Saturday, February 17, 2007


When I bought the Vanagon, the seller told me that the transmission needed work, it was making grinding noises and popped out of gear.

Now the weak points of these transmissions are the 4th and 5th synchronizer body that cracks and breaks, it gets stuck in gear and is hard or impossible to get out. Also the double roller pinion bearing, main shaft bearing and 5th gear needle bearing run too hot and eventually will fail, especially if a more powerful engine is installed.

To improve the internal oiling of the bearings you can install plastic drip trays that were developed for the South African Vanagon that had a 5 cyl Audi engine, but still these tranny's absorb a lot of heat from the engine and eventually fail.

On my transmission, the synchronizer body was broken, main bearing split and housing scored.To improve the lubrication, I have drilled an oil channel through the housing to the double roller pinion bearing, cut a radial groove outside around the bearing with 3 small holes to the center of the bearing. Now it will have filtered and cooled oil pumped through the bearing center.

Also I have drilled an oil channel into the main shaft to the needle bearing cages of the 4th and 5th gears, put a spray nozzle on the main shaft bearing and one on the pinion.
External oil pressure is supplied by an extra power steering pump, that pumps the oil through an oil filter and then through a cooler into the tranny.You can see all the external pressure lines on the pictures.I hope that this will keep the tranny together for a long time.

To bring the engine revs down a bit, I have installed different 4th and 5th gears, they have nice big teeth on them, the original gears have very fine teeth and are known to fail. The new ratio's are: 1.14 : 1 third gear and 0.77 : 1 for the fourth gear.


Stal frá Ásgarður said...

Hello Herman, how much power do you think a syncro gearbox can handle and with your modifications?


Herman said...

Hi, I think that it will handle more than the 200 Nm that VW designed it for, now that it has some modifications done to it.

I am sure that it will last with the SVX Subaru but you don't want to shock load the transmission by taking off with the tires spinning.
If you do, things will break.

Joe said...

Hey, Herman,

I was wondering what prep steps did you go through to paint your transaxle? I tried to paint mine with spraypaint and it keeps coming off. I've still got my syncro apart and could paint the tranny. I know how the it is, I've had my syncro apart for a year now and really want to get it on the road. By the way I enjoy your site, especially the brake upgrades.



Herman said...

Thanks Joe, I powdercoated my transmission housing when I had it all apart, you need some good primer on it before you can paint it with spraypaint.
I sure hope I get some more time in this winter, I want to drive it!
Cheers Herman

Anonymous said...

Hi Herman!!

I'm french living in Hawaii now.
I really enjoy your work (I have a TDI with mechanic pump in France, lots of things on it such as Eurovan VR6 front discs with 4 pistons calipers from Jaguar,Audi V8 discs and calipers on back etc....)
My Hawaiian Westy is going to receive a Subaru 2.2L n/a engine, so I'm rebuilding the transmission ,a 2WD (not my first job on gearboxes but I don't have a lot of tools to improve the gearbox like you did !!)

Where did you get your longer ratios pinions for the gearbox ,is it at long enterprise??

We never now, but there is some german people mounting a UN7 type gearbox on the Syncro that is really solid,the only conversion that I know like that:it comes from a french car,pretty rare:Renault 21 Quadra...still good to know ;-)

See you!


Herman said...

Hi Alex, your engine sounds really good on youtube, what timing setting did you use?
You sure did a lot of upgrades as well!

I bought my gearset from Daryl of AA Transaxle a few years ago, nice guy.

I have read about that conversion to a Renault UN7 gearbox, it is suppose to be a stronger transmission, interesting!

Cheers Herman

Anonymous said...


thanks for your reply!

I set at 1mm with the depth gauge in the injection pump,never tried to do better,was working like this ;-)
The UN7 is the strongest transmission you can ever see.
I've given up on building a VW longer transmission,too expensive and still weak I think.I've been in touch with Weddle.
AAT doesn't sell parts he replied me....
I'm going to import a UN1 5 speed gearbox (the 2WD equivalent of the UN7 model) :stronger than Porsche trannies,longer than VW,easy swap,cheap.
It has so many ratios and has been mounted on a full range of powerful Renault cars and also Alpine cars.
Check these interesting links out about gearboxes products: for products made by this factory in Australia:
And this guy offers interesting products,mostly for Subarus...

Enjoy the van!!!


Anonymous said...

Hi Herman,

Fantastic job on your van! I hope you're getting some time to enjoy it now, it looks like it's done.

I recently bought a syncro and am preparing to convert it to a TDI. I was curious if you would be interested in rebuilding the tranny? There aren't many people around with expertise on them, so otherwise it will have to go to the states. I am in Calgary. You can email me if you like,



Kevin said...

Hi Herman,
Quick question regarding your transaxle cooling setup. You mention that it's driven by a ps pump--is the oil pumping through any time the engine is running? Or have you incorporated some type of thermostatic switch? I suppose the concern would be the delay in getting the gear oil up to temp on cold days...

Alika said...

Hi Herman!

This is Alex again from Hawai'i.

I'm finally rebuilding my syncro transmission,inspired by your oiling improvements.
2 questions though:
#1: What type of fittings are you using? It seems like they are not NPT threads,but rather straight pitch and a counter locking nut.
#2: Is your supply line going in on the left side of tranny then tee'd to mainshaft end/right side of tranny ?(right side I can see on pics,so that leaves very few options to supply line :-) )

Thank you again!!


Herman said...

Hi Alex, that's great!
The fittings that I have used are made by Swagelock, some have NPT on it, one is a bulkhead type fitting and there are some T-fittings also, all are stainless steel but you could also use brass.
The suction line is on the passenger side, the pressure line from the pump is on the driver side and splits into one that goes to the pinion bearing and main shaft bearing, the other one goes to the pinion spray nozzle and the main bearing nozzle.

Cheers Herman

Herman said...

Hey Kevin, sorry about the delay, I totally overlooked your post.
I don't have a thermostat in there because I only run the van in summer, the pump supplies pressure whenever the engine runs, I have had no problems even on cooler days.

Cheers Herman

Alika said...

Very helpful Herman,thank you again for all the precious information :-)

Steven Roe said...

Hi Herman, I was wondering what your final drive ratio is and are you satisfied with your 4&5 gears? Curious what RPM you see at 65mph in top gear, and how it does on the hills? I'm down in San Mateo CA and have '87 syncro tdi now rebuilding the trans. Also are you happy with the wheels and tires, it looks like a good choice to me and I might go w Geolanders also and 17" Audi wheels as I want to do the chage to rear disks eventually
Great site, inspiring craftsmanship !
Cheers, Steve

Hinnerk said...

Hi Herman,

you have done a really interesting cooling system.
What would interest me is, if your gearbox is still running smoothly, or if you had any trouble, improvements since your original design was developed. To ask short, would you do it the same way again ?
The reason for this keen interest is, my syncro is getting a complete overhaul and at the same time the subaru 2.5l engine combined with my AVS gearbox, which i want to keep. so it is going to see quite a few revs and therefore in need of a proper cooling system.

best regards from Germany.


Alika said...

Hi Herman, Alex from Hawai'i again.

How did you clear that fitting for the gundrilled mainshaft from the chassis crossmember? I have 17mm clearance there.
Check out this picture of the fitting I made ;-) (click on link or copy and paste)