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31/05/2005 12:45:15   Steve H   As it seems i have chewed up yet another gearbox, what is the current thinking on new ones. Chris Partington used to do them I know, am I right in thinking he now suplies Highgates? Any alternative supplies, any stronger ones?

Many Thanks

Steve H  
31/05/2005 16:41:08   Richard   What do you think has happend to it, crown and pinion, freewheel, syncro?
Yes, Chris supplies Highgate and was supplying The Saab Restoration company and I believe Graham McDonald.
You should be ok with a totally rebuilt unit, at least you know what condition it is in. Other wise you need to inspect a second hand replacment. You can remove the bell housing to check the c & p for wear and backlash. You can also remove the top gearbox selector cover and see what the gear set is like and see how the syncros have worn. The gears, backlash and syncros should give you an idea how much use and abuse its had.  
01/06/2005 09:51:03   Steve H   It is still operating fine but has started to grind as the power is taken up in all gears. The speedo also drops 30 mph or so when freewheeling. It is a late type, 10 years and 40k old and was built by Chris Ode.  
01/06/2005 12:37:23   Richard   I would think it is something on the input or output shafts. It could be the pinion bearing backing off (or being damaged) which would cause the pinion to diff gear mesh to go out. This usually makes a houling sound, a bit like a straight cut box. Knacked bearings make the box loud too. I have never had a sound like something grinding against another part, but a really bad bearing could make that kind of sound and be amplified through the car body.
The speedo gear is nylon worm gear in the V4 boxes, unless its slipping round on the shaft I carnt see a reason other than a lot of backlash causing the speedo to drop 30mph. After the backlash is taken up you would expect the reading to be correct again.  
02/06/2005 07:54:34   Richard   The worm/scroll speedo gear is trapped on the pinion shaft between the two gears and two spacers, It has no key on to the shaft. If there is some slop between these two gears the speedo gear will slip.
We have pulled a few boxes apart and found the nut on the end of the pinion shaft to be loose even though it has a tab washer locating it. I have a theory that as the nylon gear has a smaller metal sleeve than the metal two stroke gear it crushes very slightly over the years and therefore makes the nut seem loose at the other end of the pinion shaft. Otherwise I would think the rear pinion bearing has backed off and/or has some damage.  
03/06/2005 12:58:53   Steve H   Thanks Richard but I think gearbox refurbishment is beyond by facilities.(I have an engine crain that I use on the street outside my flat in Hackney.)I have done engine bottom end work this way but I have to be sure of the weather and that I can finish by teatime/dark. Gearbox work is too many processes in. So i'm afriad I will have to pay the cash and get one done for me that I can just swap.
Any suggestions on what to go for and where?  
03/06/2005 17:08:23   Alistair   That grinding noise as you take up drive might also be a result of a duff gearbox mount and the box itself moving around. Check your rear mount, they make some funny noises if the box is sat on the floorpan. No idea why it could cause the speedo to fluctuate though. I've had them do that a bit, but not by 30 mph (more like 5-10), and I think only on earlier cars with the black white & red dials rather than black white & yellow - I always put it down to a worn speedo rather than a box issue?! I was probably wrong...  
06/06/2005 12:30:21   Richard   If your car is fitted with a bar behind the rear gearbox mount and you have a worn rear mount, the bar could be moving around on the outer metal ring. What Al says could be right, try seeing if you can get anything under the box.  
06/06/2005 12:33:07   Richard   We use a big rubber bush under the box between the floor in the comp cars to support the box a bit more.  
06/06/2005 14:00:11   Steve H   I was wondering about mounts and have already bought a part of volvo engine mounts to have a go at sorting out mounting generally. I will have a look.

And the speedo thing. I have got black a white dials (to match the other smiths gauges and tacho a have in a remade dash) so I am used to needle wobble, but this is a definate drop (close the thottle at 80, the speedo drops to 50, take up power again and it flicks back to 80)  
06/06/2005 16:50:42   Richard   You could try rigging up a different speedo and change the cable to see if there is any problem. I always go through the easy stuff before going to the conclusion that its something major.
The only thing that makes me think it could be the speedo gear in the box is that the gears are helical, so under power they will thrust down the staft and take up any slack, the opposite happens off the power.
A speedo cable is wound in one direction, so the same could happen to that.  
29/07/2005 14:29:19   Steve H   Last Saturday on the severn bridge the problems i've listed above seem to have been solved.

It's not the gearbox (I now hope) it was the wheel.

Heading up the bridge i lost drive and the revs span up. I mananaged to keep things going till a wide bit of the shoulder before the tolls by controlling the revs. Trying to move forward in an attempt to limp on a bit, nothing was happening except some clanking. I deceided to leave it running in gear and have a look and found the drive shaft turning...but not the wheel. Later investigation then showed the nut under the hub gap to be turning as well.

On talking with Ken, it seems the wheel carrier has worn allowing this to happen. I'm hoping that went it is replaced, all the other problems will be solved.

I will let you all know.

Steve  
15/08/2005 13:55:47   Steve H   Oh dear... The speedo still does the same speed drop thing and there is still a grinding noise (though not as bad.)

I'm gong to try changing the engine mounts, but I think I'm just not coming to terms with the enevitable.  
15/08/2005 19:55:52   John Wood ( "Woody")   Steve, are you saying that the drive shaft had failed?  


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