T19 having trouble downshifting to 3rd?

[Ciulster]

Hey all! Recently I bought a 1983 F250HD. It's a little rough around the edges but most things I have been able to solve on my own. I havent been able to drive it much since I got it as I've been changing up the meds and I've had this burning question about something I noticed when I was highway driving on the trip home after buying it.

Now to clear some technical junk up it has 3.54 gears in the rear. Supposedly it is a limited slip. If not we'll call it 3.55. But I don't know what the gearing in the transmission is. I know almost all T19's in the diesels came with the 4.02 1st but I know that the '83 year had a rare option for 5.11 gearing. And the gearing in this truck feels really short. Like 1st gear governs out at around 9 mph so there is a strong possibility for that.

With that out of the way. The issue. When I go to downshift into third it absolutely refuses to go into gear and grinds horribly. I can feel it pop against the gear but if I try push it in it just scrapes and chudders like mad. Mind you this was at 50 mph gearing down for a hill. And once this happens I am locked out of all other gears until I slow right down. But downshifts are smooth and work properly if I brake down to say 30 mph. It downshifts fine at that speed. Again this is only affecting downshifts into third. Upshifts into third are smooth as can be. So I dont know about syncros.

I hear about guys downshifting at these speeds all the time. So I don't know why my transmission dislikes going into gear at these speeds. So what do you guys think? Could this just be a case of me trying to downshift at too fast of a speed for the diesel? Is it a possibility my transmission ratios are shorter than everyone else's and I am shifting at too high a speed? Or do you think it could have been my relative inexperience with a diesel truck and going straight from a 5 speed sports car to a 4 speed diesel and expecting it to engine brake and downshift the same caused it to not want to go into gear? Or is this a more serious transmission problem?
Any insight would be appreciated.

 

[franklin2]

Your synchros could be worn some, these trucks are getting old so that is probably a given. But 50mph is pretty fast also. What does the engine sound like at 50 mph in 3rd gear? If you do not like it or it won't do it, then I would not demand the transmission to downshift at that speed.

If you and your truck are comfortable at 50mph in 3rd one other trick you can try; Get yourself in the same situation when the problem happens, move the shifter out of 4th, let the clutch out, put your foot on the throttle and rev the engine way up, let go, push in on the clutch, and then see if it goes in. This is what you have to do on the big trucks since they do not have synchros in the tranny.

 

[DaveBen]

Does your clutch work good in the other gears? Start OK from a stop?

 

[Runningaford]

try to match engine speed with what you think it should be for a given speed in a given gear, then shift with the appropriate amount of throttle. My zf5 3rd gear syncro is a little worn, and doing the above works. Treat it like it doesn't have syncros.

 

[Ciulster]

The clutch is a little slow to come up on this truck. Slower than I am used to. My father said that many old trucks were just like that and all I can do to imcrease its speed is bleed the slave cylinder. But it isnt slow enough to affect the shofting in any way. The clutch fully engages through all the gears. The truck starts from a stop awesome and rows through all the gears easily.

When I tried rev matching for 50 mph it still didnt want to go in. maybe thats in part because I dont have a tach and I had the truck for only an hour and I hadnt really had a feel for all the shift points and where exactly where to throw the shift lever during all the shifts (I noticed it isnt a perfect level H pattern like in a car and its kind of easy to overshoot third gear if you get hasty)

Not to mention that the truck was having performance issues thanks to copious ammounts of air in the return lines thanks to shot lines and orings. And a severely frayed throttle cable that was sticking and only opened about 70% of the way max. No wonder I was slowing to a crawl up hills in 4th. I am suprised it made it the 100+ miles home without stalling once.

But anyway is it really a problem if I cruise at say 30mph in 4th gear anyway? Thats the speed limit through town and in 3rd the truck seems unbearably loud for cruising. So thats my thesis. Are my gears just super short and I am overspeeding the downshifts and having trouble rev matching? I bet with practice I would be able to rev match downshift at 40 no problem. its just at 50-55 the engine is already screaming away. a revmatch to 3rd would be off the governor.

 

[Ciulster]

And I dont know if my truck could even reach 60 in 3rd gear to be honest. 30 sounds like its pretty loud and rattly. 40 sounds like its screaming. 50-55 would definitely be around governor I'd feel. I don't know why the gears in this truck feel so short.

 

[austin92]

I have a Dana 61 3.07 rear axle. 60-65 in 3rd is pretty much at the fuel shut off. I use 4th gear cruising from about 25-40 mph so you should be fine having lower rear gears. Your 3rd sounds like my wrangler I have tore apart right now. 2nd to 3rd was smooth as butter but trying to grab 3rd from 4th or 5th, well I might as well have tried to put it in reverse at 55. I found that since the second gear synchro was still good, it I just touched the synchro then went to 3rd it would go with out a fit. I could also rev match and down **** to 3rd. Although. This is a 1/4 ton 5 speed from 1997, figured I'd share


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[Ciulster]

I guess I'll just have to drive it more and see if it gives me grief. I didn't really buy it as a long distance traveler anyway. More as a cheap around town beater for the winter. So I think if I just adjust my driving style from sports car to trucker and actually use the brakes to slow the truck down instead of the downshifts it might be alright. I'll be sure to update once I get back on the road if it gives me a hard time. I think I was probably just downshifting at too high a speed and expecting the engine to do the work.

 

[franklin2]

From your other posts it does sound like you are forcing it to do something it really can't do. If you think it's going to blow up at 50mph in 3rd, then it's probably going to balk at a downshift to 3rd at that speed.

 

[Ciulster]

I had assumed so. I just wanted to check on here and make sure it wasn't a more serious problem. I think it may be because I might have the shorter ratio gear set T19 too. Because most YouTube videos I see of guys rowing through gears in the 6.9 IDI they can get going a lot faster in lower gears before having to shift, even if they have a 4.10 rear. With my truck It's: idle off into 1st, if i give it any throttle its immediately roaring and at the governor, so i might as well just immediately shift to 2nd once I'm rolling then in 2nd i can give it about 3 seconds of throttle up to about 15-20 mph before I have to go into 3rd, 3rd is good until 30-40 mph. and then 4th has a top speed and hits governor at like 75 mph. Most YouTube videos I see most guys can at least get 4 seconds in 1st, 6 in 2nd, 8 in 3rd. Etc. and much higher top speeds. Leading to me being confused as to why I cant downshift at the same points they can.