SHUDDER AT 2000RPM.

The Rovering Member

The Rovering Member

Well-Known Member
Started the engine on the P5B for the first time after the subframe swap today. After a while it became apparent that theres a vibration that kicks in around 2000rpm that makes the whole car shudder. Went round tightening everything I could think of to no avail. While it was out I replaced one engine mount which had come apart but the other seemed perfectly servicable so I left it. Should I have replaced the pair? The rear mount was replaced with a JRW item after I damaged the frame when we sort of straightened it up again & it still seems o.k. The car never felt as good afterwards hence the need for the swap & to be honest I saw the rear crossmember was absolutely mullered when I got it out. This is a very unpleasant shudder & I don't think she'll waft along 'til this is sorted. I can't feel any movement when I try & move the engine myself though I don't think I can summon 180bhp myself. :;):
Any ideas?
 
If the shudder is there just revving the engine sounds like a misfire or incorrect firing order maybe? I would check through all of the engine settings. If it occurs when you drive the car it could be the front clutch juddering. A little more info might help with a diagnosis.
 
Harvey.
Just pasted this from the P5 site (same titled posting/3.5 mechanical). No I haven't driven her at all yet. This is just sitting with the rear axle on stands. I put the rear wheels back on to see if it made a difference but it didn't as you can probably guess. How do I start checking the firing order (Lumenition fitted)??
Removed the box for re-conditioning but left the bell housing & torque-converter in place. Renewed rubbers on the engine-steady bracket (out of a large box of rubbers/mounts I have so not original but as near as dammit). Harvey has suggested a misfire & the carbs could be out of balance. I had them off to clean them out & am far from an expert on tuning/balancing & have just got the base position & wound the jet-nuts back 2 turns. Had the leads off but marked them so I think they're in the right place. I can do all the practical in/out, off/on donkey work but the finer settings/adjustments of the internal combustion engine are a bit of a black art to me.
Performance was good but she never cruised as well after the damage as the steering geometry was thrown out shown by the inner tyre wear even after tracking. Any shudder I put down to the damaged frame. The rear spar caught on a fold-down parking post which hadn't been folded down completely & which pushed the spar back & tore the rear mount which we replaced as I said when we tried to straighten it. The new frame is very good & lined up a treat with the body mount holes. I was doubtful that the original mount would cause the problem, it all seems very tight.
I think I shoud get a Gunsons colourtune. :)
 
If it does it just revving the engine it rules out a gearbox problem. If you removed the g/box from the converter housing and didn't touch them that rules out them as the problem if there was not a vibration before you dismantled. In other words, if the vibration was not there before you started on it, it's more than likely to be something you've worked on.
 
There were vibrations at speed & a rythmic hooning at 70+ but these all appeared after the damage to the frame. I don't remember any vibration from simply revving the engine. I've talked to a couple of friends (one who rebuilt the engine 15 years ago) who seem to concur with your suggestion of a misfire, plug/lead breaking down so I'll try swapping a lead at a time with one replacement to try & track it down. I found the rotor had a chunk out of it around the spindle so will replace that but opinion is that wouldn't cause the problem. I did check the firing sequence with the P6 Haynes manual which was right though my dizzy has 8 on the radiator rather than 4 (if I remember right) & she starts fine & idles fine & sounds good up to 2000. I'd already decided to get her on the road & MOT'd (hopefully) & see how she drove. Now I have a good subframe in I can stop blaming it for everything. I want her at the Enfield pageant next week. If you're there Harvey maybe we could meet up & have you give me your opinion if it's not sorted. I'll send you a pm with my number.
 
If it doesn't do it just revving the engine then it's unlikely to be a missfire, although they are usually more pronounced when you snap the throttle open.
If it's happening with the car on axle stands, and driving the rear wheels in the air, then I would suggest it was drivetrain related, does it do it at the same rpm in any gear, or at different rpm depending on gear, this would tell you which side of the gearbox the problem lies. same rpm any gear = input side, different rpm = output/prop/axle
At least that's how I see it. :)
 
Oops, also forgot, maybe it's slack in the drivetrain and at 2000 rpm it is just at the point where it takes the slack up / releases it.
 
At the moment there isn't enough fluid in the 'box to drive the wheels. I'm topping that up today. Thus far it's just been revving with no drivetrain connection. Theres actually someone on the P5 forum with the same problem (albeit with a just-fitted non-original engine & 'box) who says it doesn't affect the car on the move.
 
Are we talking about an auto box ?
If so then lack of fluid could effectively mean a lack of fluid in the torque convertor which I guess could cause all sorts of balance problems ?
Harvey tell me I'm talking out of my ...... :D
 
Forgive the ranting of an amateur’s brain. Not sure of all the right terms but;
The bit on the front of the engine that rotates round and has the fan belt connected to it. If that wasn't fitted properly and in such a way that it didn't run true you would get a "wobble" when the rotation reaches the "Natural Resonance" I think that is the correct phrase.
I maybe completely wrong but at least I tried.
 
webmaster said:
Are we talking about an auto box ?
If so then lack of fluid could effectively mean a lack of fluid in the torque convertor which I guess could cause all sorts of balance problems ?
Harvey tell me I'm talking out of my ...... :D
Click to expand...
I really don't know what to say to that.......
Not because you're talking out of your ...., but because I've never run an auto with that low a fluid level at those kind of engine revs. I suppose it's possible, and it's simple to get the level correct and see if it cures the problem. Probably not but who knows.
 
As for the Camel, if you mean the front pulley, that has a vibration damper in it so could cause problems, and there are two types of pulleys which have to be fitted to the correct one of two types of crank. So you might be right.
Another thing that can happen and cause problems, particularly after doing work around the engine, is the fan gets bent, throwing that out of balance.
 
harveyp6 said:
Another thing that can happen and cause problems, particularly after doing work around the engine, is the fan gets bent, throwing that out of balance.
Click to expand...
Aha, this means that i should check my fan too. The car had a front end crash at some point in the not too distant past that shows in the badly repaired bonnet landing panel.
Now i remembered that the *&~#\ who did the repair WELDED the front valance into the base unit and front wings :angry: :angry: :angry:

Anyway, some of the tips of the fan blades show signs of scruffing and the engine has a bad vibration at 1200 to 1500 rpm.
But since TCs weren't particularly smooth anyway, i supposed that they all do this. I 'll try to remove the fan sometime and see how it goes. ???
 
Webmaster: I didn't think of that, good call, thats a straw I can clutch at before Harvey blows us away.. :D I topped the transmission up enough to let me know the handbrake's not man enough to hold her against Drive. Got to sort that. Put the new (rechromed) rear bumper on today which took a while. The old one had a couple of bolts missing since I fitted the towbar 10 years ago. Had to file a couple of holes to get them all in but was determined to get all bolts in all holes as I'm more discerning than I was in my teens..... :;): :D

Oh! I've just read page 2 & see that Harvey has replied already, Well! I have drive, as posted & still have the vibration though will sort the handbrake before I top her right up. I want to keep her this side of the workshop wall.... :;): Though as I didn't remove the T/C it would still have had fluid in it anyway I assume, though it may have distributed it round the rest of the 'box while rotating of course.
 
Hi,
You say you've just done your rear bumper. where did you get it done,was it a good job,and how much was it??? if you dont mind divulging the info?? :D
 
I didn't get it done. My Brother got hold of it & the overiders all re-chromed for a drink & gave it to me as a Christmas present. It was shortly after he'd been offered a 3.5 Coupe' which was being disposed off after the death of the owner. He asked me if I wanted to have a look as it probably wasn't going to go for a lot of money but I'd just bought our third car & was picturing a bucket of bolts so I declined. When the bumper turned up from the same source I started kicking myself for not going to have a look & I'm still kicking now.. :angry: :;): :)
Pleased with the bumper, it looks nice but couldn't say how long it will last as chroming seems to be a bit hit & miss these days.
 
Just to fire a thought in the air......

I was reading in one of my P6 manuals today that if a vibration can be felt at certain engine revs, it may be down to the balancing bolts in the torque converter drive plate. The manual suggests moving the bolts round 180 degrees, and if this doesn't cure the problem, try different weight bolts, or moving them to different positions.
I suppose it may be possible if you have had the gearbox out :;):
 
Erik/Richard

Which manual is that in - have you a page/section reference, wouldn't mind reading that

John
 
John, it's in the factory workshop manual for the V8 section 44 17 08. you can also turn the converter on the drive plate. This gives 4 different positions for the converter relative to the drive plate. Both operations can be done with the eng/box in situ.
I've never come across one that's that far out of balance that it causes any problem other than when some one has damaged the drive plate or not fitted things back together properly.
 
I had the gearbox off but left the bell housing & T/C in place. The last time they were off was when we restored the car 15 years ago. She was smooth as silk until the frame was damaged. Unless something other than the frame was damaged it's undisturbed. The rear spar was bent back but the rear mount stretching would have prevented any damage to internals I would have thought as well as the units being firmly bolted together. It gave way completely a few months after the incident (which is testament to the strength of the Metalastik bonding process) which is when we persuaded it back to a position that was nearer originality but not entirely. Actually if we hadn't had to repair it (the rear spar) due to some tinworm in the resto' it probably wouldn't have bent so much, either in the accident or the persuasion. :)
At the time of the resto' a bloke a couple of arches up was breaking a Coupe' (coincidentally) & it had a lovely subframe but me being sentimental, I wanted to keep the original so we repaired it. The frame-bender would still have happened I imagine, but I wonder what effect it would have had overall, better or worse, the fact that the frame would have been inherently stronger as our repairs tore away on impact with the post. I still like to keep things as original as possible but haven't lost any sleep over this subframe swap. :;):
 
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