TR4/4A TR4A Gearbox Rebuild

[RJS]

Hi All,

You may have seen my earlier posts on removing my gearbox. Well, it is being rebuilt now after I starting hearing a "chattering" sound in gears 1, 2 and 3 at the end of last season. Otherwise, the gearbox worked perfectly other than an occasional "notchiness" going into third gear. Oh, and sometimes I would get a 3-5 second delay engaging the OD. I attribute that to the OD relay. The gear box was previously rebuilt in 1998 (14,000 miles ago) just before I bought the car. John at Quantum Mechanics has it and upon opening it up, found a few interesting things.
1) it has an asymmetric gear set (not original, factory correct - maybe from a later TR6?)
2) The clutch fork pin had broken and was welded. He had to cut it to remove
3) The layshaft and bearings were new and looked good
4) The OD had the earlier (TR3/4) large accumulator pump 1.75" diameter. With the TR4A IRS cars Triumph moved to a smaller accumulator pump with 1.15" dia
5) The OD clutch linings had been resurfaced and looked good.
6) The synchros were the cheaper versions (he said there are typically three levels of quality and these were the cheapest)
7) The OD relay was original

So, plan of attack is as follows:

• New cross shaft fork and hardened pin
• Upgraded triple bearing 1st cluster gear – 16 tooth, as original
• New Top Quality Synchros
• New Speedometer bushing (current one bent)
• New OD Solenoid (1966 original still on there!)
• Smaller OD Accumulator Piston
• Symmetric Gear Set with Steel Bushings (this set means new input shaft, 1st gear, 2nd gear, 3rd gear, 1/ 2 hub, 3/ 4 hub and main shaft)
• Oh, and a Magnetic Drain Plug

There was nothing wrong with the asymmetric gear set but, in order to go to steel bushings John said we had to use symmetric gears. He will give me a credit for the asymmetric gears he replaces. But, by upgrading to triple bearing cluster gear and the steel bushings, this box will be bullet proof for rest of my life time. I expect to pick it up next week but, may yet be a few more weeks before I can get it installed (my helper (read 26 year old son) is away. Can can bet I will post an update once installed and road test.

Bob

 

[CJD]

Did he account for the "chattering"?

 

[auprichard]

What were his thoughts on the 3-5 second OD delay? I doubt that would have been an electrical issue (the relay) - maybe a worn pump taking time to build sufficient pressure?

 

[Sarastro]

I guess it's possible that the OD delay could be caused by the old actuating solenoid, but I think it's more likely to be in the hydraulics. The OD has all kinds of little passages that could get plugged up, and it would be wise to make sure they are all clear. Also, make sure that the pistons that move the sliding member are not binding, the actuating valve is free and adjusted for the right lift, and the accumulator pressure is right. You should be able to do most, if not all, of this without disassembling the OD.

In any case, if the solenoid is original, it's probably prudent to replace it--as long as you can find a good-quality one.

 

[RJS]

I meant to ask on the chattering, and will when I pick it up. It was clearly a new symptom starting last season and completely silent in fourth gear. That indicates it was the bearings on the main cluster (I hope that is right term - I often see references to layshaft, counter shaft, cluster gear, etc which is not 100% clear to me TBH). I wanted to address the issue before it caused any more damage and for my own piece of mind. It was very hard to enjoy a drive listening to that and not thinking it was fatal.

I don't believe the relay issue was electrical. Being original, the rubber boot became hard and brittle with time - that caused engagement issues on its own by inhibiting the plunger movement. So I removed the rubber boot several years ago. All was good except then I believe the bore had become corroded. It would engage fine when I sprayed it with WD40 - then a few weeks later the slight delay would return. I am sure we could have tried to rehab it but, being 60 years old I was fine to retire it. It still could have been something internal to the OD. But, somehow I don't think so as the delay was a bit random.

Bob

 

[CJD]

Slow OD shift is low accumulator pressure. This can be from a bad accumulator spring, incorrect adjustment, or a weak pump...or of course, a leak in the internal plumbing reducing the accumulator pressure. The pump is bullet proof and the relay is instant, so I doubt they are the cause.

The diagnosis is to hook up a gage over the valve on the right side and watch the pressure during use.

 

[RJS]

Hi, coming back to the question on what caused the light "chattering". When I dropped the gearbox off in-person, John was able to open the top cover and take a quick look. He did say there was there was too much play in "top hat" from worn brass bushings. When I pick it up, I will be sure to ask him if that was the source of the "chattering" - or if he found something else.

Bob
PS: this is partly why I am upgrading to steel bushings. This box has 17K miles (sorry, I know I said 14K above) and I changed the fluid every 3K miles. Way too soon for bushings to wear out

 

[CJD]

The top hat never wears out, but rather the top hat cracks off the bushing from getting hammered every 2-3 shift. I assume by "metal bushings" you mean a steel top hat?

 

[KVH]

Slow OD shift is low accumulator pressure. This can be from a bad accumulator spring, incorrect adjustment, or a weak pump...or of course, a leak in the internal plumbing reducing the accumulator pressure. The pump is bullet proof and the relay is instant, so I doubt they are the cause.

The diagnosis is to hook up a gage over the valve on the right side and watch the pressure during use.

I invested in an expensive pressure gauge and electric motor (table mount) with a pulley so I could test operating pressure after rebuilding the OD. I was lucky—the pressure was right at spec. I think I followed the Buckeye Triumph write up and procedure. My kids have all asked when I’ll ever in the future be needing that motor and gauge. I sometimes think we fix these things hoping we’ll do it all over again one day, as if time is no factor.

 

[CJD]

Fancy! I just used a !/2" drill to turn mine?!?

 

[CJD]

If pressure is good, and it comes back rapidly after a shift, then I would look at the solenoid adjustment. The solenoid operates a lever on the left side of the case, which twists a rod through the entire case, to another lever on the right side, which then lifts the shift valve. There is a pin hole on the right side of the case to be used in setting the solenoid. I find if you follow the manual and just install the pin and set the solenoid, then 60 years of wear in that loooong linkage makes the valve slow to engage...or prevent engaging at all. You have to compensate for wear by setting the adjustment tighter than in the manual. I gave up entirely on the pin, and just used the rig, like you have, to adjust the link and test... and repeat until I liked the "feel" of the shift.

 

[KVH]

Fancy! I just used a !/2" drill to turn mine?!?

I gave up on my drill. It couldn’t spin the shaft. I tried over and over again. I’m not sure I owned my brute 1/2 inch power hammer drill back then, but whatever I used sure fell short.