. It would chirp at less than half throttle! LOL! It was a beast to drive. ROTFL!!!!! I would have left it for me, but the wife and kids don't normally ride around in my cars.....

Did the 3400DOHC in the GTP, Z34 come with the -60HD? I read somewhere it did. if so, I have taken two of them apart, both 95 and 96 models, and both had a stock 4T60E diff in them. My TGP now has the 96 tranny and one of my EP limited slips in it.