Blew up gearbox of my Griffith

[zob1]

Hello,

After blewing up the engine of my Griffith I replaced it with a RPI 5©3 a triple throttle Plenum ACT with a 4©6 airflow meter ¥If I have the time I will post one time the whole story including bills because such a swap is a lot of trouble, need much adapting work, lasts and costs much more than you can ever imagine in your worst nightmare¤

Whatever the result after 6 monthes from the day I brought my car to the day I could drive away from the garage was 382 lb©ft at 1950 RPM and more than 350 lb©ft up to 5000 RPM! ¥measured value¤©

Terrific isn't it! I can tell you there was a HUGE difference even if TVR specifed the V8 5l at 350 lb©ft @ 4000 ¥the well known TVR number I guess¤

Well it lasted 3000km before I blew up the gearbox ¥T5¤©©©©©©©©

Please note that the best T5 gearboxes are rated at max 300 lb/ft, once again I'm wondering how can TVR specify an engine with more torque than the gearbox can handle©©©©

Whatever I'm facing five solutions :

1¤ Replace the gearbox with an new one and drive carefully©©©©©©©

2¤ Replace the gearbox with a reinforced straight cut gearkit©©©that's a good way to become deaf

3¤ Build in a TREMEC T3550 TKO© It can handle up to 525 lb©ft but has such not the same ratio ¥3©27 1©98 1©34 1©00 0©68 instead of 2©95 1©95 1©34 1©00 0©73¤

4¤ Adapt a T56 ¥2©66 1©78 1©30 1©00 0©80 0©62¤

5¤ Any other race derivated exotic costing at least 5000 pounds ¥in general straight cut¤

Has anybody experience in this matter ?

Thanks in advance

JC

[Trefor]

Have you spoken to the guys at www.gearboxman.com - they might be able to help.

[apache]

jeez, that sounds expensive. If you get the gearbox problem solved what about the diff?

[HarryW]

apache said:

jeez, that sounds expensive. If you get the gearbox problem solved what about the diff?

Then the drive shafts .
Sorry to hear of your woes, heard a lot of good news about the 5.3's posibily the engine the 500's should have always had.
As they say go in (upgrade) with your eyes wide open about the hidden costs i.e. what ever you think it may cost then double it .

Harry

[GreenV8S]

Read this with mixed feelings. Not at all surprised you have run into these problems. I spent more on the transmission than the engine and I suspect you will end up doing the same. However, the fact that you blew up the original engine and also blew the gearbox relatively quickly (I would have recommended more than 3000 KM running in your new engine!) makes me suspect your driving technique may be contributing to the problem. This is not meant as a criticism btw. You have a massively torquey engine, and the one thing above all else that destroys gear boxes is torque - especially in the lower gears. If you tend to use the torque at low revs, you may find the box lasts better if you use more revs (and hence less torque). Also you will have a very heavy clutch to cope with this much torque, and it wll be very easy to put shock loads into the transmission when you start off and also when you change gear. The more smoothly you do this the longer everything will last. I don't think you will need to go to a straight cut gearbox, talk to some of the Tuscan race teams to see how they cope. I know of several cars who are putting that much torque through ordinary LT77 boxes without major problems, and one person with a supercharged 5.3 V8 putting out considerably more torque , with mechanical sympathy things can be made to last. But if you are brutal, you can destroy any transmission. Steve Hill's 390 BHP Chimaera is probably similar, it would be worth talking to Steve Guglielmi who prepared this car.

[shpub]

The 520 is still running the original LT77 box that it was fitted with in 1987 and I have been putting about 400 lb/ft through it for several years. Upgraded the output bearing as this is the weak spot. The box has now done 110,000 miles. Technique is everything as Pete says and if you are doing anything silly with power then the transmission and chassis need almost as much money spent on them.

In practice the transmission starts to become a set of consumabales that will need replacing more often but it all depends on how much treatment they get!

Steve
www.tvrbooks.co.uk

[zob1]

Thanks Shpub and GreenV8s (1 of 2),

Regarding the engine it was bad luck, it all began with some unoticed vibrations in the pouly (don't how to spell it in english) which affected the camshaft, the oil pump etc etc. In fact I didn't blew up the engine but due to this chain of events the wear increased dramatically within a few weeks up to a point that the original engine with 70'000km looked like a 300'000 km engine. I had to change everything or buy a new one.

Same for the gearbox. I didn't blew it away but I just killed the fifth gear, I was lucky enough being able to immediatly disengage the clutch after the first noise. A post mortem exam showed that both gears of the fifth gear lost all their cogs !

Regarding my driving style, yes I have a heavy foot. I like using the torque on the small twisty mountain roads of Switzerland (staying in the 3rd gear between 60km/h and 160km/h is just great, especially when you popping out of a curve like a bullet) but it's definitevly not brutal (being brutal on such roads can be quite an exclusiv and unique darwinistic experience).

...."If you tend to use the torque at low revs, you may find the box lasts better if you use more revs (and hence less torque)..." Yes you are absolutely right, I'm using this new engine between 2000 and max 5000 rpm, before it was 3500 to 6000 which and I'm using much more the fifth gear.

[zob1]

Thanks Shpub and GreenV8s (2 of 2),

What is the LT77 ? Is it another denomination for the T5 or the older gearbox ?

Do you think from your experience that a normal T5 should hold if I drive with higher RPM ?

I made some calculations and the T56 with 2.66-1.78-1.30-1.00-0.80-0.62 should be quite ideal with such a torquey engine. Of course costs are higher (2000$ against 1200$ for a new T5) plus probably xxxxxx$ adapting costs. What do you think ?


Regards,

JC

[shpub]

The LT77 is the original Rover gearbox used with the Rover V8 engine. TVR went to the T5 as the LT77 box didn't like the amount of torque TVR were creating.

[GreenV8S]

zob1 said:

being brutal on such roads can be quite an exclusive and unique darwinistic experience

Nice one!

[2 sheds]

Loss of 5th gear on the T5 was a common problem with the Tuscan racers, and i've heard of a few road cars with the same problem.
I think they fitted straight cut 5th to resolve this.
Tim

[zob1]

Hello,

The problem is that I'm using my TVR on a daily basis (well at least it's my intention) and straight gear are in general really loud. Glebe (www.glebe.co.uk) has such gears (www.glebe.co.uk/fdev.htm) but the final ratio is 0.897 against 0.73 for the standard one.

[dannylt]

Breaking 5th is very common, as Tim said - it's very common on the Cerbera, and have heard of a few on standard Rover 500s. I would just get the gearbox rebuilt and hope it lasts a bit longer - definitely don't recommend straight cut for your sanity, it's far more stressful than a noisy exhaust!

danny

[Mark.S]

What kind of racket does a straight cut gear cause? Is it just during the shift or continous?

[HarryW]

Continuous I beleive, like, well like, a very loud transmission whine .

H

[JonRB]

It's one of the things that Gran Turismo 3 on the PS/2 actually does quite well sound-wise. If you drop in a racing 'box then the transmission whine is almost as loud as the engine noise!

[dannylt]

On my radical, I'd say after 20 minutes or so, the transmission whine dominates EVERY other noise and vibration, and that's with the engine directly bolted to the chassis!

danny

PS That's road driving of course - on a race track everything gets very noisy!


>> Edited by dannylt on Friday 11th July 09:59

[pistol pete]

Mark.S said:

What kind of racket does a straight cut gear cause? Is it just during the shift or continous?

Like what you get in reverse in most cars, but louder ('cos gearwheels turning faster I guess), and constant I believe*

*could be completely wrong in this as its not from personal experiance

Pete

[2 sheds]

Your not wrong they are loud, when i said that they fitted the straight cut 5th to resolve breakage, i meant in the Tuscan racers, yes it can be done for a road car but a bit OTT IMO.
Tim

[ultimaandy]

Hmmmmm maybe you should try fitting a gearbox from a lotus carlton, like the one I have in my garage ready for when my T5 goes south in my cossie.

May end up costing a couple of grand (including the box) but I think it would be worth it as they were fitted to the top Corvette with huge torque (Z1?).

6 speed, 240mph crusing top gear..... nice!