Resonance at 2500rpm under load

[TR Mitch]

In 4th at c 50mph or 4th with OD (and corresponding increase in road speed) and the engine running at 2,500rpm, I get quite a loud and booming low frequency resonance when I put my foot down to the floor. If I balance the throttle, it's fairly quiet and then foot off, it booms again (not as loud as under power). If I dip the clutch and coast, it goes very quiet.

 

It happens only in a very narrow rpm range. Higher or lower speeds in top/top OD, no problems.

 

What are the things to consider looking at? Big ends? UJs?

 

 

[RogerH]

My first thought was the exhaust system. Have you got stainless steel boxes. These can make a racket.

My second thought is the bonnet ot self. Get the resonance going and get somebody to press on the bonnet in various areas.

 

Low frequency tends to relate to big things.

 

Roger

[Motorsport Mickey]

I'd go with Rogers suggestion, sounds like an exhaust system resonance.

 

Mick Richards

[stuart]

What make and shape of system have you got on the car Mitch? I would be inclined to think its resonance as well. Some systems are notorious for it at exactly that sort of RPM.

Stuart.

[TR Mitch]

That's interesting, and encouraging, thank you. The exhaust is a single pipe system with extractor manifold. Some pics ..

 

 

 

[stuart]

Check that the two "U" clamps on the rear cross tube arent touching the boot floor for a start and that you have clearance through the "T" shirt area and on the front pipe (and enough for the movement on the engine mounts when under load).A ball pein hammer in a few places can help as well!

Stuart.

[TR Mitch]

and enough for the movement on the engine mounts when under load

 

Thanks for the tip. I spent hours trying to solve a similar problem on the daughters 1994 Fiat Panda (her "classic"). I even replaced the lower engine/gearbox mount as these were a known source of trouble. Still the thing made body contact whenever it was in reverse. Eventually, and only when the pipe into back box had separated and she needed a new back section fitted, did I discover the old system had been put together wrongly at some time. Fitting the new back section and rehanging it sorted it out.

 

Will take a close look at the mounts/clearances.

[peejay4A]

That front mounting just by the speedo drive doesn't look original and looks a bit rigid - unless the TR5 is different from the 6. I can't really see from the pictures but if it is an exhaust mount and it is rigid it will be transmitting all sorts of nasties through the chassis frame and body.

Edited April 15, 2013 by peejay4A

[stuart]

That front mounting just by the speedo drive doesn't look original and looks a bit rigid - unless the TR5 is different from the 6. I can't really see from the pictures but if it is an exhaust mount and it is rigid it will be transmitting all sorts of nasties through the chassis frame and body.

Well spotted Pete. Definitely shouldnt fit like that, it should be above the gearbox mount or not at all.

Stuart.

[TR Mitch]

Those pictures were taken by Robin during the rebuild. Until I get under the car I won't know if it was left like this or the fix was temporary whilst the build was taking place. A closer examination next week. Thanks for the pointers.

 

Many years ago I had a MK1 Capri (not the Consul but the 1970s one). I really disliked the engine (the V4 from the Transit at the time). I stripped it, had the crank ground, balanced the pistons on my kitchen scales, replaced the balance shaft etc etc. Put it all back together to discover that they all did that and it was just a crappy engine (hence the need for a balance shaft). Went for anything with the V6 Essex engine after that!

[BlueTR3A-5EKT]

Just crawl under it and disconnect the front exhaust to gearbox chassis mount and I reckon it will all go quiet.

If you need a mount there replace the metal strap with a strip of rubber like the ones on the rear.

 

Cheers

Peter W

[TR Mitch]

Peter, thank you for the tip. I am just about to disconnect it (was still the rigid fixing) and try it out today. First sunny day in a long time, got my NT card in my pocket and we're out for the day.

[openroad]

Hi colin,sounds like you have solved the problem,hope so anyway....i saw your post re the national trust,and will be using that thanks.......off out today myself,just put new discs and calipers on,so bedding them in,any excuse this weather !!

All the best,

Conrad.

[Guest ntc]

It will need support from the gearbox mount and should move with the engine and gearbox,or you will end up cracking your extractor

[TR Mitch]

Well, back after 100 mile drive today, the car is very different. Firstly the rumble from the old hubs gone with Richard Good's replacements, the poly bushes all settled down and don't squeak any more, balanced the inlets it doesn't hesitate on pick up, now the resonance has gone almost completely.

 

Thanks Neil, I will support it with a strip of rubber or similar from my box of exhaust bits to lessen strain on the manifold.