45 mph Top Speed, what's wrong here? (1 Viewer)

[southern son]

I picked up a 1971 40 series in April 18 and have slowly been getting it more road worthy to enjoy through the summer until the next big project takes it down during the winter. I've been driving it for the last several weeks and not sure if I'm missing something or what, either way it doesn't seem to be the norm for the top speed in it to be 45 mph. It's a F engine and three speed on the column.

I've tried searching, but I'm not sure if I don't have the correct words or what - I'm not coming up with much of anything outside of an old top speed thread in which mine is far from what others in there are posting. Any help would be greatly appreciated and thanks in advance.

 

[1911]

What do you feel is limiting the top speed? No more power beyond a certain rpm? Rpm's too high for comfort?

Could be a lot of things, including possibly the transfer case being stuck in low range. Need more info/description.

 

[southern son]

The engine sounds like the rpm's are too high to me, almost like it hits a wall and no more. I thought the t-case may have been in low range as well but it wasn't - as best I could tell from operating it both ways and driving. Almost feels like it needs a fourth gear to keep going and bring the rpm's back down. It maxes out in third, as far as I'm willing to push it, and that's it.

 

[70fj40]

There could be something amiss but probably not. That is the way these rigs sound. Most will run above 45 but they will be screeming. With a rebuilt F motor and tight steering mine has seen 63 mph. It is comfortable at 53. One of the best FJ40 investments for a quieter more pleasant drive is a good set of earplugs.

 

[southern son]

I had it on a flat, open, empty road a couple of weeks ago to see if it’s just me or what it could do after finding the above referenced thread and 46 mph was all it would do flat out. I had a gps speed app and my wife behind me as a secondary gauge. If that’s the way it is then I can live with that but if something's wrong I was hoping some of y’all might know.

 

[1911]

What @70fj40 said. These F-series engines have flat tappets, timing gears instead of a chain or belt, etc. They are very noisy and when you first drive them they sound like they will fly apart! You get used to it after while. They will rev higher than you think.

 

[1911]

The clutch is not slipping?

If not, then the next things are probably a tune-up.

 

[southern son]

The clutch doesn’t feel like it’s slipping. Engine definitely sounds as if it’s wound up, good to know that I’m not doing any damage to it. I’ll get everything together for a full tune up and then see what it’s like after.

Thanks for all the help and quick replies!

 

[65swb45]

What size tires?

 

[southern son]

31x10.50x15 BFG All Terrains - 3 ply if it matters

 

[65swb45]

31x10.50x15 BFG All Terrains - 3 ply if it matters

So you should be tach-ing about 2700 rpm on a motor HP rated at 4K.

With no other mechanical specs, my WAG is you’re running out of advance on a vacuum retard dizzy.

 

[southern son]

I will check that as well while I’m there for the time up, thank you.

 

[Tancruiser]

I would check the gap on your points and check the timing.

 

[AZOKIE]

I would check gear ratio. PO may have changed to lower gearing. Stock would be 4.11. just another WAG.

 

[brian]

oh and pictures of the cruiser, otherwise it didnt happen

 

[southern son]

Here’s one of the pictures I can find on my phone at the moment. I’ve been trying to right the wrongs of PO’s past since last year, take notice of the “custom” side markers aka: LED trailer lights with sheet metal screws...

Thanks all for the replies and I’ll Ben working on my tune up, etc.

 

[Martyt]

Mine is an original 69' FST with 3 on tree. Mine will go up to 65 no problem and probably 70-75 if I pushed it. I like to keep it at 55-65 on the freeway. With that said, I don't go on the freeway that often given that everyone in CA is doing 75+ it seems. A 46 top speed seems like something is off to me. mt

 

[middlecalf]

A little more info is needed to even start guessing. At your “top speed” of 45 is the gas peddle smashed to the floorboard? What is the RPM at this speed (you’ll need to temporarily hook a tach up if you don’t have one)? Once that’s hooked up, what RPM are you at when your doing 15mph in first gear? And 30mph in 2nd? What’s the compression in each of the cylinders? What’s your vacuum pulling at WOT and not? Otherwise, I don’t know.

 

[cruiserpilot]

Double check that it is coming out of low range. I don’t think it is. Unless you have 5.39 gears or something like that

 

[middlecalf]

I drove to a fire a couple of years ago in one of our old big (deuce and a half) brush trucks, getting passed by every vehicle, even though I had the emergency lights blazing, cuz I was in low range, which I didn’t know, and couldn’t get over about 35mph. Such a dork sometimes.