Is the T18 truly hard to shift at high RPMs? And how high?

[robroy]

Good morning,

I read a comment in another thread about the T18 being difficult to shift at high RPMs. Since the T18's a truck transmission I don't doubt this, but I'd like to know more about it.

Is it truly difficult to shift at high RPMs? And how high is high? 3,500? 4,500? 5,500?

Since my new engine redline is 6,000RPM maybe I don't have anything to worry about?

Thanks!
-Robroy

[averagef250]

A T-18 is a truck transmission that uses normal brass synchros. The reason why shifting can be difficult is because the gears and shafts are made ruggedly to last a long time. Heavier components mean that in shifting, when you move the shifter to engage the next gear the synchro rings are working extra hard to match the speeds of input/cluster to the mainshaft. Car transmissions are much lighter to synchronize faster.

A different way to look at it is every manual transmission is capable of shifting just as quickly as the next, virtually instantly. What increases shifting difficulty/time it takes to shift between gears is the transmissions ability to synchronize it's internal components when they vary increasingly in speed. To get a truck transmission to upshift fast even when there is a large difference in input/cluster and mainshaft speed the trick is to use the engine to help match the speeds in the transmission. With a high compression engine this isn't easy because the RPM's drop very fast without throttle.

Honestly, I don't think it's that bad. I've had some pretty hot motors in front of NP435's and had no problem banging gears like a Honda civic. NP435's don't have nearly the synchronizing ability of a T-18 with it's brass synchros. T-18 synchros will wear out much faster than 435's will though. Bottom line, the harder you push that stick, the harder the synchro will be working to make your shift happen. Hammer that shifter like you stole the truck and it'll shift as fast as you want it to, it'll just wear the brass out much quicker than normal driving. The good side is a T-18 is an easy piece of iron to work on. When the synchros are gone it's something you can fix without too much headache.

[FLATBEDFORD]

Mine has a T18. I wouldn't want to do any racing with it, that's for sure. Once you learn to shift at the right time it goes pretty nicely. Just don't try to put it in 5th gear.

[papabug71]

robroy, I would think you would be ok with the t-18. It should be ok for a good hard run every now & then. Just dont do it every time you take off from a start.

After all its a truck tranny that was made for pulling, not drag racing.

Anyone remember the M22 rock crusher?? My uncle had a 70 el camino with one & you could bang gears with that thing all day & night. It made a wicked growling sound too. <EDIT: It was more of a whine than a growl.....

[robroy]

Dustin, Steve, and Papabug71, thanks very much for the great replies!

I'm leaving my old, worn T18 in the truck when installing my new engine so I can get a
feel for whether or not I want to keep it or switch to a different transmission; I don't
want to bother putting in a rebuilt T18 if I ultimately want to swap to something else.

Its synchros seemed fine when I last drove it, but I did notice that the difference between third and reverse was difficult to feel out. When friends drove it they usually made a huge grinding noise when trying to shift in to third. I took a while to learn the exact right stick position for third.

But from what I hear it sounds like it'll work fine. I don't really mind the shifting action being stiff, as long as it'll shift, and I don't mind wearing it out relatively quickly with fast shifting. I figure it'll still hold up for years regardless!

I'll try it out once it's all put together and post back to this thread with the results.

Thanks very much for the outstanding advice!
-Robroy

[averagef250]

Robroy, the trying for 3rd, but getting reverse routine is very common for the first generation of T-18's. It's an indication that the top plate of the tranny has a lot of wear inside.

I think you're making the right choice deciding to see how you like it before choosing what to do.

[robroy]

Robroy, the trying for 3rd, but getting reverse routine is very common for the first generation of T-18's. It's an indication that the top plate of the tranny has a lot of wear inside.

Hey Dustin! That's very good to know, thanks!

I think you're making the right choice deciding to see how you like it before choosing what to do.

Great, thanks. It's good to have confirmation on this decision from somebody way more experienced than I am. Since the T18 is super easy to remove at the moment I wasn't sure if my decision was the best, but I guess it's not excessively hard to remove down the road when the engine's in and everything. I might even hire that out to the shop that rebuilds it.

Thanks very much Dustin!
-Robroy

[robroy]

Well, since my last post on this thread I've changed my mind about waiting to see how I like the T18; I'm going to pull it out and have it rebuilt, then install it together with the new engine.

There are a couple of reasons for this. For one, even if I left the T18 in there and didn't turn out to like it that much, I'd probably keep it in there for a year or two anyways before bothering to deal with swapping it for something else. For two, it sounds significantly easier to install the new engine with the transmission already all bolted up, and since I'm working alone, in the dirt, and am a novice, I like easy. For three, even if I do decide to try something else down the road, pulling out a relatively fresh T18 won't be such a painful thing--I'm sure it would wind up in the hands of an appreciative new owner.

Another reason I'm not jumping to the idea of installing a five speed--and I'm sure this is entirely arguable--is that I read on the Gear Vendors site that five speed transmissions are much more fragile than four speeds with a 1:1 top gear.

I'm aware that Gear Vendors is motivated to make claims that help people justify purchasing from them, but this claim is interesting to me.

Is it truth or a myth? Or perhaps it only applies to car transmissions?

Thanks very much for the truly excellent advice!
Special thanks to Dustin for those articulate and experienced explanations of how transmissions work!

-Robroy

[Fordnatic]

That would be true about the tranny being stronger in 4th (direct drive). The power is not going through the countershaft, but just straight through the transmission. The 1:1 gear of any manual trans is considered to be the strongest by far.