Jump to content

That gearbox weight....


Recommended Posts

My TR4A has one of those Fred Flintstone weights bolted on the rear of the gearbox by the drive flange.  It was there when I bought the car in 1975 but since then the gearbox has been rebuilt twice, the propshaft has been replaced, the engine has a different crankshaft, a lightened flywheel and the fan and pedestal have been removed and replaced with a thin belt harmonic damper.  I just happen to have the gearbox out of the car at the moment and sitting on the garage floor, a job that I really didn’t want to do but the car has been in storage for the last 25 years and the clutch (which has 100 miles on it) was seized solid.  I removed the friction plate from the flywheel with a lump hammer and bolster chisel after all the usual tricks failed!!

My question is, does anyone actually still drive around with this weight on the gearbox? 

I know why the factory resorted to this modification but I don’t think all TR’s were fitted with it.  Mine is a bit like Paddy’s shovel and bears no relationship to the car that left the Canley factory back in January 1967.  I’m tempted to remove it. 

Should I?

Link to post
Share on other sites
3 minutes ago, Geko said:

It's an anti rattling damper. Delete.

Although you may find then that your car/gearbox then has an audible noise from that area, it cost Triumph money in the first place to fit it, companies (especially car companies who are noted for only fitting items they think you really, really need) think they are supplying these items for a reason. I have left mine on for that reason.

Mick Richards

 

Link to post
Share on other sites

My 4A has one the 6 hasn't (can't recall if it used to or if it never had)

I'm sure sure Triumph thought it was a good way of balancing or damping something but I doubt it works like a pendulum in a tower block in an earthquake zone!

Link to post
Share on other sites

I guess the thing to do is leave the lump off and only refit if I get a vibration. It looks a simple retrofit.

To be honest  I'm as much concerned at minimising the weight when I finally pluck up enough strength to lift the box back in!!

Reading through my service history notes I've had the gearbox out 5 times; three times out through the floor and twice with the engine. I was just 23 years old when I first took it out, swapped the clutch and put it back single handed in a day and a half. Now, 45 years later the car is cruelly exposing the frailties of ageing, but I'm damned if I let it get the better of me.

......and just to add insult, the spellcheck auto correct changed lump to limp!!

Link to post
Share on other sites
32 minutes ago, twostrokekid said:

I guess the thing to do is leave the lump off and only refit if I get a vibration. It looks a simple retrofit.

To be honest  I'm as much concerned at minimising the weight when I finally pluck up enough strength to lift the box back in!!

Reading through my service history notes I've had the gearbox out 5 times; three times out through the floor and twice with the engine. I was just 23 years old when I first took it out, swapped the clutch and put it back single handed in a day and a half. Now, 45 years later the car is cruelly exposing the frailties of ageing, but I'm damned if I let it get the better of me.

......and just to add insult, the spellcheck auto correct changed lump to limp!!

Problem is its really difficult if not impossible to fit to a built car.

Stuart.

Link to post
Share on other sites

I removed the lump from 4VC's gearbox when the box chewed its innards back in 1970 and had to come out.

I had no idea what the lump was for, so binned it. Have never missed it!

Ian Cornish

Link to post
Share on other sites

You can fit the weight and its steady bracketry after the box is relocated in the car, but before the tunnel is fitted. The clamp around the tail of the box may need bending to open out to fit. On the (too many!) occasions I have had the box out, I haven't been able to remove the clamp part from the weight, so just pulled it (with the weight attached) sideways off the tail with a bit of brute force. 

Personally I would refit it. As has been said, it might make a difference.

Mike

Link to post
Share on other sites

Let's speculate what that difference it makes might be.

Essentially the 4a and 6 gearboxes are the same bar a few holes so it's not for the gearbox.

Will a lump hanging off the tail of the gearbox balance much of the vibration related to the engine?

 

Link to post
Share on other sites
1 hour ago, Andy Moltu said:

Will a lump hanging off the tail of the gearbox balance much of the vibration related to the engine?

 

Thats exactly what it was for, Triumph didnt have money to throw around so if they deemed it needed then it was fitted.

Unfortunately the 4/4a registrar doesnt post on here otherwise he could probably quote you the relevant factory service bulletin describing it.

Stuart.

Link to post
Share on other sites

One for sale on e-bay:

https://www.ebay.co.uk/itm/Rare-OEM-Stanpart-Transmission-Vibration-Damper-for-Triumph-TR4-and-TR4A-Gearbox/323649823619

Quote:

" This service bulletin states that this vibration damper was incorporated on TR4 models at approximately commission number CT 18000.  This afore-referenced service bulletin states that fitting this vibration damper will only reduce vibration between engine speeds of 2700 and 3000 RPM.  Dealership service centers were instructed to retrofit this crude device to customer's cars if they complained about excessive vibration."

I found another reference which states there are different damper weights for O/D and non O/D boxes. 

Link to post
Share on other sites

It's a classic vibration absorber; a mass attached via a rubber insert. The engineers would measure output flange vibration with an accelerometer and determine the (always) very narrow band of resonance and then attach a calculated spring mass to damp it out. Standard practice in heavy engineering but not so much in today's automotive industry.

I managed to remove the lump with the gearbox in situ to lighten the load when lifting out.  Now, my genius idea is to turn the mounting prong through 180 degrees so it is pointing upwards and make some sort of temporary handle to help with the fiddly gearbox lift. It's difficult otherwise to hold the rear flange without it turning.

Always knew that feature would come in useful one day!

Link to post
Share on other sites
  • 1 year later...
On 6/26/2020 at 5:17 PM, RobH said:

I found another reference which states there are different damper weights for O/D and non O/D boxes. 

Hey Rob,  would you happen to have any more specifics on this ?

Thanks, Pete.

Link to post
Share on other sites

Sorry Pete but no details I'm afraid - it is in the 4A parts catalogue.  This is a shot of the relevant bit and you can see there are two separate part numbers (circled):

 

wght.jpg.26f820540e3a96072e2c9ce8eb83ec5f.jpg

Link to post
Share on other sites

Thanks Rob,  I appreciate your retrieving and posting this info for me.   It confirms that this damper weight was deemed desirable enough to override objections from Triumph's bean counters - on both the gearbox and gearbox+overdrive 4-cylinder cars. 

I was specially wondering if the weight or smoothness of the overdrive unit might negate its function but, of course, the weight is designed as a damper and not a counterweight.  The part numbers may reflect a different size, between overdrive and non-overdrive configurations, or else their rubber may be of a different-shore hardness.  Perhaps the latter is a mute point after 50+ years of rubber deterioration..

I'll have one fitted in the hope that mechanical vibration is indeed dampened.

Cheers, Pete.

 

   

Link to post
Share on other sites

Hi Pete,

The Dampers used on the TR4 and TR4A were exactly the same weight.

The Damper supplied for the TR4A did have one seemingly odd variation to the TR4 version.

The TR4 version was fitted to all TR4A’s with the overdrive gearboxes.

Whereas TR4A’s with a non-overdrive gearbox had one different component, the silentbloc bush which is listed as part number 144313.

Regards, Richard

Link to post
Share on other sites
2 hours ago, RAHTR4 said:

Hi Pete,

The Dampers used on the TR4 and TR4A were exactly the same weight.

The Damper supplied for the TR4A did have one seemingly odd variation to the TR4 version.

The TR4 version was fitted to all TR4A’s with the overdrive gearboxes.

Whereas TR4A’s with a non-overdrive gearbox had one different component, the silentbloc bush which is listed as part number 144313.

Regards, Richard

Do you have any sort of image of that bush Richard?

Stuart.

Link to post
Share on other sites
29 minutes ago, RAHTR4 said:

Hi Stuart,

Apologies, my description was possibly not as clear as it should have been.

The "silentbloc" bush had a different Shore rating.

Regards, Richard

OK thanks

Stuart

Link to post
Share on other sites

Thanks Richard, that's what I was anticipating for a damper aiming to cancel vibration of engine speeds of 2700 and 3000 RPM.  This range presumably initiated harmonics between the engine and other parts, whether within the gearbox or perhaps something like the prop shaft (.. evident as an annoying hum ?).   As engine speeds drop when the overdrive is engaged so too would the harmonics be altered ..and so the hardness of the damper's bush would need altering if the same damper bob-weight is to correspondingly neutralise those.

Cheers Gents,

Pete.  

Link to post
Share on other sites

Something says we used 119451 silentbloc bushes to service these lumps.  The bush is from the front suspension inner wishbone of Herald/Spitfire   Or was it 141481 the lower wishbone bush for IRS car front suspension.

No guarantee but perhaps worth a measurement.  Spit bush is 3/8” hole TR is 1/2” hole

Peter W

Edited by BlueTR3A-5EKT
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.