I can't drive 55 (1 Viewer)

[MatthewMcD]

I'm starting to dream about a 40 I've never seen, its worse than Work Dreams. Has the condition of the emergency brake been raised in this discussion? I know its a long shot since they mostly barely work as opposed to actually impeding forward movement.

It has, I rebuilt it last year. With it off the prop shaft spins easily by hand.

 

[MatthewMcD]

OK, I concede on the muffler... Dangit.

Don't give up, I need to check from the manifold down. But I agree, I don't think that's the issue.

 

[zerotreedelta]

Chambered heads for reference:

 

[456z]

I know just enough to be dangerous around these things. As one of the two humans active on this thread to have laid hands on Matt’s rig, I’ll just say it just feels like it’s in the gearing.

Maybe when Kelly @77mustard40, who I’m certain far surpasses my meager knowledge, checks the truck out, we’ll have a sense of resolution.

It really isn’t that the truck is just slow, something is holding it back.

Hats off to you for lending a helping hand on this puzzler.
Gearing I believe could easily be checked by (leaving key off) getting one rear wheel off the ground in 2H/4th then using a hand starter turn the motor one revolution then driveshaft should I turn rotate one turn.
Thinking this would give the 1/1 ratio??
Good luck.
Looking forward to learning the fixing answers.

I was just over there loaning him a brake reservoir cap, there has been more fact finding.

 

[456z]

Second thought
Does the 1/1 ratio in high include the differential and inturn the rear wheel would match engine rotation????
Someone here will know.

 

[MatthewMcD]

Definitely curious on the mech advance numbers as it's one of the remaining concrete tests that's easy.

With the vacuum ports on the carb plugged, I dialed in 11* of advance at 750 rpm idle.
I increased the RPM so that the only thing advancing the distributor was the mechanical advance.
15* @ 1000
20* @ 1200
24* @ 1300
28* @ 1600
30* @ 2000 (all in)

Someone asked about taking it to 3000 RPM in neutral, no problem, ran right up and past 3000 RPM.

Back to the Rochester base plate, you had that one vac hose with a torx screw in it, that is a good source to tap manifold-vacuum, instead of ported vacuum, on your distributor advance.

I swapped the vacuum input to the distributor and you are right. It runs better on manifold vacuum.

50 MPH, but it still feels like it's working to hard for the last 5-8 MPH.

Oh, and I found my brake reservoir cap.

 

[MatthewMcD]

Have you considered using a laser thermometer to check for hot spots after running it for a while, especially after trying for max speed. If it’s a power loss issue you should be generating a lot of heat somewhere.

I noticed today that the front hubs (Warn running in 2x4 mode) are hot to the touch after the test drive. When I assembled them, I was careful to check preload per the FSM.

 

[BOBWhite74]

Well I don't know if that means anything but at least it's SOMETHING!

Another test you could do is remove the front driveshaft and see if that makes any difference. Then put the front driveshaft back in and remove the rear to see if it makes any difference driving around on the front wheels only. My knowledge on body/drive train stuff is very limited but you may isolate the problem to the front or rear.

 

[pb4ugo]

Your advance numbers with the vacuum advanced disconnected and plugged? If so, the mechanical advance is working fine. 30 degrees is ok. Your hubs should be maybe warm, not hot unless you're riding the brake. Do you have a floor jack? If so, do your test drive, come back, if the hub is hot, jack up the tire and see if it spins freely.

 

[pb4ugo]

How old are the calipers? What brake work have you done?

 

[mrboatman]

I noticed today that the front hubs (Warn running in 2x4 mode) are hot to the touch after the test drive. When I assembled them, I was careful to check preload per the FSM.

You could have just stumbled upon a major problem

 

[MOTOV8R]

I noticed today that the front hubs (Warn running in 2x4 mode) are hot to the touch after the test drive. When I assembled them, I was careful to check preload per the FSM.

Like uncomfortably hot? That doesn’t seem right. Had you driven far? Axle shafts shouldn’t be spinning if you are in 2H and the hubs are unlocked. There shouldn’t be anything causing heat to built up in the locking hubs. Are your front wheel bearings new? Did you take it up to speed before rebuilding the front knuckles?

 

[45Dougal]

I think you looked at the brakes a couple of weeks ago, and reported a slight drag on the fronts - the disk brakes shouldn't really drag noticeably and shouldn't be hot after a short run.
I know you had some issues with the master cylinder; maybe there is still an issue there with compatibility??
Is it possible that the pedal/master is adjusted badly and you're permanently applying a slight braking force which is exacerbated by increasing vacuum at higher engine speeds?
See how free they are to spin with the engine wound up.
Alternatively, try disconnecting and plugging the vacuum to the servo (be ready to push a lot harder when you brake!!)

 

[MatthewMcD]

Like uncomfortably hot? That doesn’t seem right. Had you driven far? Axle shafts shouldn’t be spinning if you are in 2H and the hubs are unlocked. There shouldn’t be anything causing heat to built up in the locking hubs. Are your front wheel bearings new? Did you take it up to speed before rebuilding the front knuckles?

I replaced the front wheel bearings when I did the knuckles.

 

[RevISK]

I think you looked at the brakes a couple of weeks ago, and reported a slight drag on the fronts - the disk brakes shouldn't really drag noticeably and shouldn't be hot after a short run.
I know you had some issues with the master cylinder; maybe there is still an issue there with compatibility??
Is it possible that the pedal/master is adjusted badly and you're permanently applying a slight braking force which is exacerbated by increasing vacuum at higher engine speeds?
See how free they are to spin with the engine wound up.
Alternatively, try disconnecting and plugging the vacuum to the servo (be ready to push a lot harder when you brake!!)

Interesting comment about the brake pedal adjustment, I drove Matt’s rig yesterday and two things that stood out were the sensitivity of the clutch and brake pedals. Brakes were super sensitive and clutch wasn’t so. Of course I am comparing to my truck so…

I took his truck on my test road that I can get my truck up to 65-70 on pretty easy before a turn off and it was definitely a struggle getting his into the low 50’s. Low end torque is there for sure but as noted, falls flat most noticeably in 4th.

 

[pb4ugo]

Your advance numbers with the vacuum advanced disconnected and plugged? If so, the mechanical advance is working fine. 30 degrees is ok. Your hubs should be maybe warm, not hot unless you're riding the brake. Do you have a floor jack? If so, do your test drive, come back, if the hub is hot, jack up the tire and see if it spins freely.

Actually, jack up the wheels b4 the test drive 1st and see how easily they spin, then check them after the test drive also. You might have a sticking caliper or 2. If they're both drsgging then it could be the rod between the master and booster, as 45Dougal mentioned. It could be the soft lines too. As the rubber deteriorates over time, there can be delamination internally in the rubber line and a bubble can form inside it and restrict fluid from returning back to the master cylinder keeping the brakes on.

 

[MatthewMcD]

How old are the calipers? What brake work have you done?

Calipers are brand new. I replaced them and the pads when I did the knuckles.

 

[peesalot]

Oh really, your front discs are dragging, just because stuff is replaced does not mean it is functioning properly. Hot hubs = bad wheel bearings or dragging brakes. I think you have found yer problem.

 

[45Dougal]

Calipers are brand new. I replaced them and the pads when I did the knuckles.

If the calipers are brand new but still dragging then I'd definitely be looking at the adjustment and the lines (assuming you used plenty of brake grease in the right places)

 

[vfrer]

Quite the thread... been watching the whole thing. My vote for carb obvioulsy was incorrect. Just wanted to suggest using a laser thermometer to check for excessive heat. Sounds like you have 2 trucks available, go on a drive with RevISK and then compare hubs/disks/etc...