My engine has only done about 3000 miles since being rebuilt and it revs smoothly in neutral all the way up to 6500 rpm, and is smooth in top gear at over 5000 rpm.

I live in a valley which has fairly steep hills both sides and I like to open the throttle when climbing them to clear the cobwebs, as it were. On Saturday I revved harder than usual in second gear and at 5000 rpm the engine sounded rough, like a hammer drill. I changed to top gear immediately and drove normally thereafter.

Is it likely to be the gearbox that vibrated? If so, can you get wear in only one gear to produce that effect? Third gear and top gear don't vibrate. I don't think it was the engine or the differential. The gearbox wasn't reconditioned when the engine was.

Do you have overdrive? If so try it in and out. If not, check the rear final drive casing. They have been known to crack!
Have you tested under load at 5000rpm in all gears? It may be the engine damper when the engine is under load.
Was it definitely related to engine speed/road speed or could it be prop shaft related?
Can you check the ignition system, it may be breaking down at high revs under load.

I haven't previously put the car under so much strain in second gear. It was a fairly steep hill and I accelerated hard. I have cruised fast in third and top gear, but with little effort and no bad effects.

I haven't got overdrive. I agree that it might be the prop shaft under strain so I'll do some more tests.

I think the ignition is OK. The distributor was rebuilt and hasn't given any trouble. The engine wasn't missing a beat, the vibration sounded mechanical. The mixture is OK, I get good pick up at any speed in any gear.

No oil drips anywhere.

Hi, looks
like you need to check the UJ’s on you Prop Shaft .

Cheers A’l

5000 rpm in second is about 70mph, it could well be wear in the 1st/2nd gear cluster or lay shaft bearings, it isn't elated to road speed so forget the prop shaft that revolves at the same speed at about 70 mph, 3rd and 4th are on another cluster and the way the gearbox works via the lay shaft puts the layshaft load point in a different area. Not sure where you exceed 5000 rpm in top

I think I'll just avoid accelerating hard from now on, easy cruising in top gear along a straight roman road is more my style.

I guess it could be a number of things. I would certainly recommend getting an overdrive fitted as you clearly like to drive your car fairly hard.

I am sure you know never to drive it hard in first gear - no launches from the traffic lights - gearbox certainly not up to that - otherwise the gearbox is OK but I have developed a number of techniques to improve lifespan - lots of double declutching both up and down makes everything a lot more smooth and will extend the life of the syncros.

With overdrive you are unlikely to see much beyond 3500 rpm which gives 80 odd mph and in a very relaxed manner without feeling the engine is at all stressed and overall with mixed driving you can get 30 mpg and quite a lot more if dawdling around the countryside or France! I have an A type Laycock overdrive which operates on third and fourth although I think the guys are fitting later type overdrives these days which don't require any modification of the gearbox tunnel. Being an old fashioned guy, I prefer overdrives than five speed gearbox conversions which I think will cost more overall.

SimonP

simonp wrote: ↑Mon Apr 16, 2018 12:12 pm .....I have an A type Laycock overdrive which operates on third and fourth although I think the guys are fitting later type overdrives these days which don't require any modification of the gearbox tunnel....
SimonP

The usual overdrive of choice for the SP these days is the Laycock 'J' type. This still requires some widening of the gearbox cover but has the advantage of retaining the propshaft unmodified. I believe it needs shortening if the 'A' type is fitted?

simonp wrote: ↑Mon Apr 16, 2018 12:12 pm ... you clearly like to drive your car fairly hard.

Only in short bursts.

I am sure you know never to drive it hard in first gear - no launches from the traffic lights - gearbox certainly not up to that - otherwise the gearbox is OK but I have developed a number of techniques to improve lifespan - lots of double declutching both up and down makes everything a lot more smooth and will extend the life of the syncros.
SimonP

I only use first gear gently for a short time. I also always double declutch. I also know how to drive without using the clutch at all! In 1969 I had a clutch which barely worked so I drove from Bristol to Mr Mason's garage in London in the fog in early morning along minor roads (before the M4 and around diversions) and gave up using the clutch, just timing the revs when changing gear. I soon got the hang of it.

That's a nice story. I only had Majestic Majors in Ben Mason's days and I was one of his closest customers.

I lost my clutch once when a hose went. AA were going to charge me so I stuck it in first gear, started it and drove the mile or so home without changing gear. Had a gear selector cable go in another car recently and that was stuck in third gear but I managed to drive that 25 miles to the garage mostly via the motorway and few traffic lights!

What we love about the SPs are that they are so forgiving and just keep on going.

SimonP