Gearbox overdrive limit switch location

[A TR7 16V]

Wondering if anyone can help with where the overdrive limit switch should be on this gearbox, and how to access it?

Don't know what box or OD they are, so can't look at a parts manual or owt.

Must admit, I don't like the look of that drain plug. Anyone suggest where to get a better one?

Graham

[GT6 M]

its on the front of the top cover, where there is a metal plate
there will be a switch on the side,and its this switch that is the cut oot.

M

[Jonny-Jimbo]

Accessed by removing the tunnel carpet and then the cardboard cover with around 10 screws through key-hole plates. Chances of the car having all of them is slim. The cover may also be stuck down to the bulkhead, so be gentle with it or you may damage it upon removal!

EDIT - There are screws at the top corners too, tucked up behind the dash. Easy to miss.

[Pete Lewis]

you cant tell from the case underside as they all look the same

yes tunnel out and  gearbox number is stamped on the top case face, it looks like Jtype od

Dtype solenoid is on the rh side (drivers side)
J type is on the lh side ( facing the front )

which way is reverse ,   left and forwards is    3 rail
any other is single rail

Pete

[A TR7 16V]

Quoted from Pete Lewis

which way is reverse ,   left and forwards is    3 rail
any other is single rail

Never thought of specifying that. It's left and forwards, so a 3 rail box.

Graham.

[Pete Lewis]

to refine the guess you need the number off the top and compare it with the data in the tech section 'the cars' above in suffix tables .

Pete

[A TR7 16V]

Might get the limit switch found and wired in next week.

I'll check the number if I do, becuse I'm also going to need help with the speedo drive, as the speedo is overreading by 25 - 30 percent. And as its allready a 1216 tpm one, it may be hard to find one that would match the drive - 1550 to 1600 tpm.

I guess I'll also need to know the diff ratio to get the right speedo drive for the O/D. Is changing that doable on the car?

Fourth is straight through on these boxes isn't it?

Graham

[Jonny-Jimbo]

Hi Graham,

Do you mean, is changing the diff do-able on the car? The easiest way to do it is to get the car in the air, unbolt the prop and drive shafts, then loosen the rear bolt / bolts (could be one long one or two shorter ones), but do not remove it, then crack off the two front extension nuts. Get a trolley jack, with a big cup under the bowl of the diff. Then finish removing the front nuts, and finally remove the rear bolt. It may be difficult to remove, but these lumps can be heavy, depending what you're used to. You may be able to wrestle it out on your back, but I wouldn't advise that as the first way to do it.

Also be aware that other diffs have different input and output shafts, some round, some square etc.

If you meant changing the speedo angle drive, yes, that should be doable on the car, but access can be limited. If some clown has been at it before with a Stilson or similar you may find the old speedo cable hard to remove. I think they should be hand tight?

Yes, usually 4th gear is 1:1 on these cars.

[A TR7 16V]

It's the "angle drive" I mean.

Though, the question is whether it's like the LT77 box, used on so many BL cars. In that case it can be necessary to change the internal drive component as well, to get the speedo drive ratio that matches the diff ratio and wheel sizes, etc.

What I think I need are the diff ratio, speedo drive ratio, and speedo tpm as a set. I guess I can work out offsets for the rolling diameter of the tire - bigger wheels, fewer tpm, etc.

Graham

[Jonny-Jimbo]

I think the changes are made just at the speedo head? I have not heard of different internal drives in the Triumph boxes, but then I'm no specialist on these things.

[Pete Lewis]

agree,, many triumphs were standardise the cable drive and variable the speedo tmp to suit the diff /tyres,    big saloons have a variety of pinions , lesser on the small chassis
different speedo for each driveline

to get a count on the turns er mile  

stick a card needle on the cable end.  mark 52.8ft down the road ,  push car acurratley between the marks and count the needle turns ,  multiply  turns  by 100 and thats your target

tpm.


if you cant get an angle drive one alternative is a hole saw thro the floor /tunnel and run sweep of cable across the floor inside and up to the fascia ..  needs a grommet to seal the floor but ....simpulze  

[Dogsbody47uk]

Changing the internal drive means stripping the box to get to the speedo drive gear on the output shaft. Far easier to try and get a secondhand speedo that gives the required result. My 13/60 has the 4.11 diff, but has a single rail 1500 Spitfire gearbox and overdrive. Wheels are 5 J alloys with 165/80 by 13 tyres. I found , by trial and error, that a 1500 Spitfire speedo ( checked by my satnav) reads 30 mph when I'm doing 28 to 29 mph. Close enough for me!

[A TR7 16V]

I know the tpm value I need from the current reading on a 1216 tpm one and the frouny face on the LED display stuck to a lamp post [why do they never smile at me?] - . Though the speed reading on a GPS sat nav unit works fairly well too. And that gives that a 1620 tpm would be near enough for avoiding tickets.

Yes, I'm assuming the 1216 tpm value is near enough right. But:

a) I can't think of a fault in the display head that would make it over read.

b) Compared to the idea of pushing the damned thing 52 foot 9 and 6/10ths inches while counting the bloody turns, the risk in that assumption seems well worthwhile to me.

c) I haven't got a 53 foot ruler that's marked in tenths.

But I can't find a speedo head with that high a value, ne'er mind with the right set of lights, etc.

So, if either the internals of the speedo drive are not different for different cars, or like the LT77 it's too much pain to do, I need to pull the "angle drive" that's in, count the teeth and find one that's got 25 percent fewer. But, given that there won't be many teeth on any of them, unless the box, diff, wheel size combo is one Triumph used, it's going to be pot luck finding an angle drive and tpm combination that gives the correct reading.

Alternatively, I could just put bigger wheels on the car. But I'm not sure how the herald looks on 19 inch wheels and modern low profile tires. Would there be a bit of bodywork to mod as well?

Or make a new bezel for the current speedo with 30 marked where 40 currently is. But that's a bit slapdash, even by my standards.

Or get another and have that recalibrated - after checking what its error is.

Or get another and recalibrate one myself - never done one, but from what I rember from Hooke, to make it read consistently less, at least to a first aproximation, just needs more tension in the hair spring in the mechanism, i.e. make it shorter. But I don't know how the spring's fixed in; never had one apart.

Graham

[A TR7 16V]

Just had one other thought to add to the issue, but the speedo drive will be off the overdrive not the GB. Must be, otherwise the reading would change between OD on and off.

Does that affect the posibility of changing it's ratio?

Graham

[nang]

Another way is to buy a GPS speedo.
Tony.

[thescrapman]

I can not see how your speedo is so far out.

You have a 3 rail j-type box from a mk4 spitfire, so a 1100-odd tpm speedo should read about right.

Have you got your sums the right way round, if the speedo reads over, a lower tpm is needed?

Or am I getting myself confused?

[A TR7 16V]

Quoted from thescrapman

if the speedo reads over, a lower tpm is needed?

No, I don't think so: If the speedo head over-reads, the drive needs to turn fewer times in one mile to make it right. And by simple algebra, that's the same as a display head that needs more turns per mile for the same speed reading, i.e. a higher tpm value.

So I think I need an internal helical speedo drive gear with fewer starts and/or an external pinion gear with more, I was wrong before, teeth.

So, does anybody know if it's possible to count - see, feel - the number of starts on the helical gear with the OD on the car? Even if it means draining, etc., that's on the to-do list anyway.

Also, would the standard Herald 13/60 speedo cable reach to the OD speedo drive?

Graham

[A TR7 16V]

Quoted from nang

Another way is to buy a GPS speedo.

Just got  a universal GPS speedo delivered: less than £30 and 10 days from China. I've only connected it up temporarily: I couldn't find the cigarette lighter socket thingy anywhere. Had to hard wire it off the coil in the end.

It does seem to work reasonably well. There's about a 2 or 3 second lag in the display, near as I can tell. It will certainly be good enough to re-calibrate the analogue speedo. Have yet to see how long the start-up process is in a morning, but it warm starts quick enough.  

The instruction manual's is pretty funny though: "After long press the menu button over 5s, the unit of vehicle speed will switch to MPH" isn't too bad; but "In the instant energized, the LED of the host will be fully lit, and then give out a 'tick', the host back to sleeping mode, while the satellite icon starts blinking" isn't quite so translucent.

Graham

[Pete Lewis]

J type has 5 6 or 8 start worm available

pinions are 17,18,19,20

when we fitted a D type to friends Coupe we used a std cable via the hole saw in floor idea and run it inside the car without the rubbish angle drive,
Pete

[A TR7 16V]

Quoted from Pete Lewis

we used a std cable via the hole saw in floor idea and run it inside the car without the rubbish angle drive,
Pete

How did that run inside the car?

Graham