Thump!
01-08-2018, 02:31 AM
#1
Gullygump
Thread Starter
Thump!
Hi all, I have been searching a while on here now, and I can't find that anyone has the same issue, so I'll describe it in detail.
1991 f150. 5.8 litre 5sp manual 4x4
When I take off from a stop, there is a solid thump. It doesn't happen every single time, sometimes its not very noticeable, other times its very noticeable.
My first thought was engine mount, even though it seems to be coming from the back, the feel is the same at the engine being dropped back down from various heights- small to large thumps.
However, loading up the engine in first and reverse with the bonnet up, revealed no issues. Also, the thump occurs as I disengage the clutch, and increase throttle input, in my experience a broken engine mount reveals itself AFTER you let off the throttle, and remove the load from the engine.
I then replaced the gear box mount. I was very happy when the old one came out in two pieces, because I was convinced this was it. It wasn't.
A search on the forums found many users with 'slip yoke' clunks. however my tail shaft is one piece, and I don't have a slip yoke.
Further testing-
With the clutch disengaged- driving in first gear, on and off the accelerator with various degrees of aggression, and no thump. Try it in second- no thump.
It only seems to happen from a dead stop, releasing the clutch pedal to take of positively. A very easy take off with little accelerator pedal can avoid the thump.
I can't seem to make the thump happen at all by using the brake and loading up truck....like when checking engine mounts...no thump happens then. It feels exactly like a heavy object in the back shifts half a foot as you take off, like a load sliding to a stop against the tailgate.
Help.
1991 f150. 5.8 litre 5sp manual 4x4
When I take off from a stop, there is a solid thump. It doesn't happen every single time, sometimes its not very noticeable, other times its very noticeable.
My first thought was engine mount, even though it seems to be coming from the back, the feel is the same at the engine being dropped back down from various heights- small to large thumps.
However, loading up the engine in first and reverse with the bonnet up, revealed no issues. Also, the thump occurs as I disengage the clutch, and increase throttle input, in my experience a broken engine mount reveals itself AFTER you let off the throttle, and remove the load from the engine.
I then replaced the gear box mount. I was very happy when the old one came out in two pieces, because I was convinced this was it. It wasn't.
A search on the forums found many users with 'slip yoke' clunks. however my tail shaft is one piece, and I don't have a slip yoke.
Further testing-
With the clutch disengaged- driving in first gear, on and off the accelerator with various degrees of aggression, and no thump. Try it in second- no thump.
It only seems to happen from a dead stop, releasing the clutch pedal to take of positively. A very easy take off with little accelerator pedal can avoid the thump.
I can't seem to make the thump happen at all by using the brake and loading up truck....like when checking engine mounts...no thump happens then. It feels exactly like a heavy object in the back shifts half a foot as you take off, like a load sliding to a stop against the tailgate.
Help.
01-08-2018, 12:27 PM
#2
Member
Join Date: Jan 2018
Location: Memphis, TN, Earth, Milky Way
Posts: 11,256
Received 1,731 Likes
on
1,487 Posts