Information about my 1963 TR4 - overdrive
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This page is all about my non standard overdrive gearbox
Originally I had a normal TR4 non overdrive gearbox, but after a year or so I decided to fit one with overdrive. Now at the time TR4 gearboxes with type A overdrives were both scarce and expensive so after reading about fitting a Triumph 2000 O/D gearbox from a pre 1973 car I decided to give it a go. I already had a Dolomite sprint gearbox that someone had given to me, but after having modifications to the input shaft done I found that as it had a J type overdrive it could not be fitted to my TR4 chassis. The rear mountings would fit the chassis, and would need the chassis to be 'cut and shut'
I phoned a local Triumph scrap car dealer and he had one that I could have for £65-00 on condition that I took it out of the car. So I got my gear and went over, and after 3-4 hours work I got the assembly out of the car, complete with solenoid relay.
I took it home and planned what to do next. I measured the splines, so that I could check for possible clutch plates at an autojumble, I was also going to put a diaphragm clutch into the car, so when I went to the TR International meeting at Stafford in the UK, I bought a flywheel for a TR4 complete with a very good starter ring for £10-00 - a bargain ! I also bought a new looking speedometer as I would need to have a recalibration done. Cost £20-00
I went to the autojumble at Newark, and found not only that a Dolomite sprint clutch plate would fit my gearbox splines, but also that it was the correct size for a diaphragm clutch. I bought the clutch plate that I had found for £18-00. I also found a clutch cover plate for £20-00 both were brand new and were absolute bargains (again)
I had to buy a clutch release bearing from a TR supplier, and also a rear gearbox/OD mounting plate from Moss UK - it came with no instructions, cost £28-00, didn't fit and was a waste of time. I also needed an internal spring for the O/D in order to bring the pressure up to the required figure for the power of the TR.
I had a spare gearbox, and took the release sleeve out of it and machined off the 3/8 inches necessary to make the clutch assembly work. Also before I started, I bought a longer speedometer cable from TRGB.
I had two weeks off work and decided to fit the gearbox on two of those days. First the flywheel had to be drilled to take the new clutch plate. I made a mandrel out of a large piece of brass bar that I had. This fitted closely into the hole in the flywheel and also inside the splines of the clutch cover plate. I made a punch that fitted exactly through the bolt holes in the cover plate and left a 'pip' in the centre. I lined up the cover plate on to the flywheel and clamped it in place. I marked the holes with tippex, and when it had dried I used the punch to mark the position of the holes. I took it all apart, and used a proper punch to emphasize the marks for the bolts. I drilled and tapped the holes to the correct size, and was then ready to start. The old gearbox came out, and I fitted the new flywheel, clutch and clutch plate, and after putting the clutch sleeve that I had shortened on to the O/D gearbox, I mated it with the engine. No Problem. Except that the rear mounting that I had bought which was specially for the job, did not fit. After several attempts I got out my angle grinder, arc welder and some hefty angle iron and made one. It fitted perfectly after some filing on the O/D mountings. I changed the output drive to the prop shaft to the TR4 one, and connected everything up, including the electrics, but when I tested it there was no overdrive.
I checked everything again and again but it still would not work. So it all had to come out again, and the old gearbox went back in!
I took the box to a local specialist, and they took everything apart. The gearbox needed a new layshaft, but the overdrive needed reconditioning. Total cost £190-00.
I put it back in to the car. It still didn't work but now made a funny noise from the overdrive area. I took it back out again and returned it to the restorers. They changed a few components (allegedly) and I got it back. Again the gearbox went in. No noise, but the O/D would not work. I was fed up of taking the thing out by now, so I left it in for a few weeks, going to Duxford for the Alfa Romeo meeting (the Air museum there is very good) and taking part in the RAC Classic run, going to Galway in Ireland for part of the week, but starting from Dublin and ending up after three days at Silverstone. It would have been nice to have an O/D on that trip as I did over 1100 miles mainly on side roads!
After the run, I decided enough was enough, and that I would take the whole car over to the reconditioners to show them that the O/D would not work. I was actually on my way there, when I flicked the O/D switch and something happened - it went in then out again. I turned around and when home. I decided that as it could not be the electrics, it must be the settings, so I removed the cover to the setting up bar, and then went out for a drive. I stopped at every lay-by and adjusted the setting by a minute amount. After driving 25 miles the O/D was working ! The setting was no where near the setting that I got when using the workshop method, but there must have been a fault with the setting bar. It has worked ever since!
The speedo posed a few problems, because I was driving the car with the old one, and the number of turns per mile was different with the two gearboxes that I had. I used the old speedo, but stuck tape on to its face to mark the settings for the O/D box. I took the speedo that I had bought to Speedograph in Nottingham and had it recalibrated, then I fitted it, starting at the same mileage that I has taken the old one off at (1500 miles)
Now for some notes about the wiring - it is definitely not standard! One of the problems with the standard set up is that you are using two devices to change the gearing, and when you want to go 1st, 2nd, 2nd o/d, 3rd, 3rd o/d,4th,4th o/d in rapid succession, then the coordination to do it is difficult when you should be looking at the road ! Even so, having a switch on the steering column is nice when you want to tootle along going from 4th to 4th o/d and back. So I devised a way of improving this.
First, the TR2000 gearbox had its standard gear change lever and gear knob which had an O/D switch on it. Unfortunately the action when changing gear was far from smooth, so I tried the original lever from my TR4 box and it worked perfectly. So I cut off the bottom part of the two levers at ssame point and arc welded them together, using a threaded stud to make the joint stronger. The top part of the TR2000 lever was needed becasue it had the hole for the wire on it, and the thread for the gear knob. Also there were isolator switches on the gearbox. I needed an double pole relay, a column switch (from an autojumble) and some more wire but that is all.
The O/D relay is switched from the new relay's contacts. This relay is 'locked on' when energised. That is, it is wired so that one pulse of electricity will switch it on, and it then feeds its coil from the contacts of one of the switches on the relay and stays on. Within the 'lock on' circuit, I wired the switch on the steering column, so that if the switch was off, nothing would happen when energised, but if ON the relay would lock on. If the relay is on, and the switch thrown off, then the relay drops out.
Also - in the same circuit are wired, in parallel, the two isolator switches on the gearbox cover. They are in series with the steering column switch. With this method they also perform their normal duty of stopping the O/D working in reverse and first gear.
The gear lever overdrive switch is wired to provide the 'pulse' to energise the relay. It can be left on as it is in parallel to the lock on switch in the relay.
Here is a wiring diagram (sorry about the bad graphics)
So - driving the car goes like this. If I want to drive it like a 'normal' TR4 with O/D I switch the gear lever switch ON and use the column switch. But for 'spirited' driving, I leave the column switch ON and use the gear lever switch. I just switch it on then straight off again to engage o/d. The locking relay keeps the O/D on, but when I change gear, the detent switches open the locking circuit and the O/D drops out. This means that I don't have to think about whether I am in O/D or not and the gearbox + o/d gives me the next available ratio.
It works when going down the gears as well, but I guess you can drop a whole gear without a problem. What it does do is if the car is in 4th O/D and I change down, then I go directly to 3rd, which is what I probably want anyway. If I want to go from 4th O/D to 3rd O/D then I just leave the gear lever switch on.
This has worked very well since I installed it, and although I mainly use the column switch, I use the 'other' method when I want to accelerate quickly. Its quite nice going past BMWs and then changing up three ratios. A lot of younger modern car drivers don't know what an Overdrive is!
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