All, I'm still new around here and new to Chevelles in general so please help me out with some ideas if you can. I'll start out with the car particulars.
Model: 70 Vert w/ LS5 454
Tranny: M21
Rear end: 3:31

Problem: When the car is first started it goes through the gears like butter. It can be slipped into third gear with no drama whatsoever, very smooth. BUT, once the car gets out on the road it is very difficult (sometimes impossible) to shift on the fly into 3rd gear from second gear meaning I'll usually just skip 3rd and put it in 4th. The other issue is that the car is running way too hot which is a separtate high priority issue that needs to be addressed . The reason I point this out though is that a tremendous amount of heat is coming up through the floorboards and makes me wonder if the heat has at least in part something to do with the problem. The car does not pop out of gear so I'm thinking the synchros might be okay but since it's really finicky about 3rd gear it's just hard to say. I'm a big down shifter and sometimes that is not the easiest thing either but again I wonder how much of this could be heat related and how much tranny related? Guys, any ideas would be greatly appreciated. Have any of you experienced a lot of heat through the floorboards? Would this come mainly from the engine or exhaust? :(

I don't think the heat has anything to do with your problem. Is it just hard to get into 3rd gear, or does it actually grind when shifting into 3rd? In either case, it sounds like you are having syncro problems, for some reason the syncro isn't able to slow down the 3rd gear. Have you tried changing the lube in the transmission? Just a few thoughts.

Yes, there has been some grinding...again, it's weird, at startup you can run through the gears with ease like cutting through butter but shortly after getting out on the road it can be a real bear. The grinding I have experienced has mainly been on ocassion getting into 1st or reverse. With 3rd gear it just seems like when I'm tyring to shift on the fly from 2nd to 3rd, it just won't go into gear- it doesn't grind all the time.
I will definitely change out the tranny lube as suggested. So heat is not really an issue with a manual tranny?

All, I'm still new around here and new to Chevelles in general so please help me out with some ideas if you can. I'll start out with the car particulars.
Model: 70 Vert w/ LS5 454
Tranny: M21
Rear end: 3:31

Problem: When the car is first started it goes through the gears like butter. It can be slipped into third gear with no drama whatsoever, very smooth. BUT, once the car gets out on the road it is very difficult (sometimes impossible) to shift on the fly into 3rd gear from second gear meaning I'll usually just skip 3rd and put it in 4th. The other issue is that the car is running way too hot which is a separtate high priority issue that needs to be addressed . The reason I point this out though is that a tremendous amount of heat is coming up through the floorboards and makes me wonder if the heat has at least in part something to do with the problem. The car does not pop out of gear so I'm thinking the synchros might be okay but since it's really finicky about 3rd gear it's just hard to say. I'm a big down shifter and sometimes that is not the easiest thing either but again I wonder how much of this could be heat related and how much tranny related? Guys, any ideas would be greatly appreciated. Have any of you experienced a lot of heat through the floorboards? Would this come mainly from the engine or exhaust? :(

It is possible the syncro is the issue but you would think it would do it cold or hot??? The heat thing bothers me and heat does have a direct relation to shifting, all that woderful stuff in the bell housing gets hot and gets a little bigger, like the clutch disk.

When the heat comes up it just might be enough of a factor that you lose a little of your clutch adjustment, making it hard to get into third gear.

If this is the case I would also think the others gears get a little harder to shift.

Yes, shifting is not easy or good in any gear once things heat up. That's what I'm thinking too, that my primary issue is heat. I just don't can't figure out why so much of the heat is coming up from the floorboards. The car is running way too hot so I know I have to look at the basics: Tstat, radiator, fan, hoses, timing. The timing thing concerns me because I'll have to have that looked at by someone who knows how, I'm still a rookie but want to get a timing light and learn how to do it. If my car was seriously hot though it would start to overheat and that has not happened. It will even restart so I'm not sure how much heat the engine is really throwing off just yet. Bottom line it's obviously still way too much heat as I can't imagine my exhaust alone gets that hot by itself.

Yes, shifting is not easy or good in any gear once things heat up. That's what I'm thinking too, that my primary issue is heat. I just don't can't figure out why so much of the heat is coming up from the floorboards. The car is running way too hot so I know I have to look at the basics: Tstat, radiator, fan, hoses, timing. The timing thing concerns me because I'll have to have that looked at by someone who knows how, I'm still a rookie but want to get a timing light and learn how to do it. If my car was seriously hot though it would start to overheat and that has not happened. It will even restart so I'm not sure how much heat the engine is really throwing off just yet. Bottom line it's obviously still way too much heat as I can't imagine my exhaust alone gets that hot by itself.

The whole timing thing seems to be some sort of mystry but it's dirt simple.

First and foremost, you need a distributor with vacuum advance, and the vacuum should come right from the intake and not ported vacuum.

Second, you need to know how much vacuum you have so you can match the vacuum advance to the source. You need to have full advance at idle, somewhere in the 26 to 28 degree range.

Once you have a light hooked up you pull the vacuum line off the distributor, block the line and set the inital at about 10 degrees, plug the line back in and the distributor should advance the timing.

Total timing is done at 3000 plus rpm add should not be much more than 36 to 38 degrees.

The firing order for a SB or BB is 18436572, clockwise. Where #1 is on the cap is your choice, just make sure you are on #1 firing by removing the plug on #1, stick your finger in the plug hole and bump the motor until you feel the air pushing out.

Easy!