PAS racks for RHD - possible source

[silverbullet]

I think that I may have identified a readily available German-made hydraulic PAS rack that could be made to fit our RHD vans and buses with a suitable carrier bracket and (possibly) a replacement relay shaft. A set of parts are on their way to my works in the next few days and I'll see if it's got potential.

I'm not sure if VW PAS suspension uprights - with their shorter steering arms - will be necessary until I've got the donor rack here and I can see how many turns lock-to-lock it has compared to the oem VW rack.

More later!

[toomanytoys]

Cool..... I expect LHD wont be a problem either then???

[silverbullet]

I guess not. I really only want to make /supply the fitting kits but the risk is that once the cat's out of the bag, I'll get ripped off so I'll have to supply the lot to keep the lid on it.

Fairly hopeful but it might take a couple of goes at ebay to get the correct rack. If the turns l-t-l works out favouably, there may be potential for quick racks

[toomanytoys]

[axeman]

[silverbullet]

Still waiting for parts to arrive...

[ELVIS]

was chatting to someone a while back (Charlie maybe?) and they had fitted non PAS uprights to a PAS van.
Although VW did it for a reason the general opinion was that he (whoever it was) couldnt tell the difference/notice any loss in performance.

[jamesc76]

oooohhhh lets hope it turns out ok!

[silverbullet]

was chatting to someone a while back (Charlie maybe?) and they had fitted non PAS uprights to a PAS van.
Although VW did it for a reason the general opinion was that he (whoever it was) couldnt tell the difference/notice any loss in performance.

Charlie's bro has put a manual rack on his SA!:shock: He must be Hurcules or something!

VW may have done it for several reasons:

Shorter steering arms mean more direct "quicker" steering; they also reduce the chance of the system being over-assisted i.e. featherlight and scary at speed; the PAS rack may have a different stroke and ratio to the manual one, so shorter arms were used to correct the Ackermann geometry too.

My parts have arrived today, so I'm laying out VW manual and PAS vs. "the mystery rack" to see how things compare.

[Aidan]

syncro 14" run same uprights with or without pas, but 16" uprights I've seen have either 2 holes for tie rod end or longer casting, the ones with 2 holes look scarey if you are using the outer one as there's a big hole and not much metal inboard of it

[silverbullet]

Thanks Aidan, VW must have done it to make sure the steering wasn't over-assisted on 2wd then, which wouldn't be good (recalls featherlight Adwest Variamatic on '60's Jaguars... well known for causing a few accidents )

For syncros they clearly didn't think it warranted the tooling and manufacturing expense for the difference in steering feel?

Double drilled steering arms from the factory eh? Unlikely to be a bodge, as you need a special taper reamer to do it correctly. The long boss is typical of the 2wd upright.

More investigation and measurement needed!

[silverbullet]

I have had a bunch of steering racks on the bench for measurement comparisons. Here's what I've found so far:

T3 manual ZF rack. 4 and 7/8 turns, 215mm stroke.

T3 OEM PAS ZF rack. 3 and 3/4 turns, 170mm stroke.

So that is why PAS vans have "shorter" steering arms, with the drillings closer to the axle. It reduces the total potential assistance available (to give some weight to the steering) but uses the assistance to compensate for the smaller stroke.

It's a win-win: quicker, more responsive steering for less effort. Precisely what PAS is all about.

(Quite how this squares with syncros all having the same steering arm length regardless of steering type, I'm not sure just now. Maybe VW or SDP had run out of budget on the project by then and the small handling benefits didn't justify the tool-up costs?)

Conversely, a PAS rack combined with the longer-armed manual steering uprights would result in reduced lock-to-lock travel at the rod ends i.e. a bigger turning circle, possible tyre scrub/bump-steer problems and over-assisted featherweight steering.

Not advised at all IMHO.

On a positive note, the ZF PAS rack that I'm investigating has 3 and 7/8 turns LTL and a 150mm stroke. This would give a slightly inferior turning circle to the OEM when fitted with genuine PAS uprights, but probably no different to a manual-steered van that most people don't have the strength to wind all the way to full lock anyway! Given that they tend to "spring back" the last bit on full lock, I can't foresee a problem.

It also has a slightly shorter effective rack length when compared to OEM (measuring across the steering arm joint centres under the boots), but this can be corrected with internal spacers, so geometry and handling will be identical to a factory set-up.

I intend to do some more measuring and on-vehicle verification but this does depend on other factors i.e extremely lowered or raised vehicles will not fall within my working criteria (standard tin-top syncro, -30 OEM 2wd bus)

So it looks like this one has got legs, time to make a prototype carrier bracket to mount the rack.

[silverbullet]

Don't suppose anyone has got an orphan wbx PAS pump bracket knocking about in the garage?

[DentedDevon]

It will be interesting to see how you get on. I have a rack in my "research" department, just been and measured it , its also 150 mm stroke but approx 3 1/3 turns LTL. Its approx 710 mm between the ball joints.
There dosnt seem to be a big choice of racks as most modern vehicles seem to have the rack behind the axle.

[silverbullet]

I took a look at the PAS pumps and their delivery/blow-off pressures the other day.

OEM T3 (petrol) 115 bar:


Donor pump that came with rack, 110 bar:


Close enough I'd say!

Weirdly the SA pump is only 75 bar I think the steering is nicely weighted even with the smaller T4 wheel, so maybe they de-rated the pump to improve steering feel? Reduced PAS oil temps? Less load on the engine for a couple of mpg?

The donor pulley is offset slightly further back (closer to the engine) compared to the T3 one, so it can take a spacer to correct the belt alignment. One less part to source!

I'm looking to re-make the now very rare diesel pump brackets too. Got a set coming on loan